A Study On Recycling Of Silicon From Silicon Wire Saw Waste

At present, the crystalline silicon solar cells have occupied a strong dominate position in the photovoltaic industry.In the process of multi-wire-saw cutting to the crystalline silicon solar cells, it inevitably leads at least about40percents of high purity silicon powders into forming silicon wire saw waste. This paper aims at recycling of silicon from silicon wire saw waste to study, which mainly divides into two parts:recycling of silicon from free abrasive wire saw waste and recycling of silicon from fixed abrasive wire saw waste.For recycling of silicon from free abrasive wire saw waste, this paper mainly studies on the characteristics of free abrasive wire saw waste, acid treatment enrichment to the preliminary separation of wire saw waste and phase-transfer to the further separation of Si/SiC mixed powders of enriched silicon. For recycling of silicon from fixed abrasive wire saw waste, this paper mainly studies on the characteristics of fixed abrasive wire saw waste and the influence on oxygen and metal impurity in wire saw waste by acid pickling. The main conclusions are as follows:1. Acid treatment enrichment can realize the preliminary separation of free abrasive wire saw waste and recycle Si/SiC mixed powders of enriched silicon. When the solid-to-liquid is1:20, impregnating with4.0wt%nitric acid for1hour and3.0wt%hydrofluoric acid for1hour can obtain the separation effect that silicon concentration is72.0%and silicon recovery rate is35.8%.2. Si/SiC mixed powders of enriched silicon can be further separated by phase-transfer after properly water oxidation. Measure the oxidation degree of silicon with the oxidation rate of silicon in Si/SiC mixed powders, when the oxidation rate of silicon is about3.3%, Si/SiC mixed powders can be well separated by phase-transfer and even obtain the separation effect that silicon concentration is close to100%and silicon recovery rate is89.1%. However, Si/SiC mixed powders can’t be separated by phase-transfer after thermal oxidation.3. The dosages of hydrofluoric acid and alcohol have an effect on deoxidation and removing metal impurity in a certain degree. On the basis of2.0wt%hydrochloric acid and6.0wt%hydrofluoric acid, adding50vol%alcohol can make oxygen content reduce to1.80%, iron content can be reduced to19ppm. Appropriate mechanical agitation can improve the effect of deoxidation.