Effect Of Impurity Getter On The Hydrometallurgical Purification Of Metallurgical Grade Silicon

Metallurgical methods take advantage of the different physical and chemical properties of impurities to purity MG-Si step by step.Metallic impurities,such as Fe,Al and Ca,concentrate at grain boundaries or defects of silicon,which can be effectively removed by hydrometallurgy purification.Instead,nonmetallic impurities,such as B and P,cannot be removed by direct leaching because they distributed evenly throughout the silicon matrix.Alloy refining has emerged in recent years,which is a promising process for the removal of impurities from MG-Si.It can reduce energy consumption and change the distribution of impurities.In this paper,vanadium(V)and tin(Sn)were respectively applied as the impurities getters of MG-Si and silicon-copper(Si-Cu)alloy to change the distrubition of impurities.And the alloy refining was combined hydrometallurgy purification with to enhance the impurity removal.The main researches and results are as follows:(1)A small amount V,as an impurity getter,was directly doped into metallurgical grade silicon(MG-Si)to investigate its effect on the distribution of of nonmetallic impurities B and major metal impurities in MG-Si.Then the sensitivity sequences of major impurity phases in the MG-Si with/without V addition to various lixiviant were studied.Finally,the influences of V addition on the leaching behaviors of impurities in the MG-Si by optimal lixiviant were investigated according to the leaching results.The results indicate that Si-Al-Fe phase is dominated impurity phase and secondary impurity phases are disorderly embedded in the Si-Al-Fe phase.The Si-V phase becomes the dominated impurity phase of MG-Si after alloyed with V.According to the results of etching and Potential vs.pH diagrams,it was found that HC1+HF mixture can efficiently remove impurity phases.The total concentration of impurities(Fe,Al,Ca,Mn,Ti,Cu,Cr,B and P)was decreased from 5199.9 ppmw to 137.2 ppmw after MG-Si was directly leached by HC1+HF mixture.After treated by the combined treatment of alloy refining and hydrometallurgy purification,the total concentration of residual impurities in MG-Si further decreases to 91.7 ppmw.Notably,the removal fraction of B can be significantly increased from 22.78%to 54.43%because of the decrease of the segregation coefficient of B impurity between the solid Si and liquid phase during the solidification process according to the thermodynamic analyses.(2)Sn was applied as an impurity getter to explore its influence on the distribution of nonmetallic impurities P and major metallic impurities in Si-Cu alloy.Then the morphology changes of the samples after in-suit etching and leaching were observed to ensure the suitable leaching process.Finally,according to the leaching results,the effect of Sn addition on hydrometallurgy purification of Si-Cu alloy obtained by different solidification conditions was discussed.The results show that Si-Cu alloy mainly includes Si phase,Si-Cu phase and Si-Cu-Fe phase,and P and Al impurity obviously aggregate in Si-Cu phase.With the addition of Sn,Cu-Sn phase and Sn phase were newly observed,where high signal of P was detected.It was found that the impurity phases in the alloy can be effectively removed after leaching by HNO3+HF mixture and aqua regia in sequence.The results of leaching showed that the addition of Sn was beneficial to the removal of most impurities in Si-Cu alloy.In the best solidification condition,the removal fraction of P,Fe,Al and Mn reached 57.05%,99.93%,99.80%and 99.98%,respectively.