Recovery and application method of silicon powder in diamond wire cutting monocrystalline silicon waste liquid

Abstract

The invention relates to the technical field of silicon powder recovery, in particular to a recovery and application method of silicon powder in diamond wire cutting monocrystalline silicon waste liquid. The recovery method comprises the following steps: carrying out suction filtration on the silicon-containing cutting waste liquid by using a suction filtration membrane rod suction filtration machine, and transferring a silicon powder enrichment layer on a suction filtration membrane rod into a collection container; adding a hydrochloric acid solution into the silicon powder enrichment layer in the collection container according to a preset proportion; pouring out an upper-layer solution to obtain a pickled silicon material, then rinsing the pickled silicon material to be neutral, recovering silicon powder, adding all or more of a binding agent, a dispersing agent, a stabilizing agent and water into the silicon powder, and carrying out ball-milling dispersion to prepare uniform slurry; and carrying out spray granulation and drying on the ball-milled slurry to obtain the silicon powder aggregate. The silicon powder aggregate prepared by the recovery method can be directly applied without high-temperature purification, so that the energy consumption is low.

Description

Technical Field

[0001] The invention relates to the technical field of silicon powder recovery, and in particular to a method for recovering and applying silicon powder in waste liquid from diamond wire cutting of single crystal silicon. Background Art

[0002] With the rapid development of the photovoltaic industry, solar energy accounts for more than 10% of the world's energy consumption structure. As the global energy structure shifts from fossil energy to clean energy, the proportion of solar photovoltaics will continue to grow. Solar panel silicon wafers are one of the main materials for photovoltaic devices. They are divided into monocrystalline silicon and polycrystalline silicon. Their purity is higher than 99.9999%, and their production cost accounts for about 20% of the total production cost of solar cell modules. As the basic component for making solar cells, silicon wafers need to be cut into silicon wafers of target thickness on crystalline silicon ingots, and then go through processes such as cleaning, texturing, diffusion doping to form PN junctions, coating with reflective coatings, screen printing and sintering to form cells to be assembled.

[0003] Diamond wire is a metal wire that is fixed with diamond abrasive by electroplating. It has the advantages of high production efficiency, low silicon loss and high cutting accuracy when cutting single crystal silicon, making the diamond wire cutting technology of crystal silicon wafer replace the mortar cutting technology. The diameter of the diamond wire cutting wire is between 0.06-0.2mm, which is not much different from the thickness of the single crystal silicon wafer (180-220um), so the silicon powder ground off when cutting silicon wafers accounts for 35-50% of the total mass of silicon ingots. The discharge of waste liquid containing silicon powder not only brings huge costs to pollution control, but also loses the high-value silicon powder in it, so it is necessary to recover the silicon powder in the cutting waste liquid. The recovery and reuse of silicon materials can not only save resources, but also reduce the production cost of silicon wafers.

[0004] In the process of cutting single crystal silicon ingots, diamond wire uses water-based cutting fluid for cooling and lubrication. Diamond particles with high hardness constantly move against silicon, and silicon powder with lower hardness falls off to achieve the cutting effect. Therefore, there are silicon powder and silicon dioxide formed by high-temperature oxidation of silicon powder, small diamond particles, metal impurities, cutting fluid and other substances in the cutting waste liquid. The existing enrichment processes for silicon powder in waste liquid include filter pressing, vacuum filtration, ceramic membrane filtration, centrifugal precipitation, etc., so that the solid phase and liquid phase in the waste liquid are separated and dried, and then the waste silicon powder is removed by other methods.

[0005] The invention patent application with publication number CN105523557A introduces a method for recovering high-purity silicon powder from crystalline silicon cutting waste, and the specific operations are solid-liquid separation → magnetic separation → acid leaching → cleaning → solid-liquid separation → drying and screening → high-purity silicon powder, and the purity of high-purity silicon powder is above 98%. The invention patent application with publication number CN106115714A discloses a high-temperature purification method, and the specific operations are acidification and impurity removal → solid-liquid separation → granulation into balls → high-temperature smelting with reducing agent → crushing and screening.

[0006] It can be seen from the above treatment process that the extraction of silicon powder in the cutting waste liquid requires the use of an acid solution to react with metal impurities, and then a high-temperature method is used to remove impurities from the silicon dioxide on the surface of the silicon powder to obtain high-purity silicon.

[0007] It can be seen that the application direction of silicon powder extracted from cutting waste liquid is relatively single, which is only used for melting single crystal silicon or multi-crystalline silicon ingots. This also puts forward higher purity requirements for the recycled silicon powder, resulting in a long silicon powder extraction process, complex process operation and high-temperature treatment consuming a lot of energy. Based on this, the existing technology still needs to be improved. Summary of the invention

[0008] During the diamond wire cutting process, the friction between the diamond wire and the silicon ingot generates heat, which will cause the surface of the silicon powder entering the cutting fluid to be covered with a layer of silicon dioxide oxide layer. If the recycled silicon powder is to be used as the raw material for single crystal silicon ingots, a high-temperature refining process is required to increase the silicon content in the silicon powder. In order to meet the preparation conditions of single crystal silicon ingots, the existing technology needs to heat the silicon particles after metal impurities are removed to 1450-1700℃, and then cool them to room temperature after purification, which consumes a lot of energy.

[0009] Reaction sintered silicon carbide products, with their high density, high strength, high hardness and high temperature stability, are widely used in the sintering of positive and negative raw materials of new energy lithium batteries, thermal diffusion and coating of solar cells, human protection and armor protection. The production process is as follows: under vacuum or protective atmosphere, as the temperature rises, silicon particles gradually turn into liquid or silicon vapor, penetrate into the interior of the porous silicon carbide blank and react with carbon to produce silicon carbide to obtain dense silicon carbide samples. Therefore, in the reaction sintering process, a large amount of silicon powder is required. If the silicon powder recovered from the cutting fluid can be applied to the production process of silicon-infiltrated reaction sintered silicon carbide products, it will increase the direction of direct application of recycled silicon powder without high temperature treatment.

[0010] In view of this, the present invention provides a method for recovering silicon powder in waste liquid produced by diamond wire cutting of single crystal silicon, which can at least solve the technical problem of high energy consumption of existing silicon powder recovery methods.

[0011] The first aspect of the present invention provides a method for recovering silicon powder in waste liquid from diamond wire sawing of single crystal silicon, comprising the following steps: S1, using a suction membrane rod suction filter to filter the silicon-containing cutting waste liquid, and transferring the silicon powder enriched layer on the suction membrane rod to a collection container; S2, adding hydrochloric acid solution to the silicon powder enriched layer in the collection container according to a preset ratio to remove metal impurities in the silicon powder enriched layer; S3, pouring out the upper solution to obtain the acid-washed silicon material, then rinsing the acid-washed silicon material to neutrality, recovering silicon powder, adding all or more of a binder, a dispersant, a stabilizer and water to the silicon powder, and preparing a uniform slurry by ball milling and dispersion; S4, spray granulating and drying the ball-milled slurry to obtain silicon powder agglomerates.

[0012] In some embodiments, in step S2, the concentration of the hydrochloric acid solution is 20%-30%, and the ratio of the added hydrochloric acid solution to the silicon powder enriched layer is 6-10:1.

[0013] In some embodiments, in step S2, after adding the hydrochloric acid solution, the step further includes: subjecting the mixed solution to ultrasonic stirring treatment, wherein the ultrasonic stirring time is 1 to 3 hours.

[0014] In some embodiments, in step S3, rinsing the pickled silicon material and recovering silicon powder includes: rinsing the pickled silicon material with pure water having a conductivity of less than 5 us / cm, and enriching the silicon powder by centrifugal dehydration, until the conductivity of the supernatant of the pickled silicon material is less than 10 us / cm, the rinsing is completed, and the silicon powder is enriched by centrifugal dehydration.

[0015] In some embodiments, in step S3, the binder, dispersant and stabilizer include 5% by mass of PVA, water-soluble dextrin and polyacrylic acid.

[0016] In some embodiments, in step S4, ball milling dispersion is performed using SiC balls with a diameter of 10 to 15 mm, a ball-to-material ratio of 1.5 to 3:1, a ball milling speed of 30 to 70 rpm, and a ball milling time of 4 to 6 hours.

[0017] In some embodiments, in step S1, the surface of the filtration membrane rod is composed of an organic membrane with a pore size of 100 nm. When an enrichment layer with a thickness of 0.5 to 1.5 cm is observed on the surface of the organic membrane, the filtration membrane rod is transferred from the silicon-containing cutting waste liquid.

[0018] The second aspect of the present invention further provides a method for applying silicon powder in waste liquid from diamond wire sawing of single crystal silicon, based on the silicon powder agglomerates recovered by the recovery method proposed in any of the above embodiments: The silicon powder agglomerate and the porous silicon carbide blank are placed in a graphite crucible in a mass ratio of 1:1 and subjected to vacuum reaction sintering to obtain a reaction sintered silicon carbide blank.

[0019] In some embodiments, the preparation of the flat plate-shaped reaction-sintered silicon carbide blank further includes: pressing the silicon powder agglomerates into a block having a shape consistent with the porous silicon carbide blank to be reacted.

[0020] In some embodiments, the reaction sintering is performed at a temperature above 1550° C. for 1 hour.

[0021] The beneficial effects of the present invention are as follows: the present invention adds a binder, a dispersant, a lubricant, water, etc. to the acid-treated silicon powder, and ball-mills and disperses to prepare a uniform slurry. The silicon powder agglomerates prepared by spray granulation and drying can be directly used without high-temperature purification, thereby reducing energy consumption. As described in the present application, the silicon powder agglomerates prepared by the above-mentioned recovery method can be directly placed in a graphite crucible with a porous silicon carbide blank at a mass ratio of 1:1 for vacuum reaction sintering to prepare a reaction-sintered silicon carbide blank, which has a low preparation cost and saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A flow chart of a method for recovering silicon powder from waste liquid from diamond wire sawing of single crystal silicon provided in one embodiment of the present invention; Figure 2 The present invention is a schematic diagram of the structure of silicon powder agglomerates prepared by a method for recovering silicon powder from waste liquid of single crystal silicon cut by diamond wire cutting provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0025] The present invention provides a method for recovering silicon powder from waste liquid of diamond wire cutting of single crystal silicon, such as Figure 1 As shown, the following steps are included: S1, use a suction membrane rod filter to filter the silicon-containing cutting waste liquid, and transfer the silicon powder enriched layer on the suction membrane rod to a collection container. Specifically, the silicon powder enriched layer on the surface of the suction membrane can be back-blown into the collection container by back-blowing. The filtered cutting liquid can continue to be used to achieve the purpose of recycling and reduce the generation and treatment costs of waste liquid.

[0026] S2, adding hydrochloric acid solution to the silicon powder enriched layer in the collection container according to a preset ratio to remove metal impurities in the silicon powder enriched layer; S3, pouring out the upper solution to obtain the acid-washed silicon material, then rinsing the acid-washed silicon material to neutrality, recovering silicon powder, adding all or more of a binder, a dispersant, a lubricant and water to the silicon powder, and preparing a uniform slurry by ball milling and dispersion; S4, spray granulation and drying the ball-milled slurry to obtain silicon powder agglomerates (such as Figure 2 as shown).

[0027] Compared with the prior art, the present invention adds a binder, a dispersant, a lubricant, water, etc. to the acid-treated silicon powder, and prepares a uniform slurry by ball milling dispersion. The silicon powder agglomerates prepared by spray granulation and drying can be directly used without high-temperature purification, thereby reducing energy consumption.

[0028] In some embodiments, in step S2, the concentration of the hydrochloric acid solution is 20%-30%, and the ratio of the added hydrochloric acid solution to the silicon powder enriched layer is 6-10:1. Hydrochloric acid, as a strong acid, can react with many metals to generate soluble metal chlorides. The appropriate concentration and ratio can ensure that the reaction proceeds fully without causing unnecessary damage to the silicon powder due to excessive acidity. In this example, a hydrochloric acid concentration of 20%-30% and an addition ratio of 6-10:1 are selected to ensure the impurity removal effect while avoiding excessive corrosion or damage to the silicon powder.

[0029] In some embodiments, in step S2, after adding the hydrochloric acid solution, the step further includes: subjecting the mixed solution to ultrasonic stirring treatment, the ultrasonic stirring time is 1~3H, specifically, placing the collection container in an ultrasonic water pool, and turning on the ultrasonic generator; the mixed solution is pneumatically stirred for 1~3H using a stirring rod wrapped with polytetrafluoroethylene, which can accelerate the reaction between hydrochloric acid and metal.

[0030] In some embodiments, in step S3, rinsing the pickled silicon material and recovering silicon powder includes: rinsing the pickled silicon material with pure water having a conductivity of less than 5 us / cm, and enriching the silicon powder by centrifugal dehydration, until the conductivity of the supernatant of the pickled silicon material is less than 10 us / cm, rinsing is completed, and the silicon powder is enriched by centrifugal dehydration. Through the above steps, the purity of the silicon powder can be significantly improved to meet the standards of solar grade silicon material (such as conductivity less than 5 us / cm). High-purity silicon material is essential for the production of high-performance solar panels.

[0031] In some embodiments, in step S3, the binder, dispersant and stabilizer include 5% by mass of PVA (polyvinyl alcohol), water-soluble dextrin and polyacrylic acid. Specifically, 5% by mass of PVA, water-soluble dextrin, polyacrylic acid, water and silicon powder can be prepared into a slurry in a mass ratio of 10:4.5:0.5:50:85, and ball milling, mixing and dispersing can be performed on a ball mill to effectively help the solid particles to be evenly dispersed in the liquid, forming a stable slurry and preventing the particles from agglomerating and settling.

[0032] In some embodiments, in step S4, the ball milling dispersion uses SiC balls with a diameter of 10-15 mm, a ball-to-material ratio of 1.5-3:1, a ball milling speed of 30-70 rpm, and a ball milling time of 4-6 hours. Through the mechanical action of the ball mill, the SiC balls exert strong shearing and impact forces on the silicon powder slurry, which helps to break the aggregation and agglomeration between the silicon powder particles, making the particles finer and more evenly dispersed in the liquid medium.

[0033] In some embodiments, in step S1, the surface of the filtration membrane rod is composed of a layer of organic membrane with a pore size of 100 nm. The filtration membrane rod can filter solid phase substances to the surface of the organic membrane during the waste liquid filtration process, and the filtered solution can be reused. When an enrichment layer of 0.5 to 1.5 cm thick is observed on the surface of the organic membrane, the filtration membrane rod is transferred from the silicon-containing cutting waste liquid to the top of the collection container. If the enrichment layer is too thick, the filtration resistance will increase, resulting in a decrease in the filtration speed or even complete clogging of the filter membrane. Therefore, when it is observed that the enrichment layer reaches a certain thickness (such as 0.5 to 1.5 cm), timely transfer of the filtration membrane rod can effectively avoid this problem.

[0034] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

[0035] (1) Use a membrane rod filter to filter the silicon-containing cutting waste liquid at a pressure of 0.1 MPa. When a 0.5-1.5 cm thick enrichment layer is observed on the surface of the filter membrane, remove the membrane rod from the silicon-containing cutting waste liquid and transfer it to a collection container. Backflush the enriched material on the surface of the filter membrane into the collection container. The filtrate from the filtration process is promptly removed and recycled.

[0036] After drying some of the enriched materials, XRF and ICP-OES tests were performed, and it was found that the main elements in the enriched materials were Si, Fe, Ni, Al, O, Ca, and Mg. According to XRF test analysis, Si accounted for 82.33% and O accounted for 17.51% in the enriched materials, and the rest were metal impurities.

[0037] The particle size of the enriched product was analyzed using a laser particle size analyzer, where D50 = 0.85um and D99 = 1.25um, indicating that the particle size of the recovered silicon powder was less than 1.25um and the median value was 0.85um.

[0038] (2) Prepare a hydrochloric acid solution with a concentration of 20%-30%, and mix it in a ratio of 8:1 between hydrochloric acid and wet silicon material. Place the mixture container in an ultrasonic water pool and turn on the ultrasonic generator; pneumatically stir the mixture using a stirring rod wrapped with polytetrafluoroethylene, and the ultrasonic stirring time is 2 hours.

[0039] (3) The silicon material acid-liquid mixture settles naturally, and the upper hydrochloric acid solution is poured out and collected. This acid recovery solution can be reused. The pickled silicon material is rinsed with pure water with a conductivity of less than 5us / cm, and the silicon powder is enriched by centrifugal dehydration. When the conductivity of the supernatant of the pickled silicon material is less than 10us / cm, the rinsing is completed, and then the silicon powder is enriched by centrifugal dehydration. The solid content is detected to be 78.20%.

[0040] (4) Recycled silicon powder, 5% PVA, water-soluble dextrin, polyacrylic acid and water were prepared into an original slurry at a mass ratio of 85:10:4.5:0.5:50, and ball milled, mixed and dispersed on a ball mill. SiC balls with a diameter of 15 mm were used, the ball-to-material ratio was 2:1, the ball milling speed was 50 rpm, and the ball milling time was 5 hours.

[0041] (5) The slurry after ball milling was spray granulated and dried with an inlet air temperature of 200°C, an outlet air temperature of 90°C, and a liquid feed rate of 240 ml / min, and finally silicon powder agglomerates of 0.5 to 1 mm were obtained.

[0042] The second aspect of the present invention also provides a method for applying silicon powder in waste liquid from diamond wire sawing of single crystal silicon, which is based on the silicon powder agglomerates recovered by the above recovery method and is implemented as follows: The prepared silicon powder agglomerates and porous silicon carbide blanks were placed in a graphite crucible at a mass ratio of 1:1 for vacuum reaction sintering to obtain a reaction sintered silicon carbide blank. The performance test results of the reaction sintered silicon carbide blanks prepared according to the above specific examples are shown in Table 1.

[0043] Table 1: Properties of silicon carbide samples sintered by reaction of silicon powder agglomerates

[0044] Silicon powder agglomerates can be directly applied to the production process of reaction sintered silicon carbide to provide silicon source for the reaction of porous silicon carbide blanks. The process conditions for reaction sintered silicon carbide are vacuum. Under this condition, as the temperature rises, the binder in the silicon powder agglomerates will first crack and leave residual carbon. As the temperature rises, the activated carbon will reduce the SiO2 layer on the surface of the silicon particles to SiC and Si. There are gaps between the silicon powder particles in the silicon powder agglomerate particles. The SiC generated by the reduction of the SiO2 layer and the SiC generated by silicon and other residual carbon can maintain the overall state of the silicon particle agglomerates, which is more conducive to the release of silicon vapor during the heating process.

[0045] In some embodiments, the preparation of the flat plate-shaped reaction-sintered silicon carbide blank further includes: pressing the silicon powder agglomerates into blocks having the same shape as the porous silicon carbide blank to be reacted, so as to improve the kiln loading efficiency of the flat plate-shaped reaction-sintered silicon carbide product.

[0046] In some embodiments, the reaction sintering is performed at a temperature of 1550° C. or higher for 1 hour. By increasing the temperature to above 1550° C. and performing a heat preservation treatment, the reaction rate between silicon and carbon can be significantly increased, thereby increasing the amount of silicon carbide generated and improving the conversion rate of the reaction.

[0047] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for recovering silicon powder from waste liquid from diamond wire cutting of single crystal silicon, characterized in that: The following steps are involved: S1, using a suction membrane rod suction filter to filter the silicon-containing cutting waste liquid, and transferring the silicon powder enriched layer on the suction membrane rod to a collection container; S2, adding hydrochloric acid solution to the silicon powder enriched layer in the collection container according to a preset ratio to remove metal impurities in the silicon powder enriched layer; S3, pouring out the upper solution to obtain the acid-washed silicon material, then rinsing the acid-washed silicon material to neutrality, recovering silicon powder, adding all or more of a binder, a dispersant, a stabilizer and water to the silicon powder, and preparing a uniform slurry by ball milling and dispersion; S4, spray granulating and drying the ball-milled slurry to obtain silicon powder agglomerates.

2. The method for recovering silicon powder from waste liquid of diamond wire cutting of single crystal silicon according to claim 1, characterized in that: In step S2, the concentration of the hydrochloric acid solution is 20%-30%, and the ratio of the added hydrochloric acid solution to the silicon powder enriched layer is 6-10:

1.

3. The method for recovering silicon powder from waste liquid of diamond wire sawing single crystal silicon according to claim 2, characterized in that: In step S2, after the hydrochloric acid solution is added, the method further comprises: subjecting the mixed solution to ultrasonic stirring treatment, wherein the ultrasonic stirring time is 1 to 3 hours.

4. The method for recovering silicon powder from waste liquid of diamond wire sawing single crystal silicon according to claim 1, characterized in that: In step S3, rinsing the pickled silicon material and recovering silicon powder includes: rinsing the pickled silicon material with pure water having an electrical conductivity of less than 5 us / cm, and enriching the silicon powder by centrifugal dehydration, until the conductivity of the supernatant of the pickled silicon material is less than 10 us / cm, the rinsing is completed, and the silicon powder is enriched by centrifugal dehydration.

5. The method for recovering silicon powder from waste liquid produced by diamond wire sawing of single crystal silicon according to claim 4, characterized in that: In step S3, the binder, dispersant and stabilizer include 5% by mass of PVA, water-soluble dextrin and polyacrylic acid.

6. The method for recovering silicon powder from waste liquid produced by diamond wire sawing of single crystal silicon according to claim 1, characterized in that: In step S4, the ball milling dispersion is carried out using SiC balls with a diameter of 10-15 mm, a ball-to-material ratio of 1.5-3:1, a ball milling speed of 30-70 rpm, and a ball milling time of 4-6 hours.

7. The method for recovering silicon powder from waste liquid produced by diamond wire sawing of single crystal silicon according to claim 1, characterized in that: In step S1, the surface of the filtration membrane rod is composed of an organic membrane with a pore size of 100 nm. When an enrichment layer with a thickness of 0.5 to 1.5 cm is observed on the surface of the organic membrane, the filtration membrane rod is transferred from the silicon-containing cutting waste liquid.

8. A method for applying silicon powder in waste liquid from diamond wire cutting of single crystal silicon, characterized in that: The silicon powder agglomerates recovered by the recovery method according to any one of claims 1 to 7 are implemented as follows: The silicon powder agglomerate and the porous silicon carbide blank are placed in a graphite crucible in a mass ratio of 1:1 and subjected to vacuum reaction sintering to obtain a reaction sintered silicon carbide blank.

9. The method for applying silicon powder in waste liquid from diamond wire cutting of single crystal silicon according to claim 8, characterized in that: The preparation of the flat plate-shaped reaction-sintered silicon carbide blank also includes: pressing the silicon powder agglomerate into a block having the same shape as the porous silicon carbide blank to be reacted.

10. The method for applying silicon powder in waste liquid from diamond wire cutting of single crystal silicon according to any one of claims 8 or 9, characterized in that: The reaction sintering is carried out at a temperature above 1550° C. for 1 hour.

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