Technology and process integration for producing 2N-grade low-boron silicon by utilizing waste silica powder produced by diamond wire cutting

Abstract

The invention relates to technology and process integration for producing 2N-grade low-boron silicon by utilizing waste silica powder produced by diamond wire cutting. The process comprises the following steps of air classifying: drying the waste silica powder produced by diamond wire cutting, adopting as a raw material, and utilizing an air classifier for collecting the silica powder with the particle size being 0.1 to 10mu m, wherein the collected silica powder is low-boron silica powder; blank making and vacuum drying: mixing the low-boron silica powder and pure water, obtaining a clay, using the clay to make a blank, putting in a drying oven, and vacuum drying to obtain a dried blank material; vacuum sintering: sintering the obtained dried blank material in a sintering furnace at hightemperature, and obtaining the 2N-grade low-boron silicon. According to the adopted process, an existing acid liquor cleaning process is thoroughly abandoned, the purity and the later-period purification yield of the silica powder can be effectively ensured through physical-method separation, the silica powder is cured by adopting a sintering method, the process route is compact, and secondary pollution is avoided.

Description

technical field [0001] The invention relates to the technical field of diamond wire cutting waste of crystalline silicon in the photovoltaic industry, in particular to a technology and process integration for producing 2N-level low-boron silicon powder by using diamond wire cutting waste silicon powder. Background technique [0002] Solar cells are produced by slicing and related post-processing of crystalline silicon after ingot casting or crystal pulling; the application of mortar multi-wire cutting began in the 1990s, and its cutting principle is mainly based on the principle of tribology: three-body wear, that is, steel wire and silicon The material phase wears, silicon carbide powder resides in it, and polyethylene glycol is used as a lubricant; it is expected that all polysilicon wafers will be converted from mortar wire cutting to diamond wire cutting before 2019, and diamond wire cutting polysilicon wafers uses the two-position cutting method. The diamond particles a...

AI Technical Summary

Problems solved by technology

According to the analysis of actual industry data, at least 200kg of cutting silicon powder will be produced for every 1000kg of silicon wafers produced; at present, the problems of environmental pollution and resource waste in the diamond wire cutting waste of crystalline silicon in the photovoltaic industry are still in some large and medium-sized institutions, such as: Northeastern University, Xiamen University, etc., and enterprises, such as: Longji Silicon Industry, Luoyang Sinosilicon, etc., are still in the blank period of real recycling and industrialization.

[0003] At present, the research route in the industry basically adopts: physical enhanced separation (separation of SiC and Si by sedimentation method) → wet chemical separation (removal of metal impurities) → smelting and refining (removal of B and P, while realizing the conversion of silicon powder to silicon block) , the main problems that this process cannot form a pilot test are the low separation rate of "silicon-non-silicon", difficult operation, and process control that easily causes secondary pollution

The main problems are: 1) Oxidation of silicon powder: the most concentrated particle size of silicon powder produced by cutting is 0.1-10 μm, and the separation process takes a long time to easily cause the surface oxidation of silicon powder, and the separation of Si-SiO2 again will remove the invisible 2) Silicon powder hydrolysis problem: chemical method to remove metal impurities, in addition to low separation efficiency, there is another main problem: Si+3H 2 O=H 2 SiO 3 +2H 2 , too fine Si powder will undergo a slow hydrolysis reaction when it meets water

The intercalation relationship between SiC fine particle size and Si powder is complex, H 2 SiO 3 The formation of SiC will lead to difficult separation

3) Refining to remove B and P, and turn powder into solid: Si powder itself is solar-grade silicon, and the B content is already low; if B is removed again, the production process line will increase, the purification cost will increase, and the output rate will decrease; traditional solidification The method adopts smelting method to solidify the silicon powder. Both the vacuum induction furnace and the intermediate frequency smelting furnace are open in the process, and the degree of automation is not high. It is easy to introduce secondary pollution to the product, and the product quality cannot be guaranteed.