Simulation And Experimental Study On B - Molecular Dynamics Of Hydrometallurgy In UMG - Si Preparation

In the purification process for the metallurgical preparation of SoG-Si, hydrometallurgy is an important pre-processing technology, it can purify the2N metallurgical grade silicon (MG-Si) to3.5-4N upgrade metallurgical grade silicon (UMG-Si), reduces the difficulty and cost of followed fire purification greatly. Hydrometallurgical purified MG-Si can remove most of the metal impurities such as Fe, Al, Ca etc., however, the reasearch for the removal of non-metallic impurities B, P lack of in-depth study. Removal of B has becomed the importantance and difficulty of purified MG-Si to prepare SoG-Si. Due to the special physical and chemical properties of B in MG-Si, the direct use of experimental research methods are difficult to clearly understand the nature of the removal of B by hydrometallurgy. In this paper, the non-metallic impurities B in MG-Si as the study, experimental research as the basis, combined with ab initio molecular dynamics to study the thermodynamics for the B removal by hydrometallurgy and molecular dynamics, revealing the essence of B removal by hydrometallurgy on the atomic scale.According to the thermodynamic calculation of B removal by hydrometallurgy, under appropriate conditions, the impurity element B can react with oxidizing acid or strong complexing ability of the F-. Exploratory experimental study of hydrometallurgy showed that B can be removed effectively in medium containing F-under pressure leaching. The content of impurity B can be reduced from22.5ppm8.8ppm, the removal rate was60.89%.The Materials Studio software was use to build the model of B removal by hydrometallurgy, Si (110) was selected for the reaction interface, and doped B on the interface to form Si(110)-B, then selected the main particle such as H+、OH-、O2、F-、Cl-、 SO42、NO3-、NH4+to interacted with Si(110)B. The structural changes, the density of states (DOS), bond length and Mulliken population analysis showed that the use of acidic medium is more conducive than the alkaline medium to the removal of B, F-and NO3has the better removal efficiency, access O2can facilitate the reaction process for the removal of B. Simulation results and tentative experimental results is good agreement. It provides a theoretical basis for the removal of B by hydrometallurgy.Molecular dynamics simulation of the process for the B removal using F-and NO3, simulation conditions were298K,0.1MPa and473K,1.5MPa, respectively, the simulation time is lps. The simulation results showed that a strong interaction between F-and B, resulting in Si-B bond cleavage, then generated complexed form BF3further soluble BF4-formed and removed from the Si substrate, elevating temperature and pressure were help to enhance the interaction between F-and B. The process of B removal using NO3-is that B is mainly oxidized to BO32-, and NO3-is reduced to NO2.In addition, the influence of metal impurities Fe, Al, Ca in MG-Si on the structure of Si-B system were studied. The results showed that the incorporation of metal impurities weakened the bond strength of Si-Si bond and Si-B bond. Si-Si bond strength weakens according to the order Al>Ca>Fe, Si-B bond strength weakens according to the order Al> Fe>Ca, the order of bond strength are Fe-Si>Al-Si>Ca-Si, Al-B>Fe-B>Ca-B. MG-Si powder, B powder, Fe powder, Al powder were used in verification experiment and the powder were smelted to prepare Si-Fe-B, Si-Al-B, Si-Ca-B alloys, respectively, and then acid leaching, analysised the B content of the solid samples. The results showed that the best B removal effect was that of doped Ca, Al followed, however, Fe had no effect to it. which were related to the simulation results of lowest bond strength Ca-B bond, the experimental results are consistent with the calculated results.