Industrial silicon low-iron powdering method based on self-milling protective layer

Abstract

The application discloses an industrial silicon low-iron powdering method based on self-milling protective material layer. A predetermined coarse particle grade of the same batch of industrial silicon coarse particles is separated from the industrial silicon to be powdered, and is circulated and milled before continuous powdering, so that the contact area of the material and the metal part in the milling area is circulated and distributed and a self-milling protective material layer is formed; during the starting stage, the industrial silicon powder is separately collected and the iron content increment is detected relative to the same batch of raw materials, and after the control requirement is met, the continuous powdering is started. During the continuous powdering, the material discharged from the mill is classified, and the self-milling protective material layer is continuously updated by using the return material of the predetermined coarse particle grade of the industrial silicon; by monitoring the return material amount, when the return material continuously decreases, the iron content increment is separately collected and detected, according to the detection result, the isolation is maintained until the return material is restored, or the proportion of the predetermined coarse particle grade of the industrial silicon in the material entering the mill is increased to rebuild the self-milling protective material layer, so that the additional iron increment in the continuous powdering process and the risk that abnormal powder is mixed into normal products are reduced.

Description

Technical Field

[0001] This application relates to the field of industrial silicon powder preparation technology, specifically to a method for preparing low-iron industrial silicon powder based on a self-grinding protective layer. Background Technology

[0002] Industrial silicon is typically further processed into industrial silicon powder with a specific particle size range during the preparation of photovoltaic materials, organosilicon raw materials, aluminum alloys, and related silicon-based materials to meet the requirements of subsequent batching, reaction, and processing. Industrial silicon has a high hardness, and continuous mechanical grinding requires grinding media, liners, and other metal grinding components to continuously apply impact, compression, and friction to the material. During repeated crushing, grading, and re-grinding, industrial silicon particles maintain high-frequency contact with metal components. Therefore, additional iron addition during the grinding stage directly affects the quality stability of the industrial silicon powder.

[0003] Currently, continuous industrial silicon powder production typically employs a closed-loop process combining mechanical grinding and graded return. Industrial silicon powder meeting the required particle size is collected as the final product, while silicon exceeding the upper limit is returned to the grinding process for further processing. During production, continuous operation is generally maintained by controlling the feed rate, grinding intensity, grading status, and circulating load. Periodic sampling is used to test the iron content of the product. When abnormal test results are detected, grinding conditions are adjusted, the corresponding powder is diverted, or the equipment's operating status is addressed to reduce the impact of metal wear on product quality.

[0004] In the aforementioned production method, industrial silicon and metal grinding components are in continuous mechanical contact during continuous grinding and re-grinding. As the grinding operation and material circulation status change, the additional iron content in the industrial silicon powder will also change accordingly. The iron content detection of the product is a quality result after the powder has formed. When abnormal iron content has already formed during the grinding process, the industrial silicon powder of the corresponding time period has already entered the product logistics or is in the process of product transportation. This can easily cause the abnormally iron-enriched industrial silicon powder to mix into the normal product, affecting the low iron stability and product quality consistency of the continuous grinding process. Summary of the Invention

[0005] In view of the above-mentioned actual situation, this application proposes an industrial silicon low-iron powder production method based on a self-grinding protective material layer, in order to solve the problem that in the existing continuous mechanical powder production process of industrial silicon, the continuous contact between industrial silicon and metal grinding parts can easily generate additional iron, resulting in abnormally iron-enriched industrial silicon powder entering the normal product.

[0006] 1. A method for producing low-iron industrial silicon powder based on a self-grinding protective layer, comprising: S1. Separate coarse industrial silicon particles of the same batch at a predetermined coarse particle level from the industrial silicon to be pulverized, and circulate and grind them before continuous pulverization, so that the coarse industrial silicon particles are circulated and continuously replaced in the contact area between the material and the metal parts in the grinding zone, forming a self-grinding protective material layer composed of the coarse industrial silicon particles. S2. Collect the industrial silicon powder produced by the cyclic grinding in step S1 separately and take samples to test the iron content to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be ground; when the increase in iron content does not exceed the predetermined upper limit of iron content increase, end the separate collection and switch to continuous grinding. S3. Continuously feed in industrial silicon to be ground for grinding, classify the material exiting the mill, collect industrial silicon powder within the product particle size range, and return industrial silicon material above the upper limit of the product particle size to the grinding process. The predetermined coarse-grained industrial silicon coarse particles continue to be circulated and ground with the returned material to renew the self-grinding protective layer. S4. During the continuous powdering process, when the feed rate and classification conditions of the industrial silicon to be powdered are within the predetermined operating range, monitor the amount of the predetermined coarse-grained industrial silicon returned in the classification return process; when the amount of returned material continuously decreases, switch the industrial silicon powder from product collection to separate collection, and take samples to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be powdered. S5. When the iron content increment does not exceed the predetermined upper limit of the iron content increment, continue to collect separately until the return material amount recovers to the level before the continuous decline, and then resume product collection; when the iron content increment exceeds the predetermined upper limit of the iron content increment, increase the proportion of predetermined coarse-grained industrial silicon in the mill feed material to rebuild the self-grinding protective material layer. During the reconstruction process, restore the feed amount and classification conditions to the operating range before the continuous decline of the return material, and resume product collection when the return material amount recovers to the level before the continuous decline and the iron content increment does not exceed the predetermined upper limit of the iron content increment.

[0007] The proposed method for low-iron industrial silicon powder production based on a self-grinding protective layer enables the establishment and continuous updating of a self-grinding protective state in the grinding contact area using coarse industrial silicon particles from the same batch. It also identifies the supply reduction of protective coarse particles in advance by the continuous decrease in the predetermined amount of coarse-grade industrial silicon return material. Before the iron content abnormality further develops, the corresponding industrial silicon powder is collected separately. Then, the target coarse particle participation ratio is adjusted according to the iron content increase, and the self-grinding protective layer is restored, thereby reducing the risk of additional iron addition and abnormal powder mixing into normal products during continuous powder production. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the overall process flow of the industrial silicon low-iron powder production method based on a self-grinding protective layer according to this application; Figure 2 This is a magnified schematic diagram showing the formation and partial enlargement of the self-grinding protective layer in the grinding contact area of ​​this application; Figure 3 This is a schematic diagram illustrating the time-series relationship between the amount of coarse-grained industrial silicon returned, the increase in iron content, and the product collection status as per the present application. Detailed Implementation

[0009] To clarify the process steps, material handling relationships, operational boundaries, and technical relationships shown in the accompanying drawings, the specific implementation methods of this application are further described in detail below with reference to the accompanying drawings. It should be noted that this application organizes the start-up layering, iron content benchmark establishment, continuous grinding, target coarse particle replenishment during operation, and batch-end discharge for the same production batch. The industrial silicon material at each stage is continuously connected along the actual logistics path of grinding, grading, return, and collection. The iron content increment is used to characterize the additional iron content change that occurs after the same batch of industrial silicon enters the mechanical grinding process from the raw material state. Product collection and separate collection correspond to distinct industrial silicon powder logistics paths. The process nodes, grinding contact areas, and timing states in the accompanying drawings correspond to the corresponding process actions. In specific implementation, the process is carried out in the order of material entering the grinding process, milling and grading, coarse particle return, industrial silicon powder collection, and changes in operational status.

[0010] This application applies to the mechanical powdering process of industrial silicon, and is particularly applicable to the continuous closed-circuit powdering process in which industrial silicon material comes into mechanical contact with metal grinding media, metal liners and other metal grinding components in a grinding equipment, and after the material exiting the mill is classified by particle size, industrial silicon powder within the product particle size range is discharged and collected, and industrial silicon material exceeding the upper limit of the product particle size is returned to the grinding process for further grinding.

[0011] In the aforementioned mechanical grinding process, after the industrial silicon raw material enters the grinding zone, it continuously undergoes inter-particle collisions, collisions between particles and grinding media, contact with the liner, compression, and friction under the action of the grinding media and the material movement within the mill. Larger industrial silicon particles are gradually broken down and refined, and then enter the subsequent classification process from the mill outlet. Materials exceeding the upper limit of the product particle size are classified and then reformed into a return grinding stream, which re-enters the grinding zone, thus constituting the grinding-classification-re-grinding cycle in the mechanical grinding of industrial silicon.

[0012] Industrial silicon has a high hardness. During mechanical grinding, the repeated contact between industrial silicon and steel balls, metal liners, and corresponding metal grinding components leads to wear on the surface of these metal components. This wear material, after entering the industrial silicon powder, manifests as additional iron gain during the powdering stage. This application introduces coarse industrial silicon particles, already at a predetermined coarse particle size, into the aforementioned closed-loop grinding cycle. This allows these coarse particles to continuously enter the grinding zone where the material comes into mechanical contact with the metal components, and the process utilizes graded return material to continuously replenish these coarse particles.

[0013] The predetermined coarse-grained industrial silicon mentioned here is both a component of the industrial silicon to be pulverized and used as a process material for contact during continuous grinding. During the start-up phase, the corresponding coarse particles are separated from the same batch of industrial silicon to be pulverized, and a circulating grinding state for these coarse particles is established before continuous normal feeding. After continuous production is established, the industrial silicon at the predetermined coarse-grained level in the graded return material continues to return to the grinding process. When the return material of the target coarse particles shows a continuous decline, new predetermined coarse-grained industrial silicon is added from the same batch of industrial silicon. This material path ensures that the source, consumption, and replenishment of the predetermined coarse-grained industrial silicon are all within the industrial silicon pulverization process of this batch.

[0014] The term "feed material" as used in this application refers to industrial silicon to be pulverized, supplemented pre-selected coarse-grained industrial silicon, and industrial silicon material returned to the pulverizing process under the corresponding operating conditions.

[0015] This embodiment uses a ball mill for industrial silicon powder grinding. During the ball milling process, steel balls constitute the main grinding media, and metal liners are installed on the inner wall of the mill. The industrial silicon raw material, the returned material, and the predetermined coarse-grained industrial silicon all enter the corresponding grinding space. The rotation of the ball mill causes the steel balls and industrial silicon material to fall, roll, and squeeze against each other, and the industrial silicon particles are gradually refined under the above mechanical action. The material exiting the mill enters the coarse-grain screening and product fine classification process, while the returned material is returned to the ball mill.

[0016] Other mechanical grinding processes involving mechanical contact between industrial silicon materials and metal grinding components, mill classification, and return material recycling are implemented according to the material receiving relationship described in this application. The driving device, feeding and discharging device, return material conveying device, screening device, classification device, and product collection device of the grinding equipment are configured according to the corresponding production capacity, material particle size, and processing load.

[0017] This application focuses on the continuous participation state of predetermined coarse-grained industrial silicon after it enters the grinding contact area, the circulation state of the corresponding coarse particles in the closed-loop return process, and the process connection between the circulation state and the change in iron content of industrial silicon powder.

[0018] like Figure 1 As shown in one specific embodiment, this application provides a method for producing low-iron industrial silicon powder based on a self-grinding protective layer, comprising the following steps.

[0019] S1. Separate coarse industrial silicon particles of the same batch at a predetermined coarse particle level from the industrial silicon to be pulverized, and circulate and grind them before continuous pulverization, so that the coarse industrial silicon particles are circulated and continuously replaced in the contact area between the material and the metal parts in the grinding zone, forming a self-grinding protective material layer composed of the coarse industrial silicon particles. S2. Collect the industrial silicon powder produced by the cyclic grinding in step S1 separately and take samples to test the iron content to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be ground; when the increase in iron content does not exceed the predetermined upper limit of iron content increase, end the separate collection and switch to continuous grinding. S3. Continuously feed in industrial silicon to be ground for grinding, classify the material exiting the mill, collect industrial silicon powder within the product particle size range, and return industrial silicon material above the upper limit of the product particle size to the grinding process. The predetermined coarse-grained industrial silicon coarse particles continue to be circulated and ground with the returned material to renew the self-grinding protective layer. S4. During the continuous powdering process, when the feed rate and classification conditions of the industrial silicon to be powdered are within the predetermined operating range, monitor the amount of the predetermined coarse-grained industrial silicon returned in the classification return process; when the amount of returned material continuously decreases, switch the industrial silicon powder from product collection to separate collection, and take samples to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be powdered. S5. When the iron content increment does not exceed the predetermined upper limit of the iron content increment, continue to collect separately until the return material amount recovers to the level before the continuous decline, and then resume product collection; when the iron content increment exceeds the predetermined upper limit of the iron content increment, increase the proportion of predetermined coarse-grained industrial silicon in the mill feed material to rebuild the self-grinding protective material layer. During the reconstruction process, restore the feed amount and classification conditions to the operating range before the continuous decline of the return material, and resume product collection when the return material amount recovers to the level before the continuous decline and the iron content increment does not exceed the predetermined upper limit of the iron content increment.

[0020] Figure 1 In this process, S1 is set before normal continuous feeding, where coarse industrial silicon particles from the same batch are used to establish a circulating grinding state. S2 receives the industrial silicon powder generated in S1, and the iron content increment is detected separately to determine the iron-enhancing state corresponding to the start of the cycle. After the start-up release conditions are met, the process proceeds to S3, where industrial silicon powder to be ground is continuously added to the grinding process. The product powder and the returned material are classified and enter their respective material paths. The predetermined coarse-grained industrial silicon continues to return to the grinding area and joins the aforementioned granular material layer.

[0021] S4 is set in the continuous production stage. The predetermined amount of coarse-grained industrial silicon returned in the graded return process continuously reflects the target coarse-grained supply status for the next cycle entering the grinding zone. After the return amount reaches the condition of continuous decline, the industrial silicon powder is immediately switched from the product collection path to a separate collection path, at which time the iron content increment is detected simultaneously. S5 continues in this separate collection state, and performs the corresponding coarse-grained replenishment, protective layer reconstruction, and product collection recovery processes according to the range of iron content increment and the return recovery status.

[0022] Figure 2 The spatial relationship of the self-grinding protective layer formed after the predetermined coarse-grained industrial silicon in S1 and S3 enters the typical grinding contact area is further shown. Figure 3 The diagram further illustrates the interrelationship between the predetermined amount of coarse-grained industrial silicon return, the increase in iron content, and the changes in product collection status along the production time in S4 and S5.

[0023] The following provides a detailed explanation of the following aspects of the overall process: material boundary in the same batch, self-grinding protective material layer, separate collection, start-up circulation, continuous return material, and operation state transition.

[0024] In this application, "industrial silicon to be pulverized in the same batch" refers to industrial silicon with a uniform production batch identification that serves as the raw material for this continuous pulverization process. This batch of industrial silicon constitutes the uniform material basis for this pulverization process.

[0025] The coarse industrial silicon particles used to form the self-grinding protective layer during the start-up phase are separated from the same batch of industrial silicon to be pulverized; the reference sample used to determine the basic iron content of the raw material is obtained from the same batch of industrial silicon to be pulverized; the predetermined coarse-grained industrial silicon used to supplement the supply of target coarse particles during continuous pulverization is also separated from the same batch of industrial silicon to be pulverized; the reserved coarse industrial silicon particles used to maintain the tail-end grinding and return material at the end of this batch of continuous pulverization also come from this batch of industrial silicon.

[0026] By adopting the aforementioned batch material relationships, the start-up layer-building materials, normal production raw materials, iron content comparison benchmarks, in-process supplementary coarse particles, and batch-end discharge coarse particles all have a unified raw material source. The batch basis corresponding to the iron content of the raw materials themselves and the composition of internal impurities in the raw materials remains consistent, and the iron content increment detected after powdering can be compared with the original iron content of this batch of industrial silicon.

[0027] The boundary of the same batch of materials also extends throughout the start and end of continuous production. When a batch enters the start-up layering stage, the corresponding coarse-grained cycle, reference sample, and subsequent normal raw materials are all organized according to this batch; after the production of this batch is completed, the corresponding tail-end discharge is completed. When production is switched to a new industrial silicon batch, the reference sample and the predetermined coarse-grained industrial silicon required for start-up are obtained again according to the new batch, and the start-up cycle state corresponding to this batch is re-established.

[0028] The "same batch relationship" mentioned here mainly refers to the consistency of raw material sources. After industrial silicon raw materials enter the screening, grinding, grading, return, and collection processes, their physical particle size and material flow path will change, but the corresponding materials still retain the original production batch attributes. Through this material boundary, subsequent start-up powder, normal product powder, powder collected separately during abnormal stages, and powder at the end of the batch can all be mapped to the powder production process of this batch.

[0029] The self-grinding protective layer in this application is formed by the coarse industrial silicon particles at a predetermined coarse particle level during the cyclic grinding process of the industrial silicon to be pulverized, and is a dynamic industrial silicon particle layer that continuously undergoes particle replacement with grinding, classification and return, and subsequent coarse particle replenishment.

[0030] After the pre-selected coarse-grained industrial silicon enters the grinding zone, it moves with the material and grinding media into the area where the industrial silicon material and metal components come into mechanical contact. At this location, the pre-selected coarse-grained industrial silicon participates in the grinding contact along with the finer industrial silicon material, the grinding media, and the metal liner. The impact, compression, and friction generated by the grinding media are transmitted through the pre-selected coarse-grained industrial silicon and the surrounding industrial silicon particles, while the target coarse particles themselves simultaneously undergo grinding action and gradually break down.

[0031] Therefore, the self-grinding protective layer corresponds to a certain number of predetermined coarse-grained industrial silicon particles that are continuously distributed, continuously participate in mechanical contact, and continuously replace each other in the grinding contact area. A single predetermined coarse-grained industrial silicon particle is a constituent unit of this particle layer, and the continuous participation of multiple target coarse particles in the actual grinding contact area together constitutes the self-grinding protective layer.

[0032] The term "self-grinding" is used to characterize that the coarse particles constituting the particulate layer originate from the industrial silicon itself during the grinding process. The coarse industrial silicon particles undergo grinding action and are gradually broken down during the contact process, with the mechanical energy required for grinding provided by the grinding media and corresponding grinding components. Therefore, the coarse industrial silicon particles themselves both enter the particle size refinement process as material to be pulverized and participate in particle receiving within the grinding contact area while still at the predetermined coarse particle size level.

[0033] The self-grinding protective layer features continuous material replacement. The predetermined coarse-grained industrial silicon introduced during the start-up phase gradually becomes finer during the recycling process; new predetermined coarse-grained industrial silicon re-enters the grinding process through graded return material; when the supply of the target coarse particles decreases during continuous production, new predetermined coarse-grained particles are added using the same batch of industrial silicon. As the above material flow continues, the specific coarse particles in the grinding contact area continuously change, while the process state in which the predetermined coarse-grained industrial silicon participates in the corresponding contact continues continuously.

[0034] Figure 2 The distribution of the self-grinding protective layer in a typical grinding contact area under ball milling conditions is shown. Figure 2 The specific spatial relationships between the grinding media, industrial silicon material, predetermined coarse-grained industrial silicon particles, metal liner, and contact area are further explained in the embodiments described later.

[0035] In this application, separate collection refers to separating the industrial silicon powder generated in the corresponding process stage from the normal product logistics and introducing it into an independent collection path or independent receiving unit, so as to maintain physical logistics separation between the industrial silicon powder formed in this stage and the industrial silicon powder in the normal product collection state.

[0036] Both product collection and individual collection occur after the industrial silicon powder has completed its classification. During normal continuous powder production, industrial silicon powder that meets the product particle size requirements enters the corresponding product receiving unit along the product path. During process stages such as start-up verification, continuous return material descent, protective material layer reconstruction, and batch end discharge, the corresponding industrial silicon powder enters the individual collection path after material switching.

[0037] Separate collection is used to maintain independent logistics boundaries for industrial silicon powder at the corresponding production stage. After obtaining the iron content test results of the corresponding samples and the return material operation status for the corresponding time period, the industrial silicon powder is collected separately and then processed according to the production quality management procedures. After this processing, the powder from the start-up stage, the normal product from continuous powder production, the powder from the abnormal stage, and the powder at the end of the batch each have their corresponding process origins.

[0038] On the specific production line, corresponding powder diversion points are set between the product collection path and the individual collection path, and industrial silicon powder enters the corresponding receiving unit according to the current process state. The diversion mechanism, conveying mechanism, and receiving bin adopt conventional industrial structures adapted to the conveying of industrial silicon powder and preventing cross-mixing.

[0039] The industrial silicon powder generated during the start-up phase is collected separately to keep the powder generated during the start-up cycle independent. After the predetermined amount of coarse-grained industrial silicon return material decreases continuously during continuous powder production, separate collection is implemented to ensure that the industrial silicon powder generated in this state exits the normal product logistics in advance. Separate collection continues during the rebuilding phase to keep the industrial silicon powder generated during the rebuilding process independent. The tail end of the industrial silicon powder generated after the normal feeding stops at the end of the batch also enters the independent collection path.

[0040] Before continuous grinding begins, coarse industrial silicon particles at a predetermined coarse particle size are separated from the same batch of industrial silicon to be ground, and these coarse particles are sent to the grinding process for start-up cyclic grinding.

[0041] The initial feed during the recycling phase primarily consists of pre-determined coarse-grained industrial silicon. After entering the grinding zone, the coarse silicon particles undergo mechanical grinding, and the discharged material proceeds to the classification process. Industrial silicon that remains at the pre-determined coarse-grained level after classification is returned to the grinding process, while the refined industrial silicon powder is discharged through its corresponding powder path.

[0042] As the predetermined coarse-grained industrial silicon continuously passes through the grinding zone, exits the mill, is classified, and returns to the grinding zone, it gradually forms a continuously circulating target coarse-grained material stream. Industrial silicon at the predetermined coarse-grained level continuously enters the grinding contact area and participates in mechanical contact. Particles that have been further refined leave the corresponding target particle size, while those still at the target particle size and the subsequently returned target coarse particles continue to enter the next cycle, thereby establishing a self-grinding protective material layer during the start-up phase.

[0043] The industrial silicon powder generated during the start-up cycle enters a separate collection path. Samples are obtained from the corresponding industrial silicon powder stream according to a predetermined sampling method, and their iron content is tested. The iron content increment is determined by combining the iron content of the benchmark established from the same batch of industrial silicon powder to be processed.

[0044] During the start-up phase, the iron content increment is used to confirm the actual iron enrichment state after the cyclic grinding is formed. As the target coarse-grained cycle is gradually established, and the continuously obtained industrial silicon powder samples reach the predetermined iron content increment control conditions, the industrial silicon powder from the start-up phase is collected separately and continuously fed into the grinding process.

[0045] Therefore, the start-up process has already completed the establishment of coarse-grained circulation and the confirmation of the corresponding iron-enriched state of industrial silicon powder before normal continuous feeding. When continuous production begins, the grinding zone already has the material basis for the predetermined coarse-grained industrial silicon to continuously participate in mechanical contact. The specific particle size range of the predetermined coarse-grained grade, the corresponding sieving path, and the particle contact relationship are further explained in the following embodiments; the specific determination process of the same batch of reference samples, low-iron contamination sample preparation, and iron content increment is also described in the following embodiments.

[0046] After the low-iron release is completed, the same batch of industrial silicon to be powdered is continuously fed into the grinding process, and the powdering process enters the normal continuous operation stage.

[0047] The industrial silicon to be ground is subjected to mechanical grinding together with the existing recycled material in the grinding zone. The material exiting the mill is sent to the classification process. Industrial silicon powder within the product particle size range is discharged and collected through the product path, while industrial silicon material exceeding the upper limit of the product particle size enters the re-grinding path and is sent back to the grinding process.

[0048] The regrind stream contains industrial silicon of different particle sizes to be further ground, among which the industrial silicon at the predetermined coarse particle size is the target coarse particle stream used to continue the self-grinding protective layer. After this portion of industrial silicon re-enters the grinding zone with the regrind stream, it re-enters the area where the industrial silicon material comes into mechanical contact with the metal parts, and continues to participate in interparticle contact and the transmission of grinding action.

[0049] During continuous production, the coarse industrial silicon particles that initially participated in the start-up and layer formation are continuously crushed and refined, while new, predetermined coarse-grained industrial silicon particles from the graded return material continuously enter the grinding process. In this way, the specific coarse industrial silicon particles responsible for contact with the corresponding particles in the grinding zone are constantly replaced, and the self-grinding protective layer is continuously renewed during the continuous grinding process.

[0050] Product powder discharge, return of re-milled material, and re-entry of target coarse particles into the grinding zone are all continuous material flows within the same closed-circuit grinding process. Product classification, on the one hand, completes the particle size separation between finished industrial silicon powder and re-milled material, and on the other hand, continuously supplies the predetermined coarse-grained industrial silicon to the grinding process, establishing a material receiving relationship between the renewal of the self-grinding protective layer and the normal closed-circuit re-milling process.

[0051] The specific millimeter-level coarse particle screening, product sub-grading, target coarse particle identification, and re-grinding path in the continuous milling stage are further elaborated in the following embodiments.

[0052] During continuous milling, the amount of pre-determined coarse-grained industrial silicon returned in the graded return process is continuously monitored. This return amount corresponds to the target coarse-grained stream that re-enters the milling process within a statistical period, reflecting the supply status of the pre-determined coarse-grained industrial silicon participating in the renewal of the self-grinding protective layer in the next cycle.

[0053] As continuous milling proceeds, the predetermined coarse-grained industrial silicon is continuously crushed and converted into finer particles. When the supply of the corresponding particle size in the regrind stream begins to decrease, the amount of predetermined coarse-grained industrial silicon returned will decrease accordingly. Once the return amount reaches the condition of continuous decline, the industrial silicon powder generated at that time is switched from the product collection path to a separate collection path.

[0054] The process sequence employed here is as follows: first, the coarse particle participation status in the next stage of the grinding zone is identified based on the target coarse particle return material flow; then, samples are continuously obtained from the already diverted industrial silicon powder, and the increase in iron content is detected. The predetermined amount of coarse-particle industrial silicon return material acts on the material side of the grinding process, while the increase in iron content acts on the quality side of the industrial silicon powder. These two types of process quantities correspond to the front-end material state and the back-end quality state in the continuous powder production process, respectively.

[0055] After the continuous decline in returned materials was triggered, normal product logistics were immediately switched to separate collection, and the industrial silicon powder was kept separate from the products collected under the previous stable operating conditions. The subsequent increase in iron content was used to determine the iron-increasing state corresponding to the current decline in the supply of target coarse particles, and based on this, the subsequent process of replenishing ordinary target coarse particles or rebuilding the self-grinding protective layer was initiated.

[0056] Figure 3 The corresponding changes in the predetermined amount of coarse-grained industrial silicon recycled, the increase in iron content, and the product collection status over production time are illustrated. The specific statistical method for the continuous decrease in recycled material amount, the method for determining the recycled material level before the continuous decrease, and the corresponding time status are further explained in the implementation method described later.

[0057] After the industrial silicon powder is switched to separate collection mode, the planned coarse-grained industrial silicon return material is monitored, and corresponding industrial silicon powder samples are continuously obtained to determine the increase in iron content.

[0058] When the increase in iron content is within the predetermined upper limit of iron content increase, new predetermined coarse-grained industrial silicon is separated from the same batch of industrial silicon to be powdered and sent to the grinding process, so that the newly added target coarse particles and the target coarse particles in the graded return material participate in the circulating grinding. Industrial silicon powder continues to be collected separately at this stage, and the status of the target coarse particle return material is monitored simultaneously.

[0059] When the increase in iron content exceeds the predetermined upper limit of iron content increase, the grinding process enters the self-grinding protective material layer reconstruction stage. During the reconstruction stage, the feed rate of the normal industrial silicon to be ground is reduced, while the same batch of predetermined coarse-grained industrial silicon continues to be added and the existing target coarse-grained return material is maintained, so that the relative participation of predetermined coarse-grained industrial silicon in the material entering the grinding process is increased.

[0060] During the reconstruction process, the grinding, grading, and reprocessing processes continue to operate, and the added target coarse particles gradually enter the grinding-grading-reprocessing cycle. After the target coarse particle reprocessing gradually changes from the aforementioned decay state to the recovery state, the normal industrial silicon feed rate and corresponding grading conditions are restored to the operating state before the continuous decline in reprocessing, so that the subsequent reprocessing volume can be compared under the corresponding production conditions.

[0061] When the amount of recycled material reaches the level before the continuous decline, it indicates that the target coarse-grained circulating supply has returned to the corresponding baseline state. Industrial silicon powder continues to be collected separately, and product recovery is confirmed by combining the subsequent recycling status and iron content increment detection results. After the corresponding recovery conditions are met, industrial silicon powder switches from the separate collection path back to the normal product collection path, and continuous powdering enters the normal product collection state.

[0062] Figure 3 This is used to represent the temporal sequence between the aforementioned recycle attenuation, product diversion, changes in iron content, protective layer reconstruction, recycle recovery, and product recovery. The following implementation methods further explain the recycle statistical cycle, determination of the target coarse-grained recycle amount, replenishment of ordinary coarse-grained materials, reconstruction operating conditions, and recovery confirmation conditions.

[0063] During the start-up cycle, coarse industrial silicon particles from the same batch are continuously subjected to impact, compression, and friction from the grinding media after entering the grinding zone. The particle size gradually decreases as the grinding process progresses and shifts towards a finer particle size. The coarse industrial silicon particles used to form the self-grinding protective layer need to have a clearly defined target particle size, ensuring that this portion of industrial silicon remains in a relatively coarse particle state within the grinding contact area and continues to return to the grinding process after mill classification, continuously forming the source of the target coarse particle material for the next cycle.

[0064] In some implementations, step S1, the formation of the self-grinding protective layer specifically includes the following steps.

[0065] S11, the lower limit of the predetermined coarse particle size is higher than the upper limit of the product particle size of industrial silicon powder, and the particle size range of the predetermined coarse particle size is 2-3 mm; the coarse industrial silicon particles separated from the same batch of industrial silicon to be powdered are sent to the grinding process for cyclic grinding, and the material obtained from grinding is classified.

[0066] S12, the industrial silicon coarse particles that are still in the predetermined coarse particle level after grading are returned to the grinding process for continued cyclic grinding, so that the industrial silicon coarse particles are cyclically distributed in the contact area between the material and the metal parts in the grinding zone.

[0067] S13, the coarse industrial silicon particles are continuously replaced by the continued grinding and return material cycle, forming an industrial silicon particle material layer in the contact area, which is composed of the coarse industrial silicon particles of the industrial silicon to be ground and is continuously renewed with the cycle grinding. The industrial silicon particle material layer participates in the grinding contact and bears part of the contact load, thus forming the self-grinding protective material layer.

[0068] Step S11 establishes the particle size boundary of the predetermined coarse-grained industrial silicon and initiates the circulating material. Step S12 establishes the material path for the target coarse particles to return to the grinding zone after being classified at the mill outlet. Step S13 corresponds to the particle group participation state formed after the target coarse particles enter the actual mechanical contact position. The target coarse particles enter the mill outlet material from the grinding zone, are classified and identified, re-enter the return material, and then re-enter the grinding zone. The entire process is synchronized with the continuous crushing of industrial silicon particles.

[0069] From a process perspective, the predetermined coarse-grained industrial silicon serves two purposes: firstly, it is the raw material to be pulverized, and secondly, it plays a role in the grinding contact area while maintaining its target particle size. As the target coarse particles break down, their particle size gradually shifts towards a finer size; simultaneously, the industrial silicon still at the predetermined coarse-grained size continues to be returned to the grinding zone, thus forming a continuous process of target coarse particle succession.

[0070] The predetermined coarse particle size in this application refers to the industrial silicon particle size determined from the same batch of industrial silicon to be powdered, which maintains a relatively coarse particle state during the mechanical grinding process, enters the grinding contact area, and serves as a self-grinding protective layer to continuously participate in the grinding contact.

[0071] The lower limit of the predetermined coarse particle size is higher than the upper limit of the industrial silicon powder product particle size, so that the industrial silicon of this particle size enters the re-grinding direction during the mill classification process and continues to participate in the closed-circuit grinding cycle. In this embodiment, 2-3 mm is used as the predetermined coarse particle size, and the upper limit of the product particle size control is 75 μm, forming a clear particle size hierarchy between the target coarse particles and the product powder.

[0072] When 2-3 mm industrial silicon enters the grinding zone, its particle size is significantly larger than that of the finished industrial silicon powder. This results in relatively prominent coarse particles being involved in the grinding process, particularly between the grinding media, near the metal liner, and in contact with the material bed within the mill. As mechanical grinding continues, the target coarse particles gradually undergo angular breakage, surface peeling, and overall refinement, with the particle size gradually decreasing from 2-3 mm to a finer range.

[0073] In actual grinding processes, 2–3 mm corresponds to a target intermediate particle size range for industrial silicon particles during particle size refinement. Larger industrial silicon particles undergo one or more grinding cycles, gradually reducing their size to the 2–3 mm range. This portion of industrial silicon, along with the mill output, enters the millimeter-level screening stage, is identified as the predetermined coarse-grained industrial silicon, and then returns to the grinding process, re-entering the grinding contact area. Thus, the target coarse particles have a continuous source of material for formation during continuous production.

[0074] The 2-3 mm particle size also forms a clear screening boundary. During the start-up phase, coarse particles of this particle size are obtained from the same batch of industrial silicon to be pulverized. During the continuous pulverization phase, target coarse particles of the same particle size are identified from the recycled material. Subsequent recycled material monitoring and abnormal replenishment are also carried out around this particle size, so that the same target material is used for start-up, renewal, monitoring and replenishment.

[0075] During the start-up phase, 2-3 mm coarse industrial silicon particles are obtained from the same batch of industrial silicon to be powdered, and these coarse particles are sent to the grinding process to establish a start-up cycle.

[0076] After a grinding process, the material exiting the mill forms multiple particle size levels. Industrial silicon still in the 2-3 mm range is re-entered into the re-grinding path as the predetermined coarse-grained industrial silicon; industrial silicon with a particle size below 2 mm but above the upper limit of the product particle size continues to be returned to the grinding process as the material to be ground; industrial silicon powder that has reached the product particle size range is discharged from the circulating material and enters a separate collection path during the start-up phase.

[0077] When the milled material still contains industrial silicon particles larger than 3 mm, this portion of the material continues to be recycled as larger particles and undergoes further grinding. As the particle size continues to decrease, some of the particles fall into the 2-3 mm range and are then identified as the predetermined coarse-grained industrial silicon by the corresponding screening process.

[0078] Therefore, the industrial silicon material in the start-up cycle continues to operate along the path of "continuous grinding of larger particles, recycling of 2-3mm target coarse particles, further crushing of finer re-grinding material, and separate collection of product powder".

[0079] This particle size distribution creates two processes simultaneously during the start-up phase. One process involves the target coarse particles establishing a cycle in the grinding-classification-return path; the other process involves the industrial silicon, which has already undergone appropriate refinement, gradually leaving the target coarse particle cycle and entering the subsequent re-grinding or product collection path.

[0080] In this application, the contact area refers to the local grinding area where industrial silicon material is impacted, squeezed, or rubbed by metal grinding media, metal liners, or corresponding metal grinding components during the grinding process.

[0081] During ball mill operation, typical contact locations include areas where industrial silicon material is trapped between adjacent grinding media, areas where industrial silicon material is trapped between the grinding media and the metal liner, and areas where the grinding media interacts with the industrial silicon material bed inside the mill. The intended coarse-grained industrial silicon continuously enters these localized locations as the material moves within the mill.

[0082] like Figure 2 As shown, the main diagram includes grinding media, a metal liner, industrial silicon material, predetermined coarse-grained industrial silicon particles, a contact area, and a self-grinding protective layer. The grinding media performs the main grinding mechanical function, the metal liner forms a typical metal contact boundary, the industrial silicon material constitutes the group of particles to be pulverized inside the mill, and the predetermined coarse-grained industrial silicon particles, as larger particles with the target particle size attributes, enter the corresponding local contact space.

[0083] Figure 2 The label "predetermined coarse-grained industrial silicon coarse particles" corresponds to a single typical target coarse particle, while the label "self-grinding protective layer" corresponds to a particle group area where multiple predetermined coarse-grained industrial silicon coarse particles are distributed together. A single target coarse particle is a component particle of the particle layer, and multiple target coarse particles continuously appear and replace each other at multiple local contact locations, forming a dynamic distribution of the self-grinding protective layer in the grinding zone.

[0084] The cyclic arrows in the diagram represent the overall process direction of the predetermined coarse-grained industrial silicon as it moves within the mill, exits for grading, and re-enters the grinding contact area via return material circulation. In actual operation, individual coarse-grained industrial silicon particles continuously change their spatial position due to mill rotation, grinding media movement, material accumulation, and their own breakage.

[0085] Figure 2 The AA position is selected as a typical grinding contact area and magnified locally to further express the spatial relationship between the grinding media, target coarse particles, ordinary industrial silicon material and metal liner.

[0086] Figure 2 The magnified view of part AA corresponds to a typical contact position of abrasive media—industrial silicon material—metal liner.

[0087] In the AA local position, the grinding media is located above the industrial silicon material, and the metal liner is located below the corresponding material. The predetermined coarse-grained industrial silicon and finer industrial silicon materials are distributed in the grinding space adjacent to the grinding media and the metal liner.

[0088] When the grinding media exerts instantaneous impact and compression on the area under the action of the mill movement, the predetermined coarse-grained industrial silicon and the surrounding industrial silicon material jointly enter a state of stress. The target coarse particles have a relatively large particle size, occupy a significant local space at the corresponding contact moment, and participate in the process of the grinding media transmitting mechanical force to the industrial silicon particle group.

[0089] In actual operation, the same type of local contact position will appear continuously as the mill rotates. At a certain moment, one or more target coarse particles enter the corresponding contact position, and at subsequent moments, other industrial silicon particles still at the predetermined coarse particle level will enter in succession. The number of particles, particle spacing, and geometric arrangement in the figure are used to express the typical spatial state. The actual particle state is formed by the mill charge, the movement of the grinding media, the number of coarse particles, and the particle crushing process.

[0090] The self-grinding protective layer in the main image reflects the distribution of target coarse particles at multiple local contact locations. The magnified AA view expands one typical location to show the spatial relationship between the grinding media, target coarse particles, surrounding industrial silicon material, and metal liner.

[0091] The self-grinding protective layer in the actual grinding zone exhibits a dynamic particle group distribution of multiple discrete, predetermined coarse-grained industrial silicon particles at multiple local grinding contact locations.

[0092] The particle group continuously changes its spatial position as the mill rotates, the industrial silicon material tumbles, and the return material circulates. The local contour, particle spacing, and particle arrangement of the particle layer change with the instantaneous state of the material inside the mill. At a certain grinding moment, a group of target coarse particles participate in the corresponding mechanical contact, and at subsequent grinding moments, another group of industrial silicon particles still at the predetermined coarse particle level enters the same or adjacent contact positions.

[0093] The continuity of the self-grinding protective layer is manifested in the continuous presence of the target coarse particles along the grinding time. A single industrial silicon coarse particle has a particle history of entering the target particle size, entering the contact area, being subjected to mechanical action, being broken and transferred to a finer particle size; the particle history of multiple target coarse particles is continuous during the continuous grinding process, so that the grinding contact area is continuously equipped with the predetermined coarse-sized industrial silicon.

[0094] thus, Figure 2 The self-grinding protective layer shown in brackets corresponds to a particle group region that continuously changes during the grinding process. This region is formed by the coarse particles of industrial silicon itself, and its specific constituent particles are constantly renewed with grinding, classification, and reprocessing.

[0095] The impact and compression forces generated by the movement of the grinding media are transmitted to the industrial silicon material through local particle contact. After the predetermined coarse-grained industrial silicon enters the corresponding contact area, it is situated within the force-bearing space formed by the grinding media, the surrounding industrial silicon material, and the corresponding metal grinding components.

[0096] by Figure 2 Taking the AA local position as an example, when the grinding media moves towards the industrial silicon material area, the predetermined coarse-grained industrial silicon located at the corresponding position is subjected to instantaneous impact and compression. At the same time, the coarse grains come into interparticle contact with the surrounding industrial silicon particles, and the corresponding mechanical action continues to be transmitted along the target coarse grains and adjacent industrial silicon particles.

[0097] In the material zone between adjacent grinding media, the intended coarse-grained industrial silicon is also situated within a localized clamping space formed by multiple moving media. At this location, the target coarse particles experience instantaneous mechanical forces from different directions and continue to transmit the grinding action through contact with adjacent industrial silicon particles.

[0098] Therefore, the coarse-grained industrial silicon is intended to bear a portion of the total contact load in the aforementioned mechanical contact process. This portion of the load varies with the coarse particle position, the movement state of the grinding media, the local material filling state, and the particle contact geometry.

[0099] After the target coarse particles participate in the corresponding contact, the portion transmitted between industrial silicon particles during the grinding mechanical action increases, and the contact state between the industrial silicon material and the metal grinding components changes accordingly. The direct material impact and friction state experienced by the surface of the metal components changes accordingly, and the wear of the steel and the additional Fe entering the industrial silicon powder show corresponding differences as the grinding contact state changes.

[0100] The coarse particles undergo the aforementioned grinding process while simultaneously undergoing their own crushing. The smaller particles formed after being subjected to stress still belong to the same batch of industrial silicon material and continue to be processed along the grinding, grading, and product formation path of industrial silicon.

[0101] The "self-grinding" in the self-grinding protective layer described in this application refers to the fact that the material constituting the protective particles is of the same origin as the industrial silicon to be pulverized, and that the coarse particles of this industrial silicon continue to enter the normal particle size refinement process of this batch of industrial silicon after participating in the grinding contact.

[0102] In the ball milling implementation, the movement of steel balls and the mill provides the main mechanical grinding action, while the predetermined coarse-grained industrial silicon enters the mechanical action area as the material to be ground. The target coarse particles have a dual process role in the corresponding stage: on the one hand, they are ground and gradually refined as industrial silicon raw materials; on the other hand, while they are in the predetermined coarse-grained stage, they participate in part of the load transfer in the grinding contact area in a relatively coarse particle form.

[0103] After the target coarse particles are further crushed, they continue to enter the subsequent re-grinding or product sub-grading processes of this batch of industrial silicon. The predetermined coarse-grained industrial silicon used for start-up layer building, continuous return material renewal, and abnormal stage replenishment all come from the same batch of industrial silicon to be powdered, so that the source and destination of the target coarse particles are embedded in the powdering logistics of this batch of industrial silicon.

[0104] After coarse-grained industrial silicon undergoes mechanical contact in the grinding zone, its particle size gradually decreases during the grinding process.

[0105] When a target coarse particle moves from 2-3 mm to a particle size below 2 mm, the particle enters the corresponding ordinary re-grinding or fine re-grading path according to its actual particle size; at the same time, other industrial silicon that is still in the 2-3 mm particle size continues to enter the grinding zone through the target coarse particle return path.

[0106] From the perspective of the particle group inside the mill, the crushing of the original target coarse particles constitutes the continuous consumption of the self-grinding protective layer, while new target coarse particles continuously enter to form the self-grinding protective layer. The simultaneous changes of these two materials ensure that the self-grinding protective layer remains dynamically replenished under continuous grinding conditions.

[0107] During normal continuous feeding, larger industrial silicon particles are ground once or multiple times, gradually reducing their size to 2-3 mm. This portion of industrial silicon is then identified by millimeter-level sieving after exiting the mill and returned to the grinding process to form a new source of pre-determined coarse-grained industrial silicon.

[0108] In actual production, this process involves gradually grinding larger industrial silicon particles to a size of 2-3 mm, then screening them and sending them back into the target coarse particle return path. There, they re-enter the grinding contact area and continue grinding until they reach a finer particle size. New, larger industrial silicon particles then undergo the same particle size evolution process to form the next batch of target coarse particles.

[0109] Therefore, the target coarse particles have a particle life cycle of continuous formation, continuous return, and continuous consumption in continuous production.

[0110] The predetermined coarse particle size simultaneously affects the number of particles corresponding to a unit mass of target coarse particles, the grinding process of a single target coarse particle maintaining the predetermined particle size, and the mechanical action required for the particle to continue to be ground into a finer particle size.

[0111] When the target coarse particle feed quality is within the corresponding production range, the number of industrial silicon particles corresponding to the smaller particle size is greater, and the distribution points of the particles in the mill increase accordingly. At the same time, the smaller coarse particles enter the finer particle size after a shorter grinding process, and the duration for which they maintain the target coarse particle state and participate in the corresponding contact is shortened, thus increasing the frequency of return material circulation to the target particle size.

[0112] As the particle size increases further, a single coarse target particle requires a longer grinding process to move from its current size to a finer size, and its residence time in the grinding contact area increases accordingly. At the same time, under the same or similar target coarse particle mass conditions, the total number of particles corresponding to the increase in single particle size decreases, and the basis for the number of target coarse particles forming a group distribution at multiple local contact locations changes accordingly; the mechanical crushing action required for further refinement of larger particles also increases accordingly.

[0113] Therefore, the actual effect of the predetermined coarse particle size in the grinding contact area is simultaneously influenced by the particle size distribution, the lifespan of a single target coarse particle, and the subsequent grinding load. The target coarse particle needs to maintain a corresponding particle size distribution at multiple local contact locations, while having a sufficient lifespan to complete the return cycle, and ensuring that the subsequent grinding load is compatible with industrial continuous grinding conditions.

[0114] The three process factors mentioned above work together to influence the particle size distribution of the self-grinding protective layer. When the target coarse particle size changes, the number of particles, the distribution of contact positions, the coarse particle duration, and the continuing grinding load change synchronously, and the low-iron grinding effect shows a corresponding particle size correlation.

[0115] Under the ball milling conditions described in this implementation, a corresponding process match is achieved between the particle size distribution, the existence of the target particle size, and the continued grinding load of 2-3 mm industrial silicon.

[0116] Industrial silicon at this particle size has clear millimeter-level sieve boundaries, forming a clearly defined target coarse-grained return material stream after mill screening. This portion of industrial silicon re-enters the grinding zone, where it is distributed as relatively coarse particles at multiple local contact points, gradually shifting towards a finer particle size during continued grinding. New 2-3 mm industrial silicon is continuously formed through the normal grinding process and then re-enters the grinding process as return material.

[0117] Smaller particle sizes correspond to a higher number of particles per unit mass, while their target particle size duration is shorter; larger particle sizes correspond to a longer coarse particle duration, while the number of particles per unit mass decreases and is accompanied by a higher subsequent grinding load. In this implementation, a 2–3 mm particle size range creates a suitable combination of particle size, contact duration, and subsequent grinding process.

[0118] This process matching is also reflected in the participation of particle groups at multiple contact points. The 2-3mm target coarse particles maintain a certain particle quantity base and have a corresponding coarse particle existence history, so that multiple target coarse particles are continuously distributed in the grinding contact area, and after the original target coarse particles are refined, they are continued by the subsequent return material coarse particles.

[0119] This embodiment sets up comparisons of smaller coarse particles, 2-3 mm target coarse particles, and larger coarse particles to evaluate the Fe increment of industrial silicon powder, steel wear, unit energy consumption, and product particle size. The results under different coarse particle conditions show the advantage of intermediate particle size; the corresponding complete comparison data are given in the industrial examples and comparison conditions described later.

[0120] After the self-grinding protective layer is established during the start-up phase, the same batch of industrial silicon to be powdered continuously enters the grinding process, and normal product logistics and regrind logistics are established accordingly. The pre-designated coarse-grained industrial silicon that participated in the layer building during the start-up phase continues to be ground and gradually becomes finer-grained. During continuous production, new pre-designated coarse-grained industrial silicon is continuously supplied to the grinding zone by the normal regrind logistics.

[0121] In some implementations, the graded return process in step S3 specifically includes the following steps.

[0122] S31 collects industrial silicon powder within the product particle size range as the product.

[0123] S32, industrial silicon materials exceeding the upper limit of product particle size are returned to the grinding process for further grinding.

[0124] S33, the industrial silicon coarse particles in the predetermined coarse particle level in the returned material are fed back into the grinding process for cyclic grinding, so that the industrial silicon coarse particles re-enter the contact area between the material and the metal parts in the grinding zone, and the self-grinding protective material layer is renewed with the return material cycle.

[0125] Step S31 forms the discharge path of industrial silicon powder for the product; step S32 forms the re-grinding path for materials with a particle size higher than the upper limit of the product; and step S33 further determines the update path for the predetermined coarse-grained industrial silicon in the re-grinding material to re-enter the grinding contact area.

[0126] As continuous grinding proceeds, larger industrial silicon particles are gradually ground to 2-3 mm size. The 2-3 mm target coarse particles are screened and re-enter the grinding process, while the finer industrial silicon continues to be ground or enters the product sub-grading, thus forming a continuous particle size transfer and return material relay.

[0127] After being graded, the industrial silicon exiting the mill is divided into product logistics, ordinary re-milling logistics, and pre-determined coarse-grained industrial silicon return material according to the actual particle size.

[0128] The product logistics consists of industrial silicon powder that meets the product particle size range. This portion of industrial silicon powder is discharged from the closed-loop grinding cycle and enters the product collection path.

[0129] The typical regrind material consists of industrial silicon material that is above the product particle size limit and continues to be ground, including larger industrial silicon with a particle size greater than 3 mm and industrial silicon with a particle size less than 2 mm but above the product particle size limit.

[0130] The planned coarse-grained industrial silicon return material consists of 2-3 mm industrial silicon. This part of the material stream is also a specific particle size sub-stream within the overall regrind material stream, and it plays a role in supplying the target coarse-grained material for the continuous renewal of the self-grinding protective layer.

[0131] In actual operation, industrial silicon with a particle size greater than 3mm is re-entered into the grinding process as ordinary coarse re-grinding material; industrial silicon with a particle size in the range of 2-3mm is re-entered into the grinding process as predetermined coarse-grained industrial silicon re-grinding material; industrial silicon with a particle size in the range of the upper limit of product particle size to 2mm is re-grinded as ordinary re-grinding material; and industrial silicon powder within the product particle size range enters the product collection and logistics.

[0132] Through the above particle size hierarchy, the entire re-grinding material stream represents the overall re-grinding load of the closed-circuit milling system, while the predetermined coarse-grained industrial silicon re-grinding material represents the specific material flow that actually re-enters the milling contact area as the target coarse particles.

[0133] During the initial layer-building stage, the same batch of industrial silicon to be powdered is subjected to millimeter-level sieving to obtain 2-3 mm coarse industrial silicon particles, and this portion of industrial silicon is sent to the grinding process to establish the start-up cycle.

[0134] In the continuous grinding stage, the material exiting the mill enters the mill-level coarse particle screening process. By using the screening boundaries corresponding to 2mm and 3mm, the predetermined coarse-grained industrial silicon is identified from the material exiting the mill, and this portion of industrial silicon is directed into the target coarse particle return path.

[0135] Industrial silicon with a particle size larger than 3mm is returned to the grinding process via the standard coarse regrinding path. Industrial silicon with a particle size in the range of 2-3mm is returned to the grinding process via the target coarse particle return path. Industrial silicon with a particle size smaller than 2mm enters the subsequent product sub-grading process.

[0136] The product is further separated into finer industrial silicon materials according to the 75μm product particle size control requirement. Industrial silicon powder within the product particle size range enters the product collection path, while industrial silicon materials with a particle size higher than the upper limit of the product particle size but lower than 2mm enter the ordinary re-grinding path for further grinding.

[0137] This embodiment employs millimeter-level sieving to identify 2-3 mm target coarse particles, and air classification to control the product particle size to 75 μm. Millimeter-level sieving handles target coarse particle identification and return material diversion, while product sub-classification handles the separation of micron-sized product powder from finer return materials.

[0138] The corresponding screening equipment, air classification equipment, return material conveying equipment, and product collection equipment are arranged in the actual particle size processing sequence of the material exiting the mill, so that the target coarse particle return material and product powder output form a clear logistics path.

[0139] After the industrial silicon to be ground is continuously fed into the grinding process, the larger particles undergo a continuous particle size reduction process. Some of the industrial silicon reaches the target particle size of 2-3 mm during the grinding process.

[0140] Industrial silicon particles in the 2-3 mm size, after entering the mill-level screening process along with the mill output material, are classified as pre-determined coarse-grained industrial silicon return material and re-entered into the grinding process. These particles then enter the next cycle as the target coarse-grained particles. Figure 2 The grinding contact area shown participates in the corresponding particle contact and part of the load transfer.

[0141] After further grinding, the target coarse particles are reduced to a particle size of less than 2 mm, and then enter the ordinary re-grinding or product sub-grading path according to the actual particle size. At the same time, new, larger industrial silicon particles are ground to a size of 2-3 mm, forming the next batch of target coarse particles.

[0142] The source of the target coarse particles in continuous production thus exhibits a clear process continuity. The initial 2-3 mm coarse particles introduced during the start-up phase establish the initial particle participation state. During the continuous production phase, the 2-3 mm intermediate particle size formed during the normal industrial silicon pulverization process continues this state. When the target coarse particles are returned and depleted, 2-3 mm coarse particles are added again from the same batch of industrial silicon to be pulverized.

[0143] This material process of "grinding formation - screening and identification - return material continuation - re-grinding" integrates the self-grinding protective material layer with the normal closed-circuit grinding process in the same logistics system.

[0144] The 2-3mm pre-selected coarse-grained industrial silicon has a clearly defined particle size boundary, a clearly defined sieving location, and a clearly defined regrinding path. The 2-3mm industrial silicon that re-enters the grinding process through this regrinding path within a statistical cycle corresponds to the material source used to replenish the target coarse particles in the grinding contact area in the next cycle.

[0145] The 2-3mm industrial silicon in the recycled material enters the grinding process again. Figure 2 The area of ​​contact between the material and the metal component is shown. When the material flow remains stable, the grinding zone continuously receives new, predetermined coarse-grained industrial silicon; when the material flow continues to decline, the target coarse-grained supply for the next cycle changes synchronously.

[0146] All regrinding materials continue to perform the task of re-grinding industrial silicon with a particle size exceeding the upper limit of the product size. The 2-3mm pre-designated coarse-grained industrial silicon regrind material simultaneously undertakes the task of continuing the particle generation of the self-grinding protective layer in this regrinding system. Both types of regrind materials run in the same regrinding direction, but their process action levels are different.

[0147] Therefore, the amount of coarse-grained industrial silicon returned during subsequent continuous grinding processes is independently statistically analyzed, corresponding to the target particle size stream of industrial silicon with clearly defined physical boundaries. This stream is formed through screening, returned to the grinding zone, participates in mechanical grinding in the contact area, and completes one target coarse-grained life cycle as the particles continue to be crushed. Continuously statistically analyzing this stream corresponds to continuously observing the changes in the supply status of the target coarse particles required for the self-grinding protective layer.

[0148] Industrial silicon raw materials inherently possess a certain Fe content, and the corresponding Fe base of the raw material is already formed within the same production batch before mechanical milling. In industrial silicon powder obtained after mechanical milling, the Fe measurement results simultaneously include both the Fe base of the raw material itself and the incremental changes resulting from the milling process. When judging the iron gain state during the mechanical milling stage, it is necessary to use the Fe base of the current batch of industrial silicon before milling as a starting point for comparison.

[0149] In actual production, industrial silicon to be powdered is usually in the form of raw material particles at the millimeter level or larger, while the industrial silicon powder to be tested has already undergone grinding and product fine grading. There are significant differences between the two in particle size and pretreatment load before testing. When the reference sample enters the testing state from the raw material state, it needs to undergo corresponding particle size treatment; this treatment process involves contact between the sample and the sample preparation equipment, and the control level of Fe introduced directly affects the process judgment at the 100ppm level.

[0150] Therefore, the determination of the iron content increment is based on the same production batch, corresponding particle size, and the aforementioned low-iron contact sample preparation conditions.

[0151] In some implementations, the iron content increment in steps S2 and S4 is determined according to steps S21-S23.

[0152] S21. Obtain a reference sample from the same batch of industrial silicon to be powdered, and prepare the reference sample to a particle size range corresponding to the industrial silicon powder to be tested using low-iron contact sample preparation conditions determined by parallel sample preparation comparison of the same sample.

[0153] S22. Use low-iron contact sample preparation conditions to prepare the reference sample and the industrial silicon powder to be tested before testing. Detect the iron content of the reference sample and the industrial silicon powder to be tested respectively, and use the iron content of the reference sample as the reference iron content.

[0154] S23, the difference between the iron content of the industrial silicon powder to be tested and the reference iron content is taken as the iron content increment.

[0155] S21 is used to establish the particle size correspondence between the reference sample and the industrial silicon powder to be tested; S22 is used to establish the sample state correspondence between the two types of samples before entering Fe analysis; and S23 forms the iron content increment used in the current production batch based on the above.

[0156] The reference sample was obtained from the same batch of industrial silicon currently being pulverized, and retained the same production batch identification as that batch of industrial silicon.

[0157] This batch of industrial silicon serves as the raw material source for coarse grains used in start-up layer building, normal feed for continuous milling, replenishment of target coarse grains during operation, and reserve coarse grains at the end of the batch. The reference sample and the aforementioned process materials share the same raw material source, ensuring that the determination of Fe increment for the entire batch is based on the same raw material Fe.

[0158] After obtaining the reference sample, it is representatively mixed and sampled to form a reference sample for subsequent particle size matching processing. The specific sampling location and reduction operation are carried out in accordance with the existing raw material quality sampling procedures of the production line, and the sampling range covers the actual raw material state of this batch of industrial silicon to be powdered.

[0159] After particle size matching and low-iron contamination detection pretreatment, the Fe determination results of the reference sample form the reference iron content for this batch of industrial silicon. For industrial silicon powder samples obtained during the start-up phase, normal continuous powder production phase, and phases of operational status change, this reference iron content is used as the starting point for calculating the Fe increment of this batch.

[0160] When switching production to a new batch of industrial silicon, a new reference sample is obtained for the new batch, and the reference iron content for the new batch is established according to the same particle size matching and testing procedures.

[0161] Batch matching is used to unify the source of raw materials, while particle size matching is used to unify the particle state of samples before testing.

[0162] The surface area, homogenization state, and pretreatment amount of industrial silicon raw materials vary depending on their particle size. When raw material-grade reference samples are directly introduced into the analytical process, they are in a different particle size state from the industrial silicon fine powder formed by mechanical grinding. After the reference samples are processed to a particle size range corresponding to the industrial silicon powder to be tested through S21, the two types of samples have a closer particle size and sample homogenization basis when entering the subsequent Fe analysis.

[0163] Therefore, this application uses both "same batch" and "corresponding particle size range" as comparison conditions for Fe increment. "Same batch" determines that the comparison objects come from the same raw material batch, and "corresponding particle size range" determines that the comparison objects have similar particle sizes before testing.

[0164] After this processing, the comparison relationship corresponding to the Fe increment changes from a simple "comparison between raw material Fe and product Fe" to "comparison between the reference Fe of the same batch of raw materials and the Fe of industrial silicon powder after powdering".

[0165] The low-iron contact sample preparation conditions in this application refer to the sample preparation conditions determined by comparing the iron content determination results after parallel sample preparation under different sample preparation contact conditions. These conditions are used to control the level of additional Fe introduction in industrial silicon samples during sampling, reduction, crushing, grinding, sieving, transfer, storage, and pretreatment before detection.

[0166] Method validation used the same homogenized industrial silicon sample as the sample source. Samples were prepared under both low-iron contact and comparative preparation conditions, and parallel determinations were performed under the same Fe analysis conditions. The difference in Fe results corresponding to the two preparation conditions was used to evaluate the influence of the sample preparation process itself on the formation of Fe results.

[0167] The low-iron contact sample preparation conditions, determined through parallel sample preparation comparisons of the same sample, are used for reference sample particle size matching, reference sample pretreatment, and pretreatment of industrial silicon powder to be tested. The reference sample and the industrial silicon powder to be tested are subjected to the same low-Fe contamination control principles during Fe analysis, ensuring that the measurement results of the two types of samples are based on a unified sample preparation foundation.

[0168] The methodological comparison results described later show that the difference in Fe results formed under ordinary steel contact conditions has reached an order of magnitude close to the 100ppm process control scale. Therefore, this embodiment applies low-iron contact sample preparation conditions throughout the entire detection chain of the reference sample and the industrial silicon powder to be tested.

[0169] The specific sample preparation equipment, crushing method, transfer method, and pre-analytical treatment operations adopt low-Fe contamination conditions that are compatible with the 100ppm process control scale after comparison and verification of the above methodologies. The reference sample and the industrial silicon powder to be tested are processed according to the same low-Fe contamination control principle.

[0170] S21 corresponds to the process of the reference sample changing from the state of raw material particles to the state of particle size matching.

[0171] After representative reduction, the reference sample obtained from the same batch of industrial silicon powder is subjected to stepwise crushing, grinding and sieving according to the low-iron contact sample preparation conditions, so that the particles of the reference sample are within the particle size range corresponding to the industrial silicon powder to be tested.

[0172] The corresponding particle size range is determined according to the actual particle size state of the industrial silicon powder to be tested. In this embodiment, the upper limit of the particle size control of the industrial silicon powder is 75 μm, and the reference sample is processed with corresponding low iron contamination particle size to form a fine powder sample corresponding to the detection state of the product powder.

[0173] After the particle size matching process is completed, the reference sample has been transformed from raw material-grade particles into a particle size suitable for comparison with industrial silicon powder for Fe content. Subsequently, the reference sample enters the pre-detection sample processing stage described in S22.

[0174] S21 processes the particle size of the reference sample, resulting in a particle size-matched reference sample. Subsequent sample homogenization, reduction, and pre-analytical processing required for Fe detection are carried out in S22.

[0175] S22 corresponds to the sample processing of the reference sample and the industrial silicon powder to be tested before entering the Fe analysis.

[0176] After step S21, the reference sample has reached the particle size range corresponding to the industrial silicon powder to be tested. At this point, the particle size-matched reference sample and the industrial silicon powder to be tested obtained from actual production undergo sample homogenization, reduction, transfer, and pre-treatment suitable for ICP-OES analysis.

[0177] For industrial silicon powder already in the particle size testing stage, pre-analytical sample preparation involves homogenization, reduction, and subsequent pretreatment at its existing particle size. For reference samples, the same stage is performed after completing particle size matching (S21).

[0178] After processing with S22, the reference sample becomes the reference test sample, and the industrial silicon powder to be tested becomes the production test sample. The Fe content of the two types of samples is determined separately. The Fe result of the reference test sample becomes the reference iron content, and the Fe result of the production test sample becomes the Fe content of the industrial silicon powder to be tested.

[0179] S21 and S22 are carried out continuously in the order of "raw material particle state - particle size matching state - detection state", thus giving clear process boundaries to the particle size change of the reference sample and the pretreatment of the two types of samples.

[0180] After the particle size matching reference sample is prepared before testing and the Fe is measured, the Fe result is used as the reference iron content for the batch of industrial silicon to be powdered.

[0181] After establishing the baseline iron content, the reference sample retains the corresponding batch identifier, sample number, and sample preparation record. The retained sample is managed according to the sample storage conditions for industrial silicon quality testing and is used for verification of testing records during the production process of this batch.

[0182] The reference iron content is recorded in the batch release and continuous powder production quality assessment records. A correspondence is established between the industrial silicon powder samples obtained within a production batch and the reference iron content of that batch.

[0183] In this embodiment, the baseline Fe content of the industrial silicon to be powdered in the same batch is about 2000 ppm, or about 0.20%.

[0184] The production sampling location for the industrial silicon powder to be tested is set after the product sub-grading and before the industrial silicon powder enters the corresponding product receiving unit, at the powder logistics location.

[0185] Under normal continuous powder production conditions, this location corresponds to the industrial silicon powder logistics. Under the conditions of start-up layer building, continuous material return descent, and self-grinding protective material layer reconstruction, the same powder outlet enters a separate collection path after logistics switching.

[0186] Samples at each stage were obtained from industrial silicon powder logistics after the corresponding product particle size classification was completed, so that the start-up samples, running samples and reconstruction samples have a unified production sampling section.

[0187] Each sample record includes the corresponding production batch identifier, sampling order, and sampling time. When using continuous time segment management, the sample number is associated with the corresponding time segment for the separate collection of industrial silicon powder. After subsequent Fe results are generated, they are directly written back to the corresponding sample and the corresponding production time segment.

[0188] After this processing, the Fe measurement results not only correspond to a specific industrial silicon powder sample, but also to the actual production stage of that sample.

[0189] In this embodiment, ICP-OES was used to determine the Fe content in the reference sample and the industrial silicon powder to be tested.

[0190] After the reference sample and the industrial silicon powder to be tested are prepared into test samples according to the aforementioned low-iron contamination sample treatment requirements, they enter the same Fe analysis process. Instrument calibration, method blanks, parallel samples, and quality control samples are performed according to the actual laboratory testing procedures.

[0191] Test results are uniformly expressed in ppm and correspond to the corresponding sample number, production batch and sampling time record.

[0192] The Fe result obtained from the benchmark test sample is recorded as the benchmark iron content of this batch, and the Fe result obtained from the production sample is recorded as the Fe content of the corresponding industrial silicon powder. The difference between the two is then calculated in S23.

[0193] The iron content increments in this application are based on four corresponding measurement conditions.

[0194] The first requirement is batch consistency of raw materials; both the reference sample and the industrial silicon powder to be tested originate from the same batch of industrial silicon to be powdered. The second requirement is particle size correspondence; after S21 treatment, the reference sample forms a particle size range corresponding to the industrial silicon powder to be tested. The third requirement is consistent sample preparation conditions before testing; both the reference sample and the industrial silicon powder to be tested undergo sample preparation according to the aforementioned low-iron contact conditions. The fourth requirement is consistent production sampling locations; industrial silicon powder from both the start-up phase and the continuous powdering operation phase is obtained from the corresponding powder flow location after product sub-grading.

[0195] The above conditions together form a unified basis for comparing Fe increments, enabling continuous comparison of industrial silicon powder results obtained from different production times in the same batch along the same measurement caliber.

[0196] Let the Fe content of the industrial silicon powder to be tested be: The baseline Fe content of the same batch of particle size matching reference sample is: The increase in iron content is determined by the following formula: ,in This indicates the increase in Fe content of the current industrial silicon powder relative to the baseline state of the same batch of raw materials.

[0197] For example, if the reference Fe content of this batch of industrial silicon is 2000 ppm, and the Fe content of a certain industrial silicon powder sample is measured to be 2080 ppm, then the corresponding increase in iron content of this sample is 80 ppm.

[0198] The 80ppm level is directly used for start-up release or continuous milling quality status judgment, and is compared with the corresponding predetermined upper limit of iron content increment.

[0199] In this application, the Fe increment is used as a quality-side process characterization quantity in the mechanical grinding stage. Steel wear, target coarse particle return amount, and Fe increment are recorded from the corresponding production processes based on the state of the grinding components, the state of the target coarse particle stream, and the quality state of the finished powder, respectively.

[0200] After the Fe sample is obtained, sample processing and ICP-OES determination require a corresponding analysis time. During this period, the industrial silicon powder continues to enter the corresponding collection path according to the process conditions determined at the time of sampling.

[0201] After sampling during the start-up phase, industrial silicon powder continues to be collected separately during the start-up phase. When sampling after the return material has continuously decreased, industrial silicon powder continues to be collected separately during the abnormal phase. When sampling during the reconstruction phase, industrial silicon powder continues to be collected separately during the reconstruction phase.

[0202] In the implementation method that uses time-segmented collection, each receiving unit records the corresponding production time segment and sample number. After the Fe results are generated, the corresponding results are associated with the powder records for that time segment.

[0203] This processing method ensures a clear record of the formation time of the test results and the actual production time of industrial silicon powder, and provides a basis for subsequent time-series judgment of the status of continuous samples.

[0204] The predetermined upper limit for iron content increment is used to control the incremental level of Fe generated relative to the base Fe of the same batch of raw materials during the mechanical milling stage.

[0205] Let the upper limit of Fe content in industrial silicon powder products be: The iron content of the same batch is as follows: The upper limit of the predetermined increase in iron content is denoted as: These three satisfy the relationship The equivalent process control state satisfies In this embodiment, the Fe content of the industrial silicon powder to be powdered in the same batch is about 2000 ppm, and the upper limit of the Fe content of the industrial silicon powder product is 3000 ppm, forming a product mass margin of about 1000 ppm between the two.

[0206] In this embodiment, 100 ppm is used as the upper limit of the predetermined iron content increment, corresponding to a 0.010% Fe increment. Based on the baseline Fe level of this embodiment, when the Fe increment reaches 100 ppm, the corresponding Fe content of industrial silicon powder is approximately 2100 ppm, which still retains a corresponding mass margin from the product upper limit of 3000 ppm.

[0207] The process control value, together with the methodology of the low-iron contact sample preparation conditions described later, jointly determines the basis for its testing implementation, so that the product quality margin and the testing resolution scale are within the same process control system.

[0208] 100 ppm is a relatively small control scale for iron addition during powder preparation. The level of Fe introduction generated during sample preparation needs to be adapted to this control scale.

[0209] The methodology comparison in this embodiment used the same homogenized industrial silicon powder, and parallel measurements were performed under both low-iron contact sample preparation conditions and ordinary steel sample preparation conditions. The Fe results obtained under the two sample preparation conditions showed significant differences, and the magnitude of these differences was sufficient to affect the state judgment near the 100 ppm control limit.

[0210] Therefore, the low-iron contamination sample processing procedure, which has been validated by the above methodology, was used for the start-up sample, the sample collected separately during operation, and the reference sample in the same batch.

[0211] The specific number of parallel determinations, average Fe results, and measurement differences between the two sample preparation conditions are listed in the industrial examples described later.

[0212] After the cycle is established, the amount of coarse-grained industrial silicon circulating in the grinding-classification-returning path is gradually formed, and the Fe increment of industrial silicon powder changes accordingly with the start-up grinding state.

[0213] The release process is determined by a combination of the predetermined upper limit of iron content increment and the status of continuous samples.

[0214] In some embodiments, the reference iron content is lower than the upper limit of iron content in industrial silicon powder products, the upper limit of the predetermined iron content increment is 100 ppm, and the upper limit of the predetermined iron content increment is within the mass margin range between the upper limit of iron content in industrial silicon powder products and the reference iron content.

[0215] During the cyclic grinding process in step S1, industrial silicon powder samples are collected individually at predetermined sampling intervals of 15 minutes. When the iron content increment of at least two consecutive industrial silicon powder samples is 100 ppm or less, the individual collection of industrial silicon powder in the start-up phase ends, and continuous grinding begins.

[0216] This release condition corresponds to two consecutive production sampling sections maintaining a low iron content state, thus establishing a direct relationship between start-up status confirmation and continuous production time.

[0217] In this embodiment, 15 minutes is used as the predetermined sampling interval for industrial silicon powder.

[0218] After each 15-minute production time interval, a representative sample is collected separately from the industrial silicon powder logistics after each product sub-classification, and the corresponding batch, sampling order and sampling time are recorded.

[0219] The 15-minute sampling interval is aligned with the timescale of grinding, grading, and return material circulation during the start-up phase, and is used to continuously record the changes in the Fe state of industrial silicon powder over production time during the start-up and layer-building process.

[0220] The sampling interval serves to divide the production samples, and the ICP-OES analysis is completed according to the actual sample processing and instrument detection procedures. During the detection period, the corresponding industrial silicon powder continues to be collected separately.

[0221] During the start-up cycle, a single Fe sample corresponds to a specific production time point or a corresponding production time segment. When at least two consecutive samples are at or below 100 ppm, it means that the industrial silicon powder formed in adjacent production time segments has reached the corresponding low iron enrichment control state.

[0222] Therefore, continuous sample verification targets the continuous maintenance of the grinding state over time. Once this condition is met, the product collection process switches from separate collection during the startup phase to continuous grinding and normal product collection.

[0223] The startup process data described below are recorded sequentially in 15-minute time intervals, showing the predetermined amount of coarse-grained industrial silicon return material and the incremental amount of Fe in industrial silicon powder, to correspond to the aforementioned continuous release process.

[0224] Fe results were obtained from industrial silicon powder samples acquired during the start-up phase and from industrial silicon powder samples acquired after changes in continuous powder production status, following the same batch benchmark, the same particle size matching principle, the same low-iron contact sampling conditions, and the same product sub-grading sampling location.

[0225] Initiation phase Used to determine the low iron gain state after the establishment of the autogenous grinding protective layer; formed after the product is switched to separate collection in continuous grinding. Used to determine the quality status of the target coarse particles during the ordinary replenishment stage and the autogenous grinding protective layer reconstruction stage.

[0226] Figure 3 The Fe increment trajectory in the data originates from the unified measurement process described above. Figure 3 The predetermined upper limit for iron content increment is derived from the 100ppm internal process control limit set in this embodiment. The temporal relationship between the return material state and the Fe result in continuous milling will be further explored in subsequent operation processes in conjunction with the corresponding production states.

[0227] After continuous grinding reaches stable operation, the industrial silicon exiting the mill undergoes mill-level sieving and product sub-grading to form product streams and re-grinding streams. The re-grinding stream re-enters the grinding process, with the industrial silicon in the predetermined coarse particle size of 2-3 mm constituting the target coarse particle return material.

[0228] After entering the grinding zone, the target coarse particles participate in the aforementioned grinding contact process and are continuously crushed and refined under mechanical action. At the same time, larger industrial silicon particles gradually enter the 2-3 mm particle size range during normal grinding, and after screening, they reform into new target coarse particles for return material.

[0229] Therefore, during continuous operation, the predetermined coarse-grained industrial silicon involves both consumption and replenishment processes. Industrial silicon at the target particle size continuously leaves that particle size through further grinding, while new 2-3 mm industrial silicon is formed through normal grinding and then re-enters the grinding zone via return material.

[0230] When the formation and return of target coarse particles can continue to follow the grinding and refining process, the supply of target coarse particles entering the grinding zone remains relatively stable; when the formation and return rate of target particle size material gradually falls below its grinding and refining rate, the amount of 2-3 mm industrial silicon actually re-entering the grinding process in subsequent statistical periods decreases accordingly.

[0231] Therefore, this application uses a predetermined amount of coarse-grained industrial silicon return material as the process quantity for the target coarse-grained circulating supply state. This return material quantity corresponds to the target coarse-grained material actually sent back to the grinding process in the next cycle, and has a direct material correspondence with the continuous supply of the target coarse-grained material required for the self-grinding protective layer.

[0232] The return status of coarse-grained industrial silicon is simultaneously affected by normal feed rate, classification conditions, mill holding time, material circulation time, and the operating status of the return channel. During production, return data is obtained through continuous statistical cycles, and periodic comparisons are performed when the corresponding operating conditions are within the predetermined range.

[0233] In some implementations, the monitoring of the amount of returned material in step S4 specifically includes the following steps.

[0234] S41, during a continuous statistical period in which the continuous powdering operation is stable and the feed rate and grading conditions of the industrial silicon to be powdered are maintained within a predetermined operating range, the amount of graded return material in each statistical period is recorded, and the mass percentage of predetermined coarse-grained industrial silicon in the graded return material is determined, wherein each statistical period is 15 minutes.

[0235] S42, determine the amount of recycle material for each statistical period based on the graded recycle material amount for each statistical period and the predetermined mass proportion of coarse-grained industrial silicon in it.

[0236] S43, when the amount of returned material in at least two consecutive subsequent statistical periods is lower than the amount of returned material in the previous statistical period, it is determined that the amount of returned material is continuously decreasing, and the amount of returned material in the previous statistical period of the first statistical period in the at least two consecutive subsequent statistical periods is taken as the level of returned material before the continuous decrease; when the amount of returned material in the subsequent statistical periods recovers to a level not lower than the level of returned material before the continuous decrease, it is determined that the amount of returned material has recovered to the level before the continuous decrease.

[0237] Stable operation in this application means that the same batch of industrial silicon to be powdered continuously enters the grinding process according to the normal production rhythm, the grinding equipment, millimeter-level screening equipment, product sub-grading equipment and return material channel operate continuously, the product logistics and return grinding logistics are continuously formed, and the normal feed volume and main grading conditions are maintained within the operating range adopted for continuous production of this batch.

[0238] Normal feed rate refers to the level of industrial silicon feed to be powdered, which is continuously fed into the grinding process after the start-up and low-iron release are completed, under normal product collection conditions.

[0239] The predetermined operating range is formed by the operating records during the normal continuous powder production of the same batch of industrial silicon, using the same grinding equipment and product particle size control requirements. Normal feed rate, millimeter-level sieving status, and product sub-grading status are all included in the corresponding operating condition records.

[0240] The statistical periods before the continuous decline in return material volume and the statistical periods during the subsequent recovery phase are all established according to the operating range to correspond to the operating conditions.

[0241] The grading conditions in this application refer to the production conditions that affect the particle size distribution of milled industrial silicon among product logistics, ordinary re-milling logistics, and predetermined coarse-grained industrial silicon return material.

[0242] In this embodiment, millimeter-level sieving is used to identify 2-3 mm pre-defined coarse-grained industrial silicon, and product sub-grading is used to form industrial silicon powder and finer re-grinding material according to the upper limit of 75 μm product particle size.

[0243] The screening boundary, screen surface operating status, and feeding status during the millimeter-level screening process jointly affect the identification result of 2-3 mm target coarse particles; the air classification operating status during the product sub-grading process affects the particle size distribution between product powder and finer re-grinding materials.

[0244] During the return material monitoring period, the corresponding screening and grading operation status is recorded synchronously with the return material statistical cycle. In actual production, when the target coarse particle return material changes, the corresponding feeding and grading status can be checked against the concurrent operation records.

[0245] The return material statistics section is set after the material exiting the mill has completed the corresponding screening and grading, and before the returned material re-enters the grinding process.

[0246] The material at this statistical section has already been classified into particle sizes. The regrind material then directly re-enters the grinding process. Therefore, the 2-3 mm industrial silicon quantity obtained at this location corresponds to the target coarse particle supply quantity that actually enters the grinding zone in the next cycle.

[0247] Within a statistical period, the mass of all re-grinding materials passing through the statistical section of the re-grinding material is recorded. At the same time, a representative sample of the corresponding re-grinding material is obtained and subjected to millimeter-level sieve analysis to obtain the mass percentage of 2-3mm pre-defined coarse-grained industrial silicon.

[0248] In one specific implementation, multiple return material samples are obtained along the return material flow within a 15-minute statistical cycle. The samples are then mixed and reduced in size and sieved. The 2-3 mm mass ratio of the combined sample in that cycle is used as the target coarse particle mass ratio for the corresponding statistical cycle.

[0249] Let the total mass of all regrind material passing through the statistical section of regrind material in the nth statistical period be: Let the mass percentage of coarse-grained industrial silicon in the regrinding material during this statistical period be: The predetermined amount of coarse-grained industrial silicon recycled in the nth statistical period. for: ,in Reflects the total scale of return mill logistics within the corresponding statistical period. Reflecting the proportion of target coarse particles in the regrind material, It reflects the quality of 2-3mm industrial silicon that is actually re-entered into the grinding process within the corresponding statistical period.

[0250] The total amount of returned material is obtained by weighing in the return material channel or by the existing mass statistics method of the production line, and the target coarse particle mass ratio is obtained by sieving the results of the returned material samples in the corresponding period.

[0251] Each statistical period , and Records are kept using the same periodic numbering system and are linked to the feed volume and graded operation status during the same period.

[0252] In this embodiment, a 15-minute return material statistics cycle is used.

[0253] The quality of the returned material is continuously accumulated within a statistical period, and representative samples of the returned material are obtained. After the period ends, the total amount of returned material, the proportion of target coarse particles, and the amount of target coarse particles returned are calculated.

[0254] The 15-minute statistical length corresponds to the actual material flow rhythm of the grinding, mill exit, screening, and return processes in this implementation, so that the comparison between adjacent cycles reflects the return state with a certain duration.

[0255] The aforementioned 15-minute interval is the sampling interval for Fe samples of industrial silicon powder, while the 15-minute interval used for monitoring the amount of returned material is the statistical cycle for the returned material flow. Both are recorded along the same production time axis, and respectively form the material-side status and the quality-side status.

[0256] During stable operation, the planned amount of coarse-grained industrial silicon return material will vary around the corresponding normal level. When: and At that time, a continuous decline was formed for at least two subsequent statistical periods.

[0257] For longer periods of decline, comparisons are made sequentially according to adjacent statistical periods.

[0258] The amount of material returned before the first downward cycle in the above downward sequence is taken as the level of material returned before continuous decline, that is: .

[0259] Figure 3 The first track uses a solid line to represent the predetermined amount of coarse-grained industrial silicon returned, and a horizontal dashed line to represent the level of returned material before a continuous decrease.

[0260] Figure 3 The solid line of returned material in the diagram has already entered the descent process before T1. T1 corresponds to the operating node formed by the continuous descent criterion, which triggers the subsequent product diversion and target coarse particle replenishment.

[0261] The coarse-grained industrial silicon is continuously crushed in the mill and enters the finer-grained stage, while the corresponding target coarse particles are simultaneously formed by normal grinding and replenished by return material.

[0262] Within a continuous statistical period As the quantity decreases, it indicates that the amount of 2-3 mm industrial silicon re-entering the grinding process continues to decrease over time.

[0263] Since this portion of industrial silicon is the main source of recycled material for the next cycle's target coarse particle renewal in the contact area, a continuous decline means that the amount of target coarse particle replenishment obtained in subsequent cycles continues to decrease.

[0264] While the existing target coarse particles inside the mill continue to be crushed, the amount of return material continues to decrease, thus the subsequent supply of target coarse particles in the grinding contact area enters a state of decline.

[0265] This material relationship forms the technological basis for the early diversion of product T1.

[0266] In some implementations, in After a continuous decline, the mass ratio of 2-3mm industrial silicon in the reprocessing material is utilized. The evaluation reflects the compositional changes corresponding to the decline.

[0267] Continuous recording during stable continuous milling To establish the target coarse particle mass ratio range under normal operating conditions of the same batch.

[0268] when continuous decline and When the material decreases synchronously, the absolute mass and composition ratio of the target coarse particles in the corresponding regrind stream both decrease, indicating that the material share of the target coarse particles in the regrind stream decreases synchronously.

[0269] when continuous decline and When maintaining within the normal operating range, combined with the total return volume during the same period The changes in the overall return mill logistics scale are verified by checking the normal feed rate and grading conditions.

[0270] The dual-quantity verification and T1 triggering use the same return material base data. T1 is still based on... A continuous decline has formed. This is used to further explain the logistics composition status corresponding to the corresponding decrease.

[0271] The continuous decline criterion is generated when it is formed. Figure 3 As shown in T1.

[0272] After T1 is established, the industrial silicon powder generated from the product sub-segment export is switched from the normal product collection path to a separate collection path. The industrial silicon powder generated thereafter enters an independent receiving unit, maintaining physical separation from the industrial silicon powder that had already entered the normal product collection state before T1.

[0273] Figure 3 The third track corresponds to the industrial silicon powder collection state. Before T1, it is the product collection state; after T1, it enters the separate collection state.

[0274] During the formation of T1, industrial silicon powder Fe samples obtained concurrently or subsequently are introduced into the testing process according to the aforementioned batch-based, particle size matching, and low-Fe contamination sample preparation methods. Before the test results are generated, the industrial silicon powder continues to be discharged along a separate collection path.

[0275] In some implementations, the individually collected industrial silicon powder is received in segments according to a statistical period of 15 minutes, starting from T1.

[0276] Each collection branch is equipped with two or more receiving containers or collection bins that switch sequentially. At the end of each 15-minute production period, the industrial silicon powder is switched to the next receiving unit, so that the continuous production process forms a series of solid powder segments.

[0277] The powder segment formed in the nth statistical period has the same period number as the record of that period. , , And establish a correlation with Fe samples obtained during this production period.

[0278] After the Fe detection results are generated, the results are written into the corresponding powder segment record.

[0279] In actual production, this process makes it very intuitive to record which return state a certain segment of industrial silicon powder came from and which Fe sample it corresponds to.

[0280] During the continuous powder production process, the 2-3 mm industrial silicon obtained from grading is continuously returned to the grinding process for recycling.

[0281] When the amount of coarse-grained industrial silicon returned continuously decreases, new 2-3 mm coarse industrial silicon particles are separated from the same batch of industrial silicon to be ground, and this portion of industrial silicon is fed into the grinding process as supplementary feed.

[0282] The supplementary target coarse particles and the target coarse particles returned from classification enter the grinding zone together and participate in the circulating grinding.

[0283] In some embodiments, the replenishment of the predetermined coarse-grained industrial silicon specifically involves:

[0284] The industrial silicon coarse particles obtained from the grading process, which are in the predetermined coarse particle grade, are continuously returned to the grinding process for cyclic grinding.

[0285] When the amount of recycled industrial silicon of the predetermined coarse grade continuously decreases, coarse industrial silicon particles of the predetermined coarse grade are separated from the same batch of industrial silicon to be pulverized, and these coarse industrial silicon particles are fed into the grinding process as supplementary feed, and together with the graded coarse industrial silicon particles of the predetermined coarse grade, they participate in the cyclic grinding.

[0286] The supplementary coarse particles adopt the same particle size boundary as the normal target coarse particle return material, so that the two types of coarse particles have consistent target particle size attributes after entering the grinding zone.

[0287] After T1 is formed, the product end and the grinding end simultaneously perform the corresponding process actions.

[0288] On the product side, industrial silicon powder is switched to a separate collection path, so that industrial silicon powder formed after T1 maintains an independent logistics status.

[0289] The grinding end adds 2-3mm industrial silicon coarse particles from the same batch as supplementary feed to the existing return material cycle, thereby increasing the source of target coarse particles entering the grinding zone in the next cycle.

[0290] Product diversion acts on the logistics that have completed grinding and entered the powder outlet, while target coarse particle replenishment acts on the logistics that are about to enter the subsequent grinding cycle.

[0291] The two actions act on the downstream product side and the upstream grinding side of the powder making process, respectively, and are triggered by the same continuous decrease in return material.

[0292] Figure 3 The time windows for advance diversion are from T1 to T2.

[0293] The planned amount of coarse-grained industrial silicon returned is located on the return side, reflecting the target coarse-grained supply status for the next cycle; the Fe increment is located on the product powder quality side, which needs to be formed through the process of material residence in the mill, exiting the mill, classification, conveying, sampling and analysis.

[0294] Therefore, the change in the supply of target coarse particles on the return side is transmitted along the process flow to the product powder quality side with a production process time lag.

[0295] After T1 is formed, the industrial silicon powder is collected separately. Corresponding Fe samples are continuously acquired and analyzed.

[0296] When the Fe increment of a certain industrial silicon powder sample exceeds 100ppm and the corresponding over-limit state is confirmed by the test results, T2 is formed and the self-grinding protective layer reconstruction is triggered.

[0297] The actual time length from T1 to T2 is determined by the grinding and holding process, material circulation, powder conveying, and detection process.

[0298] After T1, industrial silicon powder is collected separately, while 2-3 mm coarse industrial silicon particles from the same batch are continuously added, and the target amount of coarse particles returned is continuously counted.

[0299] When the Fe increment of the corresponding industrial silicon powder sample is kept at 100ppm or below, the production process is in the state of normal target coarse particle replenishment.

[0300] After being fed into the mill, ground, discharged from the mill, and screened, the supplementary coarse particles re-enter the target coarse particle return path, and are included in subsequent statistical cycles. It changes as the material is fed into the process.

[0301] When the Fe increment remains within a controlled range, and the predetermined amount of coarse-grained industrial silicon returned to the level before the continuous decline, the separate collection of industrial silicon powder in this normal replenishment phase ends, and product collection resumes.

[0302] The branch corresponds to the pre-return material indicator being restored by the addition of target coarse particles, while the Fe on the quality side remains within the set process control range.

[0303] The process of adding coarse particles to the ordinary target continuously yields industrial silicon powder Fe results.

[0304] When the iron content increases by more than 100 ppm, it indicates that the industrial silicon powder formed under the current target coarse particle replenishment state has reached the reconstruction trigger condition.

[0305] At this point, the production process is upgraded from ordinary target coarse particle feeding to self-grinding protective material layer reconstruction.

[0306] Reconstruction increases the relative participation ratio of predetermined coarse-grained industrial silicon in the overall feed material by adjusting the relative relationship between the normal fresh material flow rate and the target coarse-grained flow rate.

[0307] In some implementations, the rebuilding of the self-grinding protective layer in step S5 specifically includes the following steps.

[0308] S51, during the separate collection of industrial silicon powder, industrial silicon powder samples are obtained sequentially at a predetermined sampling interval of 15 minutes, and the iron content increment of each industrial silicon powder sample relative to the same batch of industrial silicon to be powdered is determined.

[0309] S52, when the iron content increase exceeds 100ppm, the normal feed rate of the industrial silicon to be pulverized is reduced, and under the reduced feed load, the industrial silicon coarse particles separated from the same batch of industrial silicon to be pulverized and in the predetermined coarse particle size are used as supplementary feed, so as to increase the proportion of the predetermined coarse particle size industrial silicon in the material entering the grinding process, while maintaining the industrial silicon coarse particles in the predetermined coarse particle size obtained from the classification to be returned to the grinding process for recycling.

[0310] S53, during the reconstruction of the self-grinding protective material layer, grinding, grading and coarse particle return are continued, and the generated industrial silicon powder is collected separately.

[0311] S54, during the reconstruction of the self-grinding protective layer, the feed rate and classification conditions of the industrial silicon to be powdered are restored to the operating range before the continuous decrease in the return amount; when the return amount for at least two consecutive statistical periods is not lower than the return level before the continuous decrease, and the iron content increment of at least two consecutive separately collected industrial silicon powder samples does not exceed 100ppm, the reconstruction of the self-grinding protective layer and the separate collection of industrial silicon powder are terminated, and product collection is resumed.

[0312] After T2 is formed, the normal feed rate of industrial silicon to be powdered will be reduced from the normal continuous powdering level before the anomaly to the feed load during the reconstruction phase.

[0313] Meanwhile, the same batch of 2-3mm industrial silicon coarse particles continued to be fed into the grinding process as supplementary feed, and the 2-3mm target coarse particles obtained from classification were also returned to the grinding process.

[0314] The mill, millimeter-level screening equipment, product sub-grading equipment, and return material channel are kept running continuously.

[0315] Industrial silicon powder continued to enter a separate collection path, while Fe samples were continuously collected at 15-minute sampling intervals.

[0316] This operating mode maintains the existing closed-circuit grinding system while changing the material ratio between normal fresh material and target coarse particles.

[0317] Assume that the normal industrial silicon entering the grinding process per unit time before the anomaly is at a normal feed level, and the target coarse particles are formed by graded return material and supplementary feed.

[0318] After the reconstruction begins, the normal feed rate of industrial silicon to be powdered is reduced, while the replenishment of target coarse particles in the same batch continues, and the return of existing target coarse particles also continues to circulate.

[0319] After this treatment, the proportion of normal new material in the total material entering the grinding process per unit time decreases, while the relative proportion of pre-selected coarse-grained industrial silicon increases.

[0320] After the target coarse particles enter the grinding zone, they have a higher chance of participating in the aforementioned multiple local grinding contact positions, and the target coarse particle group state is gradually re-established with continuous grinding.

[0321] The key to reconstruction is to change the degree of participation of the target coarse particles in the overall feed material of the mill, rather than simply increasing the amount of coarse particles fed at a particular time.

[0322] After the target coarse particles enter the grinding process, they undergo grinding, mill exit and mill-level sieving.

[0323] Industrial silicon that is still in the 2-3mm range re-enters the target coarse-grained return path and continues to participate in the next cycle; industrial silicon that enters the finer-grained stage enters the ordinary re-grinding or product sub-grading path according to the actual particle size.

[0324] As multiple cycles continue, the newly added target coarse particles gradually enter the complete grinding-classification-return chain.

[0325] In subsequent statistical periods When the level changes from low to a sustained rise, it indicates that the target coarse particles being added have changed from a simple supplementary feeding state to a return state that actually participates in the closed-loop cycle.

[0326] This change forms the basis for the process of restoring from low-load reconstruction to normal operating conditions.

[0327] After T2 triggers reconstruction, the target coarse particle supply status begins to change from the grinding inlet and the return end.

[0328] The industrial silicon material that was previously located in the mill material layer, mill exit path, mill-level screening path, product sub-grading path, and powder conveying path continues to move toward the product powder outlet in the original material order.

[0329] Therefore, the impact of the reconstruction action on the target coarse particle contact state is first formed in the grinding zone and the return cycle, and then reflected in the downstream industrial silicon powder Fe result.

[0330] During this production time lag, the subsequent increase in Fe content of industrial silicon powder will continue to change along the original trend.

[0331] As new target coarse particles continue to enter the contact area and complete multiple grinding-classification-return cycles, the subsequent Fe increment in industrial silicon powder gradually decreases back to the control range of 100ppm.

[0332] Figure 3 The second track is set to continue rising for a short period after T2, and then turn to fall, corresponding to the time difference of the above production process.

[0333] Figure 3 T2 to T4 correspond to the stages of reconstruction and restoration confirmation of the autogenous grinding protective layer.

[0334] After T2, the system enters a low-load reconstruction phase, with a reduction in the normal feed rate of new material and continuous replenishment of coarse particles from the same batch. Grinding, screening, and return processes continue to operate.

[0335] As the target coarse particles re-enter the complete closed-loop cycle It gradually rebounded from an abnormally low level.

[0336] Once the target coarse-grained return material enters a state of continuous recovery, the production process enters the operating condition recovery phase, gradually restoring the normal feed rate and main grading conditions to the predetermined operating range before the continuous decline in return material.

[0337] After restoring the corresponding operating conditions, continue to monitor the target amount of coarse material returned. T3 is formed when the amount of returned material reaches the level before the continuous decline.

[0338] After T3, continue to collect materials separately, and continue to perform return material statistics and Fe sampling until both the conditions for continuous recovery of return material and the conditions for continuous qualification of Fe are met, thus forming T4.

[0339] During the low-load rebuilding phase, the normal feed rate of industrial silicon to be ground was reduced, and the overall scale of the regrinding logistics also changed with the feed load.

[0340] Therefore, before the target coarse material return enters the formal recovery judgment, the normal feed rate and classification conditions will be restored to the predetermined operating range before the continuous decline.

[0341] During the recovery process, the normal feed rate of industrial silicon for powder production gradually returned to the normal continuous production level, and the operating conditions of millimeter-level screening and product sub-grading were simultaneously restored to the range recorded before the anomaly.

[0342] Under this operating condition, the target coarse material return amount for subsequent statistical cycles has a corresponding working condition comparison basis with the return material level before the continuous decline.

[0343] Figure 3 In the first track, the return material curve rises from a low level during the low-load reconstruction phase, and continues to move towards the return material level before continuous decline after the normal operating conditions are restored.

[0344] After the normal feed rate and grading conditions are restored to the predetermined operating range, the target coarse particle return rate will continue to be determined according to the 15-minute statistical cycle.

[0345] In a subsequent statistical period When the level of returned material reaches or exceeds the level before the continuous decline, it forms Figure 3 The T3 return material recovery event.

[0346] T3 indicates that the target coarse-grained return state has reached the baseline before the anomaly for the first time.

[0347] At this point, industrial silicon powder will continue to be collected separately, and records will continue to be kept in subsequent statistical periods. Fe samples were continued to be obtained at 15-minute intervals.

[0348] T3 is therefore classified as a target coarse-grained logistics recovery event.

[0349] After T3, maintain normal feed rate and grading conditions within the predetermined operating range, and continue to conduct return material statistics and Fe sampling.

[0350] When the predetermined amount of coarse-grained industrial silicon returned for at least two consecutive statistical periods reaches or exceeds the level of returned silicon before the continuous decline, and the Fe increment of at least two consecutive separately collected industrial silicon powder samples is at or below 100 ppm, product recovery is confirmed.

[0351] The conditions for continuous return material and continuous Fe were determined according to their respective statistical sequences. By the time the final confirmation point was reached, both sets of conditions had been met. Figure 3 T4 in the figure represents the point in time when the final confirmation was completed. After T4 is established, the industrial silicon powder is switched from a separate collection path back to the normal product collection path.

[0352] Figure 3 The first track represents the planned amount of coarse-grained industrial silicon returned. During normal production, the amount of returned material is stable, and then it decreases continuously; when the continuous decrease criterion is met, T1 is formed; after the returned material reaches a low level, it gradually recovers under the action of normal replenishment and reconstruction; after the normal operating conditions are restored, it reaches the level of returned material before the continuous decrease and forms T3.

[0353] Figure 3 The second track represents the iron content increment determined according to the aforementioned detection method. During the stable operation phase, it remains within the predetermined control range. After the return material decays, it gradually increases with the production process. When it exceeds 100 ppm, T2 is formed. During the initial reconstruction phase, it continues to experience the production process time difference, and then gradually decreases as the target coarse-grained cycle is re-established. After T3, continuous Fe samples are obtained until T4, which forms the final quality confirmation.

[0354] Figure 3 The third track indicates the industrial silicon powder collection status. Before T1, industrial silicon powder enters the normal product collection path; after T1 is formed, it enters a separate collection path; this status spans normal replenishment, T2, low-load reconstruction, T3, and subsequent confirmation; after T4 is formed, normal product collection resumes.

[0355] Figure 3 T1 to T2 in the diagram represent the advance diversion time window, while T2 to T4 represent the stage for rebuilding and confirming the self-grinding protective material layer.

[0356] The initial layering occurs before the establishment of normal continuous feed. The target coarse-grained cycle is established by the same batch of pre-ordered coarse-grained industrial silicon, and the low-iron release is completed by starting the continuous Fe process of industrial silicon powder.

[0357] In-process reconstruction occurs after normal continuous milling has been established. At this time, the mill retains the current batch of industrial silicon material being processed, and screening, product sub-grading, and return paths continue to operate.

[0358] The reconstruction during operation is carried out along the existing closed-circuit grinding process. By reducing the normal fresh material feed rate, continuously adding the same batch of target coarse particles, and maintaining the return of the target coarse particles, the relative participation of the predetermined coarse-grained industrial silicon is increased.

[0359] The two stages use the same target coarse grains from the same batch and size, corresponding to the batch start-up state and the continuous production recovery state, respectively.

[0360] As continuous milling nears the end of a batch, industrial silicon material being processed in the current batch still exists in the milling zone, mill outlet channel, screening equipment, product sub-grading equipment, and return path.

[0361] Before continuous powder production begins, a portion of industrial silicon coarse particles at the predetermined coarse particle size is reserved from the same batch of industrial silicon to be powdered.

[0362] In one embodiment, before continuous milling begins, coarse industrial silicon particles at the predetermined coarse particle size are reserved from the same batch of industrial silicon to be milled. After the continuous milling of this batch of industrial silicon is completed, the normal feeding of the industrial silicon to be milled is stopped, and the reserved coarse industrial silicon particles from the same batch are sent to the milling process for further milling, grading, and coarse particle return. This allows the residual industrial silicon powder from the milling and grading / returning processes to be discharged, and the industrial silicon powder discharged after the normal feeding is stopped is collected separately from the product industrial silicon powder collected during the continuous milling process. The amount of reserved coarse particles is determined according to the material conditions required to maintain continuous operation of milling, sieving, and return at the end of the batch, so that the remaining material of the current batch continues to be discharged along the original milling path.

[0363] After stopping the normal feeding of industrial silicon for powder production, reserve 2-3mm coarse industrial silicon particles from the same batch and send them into the grinding process.

[0364] The reserved coarse particles are ground together with the existing batch of materials in the system. After exiting the mill, they continue to undergo millimeter-level screening and product sub-grading. Materials in the re-grinding particle size are returned to the grinding process.

[0365] As the above cycle continues, the batch of industrial silicon in the grinding zone, screening path, and return channel gradually moves toward the powder outlet.

[0366] After normal feeding stops, the industrial silicon powder formed enters a separate collection path in the tail section, and records of the corresponding batch and tail section production status are retained.

[0367] The tail-end discharge continues until the production line reaches the corresponding residual material discharge requirements. The actual termination point is determined based on the tail-end powder discharge status, return material status, and the company's batch management requirements.

[0368] After the next batch of industrial silicon enters the production line, a new benchmark sample is established according to this batch, and the target coarse-grained cycle and low-iron release process are started.

[0369] Example 1 uses a ball mill for mechanical grinding of industrial silicon. The ball mill operates at approximately 70% of its critical speed, the steel ball volume fill rate is approximately 34%, and the steel ball diameter is 30–50 mm.

[0370] Coarse industrial silicon particles of 2-3 mm were obtained from the same batch of industrial silicon to be powdered through millimeter-level sieving. During the initial layer-building stage, 100 kg of these coarse industrial silicon particles were added, along with approximately 800 kg of steel balls inside the mill. The ratio of the steel ball mass to the initial target coarse particle mass during this stage was approximately 8:1.

[0371] The upper limit for particle size control of industrial silicon powder is 75μm, and the product D50 is approximately 25μm under normal production conditions. During closed-circuit milling operation, the total circulating load is approximately 250%, which corresponds to the quality relationship between all returned materials and the product flow during the same period; the 2-3mm pre-designated coarse-grained industrial silicon return material is recorded using an independent statistical method.

[0372] The same batch of industrial silicon to be powdered was treated with particle size matching and low-Fe contamination samples to form a reference sample, with a reference Fe content of approximately 2000 ppm. The upper limit of Fe content in industrial silicon powder products is 3000 ppm, and 100 ppm is used as the predetermined upper limit of iron content increment in the powdering process.

[0373] The coarse-grained condition comparison, start-up layer building, continuous grinding, and operation recovery all adopted the above-mentioned ball mill equipment and corresponding product particle size control conditions. The main changes between the various coarse-grained comparison conditions are concentrated on the target coarse-grained particle size conditions.

[0374] In Example 1, Fe was determined using ICP-OES. The test results for the reference sample, industrial silicon powder obtained during the start-up phase, industrial silicon powder produced in continuous production, and industrial silicon powder obtained during the operational status change phase all followed the aforementioned batch reference, particle size matching, and low-Fe contamination sample processing procedures.

[0375] The amount of 2-3mm industrial silicon recycled material was statistically analyzed using a 15-minute period. Fe samples of industrial silicon powder were sampled at 15-minute intervals. The recycled material statistics and Fe sampling were recorded along the same production timeline, ensuring a clear temporal sequence between changes in the target coarse-grained material stream and the corresponding changes in the product powder quality.

[0376] The comparison of coarse-grained conditions included a baseline control condition, a 1–2 mm particle size comparison condition, a 2–3 mm implementation condition, and a 3–5 mm particle size comparison condition. Each condition was independently repeated three times. Fe increment, steel wear, unit energy consumption, and D50 are expressed as mean ± standard deviation.

[0377] The methodological comparison of low-iron contact sample preparation conditions was carried out by using the same homogenized industrial silicon powder for sample distribution, and eight parallel determinations were performed under each of the two sample preparation conditions.

[0378] During production startup, coarse industrial silicon particles (2-3 mm) obtained from screening the same batch of industrial silicon are fed into the ball milling process to establish a cycle. Industrial silicon particles that are still in the 2-3 mm particle size after exiting the mill are returned to the powder milling process, while the industrial silicon powder formed during startup enters a separate collection path.

[0379] During the start-up phase, industrial silicon powder samples were obtained sequentially at 15-minute intervals. Once the Fe increment of two consecutive samples was 100 ppm or below, the production process transitioned to normal continuous feeding of the same batch of industrial silicon.

[0380] In the continuous grinding process, the material exiting the mill undergoes millimeter-level sieving and product sub-grading to form a product stream, a general return stream, and a 2-3 mm target coarse particle return stream. The target coarse particles continuously re-enter the grinding process.

[0381] When the amount of 2-3 mm industrial silicon returned continuously decreases, the industrial silicon powder is switched to separate collection, while 2-3 mm coarse particles are added from the same batch of industrial silicon. When the Fe increment is 100 ppm or below, ordinary coarse particle addition continues; when the Fe increment exceeds 100 ppm, the normal feed rate of industrial silicon to be ground is reduced, while maintaining the target coarse particle addition and target coarse particle return cycle, so as to increase the relative proportion of the target coarse particles in the overall feed material.

[0382] After the target coarse-grained return material gradually recovers from its low level, the normal feed rate and classification conditions return to the operating range before the continuous decline in return material. Once both the continuous recovery conditions for return material and the continuous qualified conditions for Fe are met, the industrial silicon powder re-enters the normal product collection path.

[0383] After the normal batch feeding is completed, the 2-3mm coarse industrial silicon particles reserved before the start-up enter the grinding process to continue grinding, grading and return processes. After the normal feeding stops, the discharged industrial silicon powder enters the independent collection path at the tail end.

[0384] The results of industrial silicon powder production under various coarse-grained conditions are shown in Table 1.

[0385] Table 1. Coarse particle size distribution and industrial silicon powder production results

[0386] Benchmark comparison condition Target coarse particle dosage: 0 kg 190±12 0.91±0.04 42.4±0.7 24.9±0.1 0.83% Particle size comparison case 1 1~2mm 134±8 0.73±0.04 42.8±0.6 25.0±0.1 0.83% Implementation conditions 2-3mm 81±7 0.54±0.04 43.1±0.6 25.1±0.1 0.83% Particle size comparison case 2 3-5mm 123±10 0.70±0.05 44.6±0.8 25.3±0.1 0.93%

[0387] The D50 of products under various operating conditions is concentrated in the range of 24.9–25.3 μm, with particles larger than 75 μm accounting for 0.83%–0.93%, and several product groups are at similar final crushing sizes. Based on this particle size, the Fe increment and steel wear show a clear low value in the intermediate particle size range as the target coarse particle size changes.

[0388] The Fe increment was 134±8 ppm in the 1–2 mm condition and decreased to 81±7 ppm in the 2–3 mm condition, a decrease of approximately 39.6%; steel wear decreased from 0.73±0.04 kg / t to 0.54±0.04 kg / t, a decrease of approximately 26.0%. During the same period, the unit energy consumption only changed from 42.8 kWh / t to 43.1 kWh / t, a change of approximately 0.7%, and the proportion of particles larger than 75 μm was 0.83% in both cases.

[0389] When the target coarse particle size further increases to 3-5 mm, the Fe increment rises from 81±7 ppm to 123±10 ppm, a rebound of about 51.9% compared to the 2-3 mm condition; steel wear increases from 0.54±0.04 kg / t to 0.70±0.05 kg / t, a rebound of about 29.6%; and unit energy consumption increases from 43.1 kWh / t to 44.6 kWh / t, an increase of about 3.5%.

[0390] Based on this set of adjacent particle size data, when the target coarse particle size increases from 1–2 mm to 2–3 mm, both Fe increment and steel wear decrease significantly; when the size continues to increase to 3–5 mm, both indicators rise again. 2–3 mm corresponds to the intermediate particle size process window formed by Fe increment, steel wear, and unit energy consumption.

[0391] Compared to the baseline control condition, the Fe increment in the 2-3mm implementation condition decreased from 190ppm to 81ppm, a decrease of approximately 57.4%; steel wear decreased from 0.91kg / t to 0.54kg / t, a decrease of approximately 40.7%; unit energy consumption changed from 42.4kWh / t to 43.1kWh / t, an increase of approximately 1.7%; and product D50 changed from 24.9μm to 25.1μm, with the proportion of particles larger than 75μm remaining at 0.83%.

[0392] Both Fe increment and steel wear, which are related to metal contact conditions, reached their lowest values ​​simultaneously under the 2–3 mm operating condition, while the product crushing size remained concentrated. This data relationship corresponds to the synergistic relationship between particle number, target particle size survival time, and continued crushing load mentioned above.

[0393] During the start-up phase, the amount of 2-3 mm industrial silicon returned was recorded at 15-minute intervals, and corresponding industrial silicon powder samples were obtained simultaneously. Specific results are shown in Table 2.

[0394] Table 2 Record of the Start-up Layer Construction Process

[0395] 0～15 32 214 15～30 41 168 30～45 49 129 45～60 55 104 60～75 58 89 75～90 59 82 90～105 59 80

[0396] The initial return rate of 2-3mm industrial silicon was 32kg / 15min, which was subsequently increased to 41kg / 15min, 49kg / 15min, 55kg / 15min, and 58kg / 15min, and reached 59kg / 15min in the later statistical period.

[0397] During the same production process, the Fe increment changed sequentially from 214 ppm to 168 ppm, 129 ppm, 104 ppm, 89 ppm and 82 ppm.

[0398] Increasing from 32 kg / 15 min to 59 kg / 15 min corresponds to an increase of approximately 84.4% in the target coarse particle return circulation throughput; during the same period, the Fe increment decreased from 214 ppm to 82 ppm, a decrease of approximately 61.7%. The two data points show continuous changes in opposite directions along the same start-up time axis.

[0399] The 2-3mm return material volume recorded here belongs to the circulating material throughput. The target coarse particles pass through the return material statistics position again after undergoing grinding, mill exit, screening, and re-returning. Therefore, the return material statistics value reflects the degree of establishment of target coarse particle circulation.

[0400] The Fe increments of the industrial silicon powder samples obtained in the 60–75 min and 75–90 min intervals were 89 ppm and 82 ppm, respectively. The test results for both consecutive samples were at or below 100 ppm, meeting the start-up release conditions. The 2–3 mm return material volume recorded in the 90–105 min interval was 59 kg / 15 min, with an Fe increment of 80 ppm. This data was used to record the continuity of the corresponding powder-making state after the start-up release conditions were established.

[0401] During the startup process, the target coarse-grained return material is established from a low level to a stable level, which occurs in the same continuous grinding process as the industrial silicon powder Fe increment enters the low value range.

[0402] During normal continuous powder production, the amount of 2-3 mm industrial silicon return material, the Fe increment, and the corresponding production status were recorded. The results are shown in Table 3.

[0403] Table 3 Record of the process of material return attenuation, early diversion, reconstruction, and recovery

[0404] 0 59 82 Stable operation, product collection 15 54 84 The target coarse-grained return material has entered a downward state. 30 48 89 When the continuous decline condition is met, industrial silicon powder is switched to separate collection. 45 42 102 Fe increase exceeding 100 ppm indicates the onset of remodeling. 60 46 119 Low-load reconstruction 75 53 110 The target coarse-grained return material continues to rebound. 90 59 96 Returned materials have reached levels seen before the continuous decline, and industrial silicon powder continues to be collected separately. 105 60 88 Continuous recovery confirmed successful; product collection resumed.

[0405] During stable operation, the target coarse feed rate was 59 kg / 15 min, with an Fe increment of 82 ppm. Subsequently, the feed rate continuously decreased to 54 kg / 15 min and 48 kg / 15 min, forming a continuous decreasing condition at 30 min, while the Fe increments during the same period were 84 ppm and 89 ppm, respectively, both within the 100 ppm control range.

[0406] The industrial silicon powder was switched to separate collection at 30 minutes. The Fe increment of the industrial silicon powder sample obtained at the 45-minute production time point was 102 ppm. After confirmation by the test results, it entered the self-grinding protective layer reconstruction.

[0407] In this specific production record, a 15-minute production interval is formed between the achievement of the continuous decrease in return material conditions and the Fe increment exceeding 100 ppm. This time relationship directly reflects the actual role of the target coarse-grained return material state as a leading factor on the process side, indicating that the industrial silicon powder has already entered the independent logistics before the quality results reach the reconstruction conditions.

[0408] After reconstruction began, the target coarse feed rate increased from 42 kg / 15 min to 46 kg / 15 min, while the Fe increment further increased from 102 ppm to 119 ppm. After another production section, the feed rate continued to increase to 53 kg / 15 min, and the Fe increment turned to 110 ppm.

[0409] While the return material had already shifted from a decline to a recovery, the Fe result on the quality side continued to rise from 102 ppm to 119 ppm. Subsequently, as the return material volume continued to recover, the Fe increment gradually decreased. Therefore, the changes in the target coarse-grained return material state and the Fe result of the product powder exhibit a clear difference in production timing.

[0410] The target coarse-particle return rate recovered from 42 kg / 15 min to 59 kg / 15 min, an increase of approximately 40.5%. Upon reaching 59 kg / 15 min, the Fe increment had fallen back to 96 ppm. This point corresponds to the first time the return rate reached the level before the continuous decline, and industrial silicon powder continued to be collected separately.

[0411] In the next statistical cycle, the return material volume reached 60 kg / 15 min, and the Fe increment further decreased to 88 ppm. 59 kg / 15 min and 60 kg / 15 min formed two consecutive return material recovery cycles, and 96 ppm and 88 ppm formed two consecutive Fe qualified samples. Subsequently, industrial silicon powder resumed normal product collection.

[0412] This set of actual data clearly distinguishes the three production states: continuous decline in return material first triggers product isolation, excessive Fe then triggers reconstruction, and after the first recovery of return material, it continues through continuous return material and continuous Fe confirmation before entering the product recovery state.

[0413] The statistical results during the continuous and stable milling period are shown in Table 4.

[0414] Table 4 Statistics of Continuous and Stable Milling Status

[0415] 2-3mm industrial silicon return material amount 59.2±0.8kg / 15min Fe increment 80.2±10.0ppm Product D50 25.1±0.2μm Unit energy consumption 43.1±0.2kWh / t

[0416] The target coarse particle return amount is concentrated around 59.2 kg / 15 min, the Fe increment varies around 80.2 ppm, the product D50 remains at about 25.1 μm, and the unit energy consumption remains at about 43.1 kWh / t.

[0417] This stable operating state is closely correlated with the data from the later stages of the startup phase. After the startup phase entered the release state, the amount of 2-3mm industrial silicon returned reached approximately 59kg / 15min, with the Fe increment at 80-82ppm; in the continuous stable operation statistics, the corresponding values ​​were 59.2±0.8kg / 15min and 80.2±10.0ppm, respectively.

[0418] From a production perspective, the stable level established after the target coarse-grained return material is established can be maintained continuously during the continuous milling process, and coexists with the corresponding low Fe increment state.

[0419] The same homogenized industrial silicon powder was divided into two groups, and was processed under low-iron contact sample preparation conditions and ordinary steel sample preparation conditions, respectively. Each group was subjected to 8 parallel measurements, and the results are shown in Table 5.

[0420] Table 5. Fe determination results under two sample preparation conditions.

[0421] Low Fe contamination sample preparation conditions 8 2000.6±7.5 Comparison of ordinary steel sample preparation conditions 8 2069.5±9.5

[0422] The average Fe results of the two groups differed by 68.9 ppm.

[0423] The process control scale used in this embodiment is 100 ppm, and 68.9 ppm is equivalent to 68.9% of this control scale. In other words, the measurement difference caused by the sample preparation contact conditions alone accounts for a large proportion of the 100 ppm process control scale.

[0424] The Fe determination result under the low-iron contact sample preparation condition was 2000.6±7.5ppm, which was consistent with the Fe level of the industrial silicon reference in the same batch; the measurement result under the ordinary steel sample preparation condition was 2069.5±9.5ppm.

[0425] Therefore, the initiation and release, anomaly detection, and recovery confirmation at the 100ppm level were all performed according to the aforementioned low-iron contact sample preparation conditions. This methodological data provides a specific measurement scale for the aforementioned batch particle size matching benchmark and low-Fe contamination sample preparation process.

[0426] After normal continuous powder production is completed, the normal industrial silicon feed is stopped, and the reserved 2-3mm coarse industrial silicon particles from the same batch are sent to the grinding process for further grinding, classification, and return. The tail end of the industrial silicon powder enters an independent collection path.

[0427] See Table 6 for the batch final material discharge record.

[0428] Table 6 Record of the final discharge process of batch 6

[0429] 0～15 18 92 15～30 12 118 30～45 7 146 45～60 3 171

[0430] After stopping normal feeding, the discharge rate in the first 15-minute section was 18 kg, and the Fe increment was 92 ppm. In the subsequent three sections, the discharge rate decreased to 12 kg, 7 kg, and 3 kg respectively, and the Fe increment increased to 118 ppm, 146 ppm, and 171 ppm respectively.

[0431] As the powder output decreased from 18 kg to 3 kg, the amount of powder discharged at the end of the batch continued to decrease, while the Fe increment increased from 92 ppm to 171 ppm. Consequently, the powder at the end of the batch exhibited a quality state significantly different from that in the stable continuous production stage.

[0432] After the same batch of industrial silicon coarse particles (2-3 mm) are reserved for further grinding, grading, and return, the remaining material in the grinding zone, screening path, and return path of the current batch continues to be discharged along the original material flow. The tail-end powder is received independently from the normal product material flow, ensuring that the batch-end quality change is recorded in an independent batch record.

[0433] In some implementations, each 15-minute return material statistics cycle simultaneously retains the total return material amount, the 2-3 mm industrial silicon mass percentage, and the target coarse-grained return material amount determined by both.

[0434] During the stable continuous powder production stage, the normal operating range of 2-3 mm industrial silicon mass ratio is formed based on continuous statistical data.

[0435] After the target coarse particle return amount shows a continuous decline, the target coarse particle mass ratio for the corresponding period is simultaneously read. When the return amount and the target coarse particle mass ratio decrease synchronously over the same time period, the corresponding records show that both the absolute supply of target coarse particles and the proportion of target coarse particles in the return material decrease simultaneously.

[0436] When the target coarse particle return amount decreases while the target coarse particle mass ratio remains within the normal operating range, the total return amount, normal feed amount, and graded operation records are used together to identify changes in the overall return mill logistics scale.

[0437] The early diversion of products is still triggered by a continuous decrease in the target coarse-grained return material amount, and the mass ratio is used as a synchronous verification quantity for the composition status of the return material.

[0438] In one implementation, a separate collection branch is equipped with two or more receiving units that switch sequentially, and a 15-minute production time period is used as the powder receiving switching boundary.

[0439] After the continuous decline of returned material triggers separate collection, the industrial silicon powder formed in the first 15-minute segment enters the first receiving unit. The next production segment switches to the next receiving unit, and subsequent segments are received sequentially according to the production time order.

[0440] Each receiving unit records the production batch, time segment, and powder segment number. The total amount of returned material, the mass percentage of 2-3mm industrial silicon, the target amount of coarse-grained returned material, and the Fe sample obtained in the same time segment are associated with the cycle number.

[0441] Once the Fe result is formed, it is written into the corresponding powder segment record. Thus, a one-to-one correspondence is established between the target coarse-grained material state of a certain statistical period, the physical industrial silicon powder segment formed in that period, and the corresponding Fe result along the same production time axis.

[0442] In cases where the precursors to the return material material appear before the Fe analysis results, this segmented solid structure ensures that the pre-isolated industrial silicon powder retains a clear temporal attribution.

[0443] The steel wear in Table 1 adopts the original experimental statistical caliber consistent with the working conditions of each coarse particle comparison, and is converted into the steel mass loss corresponding to the unit industrial silicon powder output, with the unit being kg / t.

[0444] Unit energy consumption is calculated based on the power consumption of the grinding system and the quality of industrial silicon powder products during the same period, with the unit being kWh / t.

[0445] The total circulating load is determined based on the ratio of the total mass of all regrind material to the mass of industrial silicon powder produced during the same period. In Example 1, the total circulating load under stable closed-circuit milling conditions is approximately 250%.

[0446] The product's D50 and the proportion of particles larger than 75μm were obtained using a consistent particle size measurement caliber for each coarse-grained comparison condition. These particle size indicators are used to confirm that the product's crushing scale is at a similar level for each coarse-grained condition, ensuring that the comparison between Fe increment and steel wear is based on the corresponding product particle size.

[0447] Example 1 shows that approximately 59 kg / 15 min of 2-3 mm industrial silicon return material was repeatedly observed in multiple production stages.

[0448] When entering the low-Fe release state during the start-up phase, the target coarse particle return amount increases from 58kg / 15min to 59kg / 15min, and the corresponding Fe increment decreases from 89ppm to 82ppm; in subsequent sections, the return amount remains at 59kg / 15min, and the Fe increment is 80ppm.

[0449] In the continuous and stable production statistics, the target coarse particle return amount is 59.2±0.8kg / 15min, and the Fe increment is 80.2±10.0ppm.

[0450] Before the return material anomaly occurred, the target coarse particle return material amount was 59 kg / 15 min, and the Fe increment was 82 ppm.

[0451] After reconstruction, when the target coarse feed returned to 59 kg / 15 min, the Fe increment dropped to 96 ppm; in the next statistical cycle, when the feed returned to 60 kg / 15 min, the Fe increment further decreased to 88 ppm, and the continuous recovery was confirmed.

[0452] When the above production stages are observed under the same statistical caliber, the target coarse feed return level after startup, the normal stable operation level, the level before the anomaly, and the feed return recovery level after reconstruction are all concentrated in the range of approximately 59–60 kg / 15 min. The corresponding Fe results vary around 80.2 ppm during the stable operation stage, and continuous samples enter the process control range of 100 ppm during the recovery confirmation stage.

[0453] This cross-stage recording ensures that the target coarse-grained return material quantity has both state significance during the startup and establishment process and actual process correspondence in continuous production anomaly identification and post-reconstruction recovery judgment. The 59kg / 15min return material recovery event after reconstruction and the subsequent 60kg / 15min and 88ppm continuous confirmation processes further correspond to the aforementioned two production nodes: the return material recovery event and the product recovery confirmation.

[0454] The present application and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present application. The actual structure is not limited to this. In conclusion, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present application, such design should fall within the protection scope of the present application.

Claims

1. A method for producing low-iron industrial silicon powder based on a self-grinding protective layer, characterized in that, include: S1. Separate coarse industrial silicon particles of the same batch from the industrial silicon to be pulverized, and circulate them before continuous pulverization, so that the coarse industrial silicon particles are circulated and continuously replaced in the contact area between the material and the metal parts in the pulverizing zone, forming a self-grinding protective material layer composed of coarse industrial silicon particles. S2. Collect the industrial silicon powder produced by the cyclic grinding in step S1 separately and take samples to test the iron content to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be ground; when the increase in iron content does not exceed the predetermined upper limit of iron content increase, end the separate collection and switch to continuous grinding. S3. Continuously feed in industrial silicon to be ground for grinding, classify the material exiting the mill, collect industrial silicon powder within the product particle size range, and return industrial silicon material above the upper limit of the product particle size to the grinding process. The predetermined coarse-grained industrial silicon coarse particles continue to be circulated and ground with the returned material to renew the self-grinding protective layer. S4. During the continuous powdering process, when the feed rate and classification conditions of the industrial silicon to be powdered are within the predetermined operating range, monitor the amount of the predetermined coarse-grained industrial silicon returned in the classification return process; when the amount of returned material continuously decreases, switch the industrial silicon powder from product collection to separate collection, and take samples to determine the increase in iron content of the industrial silicon powder relative to the same batch of industrial silicon to be powdered. S5. When the increase in iron content does not exceed the predetermined upper limit of the increase in iron content, continue to collect separately until the amount of returned material recovers to the level before the continuous decline, then resume product collection. When the increase in iron content exceeds the predetermined upper limit of iron content increase, the proportion of predetermined coarse-grained industrial silicon in the mill feed material is increased to rebuild the self-grinding protective layer. During the reconstruction process, the feed rate and classification conditions are restored to the operating range before the continuous decrease in return material. When the return material rate is restored to the level before the continuous decrease and the increase in iron content does not exceed the predetermined upper limit of iron content increase, product collection is resumed.

2. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 1, characterized in that, In step S1, the formation of the self-grinding protective layer specifically includes: S11. The lower limit of the predetermined coarse particle size is higher than the upper limit of the product particle size of industrial silicon powder, and the particle size range of the predetermined coarse particle size is 2-3 mm; the coarse industrial silicon particles separated from the same batch of industrial silicon to be powdered are sent to the grinding process for cyclic grinding, and the material obtained from grinding is classified. S12. The industrial silicon coarse particles that are still in the predetermined coarse particle grade after classification are returned to the grinding process for continued cyclic grinding, so that the industrial silicon coarse particles are cyclically distributed in the contact area between the material and the metal parts in the grinding zone. S13. The coarse industrial silicon particles are continuously replaced by the continued grinding and return material cycle, forming an industrial silicon particle material layer in the contact area, which is composed of the coarse industrial silicon particles of the industrial silicon to be ground and is continuously renewed with the cycle grinding. The industrial silicon particle material layer participates in the grinding contact and bears part of the contact load, thus constituting the self-grinding protective material layer.

3. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 1, characterized in that, In steps S2 and S4, the determination of the iron content increment is specifically as follows: S21. Obtain a reference sample from the same batch of industrial silicon to be powdered, and prepare the reference sample to a particle size range corresponding to the industrial silicon powder to be tested using low-iron contact preparation conditions determined by parallel sample preparation comparison of the same sample. S22. The reference sample and the industrial silicon powder to be tested are prepared using the low-iron contact sample preparation conditions before testing. The iron content of the reference sample and the industrial silicon powder to be tested are tested respectively, and the iron content of the reference sample is used as the reference iron content. S23. The difference between the iron content of the industrial silicon powder to be tested and the reference iron content is taken as the iron content increment.

4. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 3, characterized in that, The reference iron content is lower than the upper limit of iron content in industrial silicon powder products, and the predetermined upper limit of iron content increment is 100 ppm, and is not higher than the difference between the upper limit of iron content in industrial silicon powder products and the reference iron content; the condition for switching to continuous grinding is as follows: during the cyclic grinding process in step S1, industrial silicon powder samples are collected separately at predetermined sampling intervals of 15 min. When the iron content increment of at least two consecutive samples does not exceed the predetermined upper limit of iron content increment, the separate collection of industrial silicon powder ends and continuous grinding begins.

5. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 1, characterized in that, In step S3, the graded return material specifically refers to: S31. Collect industrial silicon powder within the product particle size range as the product; S32. Industrial silicon materials with particle size exceeding the upper limit of the product size are returned to the grinding process for further grinding; S33. The industrial silicon coarse particles in the predetermined coarse particle level in the returned material are continuously fed into the grinding process for cyclic grinding, so that the industrial silicon coarse particles re-enter the contact area between the material and the metal parts in the grinding zone, and the self-grinding protective material layer is renewed with the return material cycle.

6. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 1, characterized in that, In the continuous powdering process, the replenishment of the predetermined coarse-grained industrial silicon specifically involves: The industrial silicon coarse particles obtained from the grading process, which are in the predetermined coarse particle grade, are continuously returned to the grinding process for cyclic grinding. When the amount of recycled industrial silicon of the predetermined coarse grade continuously decreases, coarse industrial silicon particles of the predetermined coarse grade are separated from the same batch of industrial silicon to be pulverized, and these coarse industrial silicon particles are fed into the grinding process as supplementary feed, and together with the graded coarse industrial silicon particles of the predetermined coarse grade, they participate in the cyclic grinding.

7. The industrial silicon low-iron powder preparation method based on a self-grinding protective layer according to claim 1, characterized in that, In step S4, the monitoring of the amount of returned material specifically involves: S41. During a continuous statistical period in which the continuous powdering operation is stable and the feed rate and grading conditions of the industrial silicon to be powdered are maintained within a predetermined operating range, the amount of graded return material in each statistical period is recorded, and the mass percentage of predetermined coarse-grained industrial silicon in the graded return material is determined, wherein each statistical period is 15 min. S42. Determine the amount of recycle material for each statistical period based on the graded recycle material amount and the predetermined mass proportion of coarse-grained industrial silicon in each statistical period; S43. When the amount of returned material in at least two consecutive subsequent statistical periods is lower than the amount of returned material in the previous statistical period, it is determined that the amount of returned material is continuously decreasing, and the amount of returned material in the previous statistical period of the first statistical period in the at least two consecutive subsequent statistical periods is taken as the level of returned material before the continuous decrease; when the amount of returned material in the subsequent statistical periods recovers to a level not lower than the level of returned material before the continuous decrease, it is determined that the amount of returned material has recovered to the level before the continuous decrease.

8. The method for producing low-iron industrial silicon powder based on a self-grinding protective layer according to claim 7, characterized in that, In step S5, the reconstruction of the self-grinding protective layer specifically involves: S51. During the separate collection of industrial silicon powder, industrial silicon powder samples are obtained sequentially at a predetermined sampling interval of 15 minutes, and the iron content increment of each industrial silicon powder sample relative to the same batch of industrial silicon to be powdered is determined. S52. When the iron content increase exceeds 100 ppm, reduce the normal feed rate of the industrial silicon to be pulverized, and under the reduced feed load, use the industrial silicon coarse particles separated from the same batch of industrial silicon to be pulverized and in the predetermined coarse particle size as supplementary feed, so as to increase the proportion of the predetermined coarse particle size industrial silicon in the material entering the grinding process, while maintaining the industrial silicon coarse particles in the predetermined coarse particle size obtained from the classification to be returned to the grinding process for recycling grinding. S53. During the reconstruction of the self-grinding protective material layer, grinding, grading and coarse particle return are continued, and the generated industrial silicon powder is collected separately. S54. During the reconstruction of the self-grinding protective layer, the feed rate and classification conditions of the industrial silicon to be powdered are restored to the operating range before the continuous decrease in the return rate. When the amount of returned material for at least two consecutive statistical periods is not lower than the level of returned material before the continuous decline, and the increase in iron content of at least two consecutive separately collected industrial silicon powder samples does not exceed 100 ppm, the reconstruction of the self-grinding protective layer and the separate collection of industrial silicon powder are terminated, and product collection is resumed.

9. The method for producing low-iron industrial silicon powder based on a self-grinding protective layer according to claim 1, characterized in that, Before continuous milling begins, coarse industrial silicon particles at the predetermined coarse particle size are reserved from the same batch of industrial silicon to be milled. After the continuous milling of this batch of industrial silicon is completed, the normal feeding of the industrial silicon to be milled is stopped, and the reserved coarse industrial silicon particles from the same batch are sent to the milling process for further milling, grading, and coarse particle return. This allows the residual industrial silicon powder in the milling process and grading return process to be discharged, and the industrial silicon powder discharged after the normal feeding is stopped is collected separately from the product industrial silicon powder collected during the continuous milling process.

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