Composition Adjustment Of Nickel Flash Smelting Slag And Its Effects On Equilibria Slag And Matte

In nickel flash smelting process,the composition and physicochemical properties of slag are decisive to ensure the smelting process and reduction iron from final residue smoothly carried out,furthermore,the distribution characteristics of valuable metals between slag and matte and the phase form of iron in final slag are the key to control.To solve the poor iron reduction difficulty of the final slag produced by nickel flash smelting process,our group proposed to adjust the composition of slag for nickel matte smelting of nickel sulfide concentrate,and to discuss the influence of slag composition on the loss of valuable metals and Fe O activity in the final slag.Based on the systematic analysis of performance and phase diagrams of Fe O_x-Ca O-Si O₂-Mg O slag,the range of slag compositions suitable for nickel matte smelting is optimized in this paper.The effects of slag composition regulation and system oxygen partial pressure on slag performance,Fe²⁺/Fe³⁺distribution ratio,metal loss and Fe O activity in slag were studied through Fact Sage thermodynamic software calculation and combined with experiments.The adjustment of slag compositions,the distribution ratio of Fe²⁺/Fe³⁺in slag,the valuable metal loss in slag and the activity of Fe O were studied by Fact Sage thermodynamic software,combined with practical experiments,and the control of residue compositions was discussed.The mechanism of slag composition adjustment,especially the influence of Ca O content on interfacial separation characteristics and equilibria between slag and nickel matte were obtained.The main results obtained are as follows:(1)As the content of Ca O increases from 5%to 15%,the complex silicone oxygen ion gradually dissociate into less combined silica oxide ions.As a result,the viscosity of slag decreases.Consequently,the valuable metal loss,such as copper,cobalt and nickel in the slag decreases.And the valuable metal loss has a relative lowest value at Ca O content of 13%.With the increase of Fe/Si O₂ ratio,the slag basicity increases and the viscosity decreases.Therefore,the distribution ratio of nickel between matte and slag decreased gradually,and the distribution ratio of copper and cobalt between matte and slag increases slightly.(2)According to the X-ray photon energy spectrum analysis(XPS)of equilibrium experiment between slag and matte,the stable structure of iron-magnesium olivine in the slag is broken to release iron due to the add of Ca O.As a result,the ratio of Fe²⁺/Fe³⁺in the slag increases progressively,and has a maximum value at Fe/Si O₂ of1.4.Besides,with the decrease of oxygen partial pressure,the formation condition of Fe₃O₄ is inhibited,the ratio of Fe²⁺/Fe³⁺are increased,which are in favor to the activity Fe O in final slag.(3)The composition vary trend of XRD phase pattern analyzed after the equilibria between slag matte is basically in accordance.With the increase of Ca O content,the structure of iron magnesium olivine in slag was broken,and the existence form of Fe has been gradually veried from(Fe,Mg,Ca)Si O₃ into Ca₂Fe₉O₁₃ and Fe₃O₄ phase.When the Ca O content was about of 13?15%,with the increase of Fe/Si O₂,the relative content of Ca₂Fe₉O₁₃ in slag was larger than that between iron and silicon ratio 1.2?1.3.With the oxygen partial pressure decreases,the relative strength of Ca₂Fe₉O₁₃ in slag becomes larger cause by the higher magnetism than neochrysolite phase,the increase of Ca₂Fe₉O₁₃ content in slag is beneficial to the iron reduction in final slag.The effect of slag composition adjustment on the physicochemical properties,the valuable metal loss,the ratio of Fe²⁺/Fe³⁺,the activity of Fe O and the phases effect in slag were taken into consideration,the optimal slag composition for nickel matte smelting favor to iron extraction in final slag can be determined as Ca O=13%,Fe/Si O₂=1.2?1.3,Mg O=9%.It should also ensure that the oxygen partial pressure of the flash furnace reaction system is reduced as much as possible.The research results have practical application value for improving the iron extraction and comprehensive utilization of the final slag of nickel matte smelting.