Applying Research On Nickel Flash Smelting Slag With High CaO-containning

In nickel pyrometallurgical process of Jinchuan Nonferrous Metal Company?JNMC?,about 1.6 million tons waste slag with high iron silicate is produced per year.These residues can be considered as effective secondary resource with great value that contains iron,nickel,copper and other valuable metals.Nevertheless,due to the poor magnetic separation character and reducibility of iron and magnesium olivine and fayalite?2FeO.SiO₂?,it is difficult to extract iron effectively from the residual slag.Many issues occurred in the iron smelting reduction recovery from residues produced by nickel pyrometallurgical process,such as high-energy consumption,large amount of slags,high cost etc.To solve the above in the problems in high-iron silicate residue comprehensive utilization,this project propose optimization research on composition and structure of the existing high silicate slag for nickel matte smelting.Specific aim is to increase the activity of FeO for the subsequent reduction of iron from silicate residues.It will be practically valuable for the comprehensive utilization of nickel waste slag.Based on the slag type control of nickel flash smeting process in JNMC,this project will study the isotherm phase diagram and liquid phase region of?NiO?-FeO-CaO-SiO₂-MgO system to uncover the multi-scale relationships among composition,microstructure evolution and physicochemical properties.The main results obtained are as follows:?1?According to the process parameters of JNMC,preliminary nickel slag composition was selected.The isotherm phase diagram and liquid phase region of?NiO?-FeO-CaO-SiO₂-MgO under different oxygen partial pressure were drawn.The results showed that with the decrease of oxygen partial pressure from 10^-5atm to10^-9atm,the Fe₃O₄ and olivine region decreases while the spinel area increase.With the increase of calcium content in nickel slag,the liquid phase area was increased gradually at 1250?and 1300?when CaO content lower than 17%.With the increase of content of MgO,the liquid phase area was decreased at 1300?,until disappeared.The content of modified nickel slag was determined:CaO?wt%?:5-17,MgO?wt%?:5-11,Fe/SiO₂:1.0-1.6.?2?Within the above ingredients,phase analysis of slag at 1000-1200?were carried out.The XRD analysis show that the Fe₃O₄ phase precipitated from slag decreased and olivine phase increased at 1150?when oxygen partial pressure decreased from 10^-6atm to10^-8atm.While CaO content are varied from 5%to 17%,the results were vs.reverse,with melilite phase when CaO content more than 13%.?3?Nickel slag melting point were determined using CQKJ-type II slag melting temperature tester.The results showed that the nickel slag melting temperature was increased with the increase of CaO centent,with a lowest point of 1181?at 13-15%;when Fe/SiO₂ were set at 1.0 to 1.6,the melting temperature decreased from 1206?to1179?;however,when MgO content varied from 5%to 11%,the melting temperature increased to 1248?,which is disadvantageous for matte smelting.?4?Viscosity of nickel slag was determined using the RTW-10 type melt comprehensive physical and chemical performance analyze in N₂.The results showed that the variation trend of viscosity-temperature for nickel slag present a typical?-T curve of weak alkaline slag.Slag viscosity increased with the increase of CaO content from 5%to 13%,and increaed after,with a lowest point of 0.11Pa·S at 13%at 1300?;when Fe/SiO₂ were set at 1.2,CaO?wt%?=15,MgO?wt%?=9,the viscosity were the lowest at 1300?.Besides that,all of the viscosity value of the tested slag samples were lower than 0.063 Pa·S at 1400?.?5?The results of electrical conductivity and surface tension of nickel slag showed that the slag electrical conductivity increased from 1.42?^-1·cm^-1 to 1.73?^-1·cm^-1,and the surface tension increased from 471N·m to 485N·m when CaO content varied from 5%to 17%at 1400?;when Fe/SiO₂ were set at 1.0 to 1.6,the electrical conductivity increased from 1.51?^-1·cm^-1 to 1.74?^-1·cm^-1;however,when MgO content varied from5%to 11%,the electrical conductivity decreased lower than 1350?.In summary,according to the results of phase diagram,physical composition and slag performance analysis under different oxygen partial pressure,a optimized high CaO-containing slag type can be determined as:CaO?wt%?:13-15%,Fe/SiO₂:1.0-1.4,under MgO?wt%?content of 9%.All of the tested samples are suitable for basic requirements of nickel flash smelting,with melting temperature lower than 1200?,viscosity lower than 0.06 Pa·S,lower than 0.5 Pa·S at 1300?.The effect of slag composition change on the characteristic of separation between nickel matte and molten slag,as well as valuable metals loss will also be studied subsequently.