Study On The Influence Of Calcium Additives On The Vacuum Carbothermic Reduction-magnetic Separation Of Silicon-magnesia-nickel Ore

Nickel as an important metal resource was widely used in modern life.The garnierite studied in this thesis is from Yuanjiang,Yunnan.Based on the comprehensive recycling of garnierite,a process of vacuum carbothermal reduction to extractive magnesium and magnetic separation to enrich FeNi is proposed,the effect of calcium additives of CaO and CaF₂ were stuied on the reduction process.When the additive was CaO,the thermodynamic calculation results indicated that CaO could reduce the initial reaction temperature of each silicate reactions,the initial reaction temperature of Ni₂SiO₄,Fe₂SiO₄ were reduced by 123?,251?,429?,221?,336?,469?under the pressure of 50Pa,respectively,and the initial reaction temperature of MgSiO₃,which is extremely difficult to react under normal pressure,were 1045?and 1142?under the pressure of 50Pa,respectively.The thermodynamic reaction equations and XRD analysis indicated that CaO will combine with silicon in the raw materials to form calcium silicate,which promoted the remove rate of Mg effectively,caused the silicon in the reduction residue to separate from FeNi and turned the residual phase into FeNi;the scanning electron microscopy analysis after magnetic separation indicated that when the addition of CaO was 22.64%?the molar ratio of Ca/Si is 1:1?,the silicon and FeNi obviously separated after magnetic separation,the content of silicon reached 97.33%in the silicon-rich region,the content of FeNi reached 93.07%in the FeNi region,which effectively increased the FeNi content in the magnetic material;at the same time,after the vacuum carbothermal reduction-magnetic separation at 1450?,the recovery of iron and nickel reached 84.33%and 97.00%,respectively,and the enrichment ratio of iron and nickel reached a maximum of 6.32and 6.72 times,respectively.When the additive was CaF₂,thermodynamic calculation results indicated that CaF₂ can reduce the initial temperature of each reaction too under the pressure of 50Pa,the initial reaction temperature of Ni₂SiO₄,Fe₂SiO₄ were reduced by 252?,487?,335?,395?,371?,411?,478?,respectively,and the initial reaction temperature of MgSiO₃,which is extremely difficult to react under normal pressure,were 1125?and 1143?under the pressure of 50Pa,respectively.The experimental phenomena,TG-DSC and thermodynamic analysis indicated that the low melting point eutectic of NiF₂ and FeF₂ were produced at 1042?and 1127?in the vacuum carbothermal reduction process,which caused the raw materials to melt and change the reaction from solid reaction to liquid reaction,accelerated the heat transfer and mass transfer of the materials,caused the Fe-Ni particles aggregate and grow up to 20 mm,and MgF₂ was produced during the experiment to further promote the melting of the materials.With an increase of the temperature and the addition of CaF₂,silicon volatilized in the form of SiO and SiF₄,resulted the recovery of silicon sharply dropped.The forsterite and alumina in the material will combine to form spinel,which caused delamination of carbon and raw materials.It hindered the reduction of magnesium,and the maximum removal rate of magnesium only reached 64.12%.The formation of low melting point eutectic of NiF₂,FeF₂ and MgF₂ indicated that CaF₂ participated in the vacuum carbothermal reduction and destroyed the silicate structure in the ore.When the addition of CaF₂ was 3%at 1450?,the recovery of iron and nickel in vacuum carbothermal reduction-magnetic separation reached 82.97%and 98.21%,respectively,and the enrichment ratios of iron and nickel reached 3.18 times and 9.35 times,respectively.