Metallurgical Grade Silicon Direct Preparation Of Solar Grade Silicon Pretreatment Experiment

Solar energy will shortly be in great demand since it is inexhaustible and cleaner than any conventional energy resources. At present, an expensive grade of silicon for semiconductor is used for a solar cell to convert solar energy into electricity. However, the amount of supply is limited and we have to develop an innovative metallurgical grade silicon (MG-Si) as a starting material for making solar grade silicon (SOG-Si) is believed to be one of the ways to make solar cells less expensive.A new method for production of solar grade silicon at low cost from MG-Si via vacuum metallurgical technique was proposed by the research team consisted of the author, which is a promising process to feedstock solar grade silicon material independence of traditional Siemens method. In this procedure, pre-treatment of MG-Si using hydrometallurgical routes to remove metallic impurities such as iron and aluminum to reduce the production cost is an important process. Also this is the process in the production of upgrade metallurgical grade silicon.In this paper, the distribution of the impurity in MG-Si was investigated at first. Then, the influences of many factors such as hydrochloric acid, reaction temperature and reaction time on the removal efficiency of iron and aluminum impurities was systematic studied, with the scale of experimental extended constantly, and the influences of pressure leaching was investigated simplely.In the scale experimental of 5g silicon powders, the influences of acid agents, acid concentrations on the removal efficiency of iron impurity was studied, respectively. The removal efficiency of iron impurity for hydrochloric acid was higher than the removal efficiency of iron impurity sulfuric acid and nitric acid in the same of concentrations. The removal efficiency of iron impurity for hydrochloric acid with high concentration was higher than the low concentrations. And elevating the reaction temperature and prolonging the reaction time can give much helpness for the removal efficiency of iron impurity.The influences of many factors on the removal efficiency of iron and aluminum impurities have much reproductivity in the scale of experimental extended. The experimental results was shown that the optimum operation condition were acid concentration 6mol/L using hydrochloric acid at 60℃for 18 hours with 50μm in diameter for raw material ground and with liquid to solid ratio of 2:1 in the scale experimental of 50g silicon powders. The optimum operation conditions of influences on the removal efficiency of iron and aluminum impurities in the scale experimental of 200g silicon powders were as same as the scale experimental of 50g silicon powders. So the rationality in the process of the experimental broaden was proved. Also, the experimental results show the removal efficiency of aqua regia was not much lower than the hydrochloric acid's. In the scale experimental of 5kg silicon powders, the residual quantity of iron and aluminum impurities can be mad in a stable level. And removal ratio of iron and aluminum impurities was up to 70% and 60%, respectively. And the removal efficiency of the iron and aluminum impurities for pressure leaching was improved more than the removal efficiency for leaching in the atmospheric pressure, and the reaction time was shortened in a great extent. For pressure leaching, removal ratio of iron and aluminum impurities was up to 70% and 60%, respectively. The study of pressure leaching can provides a feasible solution to pre-treatment of MG-Si and can presents a valuable reference for research in the purification of MG-Si and hydrometallurgy.The economy analysis on the pre-treatment of MG-Si( production of upgrade metallurgical grade silicon) was shown that it can get great economic benefit for production of upgrade metallurgical grade silicon using hydrometallurgical routes in industry.