Purification Of Industrial Silicon Refining Outside Research

In recent years, with the energy and environmental crisis highlights, photovoltaic industry as well as other renewable energy has received the widespread attention. Over the past decade, PV industry is one of the fastest growing industries, at the same time the generating capacity grows40%per year, it becomes the third largest after the hydroelectric power and wind power installed capacity of renewable energy. Currently, polycrystalline silicon solar cells in solar photovoltaic industry occupy an important position. As the key part of the solar battery photoelectric conversion material, Polycrystalline silicon is more product by the Siemens method, the method of production of solar energy silicon cost high, the environmental pollution is serious, in country, the solar energy silicon production by chemical method is difficult to break through the foreign technology blockade, which face numerous difficulties during production. Both from the technology and the economic perspective, we must find new purification method, it is urgent to research and development with independent intellectual property rights of the solar grade silicon production process to change the position of our country in the global PV market.Our group has researched the production of solar grade silicon metallurgy method for many years. We have puts forward a metallurgical route in the production of solar grade silicon invention patent by the in-depth analysis of the impurities in MG-Si. This invention patent does not rely on the traditional solar grade silicon production. It has many features such as the simple production process, the low cost, the high efficiency and little pollution to environment. In this new process, slag oxidation refining and the acid leaching is one of important link, not only it can remove the most of the impurities in the MG-Si, but also can remove the impurities that the other refined means can’t remove.The paper is on the basis of the subject invention patent, takes MG-Si experimental study to this invention patent, deeply analyses the impurity removal efficiency in large-scale trial slaging refining and acid leaching, and proposes the corresponding optimum technological conditions, the main research work are as follows: (1) Slag refining for the MG-Si by SiO2-CaO-CaF2slag, the removal of Fe, C, Ti, Cu, Mn and Zr has no obvious effect. However the amount of some impurities increased, the content of Al has decreased from690ppm to340ppmw, P reduced from10ppm to2ppm. B has no change, due to the lower activity coefficient of it, but LB is larger than3. LB and LP is increasing with the increase of the basicity. When the basicity reaches1.2, it achieves the maximum. When the basicity is over1.2, LB and LP is reduce with the increase of the basicity. LB and LP are increasing along with the addition of η. Summing up of the factor, the cost and separating rate of impurity, the optimum is4:1. The removal of Al and Ca is remarkable, when oxygen and air is inlet lade together. Al is under200ppmw and350ppmw of Ca, the effect of the removal of the metal impurities of MG-Si is obvious by oxidizing refining through bottom blowing with gas.(2) According to the slag oxidation refining effect of removing impurity and the production cost, we put forward the best LB in the process of refining slag. Research shows that the best LB is1:4, it can ensure refining effect under the premise of maximum reduce raw material costs. It has research the effect of impurity removal of the CaO-SiO2-CaF2slag series in MG-Si slag oxidation refining. The molten slag oxidation refining can remove part of the impurity of Al, B, P, etc, but has no obvious effect on the impurity of Fe, Ca, Cu, etc.(3) It has research the effect of slag basicity on the impurities (B, P) removal in MG-silicon. It shows that when the slag basicity is less than1.2, the distribution coefficient of impurities (B,P) increase with the increase of the slag basicity, when the slag basicity is greater than1.2, the distribution coefficient rate of impurities (B,P) decreases as the increase of the slag basicity.(4) It shows that the impurity removal rate of MG-Si after the ball mill, like Fe, Al, Ca and Ti, was96.7%,73.8%,98%and96.7%, with acid leaching by2wt%HF and2wt%HCl. The impurity V, Cr, Zr were not detected, the total impurity removal rate was90.9%. There is no effect on the removal of sulphur by acid leaching, but phosphorus reduced to3from14ppm. Studying the effect of acid leaching time on the impurity removal rate, we have determined the optimal pilot acid leaching time. Longer the acid leaching time, high distribution coefficient the impurity removal rate of MG-Si, when the acid leaching time reach6h, the impurity of MG-Si tend stable.