The effect of calcium fluoride on extracting magnesium from magnesite and calcium carbonate by silicothermal reduction in flowing argon

Abstract

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, anew method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride(CaF2)on decomposition rate, decomposition kinetics, reduction rate of magnesia and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoridecould reduce the decomposition reaction activation energy and the reaction temperature of carbonatein the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoridecould promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with same timeframe, the corresponding calcium fluoride contents were5%, 3% and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride could reduce the reduction rate of magnesia, but it couldpromote the transformation of dicalcium silicate to ? phase in the reduction slag.

Novel Approach to Prepare Magnesium and Mg-Al Alloy from Magnesia by Using the Closed Microwave Aluminothermic Method

“…The basic principle of this technology is that the condition of extracting magnesium from magnesia is achieved by reducing the partial pressure of magnesium vapor using high-speed argon gas flowing. Several investigators reported that magnesium could be extracted from MgO using the silicothermic reduction method in argon flowing environment, and they found that the diffusion of internal mass transfer and diffusion of reacted species are the limited steps and play an important role in magnesium smelting efficiency during the reduction of MgO [24][25][26][27][28]. Recently, it is worth noting that microwave irradiation which could solve the problems mentioned above in the magnesium smelting process, greatly improves the kinetic conditions of chemical reactions and speed up the heating transfer between reaction materials due to its three-dimensional heating, selective heating, and rapid heating characteristics.…”