Experimental Study Of Hydrometallurgical Purification Unit For Preparing Solar-Grade Silicon

Since renewable energy sources were widely appreciated in recent years,photovoltaic(PV) industry made rapid expansion and solar cells production has 30%per year rapid growing.As the main feedstock for producing solar cells,Solar-Grade Silicon(SoG-Si) fall short of demand and the conventional preparation techniques of SoG-Si needs higher cost.It is a new hot spot for researchers to seek low cost new technologies for prepare SoG-Si.Based on the distribution of the impurities in Metallurgical-Grade Silicon(MG-Si), hydrometallurgical purification of MG-Si was studied in this research.As a pre-treatment unit for preparing SoG-Si,it could remove most metallic impurities in MG-Si.Combined with pyrometallurgical process,it will be a promising new routing for preparing SoG-Si with low cost.In these experiments,suitable leaching agent was sifted,the specific influence factors such as the particle size of silicon,the mass fraction of leaching agent,leaching temperature,leaching time, etc,was studied,and a reactor suitable for hydro-purification of MG-Si was used.The results showed that the mixture of hydrofluoric acid and hydrochloric acid was the most suitable leaching agent;the leaching process was respectively controlled by reaction rates and internal diffusions at different stages;When MG-Si powder had been leached at appropriate conditions:the average size of silicon powder particle 44μm,reaction temperature 120℃,reaction time 4 h,the mass fraction of hydrofluoric acid 4%,the mass fraction of hydrochloric acid 2%,liquid-solid radio 2:1, it was found that 99.7%of Fe impurity and 85.9%of Al impurity in MG-Si powder were removed,the final Fe and Al impurities mass fraction could be reduced to 10 ppm and 64 ppm respectively.Other impurities also had high removal rates in this process,such as Ca,etc.This routing has advantages:simple equipments,low cost,large treatment volume.Further,it has high removal rate and short leaching time.After leached,the mount of metallic impurities in MG-Si are largely reduced,and lower than which in Up-Grade Silicon(UG-Si),it is promising to be combined with pyrometallurgical procedure for preparing SoG-Si with low cost.