Low grade magnetite middling high pressure roll grinding - pre-concentration grade control system and method

Abstract

The present application belongs to the technical field of beneficiation process automation control, and discloses a low-grade magnetite middlings high-pressure roller mill-preliminary separation grade control system and method; by real-time monitoring of the roller surface passing power and roller gap spacing change in the high-pressure roller mill process, combined with the analysis of the discharge particle size distribution, the protective laminated area is identified and eliminated by using a small amplitude and high frequency roller pressure adjustment strategy. According to the dissociation characteristic difference of different particle size materials in the roller mill product, a dissociation inconsistency judgment mechanism based on the magnetic proportion and the dispersion degree of the magnetic response in the particle size is established, the coarse and fine particle materials are sent into different feeding sections of the pre-separation magnetic separator respectively, and the differential magnetic field strength and feeding thickness parameters are set. Through the construction of a feedback control system, the coordination and optimization of the magnetic field strength, the roller pressure adjustment amount and the coarse particle return ratio are realized. The present application realizes the efficient and stable treatment of complex low-grade magnetite middlings, and improves the dissociation uniformity and recovery rate of magnetic minerals.

Description

Technical Field

[0001] This invention relates to the field of automated control technology for mineral processing, and more specifically, to a high-pressure roller mill-pre-selection grade control system and method for low-grade magnetite middlings. Background Technology

[0002] Existing technologies face a core challenge in processing low-grade magnetite middlings: selective crushing interference caused by uneven ore hardness distribution. In actual production, low-grade magnetite middlings typically exhibit a complex structure where magnetite particles are scattered within a high-hardness gangue matrix such as quartz and feldspar. When this ore enters a high-pressure roller mill for lamination crushing, the harder gangue minerals tend to bear the load first under the roller pressure and form a relatively stable skeletal structure. Meanwhile, the relatively softer magnetite particles embedded within are "protected" by these gangue minerals and cannot obtain sufficient crushing stress. This phenomenon results in the same batch of ore exhibiting a highly uneven dissociation state after roller milling: some magnetite particles remain in the coarser particle size as intergrowths, while other gangue minerals are excessively crushed into fine powder. Traditional control systems rely solely on pressure feedback for extensive regulation, failing to recognize the microscopic crushing behavior changes caused by hardness differences. When unevenly dissociated ore enters the subsequent magnetic separation stage, a dilemma inevitably arises under a constant magnetic field strength setting: increasing the magnetic field strength can recover magnetic components from the coarse-grained intergrowth, but it also selects a large amount of fine-grained gangue, causing a decrease in concentrate grade; while decreasing the magnetic field strength can increase concentrate grade, it causes magnetic minerals in the coarse-grained intergrowth to be lost to the tailings, forming a vicious cycle of repeated "ore loss" and "tailings runaway," making the entire process constantly unstable.

[0003] In view of this, the present invention proposes a high-pressure roller mill-pre-selection grade control system and method for low-grade magnetite middlings to solve the above problems. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a method for controlling the pre-selection grade of low-grade magnetite middlings by high-pressure roller milling, comprising:

[0005] When low-grade magnetite ore enters the high-pressure roller mill, the feed particle size distribution, roller surface power, and roller gap are continuously acquired.

[0006] Record the changes in roller surface power and roller gap spacing according to the preset sampling period, and combine them with the changes in discharge particle size distribution in the corresponding time period to determine whether a protective laminated zone formed by continuous bearing of high hardness gangue appears in the material layer.

[0007] In response to the determination of the existence of a protective lamination zone, the single change amount of roller pressure adjustment is reduced and the frequency of roller gap correction is increased. At the same time, the coarse particles with a particle size larger than the preset particle size in the discharge are separated and their return ratio is adjusted according to the magnetic ratio of the coarse particles to weaken the shielding effect of high hardness gangue on magnetic mineral particles.

[0008] The unreturned roller mill product is fed into the classification unit and separated into coarse and fine particles. The mass ratio, magnetic ratio, and magnetic response dispersion within the particle size of the coarse and fine particles are measured respectively.

[0009] When the magnetic content of coarse-grained material is higher than the preset coarse-grained magnetic threshold, and the mass content of fine-grained material is higher than the preset fine-grained content threshold, it is determined that there is dissociation inconsistency in the roller mill product.

[0010] In response to the determination that there is inconsistency in the dissociation of the roller mill products, the coarse and fine particles are fed separately into different feeding sections of the pre-selection magnetic separator, and the magnetic field strength and feeding thickness are set for each feeding section.

[0011] The concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator are collected, and the magnetic field strength, the single change amount of roller pressure adjustment, and the return ratio of coarse particles are adjusted in sequence according to the change order of concentrate grade and tailings magnetic residue, so as to stabilize the pre-selection grade and reduce magnetic loss in tailings.

[0012] A high-pressure roller mill-pre-selection grade control system for low-grade magnetite middlings is used to implement the above-mentioned high-pressure roller mill-pre-selection grade control method for low-grade magnetite middlings. The system includes:

[0013] The detection unit is used to continuously acquire the feed particle size distribution, roller surface power and roller gap of the feed ore stream when low-grade magnetite ore enters the high-pressure roller mill, and to acquire the discharge particle size distribution within the corresponding time period.

[0014] The roller mill state judgment unit is used to record the change sequence of roller surface power and roller gap according to a preset sampling period, and, in combination with the change of discharge particle size distribution, to determine whether a protective laminated zone formed by continuous bearing of high-hardness gangue appears in the material layer.

[0015] The roller mill adjustment unit is used to reduce the single change in roller pressure adjustment and increase the frequency of roller gap correction in response to the detection of the presence of a protective lamination zone.

[0016] The coarse particle separation unit is used to separate the coarse particles in the discharge that are larger than the preset particle size, and to measure the magnetic ratio of the coarse particles.

[0017] The return control unit is used to adjust the return ratio of the coarse-grained part according to the magnetic ratio of the coarse-grained part, so as to reduce the blocking effect of the high-hardness gangue on the magnetic mineral particles.

[0018] The grading and detection unit is used to grade the non-returned roller mill products to obtain coarse-grained materials and fine-grained materials, and to measure the mass ratio, magnetic ratio and magnetic response dispersion degree of coarse-grained materials and fine-grained materials respectively.

[0019] The dissociation judgment unit is used to determine that there is dissociation inconsistency in the roller mill product when the magnetic ratio of coarse-grained material is higher than a preset coarse-grained magnetic threshold and the mass ratio of fine-grained material is higher than a preset fine-grained ratio threshold.

[0020] The pre-selection feeding control unit is used to respond to the determination that there is inconsistency in the dissociation of the roller mill products, to separate the coarse and fine particles and feed them into different feeding sections of the pre-selection magnetic separator, and to set the magnetic field strength and feeding thickness for each feeding section respectively;

[0021] The feedback correction unit is used to collect the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator, and to correct the magnetic field strength, the single change in roller pressure adjustment, and the return ratio of coarse particles in sequence according to the change order of concentrate grade and tailings magnetic residue, so as to stabilize the pre-selection grade and reduce magnetic loss in tailings.

[0022] The technical effects and advantages of the high-pressure roller mill-pre-selection grade control system and method for low-grade magnetite middlings of this invention are as follows:

[0023] This invention achieves precise identification and elimination of the protective effect of hard gangue during crushing, resulting in a relatively uniform degree of liberation between magnetic minerals and gangue, fundamentally improving the material basis for subsequent sorting. This invention can capture the differences in crushing response of different hardness components in the ore and implement refined process control accordingly, effectively avoiding the liberation mismatch phenomenon caused by traditional extensive pressure control. In the magnetic separation stage, a stratified processing strategy is implemented based on the material characteristics with different degrees of liberation, achieving precise matching and synergistic optimization of the magnetic separation behavior of materials of different particle sizes. This invention can automatically adjust to the optimal operating state according to changes in the hardness characteristics of the feed, significantly improving the resource utilization efficiency of complex low-grade magnetite ore. Simultaneously, the multi-parameter coordinated control system constructed by this invention effectively eliminates mutual interference between various process stages, maximizing the recovery rate of magnetic minerals while ensuring stable product grade throughout the entire beneficiation process. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the low-grade magnetite middlings high-pressure roller mill-pre-selection grade control method of the present invention;

[0025] Figure 2 This is a schematic diagram of the low-grade magnetite middlings high-pressure roller mill-pre-selection grade control system of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Please see Figure 1 The embodiments of this application provide a high-pressure roller mill-pre-selection grade control method for low-grade magnetite middlings, which can be executed by a control system. This method may include:

[0028] S101: When low-grade magnetite enters the high-pressure roller mill, continuously acquire the feed particle size distribution, roller surface power, and roller gap distance of the feed ore stream.

[0029] In this embodiment, low-grade magnetite refers to intermediate products with lower grades of magnetic iron ore, typically containing a large amount of gangue minerals, requiring high-pressure roller milling and pre-selection processes to improve its grade. A high-pressure roller mill is a device that uses the principle of interlayer crushing between high-pressure rollers to pulverize ore. It possesses selective crushing capabilities, preferentially crushing brittle gangue while relatively protecting tough magnetic minerals. Feed particle size distribution refers to the mass proportion of different particle sizes in the ore stream entering the high-pressure roller mill, reflecting the particle size composition characteristics of the raw material and directly affecting the crushing effect and product liberation degree of the roller mill. Roller surface power refers to the actual electrical power consumed by the roller surface during the operation of the high-pressure roller mill, reflecting the pressure and crushing resistance borne by the material layer, and is an important parameter for judging the internal crushing state of the material layer. Roller gap refers to the minimum distance between two high-pressure rollers, determining the pressure borne by the material between the rollers, and is a key operating parameter for controlling product particle size and crushing intensity.

[0030] In this embodiment, when low-grade magnetite ore begins to enter the high-pressure roller mill, the control system continuously monitors three key parameters: feed particle size distribution, roller surface power, and roller gap distance. Feed particle size distribution can be collected in real-time by online particle size detection devices, such as laser particle size analyzers or image analysis systems, to understand changes in the particle size composition of the raw material and provide a benchmark for subsequent judgment of the crushing effect. Roller surface power can be recorded in real-time by a motor power sensor, reflecting the real-time load status of the roller mill. Abnormal power fluctuations may indicate abnormal conditions such as concentrated bearing of high-hardness gangue within the material layer. Roller gap distance can be monitored in real-time by a displacement sensor, recording dynamic changes in the roller gap. Unexpected contraction or expansion of the roller gap distance may reflect the degree of compaction of the material layer or the passage of high-hardness particles.

[0031] S102: Record the sequence of changes in roller surface power and roller gap according to the preset sampling period, and combine it with the changes in discharge particle size distribution within the corresponding time period to determine whether a protective lamination zone formed by continuous bearing of high-hardness gangue appears in the material layer.

[0032] In this embodiment, the preset sampling period is a fixed time interval at which the control system samples the power passing through the roller surface and the roller gap spacing, such as once every 5 seconds. This is used to track the dynamic change trend of the parameters, filter out instantaneous fluctuation interference, and ensure the accuracy of state judgment. The change sequence refers to the direction and order of change of the power passing through the roller surface and the roller gap spacing within multiple consecutive sampling periods, such as the power first increasing and then decreasing, or the roller gap first decreasing and then recovering. This specific change pattern is an important feature for identifying the protective lamination zone. The discharge particle size distribution refers to the mass proportion of different particle sizes in the product discharged from the high-pressure roller mill, reflecting the crushing effect of the roller mill. When the proportion of coarse particles in the discharge is abnormally high, it may indicate insufficient crushing strength. The protective lamination zone refers to the local area formed by the continuous bearing of high-hardness gangue particles inside the material layer. In this area, the high-hardness gangue bears most of the pressure, resulting in insufficient force on the surrounding magnetic mineral particles, poor dissociation effect, and at the same time, these high-hardness gangue particles are not easily crushed under pressure and will be discharged in the form of coarse particles, which will have an adverse effect on the subsequent pre-selection process.

[0033] In this embodiment, the control system can continuously record the values ​​of the power passing through the roller surface and the roller gap spacing according to a preset sampling period, and analyze the order of their changes. When the power passing through the roller surface first increases and then decreases, it indicates that the material layer first encounters high-resistance material (high-hardness gangue), causing the power to rise. Subsequently, the high-hardness gangue passes through the roller gap or forms stable support, causing the power to fall back. When the roller gap spacing subsequently decreases and then recovers, it indicates that the high-hardness gangue widens the roller gap when it enters the roller gap, and the gap recovers after it passes through. The simultaneous occurrence of these two change patterns is a typical signal of the formation of a protective lamination zone.

[0034] Simultaneously, the control system can make a comprehensive judgment based on the changes in the particle size distribution of the discharged material within the corresponding time period. When the roller surface power and roller gap spacing exhibit the aforementioned characteristic changes over multiple consecutive sampling periods, and the proportion of materials with a particle size larger than the preset particle size (e.g., 3 mm) in the discharged material does not decrease or even increases within the corresponding time period, it can be determined that a protective lamination zone exists within the material layer. This is because the high-hardness gangue is not fully crushed within the protective lamination zone and is discharged as coarse particles, resulting in a persistently high proportion of coarse particles. Conversely, if the proportion of coarse particles in the discharged material decreases, and the magnetic content of this portion of the material simultaneously increases, it indicates that the coarse particles containing magnetic minerals have been crushed and dissociated, and the influence of the protective lamination zone is weakened.

[0035] S103: In response to the determination of the existence of a protective lamination zone, the single change amount of roller pressure adjustment is reduced and the frequency of roller gap correction is increased. At the same time, the coarse particles with a particle size larger than the preset particle size in the discharge are separated and their return ratio is adjusted according to the magnetic ratio of the coarse particles to weaken the shielding effect of high hardness gangue on magnetic mineral particles.

[0036] In this embodiment, the single change in roller pressure adjustment refers to the magnitude of change each time the roller pressure setting of the high-pressure roller mill is adjusted. For example, increasing from 10MPa to 12MPa results in a single change of 2MPa. The larger the single change, the more aggressive the roller pressure adjustment, which may lead to drastic fluctuations in the material layer state. Roller gap correction frequency refers to the frequency at which the control system adjusts the roller gap distance, such as once every 30 seconds. A higher frequency indicates more timely roller gap adjustment and a faster response to material layer changes. The coarse particle portion refers to the collection of particles larger than the preset particle size in the discharge. This portion includes both incompletely dissociated magnetic mineral aggregates and high-hardness gangue particles. Magnetic ratio refers to the percentage of magnetically responsive particles in the coarse particle portion relative to the total mass of the coarse particles, reflecting the enrichment degree of magnetic minerals in the coarse particles. The return ratio refers to the percentage of the mass of the coarse particle portion that is sent back to the high-pressure roller mill for re-crushing relative to the total mass of the coarse particles, used to control the load of the cyclic crushing.

[0037] In this embodiment, upon determining the existence of a protective lamination zone, the control system can immediately take multiple regulatory measures. First, it reduces the single change in roller pressure adjustment by dividing the current roller pressure setting into multiple incremental adjustment levels (e.g., 10-12MPa as the first level, 12-14MPa as the second level). After determining the existence of a protective lamination zone, it suspends cross-level pressure increases and only allows adjustments within the current level (e.g., fine-tuning within 10-12MPa) to prevent large fluctuations in roller pressure from further deteriorating the protective lamination zone or introducing new unstable factors in the material layer.

[0038] Secondly, increase the frequency of roller gap correction by changing the roller gap correction to be triggered by a fixed cycle (e.g., from once every 30 seconds to once every 10 seconds). This ensures that the change in roller gap spacing between two adjacent correction cycles does not exceed the preset spacing value (e.g., 0.5 mm). By frequently fine-tuning the roller gap, the widening effect of the roller gap when high-hardness gangue passes through can be responded to in a timely manner, maintaining the relative stability of the material layer pressure and avoiding fluctuations in the crushing effect caused by the roller gap deviating from the target value for a long time.

[0039] Simultaneously, the control system can separate coarse particles larger than the preset particle size in the discharge through a screening device and measure the magnetic content of these coarse particles. When the magnetic content of the coarse particles is lower than the preset magnetic return threshold (e.g., 30%), it indicates that the coarse particles mainly consist of high-hardness gangue. The return ratio of the coarse particles should be increased (e.g., from 50% to 80%) to send more gangue coarse particles back to the roller mill for re-crushing, reducing their blocking effect on magnetic mineral particles and preventing gangue coarse particles from interfering with the magnetic separation effect in subsequent pre-selection stages. When the magnetic content of the coarse particles is higher than the preset magnetic return threshold, it indicates that the coarse particles contain a large number of incompletely dissociated magnetic mineral intergrowths. The return ratio of the coarse particles should be reduced (e.g., from 50% to 30%) to avoid excessive recycling and crushing of magnetic minerals. At the same time, the portion with a higher magnetic content should be sent to the classification unit for further processing.

[0040] S104: The unreturned roller mill product is fed into the classification unit to separate it into coarse and fine particles. The mass ratio, magnetic ratio, and magnetic response dispersion within the particle size of the coarse and fine particles are measured respectively.

[0041] In this embodiment, the non-returned roller mill product refers to the portion of the discharge that was not sent back to the high-pressure roller mill for re-crushing. This includes particles that have reached a certain degree of dissociation and need to proceed to subsequent classification and pre-selection processes. The classification unit is a device used to separate the roller mill product according to particle size, such as a hydrocyclone or vibrating screen, to separate the product into two particle sizes: coarse and fine. The coarse particle size refers to the set of larger particles separated by the classification unit, typically ranging from 0.5 to 3 mm. This portion may contain incompletely dissociated magnetic minerals and gangue aggregates. The fine particle size refers to the set of smaller particles separated by the classification unit, typically ranging from 0 to 0.5 mm. This portion has a higher degree of magnetic mineral dissociation, but may also contain over-crushed gangue. The mass percentage refers to the percentage of a particular particle size class relative to the total mass of the non-returned roller mill product, reflecting the distribution proportion of that particle size class in the product. The degree of magnetic response dispersion within a particle size refers to the degree of difference in magnetic induction response intensity among different particles within the same particle size. A high degree of dispersion indicates that the particle size contains both highly magnetic particles (monolithic magnetic minerals) and low magnetic particles (intergrowths or gangue), resulting in uneven dissociation.

[0042] In this embodiment, the control system can feed the unreturned roller mill product into the classification unit, where it is separated into coarse and fine particles according to a preset particle size limit (e.g., 0.5 mm) using equipment such as a hydrocyclone or vibrating screen. After classification, parameters are measured for both particle sizes.

[0043] First, weigh the throughput of coarse and fine particles per unit time (e.g., mass per minute) to calculate their respective mass percentages. For example, if the throughput of coarse particles is 100 kg / min and the throughput of fine particles is 150 kg / min, then the mass percentage of coarse particles is 40% and the mass percentage of fine particles is 60%.

[0044] Secondly, the magnetic ratio of coarse and fine particles is determined separately. This can be done by using a magnetic response detection device (such as an electromagnetic induction sensor) to measure the amplitude of magnetic induction change when each particle size passes through the detection zone. Multiple magnetic induction change amplitudes are recorded in the sampling order, and the average value is calculated as the magnetic ratio index of that particle size.

[0045] Finally, the dispersion of magnetic response within a particle size is determined by comparing the differences between multiple magnetic induction amplitudes within the same particle size. When the difference exceeds a preset range (e.g., the difference between two adjacent measurements exceeds 20%), the dispersion of magnetic response within that particle size is considered significant, indicating substantial differences in the magnetic properties of the particles, including both highly magnetic individual minerals and low-magnetic intergrowths or gangue, resulting in uneven dissociation. When the dispersion of magnetic response within a coarse-grained material is significant and its magnetic percentage is higher than that of the fine-grained material, it is determined that there are insufficiently dissociated intergrowths in the coarse-grained material. In these intergrowths, the magnetic minerals and gangue are still tightly bound, requiring treatment using different magnetic separation strategies. When the mass percentage of fine-grained material increases and its magnetic percentage is lower than a preset fine-grained magnetic threshold (e.g., 25%), it is determined that there is over-crushing of gangue in the fine-grained material, meaning that too much gangue has been broken into fine particles, increasing the processing load for subsequent pre-selection. The roller mill parameters need to be adjusted to avoid over-crushing.

[0046] S105: When the magnetic ratio of coarse-grained material is higher than the preset coarse-grained magnetic threshold, and the mass ratio of fine-grained material is higher than the preset fine-grained ratio threshold, it is determined that there is dissociation inconsistency in the roller mill product.

[0047] In this embodiment, the preset coarse-grained magnetic threshold is a benchmark value pre-configured in the control system to determine the enrichment degree of magnetic minerals in coarse-grained materials, such as 45%. When the magnetic content of coarse-grained materials is higher than this threshold, it indicates that the coarse particles contain a large amount of magnetic minerals. However, due to the large size of the coarse particles, these magnetic minerals are likely to exist in the form of intergrowths rather than individual dissociations. The preset fine-grained proportion threshold is a benchmark value pre-configured in the control system to determine whether the output of fine-grained materials is too high, such as 65%. When the mass proportion of fine-grained materials is higher than this threshold, it indicates that the roller mill has produced too many fine-grained products, which may contain a large amount of over-crushed gangue and some over-ground magnetic minerals. Inconsistent dissociation refers to a significant difference in the degree of dissociation of magnetic minerals in different particle sizes in the roller mill product. In the coarse-grained grade, magnetic minerals are mainly intergrowths and insufficiently dissociated, while in the fine-grained grade, although dissociation is better, over-crushing is severe. The dissociation state and magnetic distribution characteristics of the two particle sizes are significantly different, requiring segmented feeding and differentiated magnetic separation strategies for processing.

[0048] In this embodiment, the control system can comprehensively judge two indicators: the magnetic content of coarse-grained materials and the mass content of fine-grained materials. When the magnetic content of coarse-grained materials is higher than the preset coarse-grained magnetic threshold (e.g., 50% in actual measurement, higher than the 45% threshold), it indicates that the content of magnetic minerals in the coarse particles is high. However, due to the large particle size, these magnetic minerals are likely still attached to gangue and have not achieved individual dissociation. A stronger magnetic field or a longer magnetic separation time is required during the magnetic separation process for effective recovery. When the mass content of fine-grained materials is higher than the preset fine-grained proportion threshold (e.g., 70% in actual measurement, higher than the 65% threshold), it indicates that the roller mill has produced too much fine-grained product. This part of the fine particles contains both fully dissociated magnetic mineral monomers and a large number of excessively crushed gangue particles, increasing the difficulty of subsequent magnetic separation and the risk of gangue entrainment.

[0049] When both of the above conditions are met simultaneously, it is determined that the roller mill products exhibit inconsistent dissociation. In this state, the dissociation characteristics and magnetic distribution of the coarse and fine particles differ significantly. If uniform magnetic separation parameters are used, the intergrowths in the coarse particle may be lost to the tailings due to insufficient magnetic field strength, while the gangue particles in the fine particle may be entrained in the concentrate due to excessive feed thickness, resulting in unsatisfactory pre-selection grade and recovery rate. Therefore, it is necessary to process the two particle sizes separately using differentiated magnetic separation strategies.

[0050] S106: In response to the determination that there is dissociation inconsistency in the roller mill products, coarse and fine particles are fed separately into different feeding sections of the pre-selection magnetic separator, and the magnetic field strength and feeding thickness are set for each feeding section.

[0051] In this embodiment, the pre-selective magnetic separator is a device for magnetic separation of the roller mill product. It is used to discard most of the gangue tailings, produce magnetic concentrate, and improve the feed grade of subsequent processes. It typically employs a permanent magnet drum separator or a high-gradient magnetic separator. The feeding sections are different feeding positions on the pre-selective magnetic separator, used to receive materials of different particle sizes. Different feeding sections can independently set parameters such as magnetic field strength and feed thickness to achieve differentiated processing. The first feeding section is the feeding position on the pre-selective magnetic separator for receiving coarse-grained materials. Given the intergrowth characteristics in the coarse particles, a stronger magnetic field strength and a thinner feed thickness are required to ensure effective adsorption of magnetic minerals in the intergrowths. The second feeding section is the feeding position on the pre-selective magnetic separator for receiving fine-grained materials. Given the individual magnetic minerals and over-grinding characteristics of gangue in the fine particles, a constant magnetic field strength and a thicker feed thickness are required to increase throughput and remove entrained fine gangue particles by briefly reducing the magnetic field strength.

[0052] In this embodiment, when it is determined that there is inconsistency in the dissociation of the roller mill products, the control system can feed the coarse and fine particles into the first and second feeding sections of the pre-selection magnetic separator through different conveying pipelines. The coarse particles enter the first feeding section, and the fine particles enter the second feeding section. The two feeding sections are located at different positions on the magnetic separator cylinder and do not interfere with each other, allowing for independent setting of operating parameters.

[0053] For the first feeding section (receiving coarse-grained materials), the control system can set the feeding thickness to be less than that of the second feeding section, such as setting the feeding thickness of the first feeding section to 20 mm and the feeding thickness of the second feeding section to 40 mm. A thinner feeding thickness can reduce the number of stacked layers of coarse particles in the material layer, allowing each coarse particle to be closer to the surface of the magnetic separator drum, fully contacting the magnetic field, increasing the adsorption probability of magnetic minerals in the intergrown material, and preventing the lower layer of coarse particles from being lost due to insufficient magnetic force caused by an excessively thick material layer.

[0054] Meanwhile, the magnetic field strength corresponding to the first feeding section is set to gradually increase along the feeding direction. For example, the magnetic separator cylinder corresponding to the first feeding section is divided into three sections: the magnetic field strength of the first section is 1000 Gauss, the second section is 1200 Gauss, and the third section is 1400 Gauss. The design of gradually increasing magnetic field strength allows for the initial adsorption of strongly magnetic individual magnetic minerals or high-grade intergrowths in coarse particles using a lower magnetic field, followed by the adsorption of weaker, low-grade intergrowths using a progressively stronger magnetic field. This achieves the tiered recovery of coarse-grained materials and reduces the loss of magnetic minerals to tailings.

[0055] For the second feeding section (receiving fine-grained materials), the control system can set the feeding thickness to a thicker value (e.g., 40 mm) to increase the throughput of fine-grained materials. This is because the magnetic minerals in the fine particles have good dissociation and strong magnetism, and can be effectively adsorbed even if the material layer is thick. At the same time, the magnetic field strength corresponding to the second feeding section is set to a constant value (e.g., 1100 Gauss) to meet the adsorption requirements of fine-grained individual magnetic minerals and avoid excessive entrainment of gangue fine particles due to an excessively strong magnetic field.

[0056] In addition, during the magnetic separation process in the second feeding section, the magnetic field strength is briefly reduced once within a preset time interval (e.g., from 1100 Gauss to 800 Gauss, and then restored after 2 seconds). The short-term decrease in magnetic field strength causes the weakly magnetic gangue particles adsorbed on the surface of the magnetic separator to fall off and be discharged into the tailings, while the strongly magnetic individual magnetic minerals can still be adsorbed, reducing gangue entrainment in the concentrate and improving the concentrate grade.

[0057] S107: Collect the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator, and adjust the magnetic field strength, the single change of roller pressure adjustment, and the return ratio of coarse particles in sequence according to the change order of concentrate grade and tailings magnetic residue, so as to stabilize the pre-selection grade and reduce magnetic loss in tailings.

[0058] In this embodiment, concentrate grade refers to the percentage of magnetic iron minerals in the concentrate output from the pre-selection magnetic separator, reflecting the enrichment effect of magnetic separation. A higher concentrate grade indicates more thorough removal of gangue during magnetic separation, but may also result in some magnetic minerals being lost to the tailings. Tailings magnetic residue refers to the percentage of magnetically responsive minerals in the tailings output from the pre-selection magnetic separator, reflecting the recovery efficiency of magnetic minerals during magnetic separation. A higher tailings magnetic residue indicates more magnetic minerals are not recovered and are lost to the tailings, affecting the overall recovery rate. The order of change refers to the direction (increasing, decreasing, or unchanged) of the changes in concentrate grade and tailings magnetic residue relative to the previous detection cycle over multiple consecutive detection cycles, and their sequential relationship. Analyzing this change pattern can diagnose problems with the current process parameters and provide a basis for parameter correction. The detection cycle is a fixed time interval for the control system to periodically sample and analyze concentrate grade and tailings magnetic residue, such as once every 10 minutes, used to track the dynamic trend of pre-selection effect.

[0059] In this embodiment, the control system can collect the concentrate grade output from the pre-selection magnetic separator through an online grade analyzer or laboratory testing, and collect the magnetic residue of the tailings through a magnetic detection device or laboratory analysis, continuously recording the values ​​of these two indicators according to the detection cycle. Over multiple consecutive detection cycles, the control system can analyze the direction of change of the concentrate grade and the magnetic residue of the tailings relative to the previous detection cycle, identify their change patterns, and sequentially adjust the magnetic field strength, the single change in roller pressure, and the return ratio of the coarse particles according to a preset correction logic, forming a closed-loop optimization control.

[0060] When the concentrate grade decreases and the magnetic residue in the tailings increases, it indicates a deterioration in magnetic separation efficiency. This is due to both increased loss of magnetic minerals (increased magnetic residue in tailings) and increased gangue entrainment or insufficient recovery of magnetic minerals (decreased concentrate grade). In this case, the control system can first increase the magnetic field strength corresponding to the first feeding section (e.g., from 1000-1200-1400 Gauss to 1100-1300-1500 Gauss) to enhance the adsorption capacity of magnetic minerals in the coarse-grained intergrowth and reduce the loss of magnetic minerals to the tailings. This is the first priority adjustment measure.

[0061] If the magnetic residue in the tailings still increases within the preset observation period (10 minutes in the next detection period) after increasing the magnetic field strength corresponding to the first feeding section, it indicates that increasing the magnetic field strength still cannot effectively reduce the loss of magnetic minerals. The problem may lie in insufficient dissociation in the roller mill stage, i.e., too many intergrowths in the coarse particles. In this case, the control system can reduce the single change in roller pressure adjustment (e.g., reduce the single change from 2MPa to 1MPa) to avoid large fluctuations in roller pressure that cause instability in the material layer. At the same time, the dissociation effect can be gradually improved by fine-tuning the roller pressure. This is the second priority adjustment measure.

[0062] If, within another preset observation period (e.g., the next detection period, 10 minutes) after reducing the single change in roller pressure adjustment, the magnetic content of the coarse-grained material is still higher than the preset coarse-grained magnetic threshold, it indicates that there are still a large number of intergrowths in the coarse particles, requiring enhanced cyclic crushing. In this case, the control system can increase the return ratio of the coarse particles (e.g., from 50% to 70%) to send more coarse intergrowths back to the roller mill for re-crushing, thereby increasing the degree of dissociation. This is the third priority adjustment measure.

[0063] Through the above-mentioned sequential correction logic, the control system can optimize the process layer by layer from magnetic separation parameters to roller mill parameters and then to circulating crushing parameters, thereby stabilizing the pre-selected grade and reducing magnetic loss in tailings.

[0064] In one embodiment of this application, the changes in the roller surface power and roller gap spacing are recorded according to a preset sampling period, and combined with the changes in the discharge particle size distribution within the corresponding time period, it is determined whether a protective laminated zone formed by continuous support of high-hardness gangue appears in the material layer, including:

[0065] Within multiple consecutive sampling periods, record whether the power passing through the roller surface first increases and then decreases, and whether the roller gap spacing subsequently decreases and then recovers.

[0066] If the number of times the roller surface power first increases and then decreases reaches a preset number, the number of times the roller gap distance subsequently decreases and then recovers reaches a preset number, and the proportion of material with a particle size larger than the preset particle size in the discharge does not decrease during the corresponding time period, then it is determined that there is a protective lamination zone in the material layer.

[0067] If the proportion of materials with a particle size larger than the preset particle size in the discharge decreases, and the magnetic content of this part of the material increases at the same time, it is determined that the protective lamination zone is weakened.

[0068] In existing technologies, abnormal material layer conditions are usually determined based on a single abnormal fluctuation of a single parameter (such as the roller surface throughput power or the roller gap distance). This lacks multi-parameter joint monitoring and continuous cycle verification, and is prone to misjudgment due to instantaneous interference or normal fluctuations, leading to unnecessary parameter adjustments and affecting production stability.

[0069] In this embodiment, the preset number of times is a benchmark value pre-configured in the control system to determine whether the changes in the roller surface throughput power and roller gap spacing characteristics are statistically significant, such as 3 times. Only when a specific change pattern repeats itself in multiple consecutive sampling periods to reach the preset number of times is it determined to be a true protective lamination zone signal, avoiding misjudgment caused by single fluctuations. "Increase followed by decrease" refers to the change pattern where the roller surface throughput power first increases in a certain sampling period, and then decreases in the next one or several sampling periods. This reflects the process where the material layer first encounters high-resistance material (high-hardness gangue), and then the high-hardness gangue passes through or forms stable support. "Decrease followed by recovery" refers to the change pattern where, at the same time or slightly after the roller surface throughput power shows an increase followed by a decrease (the reverse effect of the high-hardness gangue widening the roller gap, i.e., the hydraulic system attempts to maintain roller pressure by reducing the roller gap), and then recovers to the normal value. This reflects the dynamic process of high-hardness gangue passing between the rollers.

[0070] In this embodiment, the control system can continuously record the numerical changes of the roller pass-through power and roller gap distance over multiple consecutive sampling cycles (e.g., 10 consecutive sampling cycles, each cycle lasting 5 seconds, for a total of 50 seconds) to identify whether the aforementioned characteristic change patterns occur. When the roller pass-through power exhibits a pattern of first increasing and then decreasing (e.g., power is 100kW in the first cycle, increases to 110kW in the second cycle, and decreases to 105kW in the third cycle), the control system records this as a "power first increase then decrease" event. When the roller gap distance exhibits a pattern of subsequently decreasing and then recovering (e.g., roller gap is 10mm in the second cycle, decreases to 9.5mm in the third cycle, and recovers to 10mm in the fourth cycle), the control system records this as a "roller gap first decrease then recover" event.

[0071] If, within multiple consecutive sampling periods, the number of times the roller surface power first increases and then decreases reaches a preset number (e.g., 3 times), and the number of times the roller gap subsequently decreases and then recovers also reaches a preset number (e.g., 3 times), it indicates that the high-hardness gangue has passed through the roller gap multiple times, forming a stable protective lamination zone. At this point, the control system can further check whether the proportion of material with a particle size larger than a preset particle size (e.g., 3 mm) in the discharge during the corresponding time period has not decreased. If the proportion of coarse particles does not decrease or even increases (e.g., from 25% to 25% or to 28%), it indicates that the high-hardness gangue has not been sufficiently crushed and is discharged in coarse particle form, further verifying the existence of the protective lamination zone. At this point, it is determined that a protective lamination zone exists within the material layer, triggering subsequent roller pressure fine-tuning, roller gap high-frequency correction, and coarse particle return ratio adjustment measures.

[0072] Conversely, if in subsequent sampling cycles, the proportion of material with a particle size larger than the preset particle size in the discharge decreases (e.g., from 28% to 22%), and the magnetic content of this material simultaneously increases (e.g., from 35% to 42%), it indicates that the high-hardness gangue in the coarse particles has been broken, and the coarse particles containing magnetic minerals have been preserved or preferentially broken, thus weakening the influence of the protective lamination zone. In this case, it is determined that the protective lamination zone has weakened, and the single change in roll pressure adjustment can be appropriately restored, reducing the frequency of roll gap correction and optimizing operating resources.

[0073] As can be seen from the above, this embodiment records the characteristic change patterns of the roller surface passing power and roller gap spacing through multiple consecutive sampling cycles. Combined with statistical verification of reaching a preset number of times and synchronous analysis of the discharge particle size distribution, it avoids misjudgment caused by a single parameter or single fluctuation. By using the dual criteria of no decrease in the proportion of coarse particles and an increase in the proportion of magnetic particles, it accurately identifies the existence and weakening of the protective lamination zone, providing a reliable basis for subsequent parameter adjustments, improving the stability and dissociation effect of the roller milling process, and ensuring the accuracy of pre-selected grade control.

[0074] In one embodiment of this application, in response to determining the existence of a protective lamination zone, the single change in roller pressure adjustment is reduced, and the frequency of roller gap correction is increased. Simultaneously, coarse particles larger than a preset particle size are separated from the discharged material, and their return ratio is adjusted according to the magnetic proportion of the coarse particles. This includes:

[0075] The current roller pressure setting is divided into multiple incremental adjustment levels. After determining that there is a protective lamination zone, cross-level pressure increase is paused, and only the increase or decrease adjustment within the current level is allowed.

[0076] Change the roll gap correction to be triggered by a fixed cycle, so that the change in roll gap spacing between two adjacent correction cycles does not exceed the preset spacing value.

[0077] The magnetic content of the coarse-grained portion was determined;

[0078] When the magnetic proportion of the coarse-grained portion is lower than the preset magnetic return threshold, the return ratio of the coarse-grained portion is increased.

[0079] When the magnetic proportion of the coarse-grained portion exceeds the preset magnetic return threshold, the return ratio of the coarse-grained portion is reduced, and it is sent to the grading unit.

[0080] In this embodiment, the current roller pressure setting value refers to the target roller pressure value currently applied to the high-pressure roller mill by the control system, such as 12MPa, which is the actual operating pressure benchmark of the roller mill. The incremental adjustment range divides the adjustable range of the roller pressure setting value into several consecutive pressure intervals, such as the first interval 10-12MPa, the second interval 12-14MPa, and the third interval 14-16MPa. Small adjustments are allowed within each interval, but leapfrogging adjustments are not permitted between intervals to avoid large fluctuations in roller pressure. Pausing cross-interval pressure increases means that after determining the existence of a protective lamination zone, the control system no longer allows the roller pressure setting value to jump from the current interval to a higher interval (e.g., from the first interval 10-12MPa to the second interval 12-14MPa). Instead, the adjustment range is limited to the current interval (e.g., fine-tuning within 10-12MPa) to prevent a significant increase in roller pressure from further deteriorating the protective lamination zone or introducing new unstable material layer factors. Fixed-cycle triggering refers to changing the roll gap correction from being triggered based on a roll gap deviation threshold to being triggered at fixed time intervals, such as once every 10 seconds. This ensures the timeliness and regularity of roll gap adjustments, regardless of whether the roll gap deviation has reached the threshold. The preset spacing value is a pre-configured reference value in the control system used to limit the magnitude of a single roll gap correction, such as 0.5 mm. This ensures that the change in roll gap between two adjacent correction cycles does not exceed this value, preventing drastic roll gap fluctuations from affecting the stability of the material layer.

[0081] In this embodiment, upon determining the existence of a protective lamination zone, the control system first divides the current roller pressure setting into multiple incremental adjustment levels and pauses any cross-level pressure increases. For example, if the current roller pressure setting is 12 MPa, falling within the first level of 10-12 MPa, then during the period the protective lamination zone exists, the roller pressure setting is only allowed to be fine-tuned within the 10-12 MPa range (e.g., adjusted to 10.5 MPa or 11.5 MPa), and is not allowed to jump to the second level of 12-14 MPa. This avoids a significant increase in roller pressure causing the high-hardness gangue to bear greater pressure and further strengthen the protective lamination zone, while maintaining the flexibility of roller pressure adjustment, allowing for fine-tuning and optimization within the current level based on the material layer condition.

[0082] Secondly, the control system changes the roll gap correction to be triggered at fixed intervals, such as once every 10 seconds, replacing the original method based on a roll gap deviation threshold. Within each correction cycle, the control system calculates the correction amount based on the deviation between the current roll gap and the target roll gap, ensuring that this correction amount does not exceed a preset gap value (e.g., 0.5 mm). For example, if the current roll gap is 10.5 mm and the target roll gap is 10 mm, with a deviation of 0.5 mm, then the correction amount is 0.5 mm, adjusting the roll gap to 10 mm; if the deviation is 0.8 mm, then the correction amount is still limited to 0.5 mm, adjusting the roll gap to 10.3 mm, and the remaining 0.3 mm is corrected in the next correction cycle. By using fixed-cycle triggering and limiting the single correction amount, high-frequency, small-amplitude adjustments to the roll gap can be achieved, responding promptly to the widening effect of high-hardness gangue passing through the roll gap, while avoiding drastic roll gap fluctuations that could lead to unstable material layer pressure.

[0083] Simultaneously, the control system separates the coarse particles larger than the preset particle size from the discharge using a screening device and measures the magnetic content of these coarse particles. When the magnetic content of the coarse particles is lower than the preset return magnetic threshold (e.g., 30%), it indicates that the coarse particles mainly consist of high-hardness gangue with a low content of magnetic minerals. If these coarse particles directly enter the subsequent pre-selection stage, they will interfere with the magnetic separation effect and increase the tailings processing load. In this case, the control system increases the return ratio of the coarse particles (e.g., from 50% to 80%), sending more gangue coarse particles back to the roller mill for re-crushing, weakening their blocking effect on magnetic mineral particles, reducing the number of gangue coarse particles entering the pre-selection stage, and improving the magnetic separation effect.

[0084] When the magnetic content of the coarse particles exceeds a preset magnetic return threshold (e.g., 30%), it indicates that the coarse particles contain a significant amount of magnetic minerals. Although these may exist in the form of intergrowths, excessive cyclic crushing could lead to over-grinding of the magnetic minerals, increasing the risk of entrainment in fine gangue. In this case, the control system reduces the return ratio of the coarse particles (e.g., from 50% to 30%) to decrease the cyclic crushing load. Simultaneously, the portion with a higher magnetic content is sent to the classification unit for subsequent particle size classification and differentiated magnetic separation, avoiding excessive crushing that could result in the loss of magnetic minerals and balancing the liberation effect with the risk of over-grinding.

[0085] As can be seen from the above, this embodiment strengthens the protective lamination zone by pausing cross-gear pressure increases through gear division, avoiding large fluctuations in roller pressure; it responds promptly to changes in the material layer and maintains stability through fixed-cycle, high-frequency, limited-amplitude roller gap correction; and it reduces gangue obstruction and avoids over-grinding of magnetic minerals by bidirectionally adjusting the return ratio of magnetic proportion. These multiple measures precisely address the protective lamination zone, optimize the roller mill dissociation effect, and improve the accuracy of pre-selected grade control.

[0086] In one embodiment of this application, the mass ratio, magnetic ratio, and intra-particle magnetic response dispersion of coarse-grained and fine-grained materials are measured, including:

[0087] Weigh the amount of coarse and fine particles passing through each unit time to calculate their respective mass percentages.

[0088] The amplitude of magnetic induction change of coarse-grained material and fine-grained material when passing through the magnetic response detection zone was measured respectively, and multiple magnetic induction change amplitudes were recorded in the sampling order;

[0089] Compare the differences between multiple magnetic induction changes within the same particle size;

[0090] When the difference is greater than the preset difference range, it is determined that the magnetic response dispersion within the particle size is relatively large.

[0091] When the magnetic response dispersion within the coarse-grained material is large and the magnetic content is higher than that of the fine-grained material, it is determined that there are incompletely dissociated intergrowths in the coarse-grained material.

[0092] When the mass percentage of fine-grained material increases and its magnetic percentage is lower than the preset fine-grained magnetic threshold, it is determined that there is over-crushed gangue in the fine-grained material.

[0093] In this embodiment, the throughput per unit time refers to the mass of a certain particle size material passing through the weighing device within a unit time (e.g., 1 minute). For example, the throughput of coarse particles is 100 kg / min, and the throughput of fine particles is 150 kg / min, used to calculate the mass proportion of each particle size. The magnetic response detection zone refers to the detection area located at the outlet of the grading unit, equipped with an electromagnetic induction sensor or magnetometer, used to measure the magnetic induction response intensity of the passing material particles. The magnetic induction change amplitude refers to the change in the magnetic induction signal detected by the sensor relative to the background value when a single material particle passes through the magnetic response detection zone. For example, a change from 0 millistas to 5 millistas results in an amplitude of 5 millistas; a larger amplitude indicates stronger magnetism of the particle. The sampling order refers to recording the magnetic induction change amplitude of each particle sequentially according to the time sequence of its passage through the detection zone, forming an amplitude sequence used to analyze the magnetic differences between different particles within the same particle size class. The preset difference range is a benchmark value pre-configured in the control system to judge the degree of magnetic response dispersion within a particle size, such as 20%. When the difference in the amplitude of magnetic induction change between two adjacent measurements within the same particle size exceeds this percentage, the degree of magnetic response dispersion is determined to be large.

[0094] In this embodiment, the control system first weighs the throughput of coarse and fine particles per unit time. For example, if 100 kg of coarse particles and 150 kg of fine particles pass through in one minute, the mass percentage of coarse particles is 100 / (100+150)=40%, and the mass percentage of fine particles is 150 / (100+150)=60%. The mass percentage reflects the distribution ratio of the two particle sizes in the non-return mill product, providing a basis for subsequent judgment on whether there is too much fine particle material (i.e., over-grinding of gangue).

[0095] Secondly, the control system measures the amplitude of magnetic induction changes in coarse and fine particles as they pass through the magnetic response detection zone. As the particles pass through the detection zone sequentially, the sensor records the amplitude of the magnetic induction change for each particle according to the sampling order. For example, the amplitude sequence for coarse particles is [5,4,6,3,7,4,8,3,6,5] (unit: millistas), and the amplitude sequence for fine particles is [4,4,5,4,4,5,4,5,4,4] (unit: millistas). By calculating the average of the amplitude sequences, the magnetic proportion of each particle size can be obtained. For example, the average amplitude for coarse particles is 5.1 millistas, and the average amplitude for fine particles is 4.3 millistas, indicating that the magnetic proportion of coarse particles is higher than that of fine particles.

[0096] Next, the control system compares the differences between multiple magnetic induction change amplitudes within the same particle size. Taking coarse-grained material as an example, the difference between two adjacent measurements in the amplitude sequence is [|4-5|,|6-4|,|3-6|,|7-3|,|4-7|,|8-4|,|3-8|,|6-3|,|5-6|], i.e., [1,2,3,4,3,4,5,3,1]. The maximum difference is 5 millistas, which is approximately 98% of the average amplitude of 5.1 millistas, much larger than the preset difference range (e.g., 20%). At this point, it is determined that the magnetic response dispersion within the coarse-grained material is relatively large, indicating that there are both highly magnetic particles (e.g., particles with an amplitude of 8 millistas, which may be single magnetic minerals) and low magnetic particles (e.g., particles with an amplitude of 3 millistas, which may be intergrowths or gangue), resulting in uneven dissociation.

[0097] When the magnetic response dispersion within coarse-grained materials is greater and the magnetic content is higher than that of fine-grained materials (e.g., the average amplitude of 5.1 millisieverts for coarse-grained materials is higher than that of 4.3 millisieverts for fine-grained materials), it is determined that there are insufficiently dissociated intergrowths in the coarse-grained materials. This is because the greater magnetic dispersion within the coarse-grained materials indicates the presence of both high-grade individual magnetic minerals and low-grade intergrowths. The higher average magnetic content compared to the fine-grained materials suggests a larger total amount of magnetic minerals in the coarse-grained materials, but due to the larger particle size, most of them exist as intergrowths, requiring stronger magnetic field strength or longer magnetic separation time for effective recovery.

[0098] When the mass percentage of fine-grained material increases (e.g., from 60% to 70%) and its magnetic content is below the preset fine-grained magnetic threshold (e.g., the magnetic content corresponding to an actual average amplitude of 4.3 millisoles is 25%, which is below the preset 30% threshold), it is determined that there is excessive crushing of gangue in the fine-grained material. This is because an increased mass percentage of fine-grained material indicates that the roller mill has produced too much fine-grained product, and a magnetic content below the threshold indicates that most of these fine particles are gangue. In other words, the gangue was excessively crushed during the roller milling process, increasing the load on subsequent pre-selected processing and the risk of gangue entrainment. It is necessary to adjust the roller pressure parameters to avoid excessive crushing.

[0099] As can be seen from the above, this embodiment calculates the mass percentage by the throughput per unit time and analyzes the magnetic percentage and dispersion degree by the magnetic induction change amplitude sequence, thereby achieving multi-dimensional and accurate characterization of coarse and fine-grained materials. It identifies coarse intergrowths by using both magnetic response dispersion degree and magnetic percentage as dual criteria, and identifies over-crushed fine gangue by using both mass percentage and magnetic percentage as dual criteria, providing reliable data support for subsequent differentiated magnetic separation strategies and improving the pertinence and effectiveness of pre-selection grade control.

[0100] In one embodiment of this application, in response to the determination that there is inconsistency in the dissociation of the roller mill products, coarse and fine particles are separately fed into different feeding sections of a pre-selective magnetic separator, and the magnetic field strength and feeding thickness are set for each feeding section, including:

[0101] Coarse-grained material is fed into the first feeding section, and fine-grained material is fed into the second feeding section.

[0102] The feeding thickness of the first feeding section is set to be less than the feeding thickness of the second feeding section;

[0103] The magnetic field strength corresponding to the first feeding section is set to increase gradually along the feeding direction.

[0104] The magnetic field strength corresponding to the second feeding section is set to a constant value and then reduced briefly once within a preset time interval.

[0105] In this embodiment, the feed thickness refers to the thickness of the material layer when it enters the surface of the magnetic separator drum in the feeding section, such as 20 mm or 40 mm. The thinner the material layer, the closer the individual particles are to the surface of the magnetic separator drum, and the stronger the magnetic force, but the lower the throughput. The thicker the material layer, the higher the throughput, but the lower the magnetic force on the lower particles, which may lead to the loss of magnetic minerals. Gradually increasing along the feeding direction means that the magnetic separator drum corresponding to the first feeding section is divided into several sections (such as three sections), with the magnetic field strength of each section increasing sequentially, such as 1000 Gauss for the first section, 1200 Gauss for the second section, and 1400 Gauss for the third section, achieving stepwise adsorption. High-magnetic particles are adsorbed first, followed by low-magnetic particles, improving the recovery rate. A constant value means that the magnetic field strength of each section of the magnetic separator drum corresponding to the second feeding section remains consistent, such as 1100 Gauss for the entire section, meeting the adsorption requirements of fine-grained individual magnetic minerals and avoiding excessive entrainment of gangue particles due to an excessively strong magnetic field. A short-term reduction refers to temporarily reducing the magnetic field strength of the second feeding section from a constant value to a lower value (e.g., from 1100 Gauss to 800 Gauss) within a preset time interval (e.g., every 30 seconds), and then restoring it to a constant value after a short period of time (e.g., 2 seconds). This instantaneous decrease in magnetic field strength causes the weakly magnetic gangue particles adsorbed on the surface of the magnetic separator to fall off and be discharged into the tailings, while the strongly magnetic individual magnetic minerals can still be adsorbed, reducing gangue entrainment in the concentrate.

[0106] In this embodiment, when it is determined that there is inconsistency in the dissociation of the roller mill products, the control system feeds the coarse and fine particles into the first and second feeding sections of the pre-selection magnetic separator through different conveying pipelines. The coarse particles enter the first feeding section, and the fine particles enter the second feeding section. The two feeding sections are located at different positions on the magnetic separator cylinder (e.g., the first feeding section is in the front half of the cylinder, and the second feeding section is in the rear half of the cylinder), and do not interfere with each other. The operating parameters can be set independently to achieve differentiated processing.

[0107] The control system sets the feed thickness of the first feeding section to be less than that of the second feeding section, for example, setting the feed thickness of the first feeding section to 20 mm and the feed thickness of the second feeding section to 40 mm. A thinner feed thickness reduces the number of layers of coarse particles stacked in the material layer, allowing each coarse particle to get closer to the surface of the magnetic separator drum, fully contacting the magnetic field and increasing the adsorption probability of magnetic minerals in the aggregate. For example, when the feed thickness is 20 mm, coarse particles (0.5-3 mm in size) only stack 2-3 layers, and each layer of particles is subjected to a strong magnetic force; however, if the feed thickness is 40 mm, coarse particles may stack 5-6 layers, the magnetic force on the lower layers weakens, and magnetic minerals in the aggregate may be lost to the tailings due to insufficient magnetic force. By setting a thinner feed thickness, the recovery rate of magnetic minerals in coarse-grained materials can be improved, and magnetic residue in the tailings can be reduced. However, correspondingly, the throughput of the first feeding section will be lower than that of the second feeding section.

[0108] The control system sets the magnetic field strength corresponding to the first feeding section to gradually increase along the feeding direction. For example, the magnetic separator cylinder corresponding to the first feeding section is divided into three sections: the first section has a magnetic field strength of 1000 Gauss, the second section 1200 Gauss, and the third section 1400 Gauss. This gradually increasing magnetic field strength design enables the tiered recovery of coarse-grained materials: the first section uses a lower magnetic field strength (1000 Gauss) to adsorb strongly magnetic individual magnetic minerals or high-grade intergrowths in the coarse particles, avoiding excessive adsorption of gangue due to an overly strong magnetic field; the second section uses a medium magnetic field strength (1200 Gauss) to adsorb moderately magnetic intergrowths, further improving the recovery rate; the third section uses a stronger magnetic field strength (1400 Gauss) to adsorb weakly magnetic, low-grade intergrowths, ensuring that magnetic minerals in the coarse particles are recovered as much as possible, reducing losses to tailings. Through tiered adsorption, the recovery rate of coarse-grained materials and concentrate grade can be balanced, reducing magnetic loss and avoiding excessive gangue entrainment.

[0109] The control system sets the feed thickness of the second feeding section to a relatively large value (e.g., 40 mm) to increase the throughput of fine-grained materials. Because the magnetic minerals in fine-grained materials are well dissociated, exist in monomeric form, and have strong magnetism, even with a thicker material layer (40 mm, where fine particles of 0-0.5 mm size may stack in dozens of layers), the lower particles can still be attracted to the cylinder surface by sufficient magnetic force, unlike coarse-grained materials where excessive material thickness leads to the loss of magnetic minerals. By setting a thicker feed thickness, the processing capacity of the second feeding section can be fully utilized, increasing the overall pre-selection capacity and adapting to operating conditions where fine-grained materials account for a high percentage (e.g., 70%).

[0110] The control system sets the magnetic field strength corresponding to the second feeding section to a constant value (e.g., 1100 Gauss). This magnetic field strength is sufficient to adsorb fine-grained individual magnetic minerals while avoiding excessive entrainment of gangue particles due to an excessively strong magnetic field. Since the magnetic minerals in the fine-grained material are uniformly dissociated and have low magnetic dispersion, it is not necessary to use a stepped magnetic field with progressively increasing magnetic field as in the coarse-grained material. A constant magnetic field strength is sufficient to meet the recovery requirements, simplifying the magnetic system design and control logic of the magnetic separator.

[0111] Furthermore, during the magnetic separation process in the second feeding section, the control system briefly reduces the magnetic field strength once every preset time interval (e.g., every 30 seconds). Specifically, in each 30-second operating cycle, the magnetic field strength remains constant at 1100 Gauss for the first 28 seconds, then briefly decreases to 800 Gauss between the 29th and 30th seconds, and returns to 1100 Gauss after 2 seconds. Utilizing this brief decrease in magnetic field strength, weakly magnetic gangue particles (with weak magnetism, barely adsorbing at 1100 Gauss) adsorbed on the surface of the magnetic separator cylinder will detach due to the weakened magnetic force and be discharged into the tailings with the material flow; while strongly magnetic individual magnetic minerals (with very strong magnetism, maintaining adsorption even at 800 Gauss) continue to adsorb on the cylinder surface and are subsequently scraped into the concentrate collection area by the scraper. By periodically reducing the magnetic field strength for short periods, gangue entrainment in the concentrate can be effectively reduced, improving the concentrate grade, while not affecting the recovery rate of magnetic minerals, because the magnetic field reduction time is very short (only 2 seconds), and strongly magnetic minerals will not detach.

[0112] As can be seen from the above, this embodiment achieves differentiated processing of coarse and fine-grained materials through segmented feeding. For coarse-grained materials, a thin material layer and progressively increasing magnetic field strength are used to improve the recovery rate of magnetic minerals in the intergrowth. For fine-grained materials, a thick material layer and constant magnetic field strength are used to increase throughput. Periodic short-term reductions in magnetic field strength reduce gangue entrainment and improve concentrate grade. These multiple measures optimize magnetic separation, stabilize pre-selection grade, reduce magnetic loss in tailings, and improve the overall economic efficiency of the high-pressure roller mill-pre-selection process for low-grade magnetite middlings.

[0113] In one embodiment of this application, the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator are collected, and the magnetic field strength, the single change in roller pressure adjustment, and the return ratio of coarse particles are sequentially adjusted according to the order of change of concentrate grade and tailings magnetic residue, including:

[0114] Within multiple consecutive testing cycles, record the direction of change of concentrate grade relative to the previous testing cycle, as well as the direction of change of tailings magnetic residue relative to the previous testing cycle.

[0115] When the concentrate grade decreases and the magnetic residue in the tailings increases, the magnetic field strength corresponding to the first feeding section should be increased first.

[0116] If the magnetic residue of the tailings still increases within the preset observation period after increasing the magnetic field strength corresponding to the first feeding section, then reduce the single change amount of the roller pressure adjustment.

[0117] If, within another preset observation period after reducing the single change in roller pressure adjustment, the magnetic proportion of coarse-grained material is still higher than the preset coarse-grained magnetic threshold, the return ratio of the coarse-grained portion is increased.

[0118] In this embodiment, the direction of change refers to the trend of change in concentrate grade or tailings magnetic residue in the current detection cycle relative to the previous detection cycle, including an increase (value increases), a decrease (value decreases), or no change (value remains basically flat). The preset observation cycle is a time window during which the control system waits for a parameter adjustment to take effect and observes its effect after the adjustment, such as one detection cycle (10 minutes). This avoids frequent parameter adjustments that could cause process fluctuations and ensures that the effect of each adjustment can be accurately evaluated.

[0119] In this embodiment, the control system continuously collects the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator within multiple consecutive detection cycles (e.g., 5 consecutive detection cycles, each 10 minutes, for a total of 50 minutes), and records the direction of change of each relative to the previous detection cycle. For example, if the concentrate grade is 42% and the tailings magnetic residue is 8% in the first cycle, and the concentrate grade is 41% and the tailings magnetic residue is 9% in the second cycle, then the direction of change of the concentrate grade in the second cycle is decreasing, and the direction of change of the tailings magnetic residue is increasing.

[0120] When the concentrate grade decreases and the magnetic residue in the tailings increases, it indicates a deterioration in magnetic separation efficiency. The decrease in concentrate grade may be due to increased gangue inclusions or insufficient recovery of magnetic minerals, while the increase in magnetic residue in the tailings indicates that more magnetic minerals are lost to the tailings. This pattern usually suggests insufficient magnetic field strength in the magnetic separation stage, failing to effectively adsorb weakly magnetic intergrowths or individual magnetic minerals. In this case, the first priority adjustment measure for the control system is to increase the magnetic field strength corresponding to the first feeding stage, such as increasing it from 1000 Gauss to 1100 Gauss in the first stage, from 1200 Gauss to 1300 Gauss in the second stage, and from 1400 Gauss to 1500 Gauss in the third stage. Increasing the magnetic field strength in the first feeding stage enhances the adsorption capacity for magnetic minerals in coarse-grained intergrowths, reduces the loss of magnetic minerals to the tailings, and prioritizes addressing the issue of increased magnetic residue in the tailings, as intergrowths in coarse-grained materials are the main source of magnetic loss.

[0121] Within a preset observation period (10 minutes for the next detection period) after increasing the magnetic field strength corresponding to the first feeding section, the control system continues to monitor changes in the magnetic residue of the tailings. If the magnetic residue of the tailings still increases (e.g., from 9% to 10%), it indicates that increasing the magnetic field strength still cannot effectively reduce the loss of magnetic minerals. The problem may not be in the magnetic separation stage, but in the insufficient dissociation in the roller mill stage, i.e., there are too many intergrowths in the coarse particles, and even if the magnetic field strength is increased, it is difficult to adsorb the magnetic minerals wrapped by gangue in the intergrowths. At this time, the second priority adjustment measure of the control system is to reduce the single change in roller pressure adjustment, such as reducing the single change from 2MPa to 1MPa. Reducing the single change can avoid the instability of the material layer caused by large fluctuations in roller pressure. At the same time, the dissociation effect can be gradually improved by fine-tuning the roller pressure. For example, within the current range of 10-12MPa, first fine-tune from the current 11MPa to 11.5MPa, observe the changes in the discharge particle size distribution and the proportion of coarse magnetic particles, and then decide whether to continue fine-tuning to gradually optimize the crushing intensity of the roller mill and improve the degree of dissociation of intergrowths.

[0122] Within another preset observation period after reducing the single change in roller pressure adjustment (e.g., the next detection period, 10 minutes), the control system continues to monitor the magnetic content of the coarse-grained material. If the magnetic content of the coarse-grained material is still higher than the preset coarse-grained magnetic threshold (e.g., if the actual measured value is 50%, higher than the 45% threshold), it indicates that there are still a large number of intergrowths in the coarse particles, and the effect of roller pressure fine-tuning is limited, requiring enhanced cyclic crushing. At this time, the third priority adjustment measure of the control system is to increase the return ratio of the coarse particles, such as from 50% to 70%. Increasing the return ratio can send more coarse intergrowths back to the roller mill for re-crushing, increasing the number of crushing cycles, gradually increasing the degree of liberation, weakening the shielding effect of high-hardness gangue on magnetic mineral particles, reducing the entry of intergrowths into the pre-selection stage, and fundamentally reducing the magnetic residue in the tailings.

[0123] Through the above-mentioned sequential correction logic, the control system diagnoses the root cause of the problem and implements optimization layer by layer, from magnetic separation parameters (magnetic field strength in the first feeding section) to roller mill parameters (single change in roller pressure adjustment) and then to cyclic crushing parameters (coarse particle return ratio), forming a three-level closed-loop control of "magnetic separation optimization - roller mill fine-tuning - cyclic strengthening", which stabilizes the pre-selected grade and reduces magnetic loss in tailings.

[0124] As can be seen from the above, this embodiment identifies abnormal patterns in magnetic separation by recording the changes in concentrate grade and tailings magnetic residue over multiple consecutive detection cycles. A three-tiered priority correction logic is used: first, magnetic separation is adjusted; then, the roller mill is adjusted; and finally, the circulation is adjusted. A preset observation period is set after each adjustment to verify the effect, avoiding frequent parameter fluctuations. By diagnosing the root causes of problems layer by layer and precisely implementing optimization measures, the stability and effectiveness of pre-selection grade control are improved, magnetic loss is reduced, and the resource utilization rate of low-grade magnetite ore is increased.

[0125] In one embodiment of this application, it further includes:

[0126] When the concentrate grade increases and the magnetic residue of the tailings remains unchanged, the current roller pressure setting value remains unchanged.

[0127] When the concentrate grade increases and the magnetic residue of the tailings also increases, reduce the feed thickness of the second feeding section.

[0128] When the concentrate grade decreases and the magnetic residue of the tailings decreases, the magnetic field strength corresponding to the first feeding section is reduced.

[0129] After adjusting only one parameter at a time, keep the remaining parameters unchanged for at least one detection cycle before adjusting the next parameter.

[0130] In this embodiment, "remaining unchanged" means that after detecting a specific change pattern, the control system determines that the current process parameters are in an optimal state, does not perform any adjustment operations, maintains the existing parameter settings, and avoids unnecessary intervention that could lead to process fluctuations. "Maintaining the remaining parameters unchanged for at least one detection cycle" means that after adjusting one parameter, the control system does not adjust other parameters for at least one detection cycle (e.g., 10 minutes), waiting for the effect of the parameter adjustment to fully manifest. This avoids the effects of multiple parameters being adjusted simultaneously, which could lead to superposition or mutual cancellation, making it impossible to accurately determine the actual effect of each parameter adjustment.

[0131] In this embodiment, when the concentrate grade increases while the magnetic residue in the tailings remains unchanged, it indicates an improvement in the magnetic separation effect: the increased concentrate grade signifies a higher enrichment of magnetic minerals and a reduction in gangue inclusions in the concentrate, while the unchanged magnetic residue in the tailings indicates that the amount of magnetic minerals lost to the tailings has not increased. This pattern suggests that the current process parameters (including roller pressure setting, magnetic field strength, feed thickness, and coarse particle return ratio) are in an optimal state, achieving a balance between improving the concentrate grade and controlling magnetic loss. At this time, the control system maintains the current roller pressure setting unchanged and does not adjust other parameters to maintain stable process operation and avoid the already improved separation effect from deteriorating again due to parameter adjustments.

[0132] When both the concentrate grade and the magnetic residue in the tailings increase, it indicates a specific problem in magnetic separation: the increased concentrate grade signifies a higher enrichment of magnetic minerals in the concentrate, but the increased magnetic residue in the tailings indicates that more magnetic minerals are lost to the tailings. This seemingly contradictory pattern usually suggests a problem in the handling of fine-grained materials: the feed thickness for fine-grained materials is too thick (e.g., 40 mm), causing the fine-grained individual magnetic minerals in the lower layers of the feed layer to be ineffectively adsorbed and lost to the tailings, while the strongly magnetic fine-grained individual minerals in the upper layers are adsorbed into the concentrate, increasing the concentrate grade. In this case, the control system reduces the feed thickness of the second feed section (e.g., from 40 mm to 30 mm), reducing the number of stacked layers, allowing more fine-grained individual magnetic minerals to contact the surface of the magnetic separator drum and be magnetically adsorbed, reducing the loss of fine-grained individual minerals to the tailings and lowering the magnetic residue in the tailings.

[0133] When both the concentrate grade and the magnetic residue in the tailings decrease, it indicates another problem in magnetic separation: a decrease in concentrate grade means an increase in gangue inclusions in the concentrate, while a decrease in magnetic residue in the tailings means a reduction in the amount of magnetic minerals lost to the tailings. This pattern usually suggests that the magnetic field strength in the first feeding stage is too strong (e.g., the magnetic field strength in the third stage is 1500 Gauss), causing gangue in the coarse particles (even if it is weakly magnetic) to be adsorbed into the concentrate, increasing gangue inclusions and reducing the concentrate grade. In this case, the control system reduces the magnetic field strength corresponding to the first feeding stage (e.g., reducing the third stage from 1500 Gauss to 1400 Gauss) to weaken the adsorption of weakly magnetic gangue, causing it to be discharged into the tailings, reducing gangue inclusions in the concentrate, and improving the concentrate grade. Due to the reduced magnetic field strength, some weakly magnetic intergrowths may also be lost to the tailings, resulting in a slight increase in the magnetic residue in the tailings. However, since improving the concentrate grade has a higher priority (the concentrate is the final product, and grade is a key indicator), this adjustment is reasonable.

[0134] After adjusting only one parameter at a time, the control system keeps the remaining parameters unchanged for at least one detection cycle (e.g., 10 minutes) before adjusting the next parameter. For example, after reducing the feed thickness of the second feeding section, the control system does not adjust the roller pressure setting, magnetic field strength, or coarse particle return ratio in the next detection cycle, waiting for the effect of the feed thickness adjustment to fully manifest (e.g., increased recovery rate of fine-grained single magnetic minerals, decreased magnetic residue in tailings). If, after the next detection cycle, the magnetic residue in tailings still has not decreased to the target range, then other parameters are considered for adjustment (e.g., increasing the magnetic field strength of the first feeding section). By adjusting single parameters sequentially and verifying through preset observation cycles, the superposition or mutual cancellation of effects caused by adjusting multiple parameters simultaneously can be avoided, ensuring that the effect of each adjustment can be accurately evaluated, gradually optimizing the process parameters to the optimal state, and improving the accuracy and stability of pre-selected grade control.

[0135] As can be seen from the above, this embodiment identifies various variation patterns of concentrate grade and tailings magnetic residue, and adopts differentiated adjustment strategies such as keeping it unchanged, reducing feed thickness, and reducing magnetic field strength to accurately address magnetic separation problems under different working conditions. By adjusting single parameters sequentially and verifying through preset observation cycles, frequent parameter fluctuations are avoided, ensuring that the adjustment effect is assessable and traceable. This achieves stable control of pre-selection grade and continuous optimization of magnetic loss, thereby improving the overall operating efficiency and economic benefits of the high-pressure roller mill-pre-selection process for low-grade magnetite middlings.

[0136] In one embodiment of this application, it further includes:

[0137] Record the feed particle size distribution, roller power variation, proportion of material larger than the preset particle size in the discharge, magnetic proportion of coarse material, concentrate grade and magnetic residue of tailings for each batch of ore source.

[0138] When the particle size distribution of the new feed ore flow falls within the range of a certain historical batch in multiple consecutive sampling periods, and the order of the roller surface power change is consistent with that historical batch, the roller pressure setting value, coarse particle return ratio and magnetic field strength corresponding to the first feeding section of that historical batch during stable operation are called as the current starting value.

[0139] If the concentrate grade and tailings magnetic residue are both within the target range for two consecutive detection cycles after adopting the current starting value, then the current starting value will be maintained and operation will continue.

[0140] In this embodiment, the ore batch refers to low-grade magnetite ore batches mined from different sources or at different time periods. Different batches of ore may differ in mineral composition, particle size distribution, and hardness characteristics, leading to different optimal parameters for the roller mill and pre-selection processes. The historical batch range refers to the numerical range of the feed particle size distribution of a specific historical batch during stable operation. For example, the feed particle size distribution of historical batch A is: 0-0.5mm 20-25%, 0.5-3mm 30-35%, and 3-10mm 40-45%. When the particle size distribution of a new feed stream falls within this range, it is considered similar to historical batch A. The roller surface power change sequence refers to the change pattern of the roller surface power over multiple consecutive sampling periods, such as the number, amplitude, and frequency of increases followed by decreases. This reflects the crushing resistance characteristics within the material layer and is a comprehensive representation of the ore's hardness and mineral composition. The current starting value refers to the initial parameter settings retrieved from the historical batch database by the control system when processing a new feed stream. These settings are used for rapid startup and stable operation, including key parameters such as roller pressing settings, coarse particle return ratio, and the magnetic field strength corresponding to the first feeding section. The target range refers to the preset acceptable range for concentrate grade and tailings magnetic residue. For example, the target range for concentrate grade is 42-45%, and the target range for tailings magnetic residue is 6-8%. When the actual values ​​are within this range, the process is considered stable and the indicators are qualified.

[0141] In this embodiment, the control system establishes a historical database based on ore source batches, recording key parameters for each batch, including feed particle size distribution (reflecting the raw material particle size composition), roller surface power variation (reflecting the crushing resistance characteristics of the material layer), the proportion of material larger than the preset particle size in the discharge (reflecting the roller mill crushing effect), the magnetic content of coarse-grained material (reflecting the degree of liberation), concentrate grade, and magnetic residue in tailings (reflecting the pre-selection separation effect). Simultaneously, it records the optimal parameter settings for each batch during stable operation, such as roller pressure settings, the proportion of coarse-grained material returned, and the magnetic field strength corresponding to the first feeding section. By establishing this historical database, process experience from different ore source batches can be accumulated, providing parameter references for subsequent processing of similar batches.

[0142] When a new feed stream enters the high-pressure roller mill, the control system collects the feed particle size distribution and the sequence of roller power changes in real time over multiple consecutive sampling cycles (e.g., 10 consecutive sampling cycles, each cycle lasting 5 seconds, for a total of 50 seconds), and compares this data with the batches in the historical database. If the feed particle size distribution of the new feed stream falls within the range corresponding to a certain historical batch (e.g., historical batch A) (e.g., 0-0.5mm accounts for 22%, 0.5-3mm accounts for 33%, and 3-10mm accounts for 43%, all within the particle size distribution range of historical batch A: 20-25%, 30-35%, and 40-45%), and the sequence of roller power changes is consistent with that historical batch (e.g., both show three instances of initial increase followed by decrease, with similar amplitude and frequency), then it is determined that the new feed stream has similar ore characteristics and crushing properties to historical batch A.

[0143] At this point, the control system retrieves the roller pressure setting, coarse particle return ratio, and magnetic field strength corresponding to the first feeding section from the stable operation of historical batch A as the current starting values ​​to quickly start the process. For example, if the roller pressure setting for historical batch A during stable operation is 11 MPa, the coarse particle return ratio is 60%, and the magnetic field strength corresponding to the first feeding section is 1000 Gauss for the first stage, 1200 Gauss for the second stage, and 1400 Gauss for the third stage, the control system sets these parameters as the current starting values. This eliminates the need to gradually explore and adjust from default parameters (such as roller pressure of 10 MPa, return ratio of 50%, and magnetic field strength of 900 Gauss for the first stage), significantly shortening the process stabilization time, reducing trial and error costs, and improving the efficiency and stability of starting a new batch.

[0144] After adopting the current initial value, the control system continuously monitors the concentrate grade and tailings magnetic residue for two consecutive detection cycles (e.g., 20 minutes). If both the concentrate grade and tailings magnetic residue are within the target range (e.g., concentrate grade of 43%, within the 42-45% target range; tailings magnetic residue of 7%, within the 6-8% target range), it indicates that the current initial value matches the new feed flow well, the process has entered a stable operating state, and no further parameter adjustments are needed. At this point, the control system continues to operate with the current initial value to maintain a stable pre-selected grade and low tailings magnetic loss, maximizing resource utilization and economic benefits.

[0145] If, within two consecutive detection cycles, the concentrate grade or tailings magnetic residue is not within the target range (e.g., concentrate grade is 40%, lower than the target lower limit of 42%; or tailings magnetic residue is 9%, higher than the target upper limit of 8%), it indicates that although the new feed stream is similar to historical batch A, there are still subtle differences, and the current starting value needs further optimization. In this case, the control system can fine-tune based on the aforementioned closed-loop optimization logic (e.g., when concentrate grade decreases and tailings magnetic residue increases, first increase the magnetic field strength of the first feeding section, then reduce the single change in roller pressure adjustment, and finally increase the coarse particle return ratio), gradually optimizing to the target range to achieve rapid stabilization of the new batch.

[0146] As can be seen from the above, this embodiment establishes a historical database of ore batches, recording key parameters and optimal settings for each batch, thereby accumulating and reusing process experience. Through dual matching of feed particle size distribution and the sequence of roller surface power changes, similar batches are accurately identified, and historically optimal parameters are used as starting values, significantly shortening the stabilization time for new batches and reducing trial-and-error costs. The applicability of the starting values ​​is verified through two consecutive testing cycles, ensuring the process quickly enters stable operation or is promptly fine-tuned and optimized. This improves the adaptability and operational efficiency of the high-pressure roller mill-pre-selection process for low-grade magnetite middlings to different ore batches, reduces the need for manual intervention, and enhances automation and overall economic benefits.

[0147] In one embodiment of this application, it further includes:

[0148] During the operation of the pre-selection magnetic separator, the thickness of the material layer in the magnetic product collection area is periodically measured, and the tailings side drop position is observed.

[0149] When the thickness of the material layer exceeds the preset thickness in a local location, and the tailings side drop position shifts towards the magnetic product collection area, it is determined that the fine gangue entrainment has increased.

[0150] In response to the determination of increased fine gangue inclusions, the feed thickness of the second feed section is first reduced, and then the preset time interval for the corresponding magnetic field strength of the second feed section to decrease once is shortened.

[0151] When the tailings side material drop position returns to the preset range and the material layer thickness is lower than the preset thickness, the feeding thickness of the second feeding section and the preset time interval before the adjustment are restored.

[0152] In this embodiment, the magnetic product collection zone is the area in the pre-selection magnetic separator used to collect the magnetic concentrate adsorbed by the magnetic field. It is located below or on the side of the magnetic separator drum. The magnetic products adsorbed on the surface of the drum are scraped into this zone by a scraper or a vibration device. The material layer thickness refers to the thickness of the magnetic concentrate layer accumulated in the magnetic product collection zone, such as 50 mm or 80 mm. The material layer thickness is affected by factors such as feed rate, magnetic separation efficiency, and concentrate discharge speed. The preset thickness is a benchmark value pre-configured in the control system to determine whether the material layer in the magnetic product collection zone is abnormally accumulated, such as 60 mm. When the material layer thickness exceeds this value, it may indicate an increase in gangue entrainment or poor concentrate discharge during the magnetic separation process. The tailings side discharge position refers to the point where the tailings (gangue not adsorbed by the magnetic field) discharged from the pre-selective magnetic separator fall off the surface of the cylinder. It is usually located in the central area of ​​the tailings collection trough. When the tailings side discharge position shifts towards the magnetic product collection area, it indicates that some weakly magnetic materials (such as fine gangue particles) that should have been discharged into the tailings have been abnormally adsorbed and carried into the magnetic product collection area. The preset range refers to the normal range of the tailings side discharge position. Using the center line of the tailings collection trough as a reference, the left and right deviation should not exceed ±10 cm. When the discharge position is within this range, the magnetic separation is considered normal.

[0153] In this embodiment, during the operation of the pre-selection magnetic separator, the control system periodically measures the thickness of the material layer in the magnetic product collection area (e.g., every 5 minutes, via a level sensor or manual observation) and observes the tailings side drop position (via a camera or manual inspection). When the material layer thickness exceeds a preset thickness in a local location (e.g., 80 mm is measured in a certain area, exceeding the preset thickness of 60 mm), and the tailings side drop position shifts towards the magnetic product collection area (e.g., the drop position shifts 15 cm to the left from the center line of the tailings collection trough, exceeding the preset range of ±10 cm), it is determined that the fine gangue entrainment has increased. This is because, although the fine gangue has very weak magnetism, under the conditions of a thicker feed layer (e.g., 40 mm) and a constant magnetic field strength (e.g., 1100 Gauss) in the second feeding section, some fine gangue may be abnormally adsorbed onto the surface of the magnetic separator drum due to excessive material layer stacking, shielding by the upper magnetic minerals, or a slightly stronger magnetic field strength. This leads to entrainment in the magnetic product collection area, resulting in a local increase in the thickness of the material layer. At the same time, the lack of these fine gangue particles in the tailings causes the tailings side drop position to shift towards the magnetic product collection area, further verifying the existence of gangue entrainment.

[0154] In response to the increased entrainment of fine-grained gangue, the control system first reduces the feed thickness of the second feeding section (e.g., from 40 mm to 30 mm) to reduce the number of stacked layers. This prevents the fine-grained gangue from being shielded by the upper magnetic minerals, allowing it to detach under weaker magnetic force and be discharged into the tailings, thus reducing the amount of gangue entrained in the magnetic product collection area. Reducing the feed thickness is the first priority adjustment measure because it is the most direct factor affecting the entrainment of fine-grained gangue and has the fastest adjustment effect.

[0155] If, after reducing the feed thickness in the second feeding section, the entrainment of fine gangue particles is still not significantly reduced (e.g., the material layer thickness still exceeds the preset thickness), the control system further shortens the preset time interval for a short-term decrease in the magnetic field strength in the second feeding section (e.g., from a short-term decrease every 30 seconds to a short-term decrease every 20 seconds). Shortening the preset time interval increases the frequency of short-term decreases in magnetic field strength, allowing more weakly magnetic gangue particles to detach and be discharged into the tailings when the magnetic field decreases, further reducing gangue entrainment and improving concentrate grade. Shortening the preset time interval is the second priority adjustment measure because adjusting the frequency of short-term decreases in magnetic field strength involves modifying the magnetic separator control logic, resulting in a slightly slower response time than adjusting the feed thickness, but the effect is more lasting.

[0156] When the tailings side discharge position returns to the preset range (e.g., the discharge position returns from a 15 cm left offset to within ±8 cm of the center line), and the material layer thickness is lower than the preset thickness (e.g., reduced from 80 mm to 55 mm), it indicates that the fine gangue entrainment has been effectively controlled, and magnetic separation has returned to normal. At this time, the control system restores the feed thickness of the second feed section before adjustment (e.g., from 30 mm to 40 mm) and the preset time interval (e.g., from every 20 seconds to every 30 seconds), restoring the normal processing capacity and magnetic separation efficiency of fine-grained materials. This avoids a decrease in processing capacity and an increase in energy consumption due to excessively small feed thickness or excessively high magnetic field reduction frequency, balancing gangue entrainment control and processing efficiency, and maintaining the economic efficiency of the pre-selection process.

[0157] Please see Figure 1 This application also provides a high-pressure roller mill-pre-selection grade control system for low-grade magnetite middlings, used in the above-mentioned high-pressure roller mill-pre-selection grade control method for low-grade magnetite middlings. The system includes:

[0158] The detection unit is used to continuously acquire the feed particle size distribution, roller surface power and roller gap of the feed ore stream when low-grade magnetite ore enters the high-pressure roller mill, and to acquire the discharge particle size distribution within the corresponding time period.

[0159] The roller mill state judgment unit is used to record the change sequence of roller surface power and roller gap according to a preset sampling period, and, in combination with the change of discharge particle size distribution, to determine whether a protective laminated zone formed by continuous bearing of high-hardness gangue appears in the material layer.

[0160] The roller mill adjustment unit is used to reduce the single change in roller pressure adjustment and increase the frequency of roller gap correction in response to the detection of the presence of a protective lamination zone.

[0161] The coarse particle separation unit is used to separate the coarse particles in the discharge that are larger than the preset particle size, and to measure the magnetic ratio of the coarse particles.

[0162] The return control unit is used to adjust the return ratio of the coarse-grained part according to the magnetic ratio of the coarse-grained part, so as to reduce the blocking effect of the high-hardness gangue on the magnetic mineral particles.

[0163] The grading and detection unit is used to grade the non-returned roller mill products to obtain coarse-grained materials and fine-grained materials, and to measure the mass ratio, magnetic ratio and magnetic response dispersion degree of coarse-grained materials and fine-grained materials respectively.

[0164] The dissociation judgment unit is used to determine that there is dissociation inconsistency in the roller mill product when the magnetic ratio of coarse-grained material is higher than a preset coarse-grained magnetic threshold and the mass ratio of fine-grained material is higher than a preset fine-grained ratio threshold.

[0165] The pre-selection feeding control unit is used to respond to the determination that there is inconsistency in the dissociation of the roller mill products, to separate the coarse and fine particles and feed them into different feeding sections of the pre-selection magnetic separator, and to set the magnetic field strength and feeding thickness for each feeding section respectively;

[0166] The feedback correction unit is used to collect the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator, and to correct the magnetic field strength, the single change in roller pressure adjustment, and the return ratio of coarse particles in sequence according to the change order of concentrate grade and tailings magnetic residue, so as to stabilize the pre-selection grade and reduce magnetic loss in tailings.

[0167] In summary, this application's embodiments accurately identify fine-grained gangue entrainment anomalies by periodically measuring the material layer thickness and observing the tailings side drop location; through a two-stage adjustment strategy of first reducing the feed thickness and then shortening the magnetic field interval, gangue entrainment is quickly and effectively controlled, improving concentrate grade; and by restoring the original parameters after anomaly elimination, excessive adjustments that could affect processing efficiency are avoided. This achieves dynamic monitoring and closed-loop control of fine-grained gangue entrainment, further optimizing the pre-selection grade stability and resource utilization efficiency of the high-pressure roller mill-pre-selection process for low-grade magnetite middlings.

[0168] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0169] It should be noted that all formulas in this manual are calculated by removing dimensions and taking their numerical values. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters and thresholds in the formulas are set by those skilled in the art according to the actual situation.

[0170] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection, characterized in that: include: When low-grade magnetite ore enters the high-pressure roller mill, the feed particle size distribution, roller surface power, and roller gap are continuously acquired. Record the changes in the power passing through the roller surface and the roller gap spacing according to the preset sampling period, and combine the changes in the discharge particle size distribution within the corresponding time period to determine whether a protective laminated zone formed by continuous bearing of high-hardness gangue appears in the material layer. In response to the determination that the protective lamination zone exists, the single change amount of the roller pressure adjustment is reduced and the frequency of roller gap correction is increased. At the same time, the coarse particles with a particle size larger than the preset particle size in the discharge are separated and their return ratio is adjusted according to the magnetic ratio of the coarse particles. The unreturned roller mill product is fed into the classification unit and separated into coarse and fine particles. The mass ratio, magnetic ratio, and magnetic response dispersion within the particle size of the coarse and fine particles are measured respectively. When the magnetic ratio of the coarse-grained material is higher than a preset coarse-grained magnetic threshold, and the mass ratio of the fine-grained material is higher than a preset fine-grained ratio threshold, it is determined that the roller mill product has dissociation inconsistency. In response to the determination that there is dissociation inconsistency in the roller mill products, the coarse-grained material and the fine-grained material are separately fed into different feeding sections of the pre-selection magnetic separator, and the magnetic field strength and feeding thickness are set for each feeding section respectively; The concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator are collected, and the magnetic field strength, the single change amount of the roller pressure adjustment, and the return ratio of the coarse particles are adjusted sequentially according to the change order of the concentrate grade and the tailings magnetic residue.

2. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 1, characterized in that, The step of recording the changes in the roller surface power and the roller gap spacing according to a preset sampling period, and combining this with the changes in the discharge particle size distribution within the corresponding time period, to determine whether a protective laminated zone formed by continuous support of high-hardness gangue appears in the material layer, includes: Within multiple consecutive sampling periods, record whether the power passing through the roller surface first increases and then decreases, and whether the roller gap spacing subsequently decreases and then recovers. If the number of times the roller surface passes through power first increases and then decreases reaches a preset number, the number of times the roller gap subsequently decreases and then recovers reaches a preset number, and the proportion of material with a particle size larger than the preset particle size in the discharge does not decrease during the corresponding time period, then it is determined that there is a protective lamination zone in the material layer. If the proportion of materials with a particle size larger than the preset particle size in the discharge decreases, and the magnetic content of this part of the material increases at the same time, then it is determined that the protective lamination zone is weakened.

3. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 2, characterized in that, In response to determining the existence of the protective lamination zone, the single change in roller pressure adjustment is reduced, and the frequency of roller gap correction is increased. Simultaneously, coarse particles larger than the preset particle size in the discharge are separated, and their return ratio is adjusted according to the magnetic proportion of the coarse particles. This includes: The current roller pressure setting is divided into multiple incremental adjustment levels. After determining that the protective lamination zone exists, cross-level pressure increase is paused, and only increase or decrease adjustment is allowed within the current level. Change the roll gap correction to be triggered by a fixed cycle, so that the change in roll gap spacing between two adjacent correction cycles does not exceed the preset spacing value. The magnetic content of the coarse-grained portion was determined; When the magnetic proportion of the coarse-grained portion is lower than the preset return magnetic threshold, the return ratio of the coarse-grained portion is increased. When the magnetic proportion of the coarse-grained portion is higher than the preset return magnetic threshold, the return ratio of the coarse-grained portion is reduced, and it is sent to the grading unit.

4. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 1, characterized in that, The determination of the mass percentage, magnetic percentage, and intra-particle magnetic response dispersion of the coarse-grained material and the fine-grained material includes: Weigh the amount of coarse-grained material and the amount of fine-grained material passing through per unit time to calculate their respective mass percentages; The amplitude of magnetic induction change of the coarse-grained material and the fine-grained material when passing through the magnetic response detection zone was measured respectively, and multiple amplitudes of magnetic induction change were recorded in the sampling order; Compare the differences between multiple magnetic induction change amplitudes within the same particle size; When the difference is greater than a preset difference range, it is determined that the magnetic response dispersion within the particle size is relatively large. When the magnetic response dispersion within the coarse-grained material is large and the magnetic ratio is higher than that of the fine-grained material, it is determined that there are incompletely dissociated intergrowths in the coarse-grained material. When the mass percentage of the fine-grained material increases and its magnetic percentage is lower than the preset fine-grained magnetic threshold, it is determined that there is over-crushed gangue in the fine-grained material.

5. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 4, characterized in that, In response to the determination that there is dissociation inconsistency in the roller mill products, the coarse-grained material and the fine-grained material are separately fed into different feeding sections of the pre-selective magnetic separator, and the magnetic field strength and feeding thickness are set for each feeding section, including: The coarse-grained material is fed into the first feeding section, and the fine-grained material is fed into the second feeding section. The feeding thickness of the first feeding section is set to be less than the feeding thickness of the second feeding section; The magnetic field strength corresponding to the first feeding section is set to increase gradually along the feeding direction. The magnetic field strength corresponding to the second feeding section is set to a constant value and then reduced briefly once within a preset time interval.

6. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 1, characterized in that, The process of collecting the concentrate grade and tailings magnetic residue output from the pre-selection magnetic separator, and sequentially adjusting the magnetic field strength, the single change in roller pressure adjustment, and the return ratio of the coarse particles according to the order of change of the concentrate grade and the tailings magnetic residue, includes: Within multiple consecutive detection cycles, the direction of change of the concentrate grade relative to the previous detection cycle, and the direction of change of the magnetic residue of the tailings relative to the previous detection cycle are recorded. When the grade of the concentrate decreases and the magnetic residue of the tailings increases, the magnetic field strength corresponding to the first feeding section is first increased. If the magnetic residue of the tailings still increases within a preset observation period after the magnetic field strength corresponding to the first feeding section is increased, then the single change amount of the roller pressure adjustment is reduced. If, within another preset observation period after reducing the single change in the roller pressure adjustment, the magnetic proportion of the coarse-grained material is still higher than the preset coarse-grained magnetic threshold, then the return ratio of the coarse-grained portion is increased.

7. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 6, characterized in that, Also includes: When the concentrate grade increases and the magnetic residue of the tailings remains unchanged, the current roller pressure setting value remains unchanged. When the grade of the concentrate increases and the magnetic residue of the tailings also increases, the feed thickness of the second feeding section is reduced. When the grade of the concentrate decreases and the magnetic residue of the tailings decreases, the magnetic field strength corresponding to the first feeding section is reduced. After adjusting only one parameter at a time, keep the remaining parameters unchanged for at least one detection cycle before adjusting the next parameter.

8. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 1, characterized in that, Also includes: Record the feed particle size distribution, roller power variation, proportion of material larger than the preset particle size in the discharge, magnetic proportion of coarse material, concentrate grade and magnetic residue of tailings for each batch of ore source. When the particle size distribution of the new feed ore flow falls within the range of a certain historical batch in multiple consecutive sampling periods, and the order of the roller surface power change is consistent with that historical batch, the roller pressure setting value, coarse particle return ratio and magnetic field strength corresponding to the first feeding section of that historical batch during stable operation are called as the current starting value. If, after adopting the current starting value, the concentrate grade and the magnetic residue of the tailings are both within the target range for two consecutive detection cycles, then the current starting value will be maintained and operation will continue.

9. The method for controlling the grade of low-grade magnetite middlings through high-pressure roller milling and pre-selection as described in claim 5, characterized in that, Also includes: During the operation of the pre-selection magnetic separator, the thickness of the material layer in the magnetic product collection area is periodically measured, and the tailings side drop position is observed. When the thickness of the material layer exceeds the preset thickness in a local location, and the tailings side drop position shifts towards the magnetic product collection area, it is determined that the fine gangue entrainment has increased. In response to the determination that the fine gangue entrainment has increased, the feeding thickness of the second feeding section is first reduced, and then the preset time interval for the corresponding magnetic field strength of the second feeding section to decrease once is shortened. When the tailings side discharge position returns to the preset range and the material layer thickness is lower than the preset thickness, the feeding thickness of the second feeding section and the preset time interval are restored to their original values.

10. A high-pressure roller mill-pre-selection grade control system for low-grade magnetite middlings, used to implement the high-pressure roller mill-pre-selection grade control method for low-grade magnetite middlings as described in any one of claims 1 to 9, characterized in that, include: The detection unit is used to continuously acquire the feed particle size distribution, roller surface power and roller gap of the feed ore stream when low-grade magnetite ore enters the high-pressure roller mill, and to acquire the discharge particle size distribution within the corresponding time period. The roller mill state judgment unit is used to record the change order of the roller surface power and the roller gap spacing according to a preset sampling period, and in combination with the change of the discharge particle size distribution, to determine whether a protective laminated zone formed by continuous bearing of high hardness gangue appears in the material layer. The roller mill adjustment unit is used to reduce the single change amount of roller pressure adjustment and increase the frequency of roller gap correction in response to the determination of the existence of the protective lamination zone. The coarse particle diversion unit is used to separate the coarse particles in the discharge that are larger than a preset particle size, and to measure the magnetic ratio of the coarse particles. The return control unit is used to adjust the return ratio of the coarse-grained portion according to the magnetic ratio of the coarse-grained portion, so as to weaken the blocking effect of the high-hardness gangue on the magnetic mineral particles. The grading and detection unit is used to grade the non-returned roller mill products to obtain coarse-grained materials and fine-grained materials, and to measure the mass ratio, magnetic ratio and magnetic response dispersion degree of the coarse-grained materials and the fine-grained materials, respectively. The dissociation judgment unit is used to determine that there is dissociation inconsistency in the roller mill product when the magnetic ratio of the coarse-grained material is higher than a preset coarse-grained magnetic threshold and the mass ratio of the fine-grained material is higher than a preset fine-grained ratio threshold. The pre-selection feeding control unit is used to separate the coarse-grained material and the fine-grained material into different feeding sections of the pre-selection magnetic separator in response to the determination that there is dissociation inconsistency in the roller mill product, and to set the magnetic field strength and feeding thickness for each feeding section respectively; The feedback correction unit is used to collect the concentrate grade and tailings magnetic residue output by the pre-selection magnetic separator, and to sequentially correct the magnetic field strength, the single change amount of the roller pressure adjustment, and the return ratio of the coarse particles according to the change order of the concentrate grade and the tailings magnetic residue, so as to stabilize the pre-selection grade and reduce the magnetic loss in the tailings.

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