Method for preparing regenerated high-purity silicon from silicon wafer cutting waste

Abstract

The present application relates to a kind of silicon wafer cutting waste preparation method of regenerative high-purity silicon, belong to silicon resource comprehensive utilization technical field.For the characteristics of many kinds of metal impurity elements and fine particle size and difficult to form in silicon wafer cutting waste, the present application is prepared into low water low oxygen silicon wafer cutting waste filter cake by diamond wire cutting silicon wafer waste slurry;Silicon wafer cutting waste filter cake is dehydrated by drying, silicon wafer cutting waste particles and chlorinating agent are uniformly mixed to obtain mixture, the mixture is placed in chlorination device and heated, heated to preset temperature I to form molten salt system and obtain low-temperature chlorination mixture by low-temperature chlorination reaction;Low-temperature chlorination mixture continues to heat to preset temperature II and carries out high-temperature smelting, obtains lower layer silicon melt and upper layer chlorinating agent molten salt liquid phase, separates out upper layer chlorinating agent molten salt liquid phase, and lower layer silicon melt continues high-temperature refining to obtain regenerative high-purity silicon.The raw material of the present application has strong adaptability, simple equipment requirement, short operation process and high product added value.

Description

Technical Field

[0001] This invention relates to a method for preparing recycled high-purity silicon from silicon wafer cutting waste, belonging to the field of comprehensive utilization technology of silicon resources. Background Technology

[0002] The main methods for recycling and regenerating high-purity silicon from silicon wafer cutting waste include direct melting, oxidation refining, and slag-forming refining using oxide slag-forming agents. While direct melting can quickly and directly remelt and solidify silicon wafer cutting waste into bulk silicon, it cannot effectively prevent secondary oxidation of ultrafine silicon particles during the direct melting process, nor does it have the ability to remove impurities, thus failing to achieve deep purification of the silicon melt. Therefore, it can only produce low-value-added primary silicon products. Although oxidation refining can effectively remove Al and Ca impurities from silicon wafer cutting waste by utilizing oxygen's affinity for them, it cannot remove Fe and Ni impurities. Slag-forming refining based on oxides can effectively overcome the secondary oxidation of silicon during direct smelting and promote the efficient separation of silicon and silicon dioxide oxide layers during smelting, and improve the removal rate of impurities. However, slag-forming agents based on oxides have two main drawbacks: firstly, they are highly selective in removing impurities, and a specific slag system can only remove a limited number of impurity elements; secondly, the slag-to-silicon ratio usually needs to be maintained at 1:1. Therefore, slag-forming refining not only has limited ability to remove impurities, but also generates a large amount of industrial silicon slag.

[0003] Against the backdrop of the vigorous development of "fine lines" and "thin wafers" in the monocrystalline silicon wafer slicing industry, the high content of metallic impurities Fe and Ni in silicon wafer cutting waste has become an urgent impurity to be removed in the current process of silicon wafer cutting waste purification and recycling. Moreover, Fe and Ni are more difficult to remove than Al and Ca impurities. Therefore, the ability to remove Fe and Ni during the recycling and purification process directly determines the end-use value of the product. Summary of the Invention

[0004] To address the practical problems of the lack of impurity removal capabilities in the direct smelting process of silicon wafer cutting waste, the limited impurity removal capacity of oxidation refining, and the low impurity removal rate and large slag volume during slag refining, this invention proposes a method for preparing regenerated high-purity silicon from silicon wafer cutting waste. Specifically, the waste slurry from diamond wire-cut silicon wafers is prepared into a low-water, low-oxygen silicon wafer cutting waste filter cake. Then, before high-temperature smelting, a chlorinating agent is added to the silicon wafer cutting waste, and it undergoes a low-temperature chlorination reaction with molten salt to protect the waste from secondary oxidation during heating and holding. Simultaneously, the molten salt reacts fully with the silicon dioxide and metallic impurities in the waste, converting silicon dioxide into silicates and metallic impurities into metal chlorides. High-temperature smelting and refining then yields regenerated high-purity silicon. This method has advantages such as strong raw material adaptability, simple equipment requirements, short operation process, high product added value, and suitability for large-scale industrial production.

[0005] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0006] (1) The waste slurry from diamond wire cutting silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the water content in the silicon wafer cutting waste filter cake is not higher than 40% by mass and the oxygen content is not higher than 7% by mass; the waste slurry from diamond wire cutting silicon wafers is silicon-containing waste from the original cutting waste slurry directly obtained from wafer production and without flocculation, sedimentation, flame retardant or other treatments.

[0007] (2) Under a vacuum or protective gas atmosphere, the silicon wafer cutting waste filter cake is dried and dehydrated to obtain anhydrous silicon wafer cutting waste particles;

[0008] (3) Mix silicon wafer cutting waste particles and chlorinating agent evenly to obtain a mixture. Granulate the mixture to obtain mixed particles. Place the mixed particles in a chlorination device and heat them. Raise the temperature at a uniform rate to the preset temperature I to form a molten salt system and carry out a low-temperature chlorination reaction for 0.5~5h to obtain a low-temperature chlorinated mixture. The main purpose of low-temperature chlorination is to raise the temperature to form a chlorinating agent molten salt liquid phase. The chlorinating agent molten salt liquid phase protects the silicon wafer cutting waste from secondary oxidation during the heating and heat preservation process. At the same time, the chlorinating agent molten salt liquid phase can fully carry out the liquid-solid phase chlorination reaction with silicon dioxide and metal impurities to convert silicon dioxide into silicates and metal impurities into metal chlorides.

[0009] (4) The low-temperature chlorination mixture is heated at a constant rate to the preset temperature II and smelted at high temperature for 0.5~5h to obtain the lower silicon melt and the upper chlorinating agent molten salt liquid phase. The upper chlorinating agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature for 0.5~48h to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point of silicon. The upper chlorinating agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0010] The method for preparing the silicon wafer cutting waste filter cake is as follows:

[0011] 1) Adjust the solid content and pH value of the waste slurry from diamond wire cutting silicon wafers to a solid content of 4-6% and a pH value of 4-6 to obtain a silicon wafer cutting waste slurry. The liquid component of the waste slurry from diamond wire cutting silicon wafers is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 90-99 wt.% of the waste slurry, and the solid component accounts for 1-10 wt.%, with a solid silicon particle size of d. 50 The particle size is 0.6~2.1μm, and the main trace impurities are Fe, Ni and Al. The content of trace impurities is not higher than 1wt.% of the solid content in the silicon wafer cutting waste raw material slurry; the pH value of the silicon wafer cutting waste raw material slurry is greater than 8 after standing.

[0012] 2) Add a filter aid modifier to the silicon wafer cutting waste slurry and mix evenly to obtain a modified silicon wafer cutting waste slurry;

[0013] 3) Silicon wafer cutting waste slurry was modified and solid-liquid separated to obtain silicon wafer cutting waste filter cake.

[0014] In step 1), sulfuric acid is used to adjust the pH value of the silicon wafer cutting waste slurry to stabilize the slurry.

[0015] The filter aid modifier in step 2) is one or more of vinyltris(2-methoxyethoxy)silane (VAMT), hexadecyltrimethylammonium bromide (CTAB), 3-glycidoxypropyltrimethoxysilane (GLYMO), 3-mercaptopropyltriethoxysilane (MPTS), and sodium dodecyl sulfate (SDS). The amount of filter aid modifier added is 5% to 25% of the volume of the silicon wafer cutting waste slurry. The filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake.

[0016] The heating method in step (3) includes, but is not limited to, induction heating, resistance heating and microwave heating.

[0017] In step (3), the chlorinating agent is one or more of sodium chloride, calcium chloride, magnesium chloride, barium chloride, potassium chloride, calcium chloride dihydrate, and magnesium chloride hexahydrate. The mass ratio of silicon wafer cutting waste particles to chlorinating agent is 1:0.1~0.5. When the chlorinating agent is a single compound, the preset temperature I is higher than the melting temperature of the chlorinating agent and lower than the melting point temperature of silicon. When the chlorinating agent is a mixture of two or more compounds, the preset temperature I is higher than the eutectic temperature of the chlorinating agent mixed molten salt system and lower than the melting point temperature of silicon.

[0018] The particle size of the mixture in step (3) is 0.1~10cm.

[0019] In step (3), a slag-forming agent is added to the mixture, and the mass ratio of silicon wafer cutting waste particles to slag-forming agent is 100:1~20.

[0020] Preferably, the slag-forming agent is CaO and / or Na2CO3.

[0021] The low-temperature chlorination reaction in step (3) is carried out under normal pressure or vacuum.

[0022] The high-temperature refining in step (4) is either vacuum refining or directional solidification refining.

[0023] The purpose of step (4) high-temperature melting and high-temperature refining is to remelt the unmelted silicon particles in the silicon wafer cutting waste into liquid silicon and to achieve secondary refining and refining of the silicon melt.

[0024] The beneficial effects of this invention are:

[0025] (1) This invention improves the properties of the slurry to enhance solid-liquid separation and promote the removal of moisture from the filter cake, thereby preparing a low-moisture and low-oxygen silicon wafer cutting waste filter cake; by reducing the moisture content and changing the form of moisture, it can effectively eliminate secondary oxidation during the drying process and reduce the transportation and drying costs of the filter cake; it only needs to be combined with existing solid-liquid separation filtration treatment, without other complicated processes, to obtain a filter cake with low moisture and low oxygen content, which is simple to operate and has significant effects.

[0026] (2) The present invention uses a low-temperature chlorination method to treat silicon wafer cutting waste particles. It can first convert the metal impurities in the silicon wafer cutting waste into easily removable chlorides, and then separate the chlorides from the silicon melt through smelting. It also uses the molten salt liquid phase as a protective layer to avoid secondary oxidation caused by direct contact between silicon microparticles in the silicon wafer cutting waste and air during the smelting process. It has strong adaptability to the raw materials of silicon wafer cutting waste and can achieve high-efficiency simultaneous removal of common metal impurities such as Al, Fe, Ni and Ti in silicon wafer cutting waste.

[0027] (3) The present invention addresses the problem that it is difficult to purify, recycle and regenerate high-purity silicon products from high-Fe and Ni type silicon wafer cutting waste at present. It proposes a process of "low-water and low-oxygen silicon wafer cutting waste filter cake - low-temperature chlorination - high-temperature melting and refining" to regenerate high-purity silicon. Compared with the existing technology where the Fe and Ni removal rate is generally only about 30%, the Fe and Ni removal rate of the present invention can reach more than 50%.

[0028] (4) The low-temperature chlorination and high-temperature smelting of the present invention can ensure the efficient removal of a variety of metal impurities, reduce the burden of impurity control during the refining process, effectively improve production efficiency and reduce unit production costs. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0030] Example 1: The waste slurry from diamond wire cutting of silicon wafers in this example is the waste slurry from silicon wafer cutting of a monocrystalline silicon slicing enterprise in Yunnan. The liquid component of the waste slurry is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 97.7 wt.% and the solid component accounts for 2.3 wt.% of the raw material slurry. The particle size of the solid silicon particles is d. 50 The particle size was 0.71 μm, and the main trace impurities were Al, Fe and Ni, with Al at 78 ppmw, Fe at 43 ppmw and Ni at 140 ppm. The pH value of the silicon wafer cutting waste slurry increased to 8.6 after being left for 48 hours.

[0031] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0032] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a water content of 6.3% by mass and an oxygen content of 6.66% by mass;

[0033] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0034] 2) A filter aid modifier (0.2 mol / L hexadecyltrimethylammonium bromide CTAB) is added to the silicon wafer cutting waste conditioning slurry and mixed evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 5% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0035] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 6.3% by mass and an oxygen content of 6.66% by mass.

[0036] (2) The silicon wafer cutting waste filter cake was vacuum dried at 60°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0037] (3) The silicon wafer cutting waste particles, chlorinating agent (superior purity NaCl), and slag-forming agent (superior purity Na2CO3) are mixed evenly to obtain a mixture, which is then granulated to obtain mixed particles with a particle size of 2cm. The mixed particles are transferred to a graphite crucible and compacted, and then placed in an induction-heated chlorination device. The vacuum is drawn to a pressure below 50Pa, and the temperature is raised at a uniform rate to the preset temperature I (1200℃) and subjected to a low-temperature chlorination reaction for 1.5h to obtain a low-temperature chlorinated mixture. The mass ratio of the silicon wafer cutting waste, chlorinating agent, and slag-forming agent is 100:8. 6:12.8; The preset temperature I (1200℃) is higher than the melting temperature of the chlorinating agent (superior purity NaCl) (800℃) and lower than the melting point of silicon (1410℃); The main purpose of low-temperature chlorination is to raise the temperature to form a chlorinating agent molten salt liquid phase, and to use the chlorinating agent molten salt liquid phase to protect the silicon wafer cutting waste from secondary oxidation during the heating and holding process. At the same time, it can also allow the chlorinating agent molten salt liquid phase to fully carry out the liquid-solid phase chlorination reaction with silicon dioxide and metal impurities, converting silicon dioxide into silicates and metal impurities into metal chlorides;

[0038] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1500℃) and smelted at high temperature for 2 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 2 hours and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0039] In this embodiment, the impurity content of the silicon ingot is Al 26 ppmw, Fe 29 ppmw, and Ni 86 ppmw, and the purity of the obtained silicon ingot is 3N.

[0040] Example 2: In this example, the waste slurry from diamond wire cutting of silicon wafers is the waste slurry from silicon wafer cutting of a single-crystal silicon slicing enterprise in Yunnan. The liquid component of the waste slurry from diamond wire cutting of silicon wafers is water-based cutting fluid, and the solid component is silicon particles and trace impurities; the liquid component in the raw slurry of silicon wafer cutting waste is 97.9 wt.%, and the solid component accounts for 2.1 wt.%, with a solid silicon particle size d. 50 The particle size was 0.88 μm, and the main impurities were Al and Ni, with Al at 1200 ppmw and Ni at 380 ppm. The pH value of the silicon wafer cutting waste slurry increased to 8.1 after being left for 24 hours.

[0041] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0042] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a water content of 8.4% by mass and an oxygen content of 4.81% by mass;

[0043] 1) The solid content of the waste slurry from diamond wire-cut silicon wafers was adjusted to 4.32% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0044] 2) Add 0.2 mol / L vinyltris(2-methoxyethoxy)silane (VAMT) as a filter aid modifier to the silicon wafer cutting waste conditioning slurry and mix evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier vinyltris(2-methoxyethoxy)silane (VAMT) added is 5% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the water content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0045] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 8.4% by mass and an oxygen content of 4.81% by mass.

[0046] (2) Under a nitrogen atmosphere, the silicon wafer cutting waste filter cake is dried and dehydrated to constant weight at a temperature of 60°C to obtain anhydrous silicon wafer cutting waste particles.

[0047] (3) The silicon wafer cutting waste particles and chlorinating agent (superior purity BaCl2·2H2O) are mixed evenly to obtain a mixture, which is then granulated to obtain a mixture particle size of 3cm. The mixture particles are transferred to a graphite crucible and compacted, and then placed in a resistance-heated chlorination device. The air is extracted, and then argon gas is introduced to a pressure of 1 atmosphere. The temperature is heated at a uniform rate to below the preset temperature I (1200℃) and a low-temperature chlorination reaction is carried out for 2 hours to obtain a low-temperature chlorinated mixture. The mass ratio of the silicon wafer cutting waste and the chlorinating agent is 100:15.95. The preset temperature I (1200℃) is higher than the melting temperature of the chlorinating agent (superior purity BaCl2) (960℃) and lower than the melting point temperature of silicon (1410℃).

[0048] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1650℃) and smelted at high temperature for 3 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 1 hour and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0049] In this embodiment, the impurity content of the silicon ingot is Al 32ppmw, Ni 6.2ppmw, and Ba 170ppmw.

[0050] Example 3: In this example, the waste slurry from diamond wire cutting of silicon wafers is the waste slurry from silicon wafer cutting of a monocrystalline silicon slicing enterprise in Yunnan. The liquid component of the waste slurry from diamond wire cutting of silicon wafers is water-based cutting fluid, and the solid component is silicon particles and trace impurities; the liquid component accounts for 97.7 wt.% and the solid component accounts for 2.3 wt.% of the raw material slurry from silicon wafer cutting waste, and the particle size of the solid silicon particles is d. 50 The particle size ranges from 0.6 to 2.1 μm, and the main impurities are Fe and Ni, with Fe at 2600 ppmw and Ni at 190 ppm. The pH value of the silicon wafer cutting waste slurry increases to 7.9 after being left for 24 hours.

[0051] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0052] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the water content of the silicon wafer cutting waste filter cake is 36.1% by mass and the oxygen content is 6.79% by mass;

[0053] 1) The solid content of the waste slurry from diamond wire-cut silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0054] 2) Add 0.2 mol / L hexadecyltrimethylammonium bromide (CTAB) as a filter aid modifier to the silicon wafer cutting waste conditioning slurry and mix evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 25% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0055] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 36.1% by mass and an oxygen content of 6.79% by mass.

[0056] (2) The silicon wafer cutting waste filter cake was vacuum dried at 70°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0057] (3) The silicon wafer cutting waste particles, CaO and chlorinating agent (superior grade MgCl2) are mixed evenly to obtain a mixture, which is then shaped and granulated to obtain mixture particles with a particle size of 5 cm. The mixture particles are transferred to a graphite crucible and compacted, and then placed in an induction heating chlorination device. The air is extracted, and then argon gas is introduced to a pressure of 1 atmosphere. The temperature is heated at a uniform rate to the preset temperature I (1000℃) and a low-temperature chlorination reaction is carried out for 1 hour to obtain a low-temperature chlorinated mixture. The mass ratio of the silicon wafer cutting waste particles, CaO and chlorinating agent (superior grade MgCl2) is 150.0:23.42:8.85. The preset temperature I (1000℃) is higher than the melting temperature of the chlorinating agent (superior grade MgCl2) (714℃) and lower than the melting point temperature of silicon (1410℃).

[0058] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1550℃) and smelted at high temperature for 3 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 1 hour. It is then directionally solidified to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0059] In this embodiment, the impurity content of the silicon ingot is Ca 220 ppmw, Fe 1300 ppmw, Ni 72 ppmw, and Mg 76 ppmw.

[0060] Example 4: In this example, the waste slurry from diamond wire cutting of silicon wafers is the silicon wafer cutting waste slurry from a single-crystal silicon slicing enterprise in Yunnan. The liquid component of the waste slurry is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 97.7 wt.% and the solid component accounts for 2.3 wt.% of the raw material slurry. The particle size of the solid silicon particles is d. 50 The particle size ranges from 0.6 to 2.1 μm, and the main impurities are Fe and Ni, with Fe at 2600 ppmw and Ni at 190 ppm. The pH value of the silicon wafer cutting waste slurry increases to 7.9 after being left for 24 hours.

[0061] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0062] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the water content of the silicon wafer cutting waste filter cake is 36.1% by mass and the oxygen content is 6.79% by mass;

[0063] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0064] 2) Add 0.2 mol / L hexadecyltrimethylammonium bromide (CTAB) as a filter aid modifier to the silicon wafer cutting waste conditioning slurry and mix evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 25% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0065] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 36.1% by mass and an oxygen content of 6.79% by mass.

[0066] (2) Under an argon atmosphere, the silicon wafer cutting waste filter cake is dried and dehydrated to constant weight at a temperature of 70°C to obtain anhydrous silicon wafer cutting waste particles;

[0067] (3) The silicon wafer cutting waste particles, CaO and chlorinating agent (superior purity NaCl and MgCl2) are mixed evenly to obtain a mixture, which is then shaped and granulated to obtain a mixture particle size of 5 cm. The mixture particles are transferred to a graphite crucible and compacted, and then placed in an induction heating chlorination device. The air is extracted, and then argon gas is introduced to a pressure of 1 atmosphere. The temperature is heated at a uniform rate to a preset temperature I (1000℃) and a low-temperature chlorination reaction is carried out for 1 hour to obtain a low-temperature chlorinated mixture. The preset temperature I (1000℃) is higher than the eutectic temperature (470℃) of the chlorinating agent (superior purity NaCl and MgCl2) and lower than the melting point temperature of silicon (1410℃). The mass ratio of silicon wafer cutting waste particles, CaO, chlorinating agent (superior purity NaCl) and chlorinating agent (superior purity MgCl2) is 150.0:23.42:7.50:8.85.

[0068] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1550℃) and smelted at high temperature for 3 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 1 hour and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0069] In this embodiment, the impurity content of the silicon ingot is Ca 320 ppmw, Fe 1200 ppmw, Ni 54 ppmw, Mg 96 ppmw, and Na 52 ppmw.

[0070] Example 5: The waste slurry from diamond wire cutting of silicon wafers in this example is the waste slurry from silicon wafer cutting of a monocrystalline silicon slicing enterprise in Yunnan. The liquid component of the waste slurry is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 97.7 wt.% and the solid component accounts for 2.3 wt.% of the raw material slurry. The particle size of the solid silicon particles is d. 50 The particle size ranges from 0.6 to 2.1 μm, and the main impurities are Fe and Ni, with Fe at 2600 ppmw and Ni at 190 ppm. The pH value of the silicon wafer cutting waste slurry increases to 7.9 after being left for 24 hours.

[0071] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0072] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the water content of the silicon wafer cutting waste filter cake is 36.1% by mass and the oxygen content is 6.79% by mass;

[0073] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0074] 2) Add 0.2 mol / L hexadecyltrimethylammonium bromide (CTAB) as a filter aid modifier to the silicon wafer cutting waste conditioning slurry and mix evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 25% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0075] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 36.1% by mass and an oxygen content of 6.79% by mass.

[0076] (2) The silicon wafer cutting waste filter cake was vacuum dried at 70°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0077] (3) The silicon wafer cutting waste particles, CaO and chlorinating agent (superior purity NaCl) are mixed evenly to obtain a mixture, which is then granulated to obtain a mixture particle size of 5 cm. The mixture particles are transferred to a graphite crucible and compacted, and then placed in an induction heating chlorination device. The air is extracted, and then argon gas is introduced to a pressure of 1 atmosphere. The temperature is heated at a uniform rate to a preset temperature I (1000℃) and a low-temperature chlorination reaction is carried out for 1 hour to obtain a low-temperature chlorinated mixture. The preset temperature I (1000℃) is higher than the melting temperature of the chlorinating agent (superior purity NaCl) (800℃) and lower than the melting point temperature of silicon (1410℃). The mass ratio of silicon wafer cutting waste particles, CaO and chlorinating agent (superior purity NaCl) is 150.0:23.42:7.50.

[0078] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1550℃) and smelted at high temperature for 3 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 1 hour and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0079] In this embodiment, the impurity content of the silicon ingot is Ca 200 ppmw, Fe 1200 ppmw, Ni 84 ppmw, and Na 26 ppmw.

[0080] Example 6: The waste slurry from diamond wire cutting of silicon wafers in this example is the waste slurry from silicon wafer cutting of a monocrystalline silicon slicing enterprise in Yunnan. The liquid component of the waste slurry is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 97.7 wt.% and the solid component accounts for 2.3 wt.% of the raw material slurry. The particle size of the solid silicon particles is d. 50 The particle size ranges from 0.6 to 2.1 μm, and the main impurities are Fe and Ni, with Fe at 2600 ppmw and Ni at 190 ppm. The pH value of the silicon wafer cutting waste slurry increases to 7.9 after being left for 24 hours.

[0081] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0082] (1) The waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water and low-oxygen silicon wafer cutting waste filter cake, wherein the water content of the silicon wafer cutting waste filter cake is 36.1% by mass and the oxygen content is 6.79% by mass;

[0083] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0084] 2) Add 0.2 mol / L hexadecyltrimethylammonium bromide (CTAB) as a filter aid modifier to the silicon wafer cutting waste conditioning slurry and mix evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 25% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0085] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 36.1% by mass and an oxygen content of 6.79% by mass.

[0086] (2) The silicon wafer cutting waste filter cake was vacuum dried at 70°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0087] (3) The silicon wafer cutting waste particles, CaO and chlorinating agent (superior grade MgCl2) are mixed evenly to obtain a mixture, which is then shaped and granulated to obtain a mixture particle size of 5 cm. The mixture particles are transferred to a graphite crucible and compacted, and then placed in an induction heating chlorination device. The air is extracted, and then argon gas is introduced to a pressure of 1 atmosphere. The temperature is heated at a uniform rate to a preset temperature I (1000℃) and a low-temperature chlorination reaction is carried out for 1 h to obtain a low-temperature chlorinated mixture. The preset temperature I (1000℃) is higher than the melting temperature of the chlorinating agent (superior grade MgCl2) (714℃) and lower than the melting point temperature of silicon (1410℃). The mass ratio of silicon wafer cutting waste particles, CaO and chlorinating agent (superior grade MgCl2) is 150.0:23.42:8.85.

[0088] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1550℃) and smelted at high temperature for 3 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 1 hour and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0089] In this embodiment, the impurity content of the silicon ingot is Ca 220 ppmw, Fe 1300 ppmw, Ni 72 ppmw, and Mg 76 ppmw.

[0090] Example 7: The waste slurry from diamond wire cutting of silicon wafers in this example is the waste slurry from silicon wafer cutting of a monocrystalline silicon slicing enterprise in Yunnan. The liquid component of the waste slurry is water-based cutting fluid, and the solid component is silicon particles and trace impurities. The liquid component accounts for 97.87 wt.% and the solid component accounts for 2.13 wt.% of the raw material slurry. The particle size of the solid silicon particles is d. 50 The particle size was 0.76 μm, and the main trace impurity was Al, with Al content of 6400 ppm. The pH value of the silicon wafer cutting waste slurry increased to 8.3 after being left for 48 hours.

[0091] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0092] (1) The waste slurry from diamond wire cutting silicon wafers is prepared into a low-water, low-oxygen silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a water content of 7.1% by mass and an oxygen content of 5.8% by mass;

[0093] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0094] 2) A filter aid modifier (0.2 mol / L hexadecyltrimethylammonium bromide CTAB) is added to the silicon wafer cutting waste conditioning slurry and mixed evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 5% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0095] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 7.1% by mass and an oxygen content of 5.8% by mass.

[0096] (2) The silicon wafer cutting waste filter cake was vacuum dried at 60°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0097] (3) The silicon wafer cutting waste particles, chlorinating agent (superior purity NaCl), and slag-forming agent (superior purity Na2CO3 and superior purity CaO) are mixed evenly to obtain a mixture, which is then granulated to obtain mixed particles with a particle size of 5 cm. The mixed particles are transferred to a graphite crucible and compacted, then placed in an induction-heated chlorination device. The vacuum is drawn until the pressure is below 50 Pa, and the temperature is raised at a uniform rate to the preset temperature I (1200℃) and subjected to a low-temperature chlorination reaction for 1.5 h to obtain a low-temperature chlorinated mixture. The silicon wafer cutting waste, superior purity NaCl, superior purity Na2CO3, and superior purity CaO are mixed evenly to obtain a mixture. The mass ratio is 100:8.6:12.8:1.7; the preset temperature I (1200℃) has a melting temperature of chlorinating agent (superior purity NaCl) of 800℃, which is lower than the melting point of silicon (1410℃); the main purpose of low-temperature chlorination is to raise the temperature to form a chlorinating agent molten salt liquid phase, which protects the silicon wafer cutting waste from secondary oxidation during the heating and holding process. At the same time, it also allows the chlorinating agent molten salt liquid phase to fully react with silicon dioxide and metal impurities in the liquid-solid phase, converting silicon dioxide into silicates and metal impurities into metal chlorides;

[0098] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1500℃) and smelted at high temperature for 2 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 2 hours and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0099] In this embodiment, the impurity content of the silicon ingot is Al 59 ppmw and Ca 87 ppmw, and the purity of the obtained silicon ingot is 3N.

[0100] Example 8: The waste slurry from diamond wire cutting of silicon wafers in this example is the waste slurry from silicon wafer cutting of a single-crystal silicon slicing enterprise in Yunnan. The liquid component of the waste slurry from diamond wire cutting of silicon wafers is water-based cutting fluid, and the solid component is silicon particles and trace impurities; the liquid component accounts for 97.87 wt.% and the solid component accounts for 2.13 wt.% of the raw material slurry from silicon wafer cutting waste, and the particle size of the solid silicon particles is d. 50The particle size was 0.76 μm, and the main trace impurity was Al, with Al content of 6400 ppm. The pH value of the silicon wafer cutting waste slurry increased to 8.3 after being left for 48 hours.

[0101] A method for preparing recycled high-purity silicon from silicon wafer cutting waste, the specific steps of which are as follows:

[0102] (1) The waste slurry from diamond wire cutting silicon wafers is prepared into a low-water, low-oxygen silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a water content of 7.1% by mass and an oxygen content of 5.8% by mass;

[0103] 1) The solid content of the waste slurry from diamond wire cutting silicon wafers was adjusted to 4.26% by ceramic membrane concentration. The pH value of the waste slurry was adjusted to 4 by adding 1 mol / L hydrochloric acid to obtain silicon wafer cutting waste slurry adjustment slurry.

[0104] 2) A filter aid modifier (0.2 mol / L hexadecyltrimethylammonium bromide CTAB) is added to the silicon wafer cutting waste conditioning slurry and mixed evenly to obtain a silicon wafer cutting waste modified slurry; the amount of the filter aid modifier hexadecyltrimethylammonium bromide (CTAB) added is 5% of the volume of the silicon wafer cutting waste conditioning slurry; the filter aid modifier is used to promote the efficient removal of water during the solid-liquid separation process, directly reduce the moisture content of the filter cake after solid-liquid separation, thereby hindering the oxidation of the filter cake and indirectly reducing the oxygen content of the filter cake;

[0105] 3) Solid-liquid separation (plate and frame filter press) of modified slurry from silicon wafer cutting waste yields silicon wafer cutting waste filter cake, wherein the silicon wafer cutting waste filter cake has a moisture content of 7.1% by mass and an oxygen content of 5.8% by mass.

[0106] (2) The silicon wafer cutting waste filter cake was vacuum dried at 60°C to constant weight to obtain anhydrous silicon wafer cutting waste particles;

[0107] (3) The silicon wafer cutting waste particles, chlorinating agent (superior purity NaCl), and slag-forming agent (superior purity Na2CO3) are mixed evenly to obtain a mixture, which is then granulated to obtain mixed particles with a particle size of 5 cm. The mixed particles are transferred to a graphite crucible and compacted, and then placed in an induction-heated chlorination device. The vacuum is drawn until the pressure is below 50 Pa, and the temperature is raised at a uniform rate to the preset temperature I (1200℃) and subjected to a low-temperature chlorination reaction for 1.5 h to obtain a low-temperature chlorinated mixture. The mass ratio of the silicon wafer cutting waste, superior purity NaCl, and superior purity Na2CO3 is 1:1. 00:8.6:12.8; The preset temperature I (1200℃) is higher than the melting temperature of the chlorinating agent (superior purity NaCl) (800℃) and lower than the melting point of silicon (1410℃); The main purpose of low-temperature chlorination is to raise the temperature to form a chlorinating agent molten salt liquid phase, and to use the chlorinating agent molten salt liquid phase to protect the silicon wafer cutting waste from secondary oxidation during the heating and holding process. At the same time, it can also allow the chlorinating agent molten salt liquid phase to fully carry out the liquid-solid phase chlorination reaction with silicon dioxide and metal impurities, converting silicon dioxide into silicates and metal impurities into metal chlorides;

[0108] (4) Under vacuum conditions, the low-temperature chlorination mixture is heated at a constant rate to the preset temperature II (1500℃) and smelted at high temperature for 2 hours to obtain a lower silicon melt and an upper chlorination agent molten salt liquid phase. The upper chlorination agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature under vacuum conditions for 2 hours and then solidified in a directional manner to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon (1410℃). The upper chlorination agent molten salt liquid phase can be returned to the low-temperature chlorination reaction in step (3) after purification.

[0109] In this embodiment, the impurity content of the silicon ingot is Al 2200 ppmw and Ca 79 ppmw.

[0110] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing recycled high-purity silicon from silicon wafer cutting waste, characterized in that, The specific steps are as follows: (1) Waste slurry from diamond wire cutting of silicon wafers is prepared into a low-water, low-oxygen silicon wafer cutting waste filter cake, wherein the water content of the silicon wafer cutting waste filter cake is not higher than 40% by mass and the oxygen content is not higher than 7% by mass; (2) Under a vacuum or protective gas atmosphere, the silicon wafer cutting waste filter cake is dried and dehydrated to obtain anhydrous silicon wafer cutting waste particles; (3) The silicon wafer cutting waste particles and the chlorinating agent are mixed evenly to obtain a mixture. The mixture is granulated to obtain mixed particles. The mixed particles are placed in a chlorination device and heated to a preset temperature I to form a molten salt system and carry out a low-temperature chlorination reaction for 0.5~5h to obtain a low-temperature chlorinated mixture. The chlorinating agent is one or more of sodium chloride, calcium chloride, magnesium chloride, barium chloride, and potassium chloride. The mass ratio of silicon wafer cutting waste particles to chlorinating agent is 100:1~10. When the chlorinating agent is a single compound, the preset temperature I is higher than the melting temperature of the chlorinating agent and lower than the melting point temperature of silicon. When the chlorinating agent is a mixture of two or more compounds, the preset temperature I is higher than the eutectic temperature of the chlorinating agent mixed molten salt system and lower than the melting point temperature of silicon. (4) The low-temperature chlorination mixture is heated to the preset temperature II and smelted at high temperature for 0.5 to 5 hours to obtain a lower silicon melt and an upper chlorinating agent molten salt liquid phase. The upper chlorinating agent molten salt liquid phase is separated, and the lower silicon melt is further refined at high temperature for 0.5 to 48 hours to obtain regenerated high-purity silicon. The preset temperature II is higher than the melting point temperature of silicon.

2. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 1, characterized in that, The method for preparing filter cake from silicon wafer cutting waste is as follows: 1) Adjust the solid content and pH value of the waste slurry from diamond wire cutting silicon wafers to a solid mass content of 4-6% and a pH value of 4-6 to obtain silicon wafer cutting waste slurry; 2) Add a filter aid modifier to the silicon wafer cutting waste slurry and mix evenly to obtain a modified silicon wafer cutting waste slurry; 3) Silicon wafer cutting waste slurry was modified and solid-liquid separated to obtain silicon wafer cutting waste filter cake.

3. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 2, characterized in that: Step 2) The filter aid modifier is one or more of VAMT, CTAB, GLYMO, MPTS, and SDS. The amount of filter aid modifier added is 5 to 25% of the volume of the silicon wafer cutting waste slurry.

4. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 1, characterized in that: Step (3) The particle size of the mixture is 0.1~10cm.

5. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 1, characterized in that: Step (3) Add slag-forming agent to the mixture. The mass ratio of silicon wafer cutting waste particles to slag-forming agent is 100:1~20.

6. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 5, characterized in that: The slag-forming agent is CaO and / or Na2CO3.

7. The method for preparing recycled high-purity silicon from silicon wafer cutting waste according to claim 1, characterized in that: Step (4) High-temperature refining is either vacuum refining or directional solidification refining.