Controllable low-oxygen silicon preparation method capable of reducing oxidation of silicon wafer cutting waste

Abstract

The invention relates to a controllable low-oxygen silicon preparation method capable of reducing oxidation of silicon wafer cutting waste, and belongs to the technical field of silicon wafer cutting waste recovery and utilization. The method comprises the following steps: crushing and shaping silicon wafer cutting waste blocks to obtain silicon wafer cutting waste particles; then the silicon wafer cutting waste particles are evenly laid in a microwave heating furnace in a layered mode, the silicon wafer cutting waste particles on the adjacent horizontal layers are isolated through cloth in the vertical direction, and gaps are reserved between the adjacent silicon wafer cutting waste particles on the same horizontal layer; according to the initial water content, the initial oxygen content, the expected oxygen content, the device vacuum degree, the set temperature and the particle size, the preset time of microwave heating controllable dewatering and drying of the silicon wafer cutting waste particles is determined; under the vacuum condition, microwave heating can controllably dehydrate and dry to reduce the actual moisture content of the silicon wafer cutting waste and the actual oxygen content of the product, so that the controllable preparation of the low-oxygen silicon product is realized by reducing the oxidation of the silicon wafer cutting waste.

Description

Technical Field

[0001] The invention relates to a method for controllably preparing low-oxygen silicon by reducing oxidation of silicon slice cutting waste, belonging to the technical field of recycling and utilizing silicon slice cutting waste. Background Art

[0002] In recent years, the solar photovoltaic industry, which is mainly based on crystalline silicon solar cells, has developed rapidly. With the substantial increase in the demand for crystalline silicon required for the application of terminal products, a large amount of high-purity silicon has been lost in the form of silicon wafer cutting waste at the production and processing end. Driven by grid parity, the silicon wafer production link has become the main battlefield for reducing costs and increasing efficiency. How to recycle high-purity silicon from silicon wafer cutting waste has gradually become a new research focus in the photovoltaic industry.

[0003] In order to avoid safety hazards and reduce the impact on the environment, companies currently often subject the fresh silicon wafer cutting waste slurry generated during the cutting process to flocculation, sedimentation, plate and frame filter pressing and flame retardant treatment to obtain a filter cake with an initial moisture content of 40% to 60%. Since silicon is easily oxidized by water (International Journal of Hydrogen Energy. 2021, 46(45): 23406-23416; Ceramics International, 2018, 44(5): 5581-5586), the oxygen content of silicon wafer cutting waste is as high as 8% to 30%. The uncontrolled oxygen content of the filter cake leads to the formation of an oxide layer on the surface of the silicon particles, which produces a shielding effect during the wet acid leaching process, hindering the reaction between impurities and acid and limiting the purity of the recovered silicon. During the pyrometallurgical refining process, the impurity oxygen is transferred as an oxidant, causing the oxidation of metal impurities, deteriorating the separation of silicon, and thus reducing the recovery rate of silicon (Journal of Cleaner Production, 2022, 358: 131961; Minerals Engineering, 2021, 169: 106966). Moreover, the impurity oxygen will introduce greater stress into the silicon wafer, causing the silicon wafer to warp and destroy the electrical properties of the silicon wafer (Journal of Applied Physics, 1995, 77 (9): 4107-4136). The inventors found in their previous studies that the use of forced air drying and vacuum drying to remove moisture from silicon wafer cutting waste results in a moisture removal time of 5 to 25 hours due to the influence of initial moisture content and particle size, and the product oxygen content is greater than 7%, which is not suitable for industrial application (Journal of Materials Research and Technology, 2024, 28: 2177-2186; Vacuum, 2024, 227: 113410). Therefore, it is urgent to develop new process methods to control and reduce the oxygen content of silicon wafer cutting waste from the source in the recycling process, so as to effectively ensure the realization of technical indicators such as product silicon purity and recovery rate in the subsequent purification process. Summary of the invention

[0004] In view of the current status and problems of the industry, such as the high water content in the existing silicon wafer cutting waste recycling process, which causes silicon to be easily oxidized by water to form an oxide layer, the initial water content is usually 40-60%, and the oxygen content is usually above 8%. The high oxygen content not only reduces the silicon recovery rate in the recycling process, but also causes the melting temperature to increase, hindering its regeneration and purification to prepare high-purity silicon, the present invention proposes a method for reducing the oxidation of silicon wafer cutting waste and controllably preparing low-oxygen silicon, that is, using microwave heating in a vacuum environment to increase the water diffusion rate, reduce the activation energy of water removal, reduce the contact between water and silicon, inhibit the oxidation of silicon, and reduce the oxidation of silicon wafer cutting waste by controlling the size and vacuum microwave conditions for controllable dehydration and drying to obtain low-oxygen silicon products. The method of the present invention can solve the problems of high water content, long water removal time, severe oxidation, and difficulty in recycling silicon in the prior art.

[0005] A method for reducing oxidation of silicon wafer cutting waste and controllably preparing low-oxygen silicon, the specific steps are as follows:

[0006] (1) crushing and shaping silicon wafer cutting waste blocks to obtain silicon wafer cutting waste particles with uniform size and regular shape;

[0007] (2) the silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together, and gaps are left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together;

[0008] (3) according to the initial moisture content and initial oxygen content of the low-oxygen silicon product, the expected oxygen content, and the vacuum degree of the device, the temperature and particle size are set, and the preset time for microwave heating controllable dehydration and drying of the silicon wafer cutting waste particles is determined;

[0009] (4) Under vacuum conditions, the silicon wafer cutting waste particles in the microwave heating furnace are subjected to vacuum microwave heating for controllable dehydration. The actual moisture content of the silicon wafer cutting waste and the actual oxygen content of the product are controllably reduced by presetting the drying time, thereby achieving controllable preparation of low-oxygen silicon products by reducing the oxidation of the silicon wafer cutting waste.

[0010] The silicon wafer cutting waste block in step (1) is a silicon wafer cutting waste filter cake obtained by plate and frame filtration of silicon wafer cutting slurry.

[0011] The particle size of the silicon wafer cutting waste particles in the step (1) is 0.5 to 5 cm; if the silicon wafer cutting waste particles are too large, the water diffusion rate is reduced and they are easily oxidized; if the silicon wafer cutting waste particles are too small, the silicon wafer cutting waste particles are easily powdered and adhered.

[0012] The gap in step (2) is 1 to 10 mm; the total height of the silicon wafer cutting waste particles in the vertical direction is 2 to 10 cm. Reasonable material stacking methods, stacking thickness and other material laying factors can enhance the dehydration rate in vacuum microwave treatment, promote water diffusion, and help eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate.

[0013] The method for determining the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in step (3) is:

[0014] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0015]

[0016] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0017]

[0018] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0019] The effective water diffusion coefficient is 1×10 -8 -5×10 -6 m 2 ·s -1 , the oxidation rate constant is 1×10 -9 -8×10 -4 g·m -2 ·s -1 ;

[0020] According to the functional relationship between the preset moisture content of the low-oxygen silicon product and the processing time and the functional relationship between the preset oxygen content and the processing time, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is calculated, wherein the functional relationship of the preset time t is:

[0021]

[0022] Wherein, t is the preset time s, t1 is the processing time s predicted according to the moisture content, and t2 is the processing time s predicted according to the oxygen content.

[0023] Preferably, the vacuum degree in step (3) is 1 to 50 kPa, and the microwave heating controllable dehydration and drying temperature is 30 to 200°C.

[0024] Preferably, the preset time t of step (4) is 40 to 120 minutes.

[0025] The actual water content of the low-oxygen silicon product in step (4) is ≤0.03%, and the oxygen content is lower than 4%.

[0026] The beneficial effects of the present invention are:

[0027] (1) The present invention improves the drying and processing environment of silicon wafer waste, utilizes vacuum and microwave to synergistically enhance the controllable dehydration of silicon wafer waste particles, and determines the preset time of microwave heating controllable dehydration and drying of silicon wafer waste particles by setting the temperature and particle size, so as to control the preparation of low-oxygen silicon products with an oxygen content of less than 4%. The oxygen content of the product is reduced from more than 7% to less than 4%, and the product indicators are excellent;

[0028] (2) The present invention utilizes the synergistic effect of vacuum and microwave technology to simultaneously reduce the activation energy required for water removal during the dehydration process and increase the water diffusion coefficient, thereby promoting efficient water evaporation and enhancing mass transfer diffusion, reducing the contact reaction time between silicon wafer cutting waste and high-temperature water vapor, blocking oxygen conduction and inhibiting surface oxidation, and the process theory and technical principles are advanced;

[0029] (3) Compared with conventional methods, the method of the present invention has excellent dehydration effect, actual moisture content ≤ 0.03%, short processing time, and significantly shortened processing time from 5 to 25 hours to 1 to 2 hours. It can achieve complete and efficient removal of moisture in a relatively short time, and the process technical indicators are advanced;

[0030] (4) The method of the present invention can realize the lossless recovery of silicon wafer cutting waste, avoid the dust loss caused by pulverization and dissolution loss such as chemical deoxidation in the recovery process of silicon wafer cutting waste, and is conducive to obtaining a higher recovery rate. In addition, it has the advantages of simple operation and significant effect.

[0031] (5) The low-oxygen silicon product obtained by the method of the present invention can be further purified and processed to prepare high-purity silicon or silicon-based functional materials, which is conducive to the efficient recovery and high-quality utilization of silicon wafer cutting waste and promotes the recycling and regeneration of waste high-purity silicon resources. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0033] Example 1: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0034] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 5 to 10 cm, initial water content 58.13%, initial oxygen content 2.39%) to obtain silicon wafer cutting waste particles (particle size 0.5 to 3 cm) of uniform size and regular shape;

[0035] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 10 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0036] (3) According to the preset moisture content (0.05%) and the preset oxygen content (3%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (20 kPa) and temperature 50° C.; specifically,

[0037] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0038]

[0039] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0040]

[0041] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g-1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0042] The effective water diffusion coefficient is 5.08×10 -7 m 2 ·s -1 The oxidation rate constant is 6.35×10 -8 g·m -2 ·s -1 ;

[0043] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 77 min and 82 min respectively. Then, the preset time t of the microwave heating controllable dehydration and drying of the silicon wafer cutting waste particles is calculated, where the functional relationship of the preset time t is:

[0044] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 79.5 min;

[0045] (4) vacuum microwave heating and controllable dehydration and drying of silicon wafer cutting waste particles in a microwave heating furnace for a preset time (79.5 min) to controllably reduce the oxygen content of the silicon wafer cutting waste to obtain a low-oxygen silicon product; controllable dehydration and drying are achieved by controlling parameters such as vacuum degree, microwave drying temperature, and time to reduce oxidation of silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0046] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.021%, and the oxygen content is 3.14% (the error with the preset oxygen content of 3% is very small).

[0047] Example 2: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0048] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 5 to 10 cm, initial water content 51.13%, initial oxygen content 1.08%) to obtain silicon wafer cutting waste particles (particle size 0.5 to 3 cm) of uniform size and regular shape;

[0049] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 10 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0050] (3) According to the preset moisture content (0.01%) and the preset oxygen content (3%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (25 kPa) and temperature 40° C.; specifically,

[0051] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0052]

[0053] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0054]

[0055] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0056] The effective water diffusion coefficient is 9.01×10 -7 m 2 ·s -1 The oxidation rate constant is 1.15×10 -7 g·m -2 ·s -1 ;

[0057] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 108 min and 115 min respectively. Then, the preset time t of the microwave heating controllable dehydration and drying of the silicon wafer cutting waste particles is calculated, wherein the functional relationship of the preset time t is:

[0058] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 111.5 min;

[0059] (4) vacuum microwave heating and controllable dehydration and drying of silicon wafer cutting waste particles in a microwave heating furnace for a preset time (111.5 minutes) to controllably reduce the oxygen content of silicon wafer cutting waste to obtain a low-oxygen silicon product; controllable dehydration and drying are achieved by controlling parameters such as vacuum degree, microwave drying temperature, and time to reduce oxidation of silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0060] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.012%, and the oxygen content is 3.41% (the error with the preset oxygen content of 3% is very small).

[0061] Example 3: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0062] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 5-10 cm, initial water content 59.75%, initial oxygen content 2.78%) to obtain silicon wafer cutting waste particles (particle size 2-3 cm) of uniform size and regular shape;

[0063] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 5 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0064] (3) According to the preset moisture content (0.01%) and the preset oxygen content (3.5%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (20 kPa) and temperature 50° C.; specifically,

[0065] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0066]

[0067] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0068]

[0069] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0070] The effective water diffusion coefficient is 5.87×10 -7 m 2 ·s -1 The oxidation rate constant is 7.57×10 -8 g·m -2 ·s -1 ;

[0071] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 74 minutes and 68 minutes respectively.

[0072] Then, the preset time t of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is calculated, wherein the function relationship of the preset time t is:

[0073] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 71 min;

[0074] (4) The silicon wafer cutting waste particles in the microwave heating furnace are subjected to vacuum microwave heating and controllable dehydration and drying for a preset time (71 minutes) to controllably reduce the oxygen content of the silicon wafer cutting waste to obtain a low-oxygen silicon product; by controlling parameters such as vacuum degree, microwave drying temperature, and time, controllable dehydration and drying are achieved to reduce oxidation of the silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0075] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.03%, and the oxygen content is 3.44% (the error with the preset oxygen content of 3.5% is very small).

[0076] Example 4: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0077] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 10-20 cm, initial water content 56.28%, initial oxygen content 2.68%) to obtain silicon wafer cutting waste particles (particle size 3-5 cm) of uniform size and regular shape;

[0078] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 6 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0079] (3) According to the preset moisture content (0.01%) and the preset oxygen content (3.5%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (15 kPa) and temperature 50° C.; specifically,

[0080] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0081]

[0082] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0083]

[0084] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c ois the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0085] The effective water diffusion coefficient is 7.53×10 -7 m 2 ·s -1 The oxidation rate constant is 9.41×10 -8 g·m -2 ·s -1 ;

[0086] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 56 minutes and 63 minutes respectively.

[0087] Then, the preset time t of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is calculated, wherein the function relationship of the preset time t is:

[0088] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 59.5 min;

[0089] (4) vacuum microwave heating and controllable dehydration and drying of silicon wafer cutting waste particles in a microwave heating furnace for a preset time (59.5 min) to controllably reduce the oxygen content of silicon wafer cutting waste to obtain a low-oxygen silicon product; controllable dehydration and drying are achieved by controlling parameters such as vacuum degree, microwave drying temperature, and time to reduce oxidation of silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0090] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.012%, and the oxygen content is 3.66% (the error with the preset oxygen content of 3.5% is very small).

[0091] Example 5: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0092] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 7-20 cm, initial water content 56.15%, initial oxygen content 2.48%) to obtain silicon wafer cutting waste particles (particle size 0.5-5 cm) of uniform size and regular shape;

[0093] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 5 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0094] (3) According to the preset moisture content (0.02%) and the preset oxygen content (3.7%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (30 kPa) and temperature 50° C.; specifically,

[0095] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0096]

[0097] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0098]

[0099] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0100] The effective water diffusion coefficient is 8.01×10 -7 m 2 ·s -1 The oxidation rate constant is 9.13×10 -8 g·m -2 ·s -1 ;

[0101] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 101min and 96min respectively.

[0102] Then, the preset time t of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is calculated, wherein the function relationship of the preset time t is:

[0103] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 98.5 min;

[0104] (4) vacuum microwave heating and controllable dehydration and drying of silicon wafer cutting waste particles in a microwave heating furnace for a preset time (98.5 min) to controllably reduce the oxygen content of the silicon wafer cutting waste to obtain a low-oxygen silicon product; controllable dehydration and drying are achieved by controlling parameters such as vacuum degree, microwave drying temperature, and time to reduce oxidation of silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0105] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.02%, and the oxygen content is 3.81% (the error with the preset oxygen content of 3.7% is very small).

[0106] Example 6: A method for reducing oxidation of silicon wafer cutting waste and preparing low-oxygen silicon in a controlled manner, the specific steps are as follows:

[0107] (1) crushing and shaping silicon wafer cutting waste blocks (particle size 10-20 cm, initial water content 46.37%, initial oxygen content 2.47%) to obtain silicon wafer cutting waste particles (particle size 0.5-5 cm) of uniform size and regular shape;

[0108] (2) The silicon wafer cutting waste particles are evenly spread in layers in the microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction to prevent the silicon wafer cutting waste particles in adjacent horizontal layers from sticking together. A gap (1 to 5 mm) is left between adjacent silicon wafer cutting waste particles in the same horizontal layer to prevent the silicon wafer cutting waste particles in the same horizontal layer from sticking together; the total height of the silicon wafer cutting waste particles in the vertical direction is 5 cm; the dehydration rate in the vacuum microwave treatment can be enhanced and the water diffusion can be promoted through reasonable material stacking method, stacking thickness and other cloth laying factors, which is beneficial to eliminate the secondary contact between water vapor and materials, thereby ensuring the degree of oxidation control and facilitating the improvement of product recovery rate;

[0109] (3) According to the preset moisture content (0.01%) and the preset oxygen content (2.8%) of the low-oxygen silicon product, the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is determined under vacuum (10 kPa) and temperature 60° C.; specifically,

[0110] The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is:

[0111]

[0112] The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is:

[0113]

[0114] Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant;

[0115] The effective water diffusion coefficient is 5.78×10 -7 m 2 ·s -1 The oxidation rate constant is 3.14×10 -8 g·m -2 ·s -1 ;

[0116] According to the functional relationship between the preset moisture content and the processing time of the low-oxygen silicon product and the functional relationship between the preset oxygen content and the processing time, t1 and t2 are calculated to be 83 min and 75 min respectively. Then, the preset time t of the microwave heating controllable dehydration and drying of the silicon wafer cutting waste particles is calculated, wherein the functional relationship of the preset time t is:

[0117] Therefore, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in this embodiment is 79 minutes;

[0118] (4) The silicon wafer cutting waste particles in the microwave heating furnace are subjected to vacuum microwave heating and controllable dehydration and drying for a preset time (79 minutes) to controllably reduce the oxygen content of the silicon wafer cutting waste to obtain a low-oxygen silicon product; by controlling parameters such as vacuum degree, microwave drying temperature, and time, controllable dehydration and drying are achieved to reduce oxidation of the silicon wafer cutting waste to prepare an ultra-low oxygen content silicon waste product;

[0119] After testing, the actual water content of the low-oxygen silicon product of this embodiment is 0.01%, and the oxygen content is 2.73% (the error with the preset oxygen content of 2.8% is very small).

[0120] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for reducing oxidation of silicon wafer cutting waste and controllably preparing low-oxygen silicon, characterized in that: The specific steps are as follows: (1) crushing and shaping silicon wafer cutting waste blocks to obtain silicon wafer cutting waste particles; (2) The silicon wafer cutting waste particles are evenly spread in layers in a microwave heating furnace, and the silicon wafer cutting waste particles in adjacent horizontal layers are isolated by cloth in the vertical direction, and gaps are left between adjacent silicon wafer cutting waste particles in the same horizontal layer; (3) according to the initial moisture content and initial oxygen content of the low-oxygen silicon product, the expected oxygen content, and the vacuum degree of the device, the temperature and particle size are set, and the preset time for microwave heating controllable dehydration and drying of the silicon wafer cutting waste particles is determined; (4) Under vacuum conditions, the silicon wafer cutting waste particles in the microwave heating furnace are subjected to vacuum microwave heating for controllable dehydration. The actual moisture content of the silicon wafer cutting waste and the actual oxygen content of the product are controllably reduced by presetting the drying time, thereby achieving controllable preparation of low-oxygen silicon products by reducing the oxidation of the silicon wafer cutting waste.

2. The method for controlling the preparation of low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 1, characterized in that: The silicon wafer cutting waste block in step (1) is a silicon wafer cutting waste filter cake obtained by plate and frame filtration of silicon wafer cutting slurry.

3. The method for controlling the preparation of low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 1, characterized in that: The particle size of the silicon wafer cutting waste particles in step (1) is 0.5 to 5 cm.

4. The method for controlling the preparation of low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 1, characterized in that: The gap in step (2) is 1 to 10 mm; the total height of the silicon wafer cutting waste particles laid in the vertical direction is 2 to 10 cm.

5. The method for controlling the preparation of low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 1, characterized in that: The method for determining the preset time of microwave heating controllable dehydration and drying of silicon wafer cutting waste particles in step (3) is: The functional relationship between the moisture content of silicon wafer cutting waste particles and the processing time during the vacuum microwave heating controllable dehydration and drying process is: The functional relationship between the oxygen content of silicon wafer cutting waste particles and the treatment time during the vacuum microwave heating controllable dehydration and drying process is: Where MR is the instantaneous moisture content of silicon wafer cutting waste, D eff is the effective water diffusion coefficient m 2 ·s -1 , d is the particle size m of silicon wafer cutting waste, t1 is the processing time s predicted based on the moisture content, c o is the oxygen content of silicon wafer cutting waste, c1 is the initial oxygen content of silicon wafer cutting waste, S is the specific surface area of ​​silicon wafer cutting waste m 2 ·g -1 , k is the oxidation rate constant g·m -2 ·s -1 , t2 is the treatment time s predicted based on the oxygen content, and C is a constant; According to the functional relationship between the preset moisture content of the low-oxygen silicon product and the processing time and the functional relationship between the preset oxygen content and the processing time, the preset time t for microwave heating controllable dehydration and drying of silicon wafer cutting waste particles is calculated, wherein the functional relationship of the preset time t is: Wherein, t is the preset time s, t1 is the processing time s predicted according to the moisture content, and t2 is the processing time s predicted according to the oxygen content.

6. The method for controllably preparing low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 1, characterized in that: The vacuum degree in step (3) is usually selected to be 1-50 kPa, and the microwave heating controllable dehydration and drying temperature is usually selected to be 30-200°C.

7. The method for controlling the preparation of low-oxygen silicon by reducing oxidation of silicon wafer cutting waste according to claim 5, characterized in that: The time for step (4) is 40 to 120 minutes.

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