Papers by Author: Xing Fu Song

Abstract: The cathodic reduction of SiO2 in KCl-CaCl2-NaCl-MgCl2 melt was studied using tungsten wires as working electrodes. The results of cyclic voltammetry
square wave voltammetry and chronopotentiometry showed that the cathodic deposition of silicon is a quasi-reversible diffusion-controlled reaction, followed by a four electrons transfer step. The results of current reversal chronopotentiometry and thermodynamic data showed that both the silicon deposition and the side reaction between SiO2 and magnesium result in the loss of magnesium and low current efficiency. A 35.2% current efficiency was obtained with the content of SiO2 0.2% at 700 .

Abstract: Magnesium chloride hex-ammoniate (MgCl2·6NH3) is an intermediate to produce anhydrous magnesium chloride (MgCl2) by method of reaction crystallization. MgCl2·6NH3 is decomposed at 670K to produce anhydrous magnesium chloride. The process of thermal decomposition and its non-isothermal kinetics of MgCl2·6NH3 is studied. Results show that the thermal decomposition process is made up of three stages, the thermal decomposition functions and the thermal decomposition kinetics parameters, such as activation energy (E), pro-exponential factor (A) of MgCl2·6NH3 for each step are obtained by means of the Acher differential, the Coats-Redfern integral and multi-accelerated heating rate method. This study provides a valuable theoretical basis for MgCl2·6NH3 decomposition process on industrialization.

Abstract: Magnesium chloride hexammoniate (MgCl2·6NH3) is an intermediate product for preparation anhydrous magnesium chloride by reaction crystallization method. An experiment study of a semi-batch reaction crystallization is presented. In a single feed operation, magnesium chloride solution is fed to a stirred methanol solution mixed with ammonia to crystallize magnesium chloride hexammoniate. The median crystal size of product increases with increasing stirring rate, reaches a maximum, and then decreases again. Decreasing feed rate or decreasing stirring time increases the crystal size significantly. The reaction temperature and concentration of magnesium ion can also influence the crystal size distribution (CSD). A double feed operation can create larger crystal size than that of single feed operation. The relationship between crystal size and the content of water of the product is discussed.

Abstract: Anhydrous magnesium chloride (MgCl2), the dehydration product from bischofite (MgCl2•6H2O) and as industrial raw material for preparation of electrolytic magnesium, is now the most advanced and perfect technological process. For long, the detailed dehydration process was not known due to its dehydration complexity and lack of appropriate experimental conditions. In this paper, quantum chemistry method based on density functional theory (DFT) was used to study the whole dehydration processes. The molecular geometries of MgCl2•6H2O, MgCl2•4H2O, MgCl2 •2H2O, MgCl2•H2O and MgCl2 were all optimized at level of B3LYP/6-31G*, the optimized geometrical parameters and correspondent energies corrected by the second order Møller-Plesset perturbation theory (MP2) were thus obtained. Results show that the energy variations corresponding to the whole dehydration steps from MgCl2•6H2O via intermediates MgCl2•4H2O, MgCl2•2H2O and MgCl2•H2O, to anhydrous product MgCl2 are 35.55, 41.30, 28.55, 31.08kcal/mol, respectively. For steps of 2H2O removal, the energy variation from MgCl2•2H2O to MgCl2 is 59.63kcal/mol, bigger than the steps from MgCl2•6H2O to MgCl2•4H2O (35.55kcal/mol) and from MgCl2•4H2O to MgCl2•2H2O (41.30kcal/mol), which means the last two water molecules are the most difficult to be removed. All these results are significant for mechanism study of bischofite dehydration and are helpful for industrial production of anhydrous magnesium chloride.