Research Of Water Vapor Oxidation Of Nickel Slag Effect On Mineral Phase Structure And Magnetic Separation

Nickel slag is the waste slag produced during the flash melting of nickel,which is a secondary resource with utilization value due to its high iron content and the presence of valuable metals such as nickel,cobalt,copper and chromium.The development and recycling of nickel slag can not only achieve the comprehensive utilization of secondary waste slag,but also generate considerable environmental and economic benefits.In this research,we use the raw material of flash smelting slag from nickel smelter.Thermodynamic calculations by Fact Sage were performed to analyze the feasibility of water vapor oxidation of nickel slag to determine the reaction temperature range.And the effects of water vapor flow rate,oxidation temperature,oxidation time,basicity,grinding fineness and magnetic field strength on the iron grade and iron recovery in the oxidation products were investigated by oxidation roasting experiments,to identify the optimal roasting conditions.The following conclusions are drawn from the study.（1）Fact Sage thermodynamic calculations show that Fe₂Si O₄can react with water vapor to generate Fe₃O₄,the addition of Ca O is beneficial to the decomposition of the fayalite phase to release Fe O,which in turn reacts with water vapor to form magnetite,the amount of Ca O added affects the product phase.As the basicity increases from 0.2to 0.6,the spinel phase area increases and the liquid phase temperature gradually decreases,and the basicity continues increasing to 1.0,the spinel phase area decreases slightly and the liquid phase temperature continues decreasing.Controlling the oxygen partial pressure at 10^-5～10^-10atm,which can make the stable iron oxide phase in the slag system as Fe₃O₄.（2）The optimized conditions for water vapor oxidation roasting were:100ml/min water vapor flow rate,oxidation time of 40min,oxidation temperature of 1000℃,basicity of 0.6,grinding fineness of oxidation product of-74μm content of 72%,and magnetic field strength of 1200 Oe,which resulted in a magnetic separation product with iron recovery of 71.1%and iron grade of 56.4%.In a certain range,increasing the water vapor flow rate,oxidation time,oxidation temperature and basicity can improve the magnetite content in the oxidation product,and increasing the grinding fineness and magnetic field strength improves the iron recovery of the oxidation product.（3）The microstructure of the oxidation products was influenced by the oxidation time and basicity,the longer oxidation time was favorable for Fe₃O₄to grow into more saturated granular particles,and the larger basicity was favorable for the separation of Fe₃O₄and silicate,with some sulfur particles distributed in the silicate.The Fe grade in the magnetic separation product is 56.1%,and the main phase is magnetite,indicating that the Fe element is well separated with the vein.