Synergistic Effect Of Aluminium On Production Of Magnesium By Pidgeon Process

Pidgeon process is the main production method of primary magnesium in China.Its output accounts for 90%of the total domestic magnesium production.This process has the problems of high energy consumption and high magnesium content in slag for high reaction temperature and long reaction time.In order to solve these problems,replacing suitable reducting agent is a feasible solution,which is of great significance for saving magnesium smelting cost and reducing production energy consumption.In this paper,calcined dolomite is used as raw material,and a certain amount of aluminium powder is mixed with ferrosilicon as reducing agent to simulate the Pidgeon process.The phase transformation of aluminum-silicon-iron and the phase transformation of slag in the process of magnesium reduction were studied experimentally.The magnesium diffusion model in the process of magnesium reduction by ferrosilicon,the reaction mechanism of magnesium reduction and the synergistic effect of aluminum powder on the reduction of magnesium in ferrosilicon are revealed.In addition,according to the model,the optimal production process parameters are calculated.The theoretical heat balance calculation was performed based on these parameters.(1)The simulation results show that when the mass fraction of aluminum is between 12.5 and 37.5%,the initial liquid phase temperature of the Al-Si-Fe alloy is between 580 and 750°C,which decreases with the increase of aluminum content.After the mass fraction of aluminum exceeds 50%,the initial liquidus temperature is 580°C.As the aluminum content increases,the total liquid phase temperature decreases,with a minimum of 700°C.(2)The kinetic calculations show that the macroscopic kinetic equation for the magnesium oxide reduction process is 1-2/3n-(1-n)2/3=0.7840exp(-8.4×103/T)t.The apparent activation energy of the reaction was 69.818kJ/mol.The model of magnesium reduction rate was established by orthogonal experiment.The model showed that there was an interaction between reduction temperature and reduction time.The optimum process conditions were aluminum powder mass fraction 4%,reduction time 90 min,reduction temperature 1000?.The magnesium reduction rate can reach 98.34%.According to this condition,the heat balance calculation shows that the experimental optimization process can reduce the heat consumption by 4976.47MJ/t compared with the current process.(3)When the mass fraction of aluminum powder accounts for 2%of the total amount of material,the reduction temperature of magnesium oxide is between 950 and1200°C,and the main component of reduced magnesium oxide is Si.When the mass fraction of aluminum powder is between 4 and 6%,the reduction temperature is between 700 and 950°C,the main component of reduced magnesium oxide is Al₃FeSi_2.When the mass fraction of aluminum powder is 8%,the reduction temperature is between 700-950°C,Al and Al₃FeSi₂ jointly reduce magnesium oxide.When the quality of aluminum powder is 10-12%,the main component of reduced magnesium oxide is Al.At 950°C,some magnesium oxide and silicon dioxide form magnesium silicate,which decomposes at 1200°C.(4)Aluminum powder has a low melting point and can be converted into a ferrosilicon phase by mixing with ferrosilicon.It can promote the reduction of magnesium oxide in both diffusion and reaction.