Phase Transformation of Limonite Nickel Ores with Na2SO4 Addition in Selective Reduction Process

Abstract

This study aims to observe the transformations, both mineralogy and morphology of limonite nickel ore with coal as reducing agent and Na2SO4 as an additive in the selective reduction processes. A series of selective reduction processes were carried out at various temperatures in Carbolite muffle furnace for 1 hour. The range of reduction temperature was determined from Thermogravimetric-Derivative Thermal Analysis (TG-DTA). The mineralogy of raw and reduced ores was characterized by using XRD analysis. The morphology, particle size, and mapping were characterized by using SEM-EDS analysis. The results showed that goethite was the main component in the raw limonite nickel ore and it was decomposed by losing the crystalline water at 300 °C. The decompositions were continued to lizardite and trevorite at 600 °C and 800 °C respectively, then Fe and Fe-Ni were formed at 900 °C. Metallization continuously occurred by increasing reduction temperature up to 1100 °C. Moreover, the particle size and porosity of reduced ore were greater up to 2.5-times. The addition of Na2SO4 on the selective reduction processes decreased silica content; it also caused the formation of fayalite and FeS at 600 °C and 800 °C respectively. The intensity of fayalite and FeS decreased when the reduction temperature was more than 900 °C.