Low-grade Nickel Laterite Vacuum Carbothermal Reduction Mechanism And Experimental Studies

Nickel as an important strategic metal, widely used in chemical industry, metallurgy, machinery manufacturing, construction, aerospace, instruments and meters, electroplating, battery, etc. Nickel is the indispensable metal resource of social and economic development. With the increasing need of nickel and decreasing of sulfide nickel resources, the study on nickel laterites is obvious. Vacuum metallurgy with low energy consumption, clean, friendly environment characteristics and get more attention. The current situation of reclaim nickel from nickel laterites was summed up in this study. The purpose of this experiment was to research the approach of carbothermic reduction in vacuum and magnetic separation to extract Mg,Ni-Fe and Si from nickel laterites with low costs, and low pollution. Several conclusions as follows:The results of thermodynamic analysis indicate that the reaction temperature is less than706K for iron, nickel oxide and C when the system pressure is under100Pa. The formations of SiC, gaseous SiO, Si and gaseous Mg occurr at1330K,1460K,1423K and1467K respectively. When the magnesium is produced the SiO will inevitable be produced, whereas SiO will pollute magnesium. The reaction between MgO and C is solid-state reduction in vacuum, and Mg will be extremely volatilize, and desublimate on condenser system. The reaction temperature of SiO2,MgO with C are found to be456-552K lower than that at atmospheric. The gibbs frees energy of the reaction of gaseous Mg with CO, O2, Si and forming MgO and Mg2Si could still negative on condenser system in low temperature at a pressure of1Pa.The research of properties of nickel laterite ore shows that the adsorption, crystallization and structural water are removaled at103.4℃,581.7℃and794.2℃respectively. The distribution of Mg,Fe and Si are dense, but the distribution of Ni is very scare.Whereas the distribution of Ni is consistent with Mg and Fe, so we can infer that Ni is replace the Mg or Fe which in silicate lattice.The microstructure of nickel laterite ore have change after roasting at700℃, it promote the decomposition and the reduction of minerals. When the roasting temperature is1450℃,the ore is melting, the crystallization of2MgO-SiO2and MgO-SiO2are formed, compact structure, low porosity, the reducing is poorer.The research of nickel laterite ore by carbothermic reduction in vacuum and magnetic separation shows that the SiC, Fe-Si alloy, Mg and SiO are found during the reduction process, and then most of SiO turns into Si and SiO2after deposition on condenser system. And a small amount of gaseous Mg is observed to react with CO, O2, and Si, forming solid phased MgO and Mg2Si on condenser system. Whereas the purity of metal magnesium is decrease. With the increases of temperature, carbon content and reaction time, the reduction ratio of Mg and the grade of Ni increases. The additive of CaO and CaF2can improve the reduction rate of nickel laterite significantly, and it promote the ferronickel particles tend to clump. The ground product size and magnetic field intensity have grate effect on the grade and recovery rate of ferronickel and SiC. The magnetic product content of Ni5.21%, Fe53.5%, and the recovery of Ni and Fe are87.7%and88.5%when grinding fineness is-400mesh, current strength is4A. Then the recovery of silicon of nonmagnetic is69.4%.The results of the behavior of silicon by carbothermic reduction in vacuum show that SiO2is found to change into gaseous SiO, most of which turned into Si and SiO2after deposition on graphite condenser. And a small amount of SiO is observed to react with graphite transform into SiC. With the increase of Fe/Si molar ratio, carbon content and the decreases of reductant grain size, the volatilization rate of silicon decreases, whereas its reduction rate increases. With the raise of heating rate and reaction time, the volatilization rate of silicon increases.The research of nickel laterite ore with iron powder and larger fineness coal shows that the magnesium in steel condenser system content of Mg67.5%,Si1.2%change to Mg69.2%,Si0.8%, the volatilization rate of silicon reduce from25.1%to20.1%when the iron powder content is6%and the coal mesh is from-140change to-250.The new and novel process of multipurpose utilization of valuable metals from nickel laterite ore is shorter, low energy consumption, and fit for the large amount of laterite resources. The cost is low, and the technique with high economic and application value.