New Slag for Nickel Matte Smelting Process and Subsequent Fe Extraction

Large quantities of residual slag with high Fe content are left behind in pyrometallurgical nickel processing. How to separate and recover iron from the high fayalite residue is still a problem because iron mainly exists as iron-magnesium silicate in slag. This article suggests that the slag for nickel smelting is adjusted by increasing the amount of lime, partly instead of quartz, to form liable reduction compounds for subsequent Fe extraction. Based on the thermodynamic analysis and phase diagram of the FeO-SiO2-CaO-MgO slag system, the new slag composition was chosen, the suitable melting point of relevant slags was measured, and the phase change was observed. The new slag with a composition of 7 to 9 pct MgO, 10 to 15 pct CaO and 1.5 to 1.8 Fe/SiO2 was found to work well for nickel matte smelting. With the increase of CaO and decrease of SiO2 content in slag, Ca(Fe, Mg)Si2O6 and Mg(Ca)Fe2O4 are the main existing phases instead of (Fe, Mg)2SiO4 in the residual smelting slag. More than 50 pct of Fe-containing phases are in the form of MgFe2O4 when 15 pct CaO is added, which is what we want because the MgFe2O4 is much better for magnetic separation and reduction than the original (Fe, Mg)2SiO4. In this way, Fe can be much more easily extracted from residual slag and have multipurpose benefits.