ANALYSIS OF THE EFFECT OF SIO2/MGO RATIO ON THE SMELTING OF SAPROLITE NICKEL ORES WITH THE ADDITION OF LIMESTONE AT 1550?C ON THE EQUILIBRIUM OF OXIDE PHASES

• Main Author: Dilla Hurnia Sari, Elsa
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/66160
• Institution: Institut Teknologi Bandung

The type of nickel ore contained in Indonesia is saprolite nickel which is processed using RKEF (Rotary Kiln – Electric Furnace) technology. However, the chemical and mineralogical properties of laterite nickel ore in nature vary greatly, which poses a challenge in obtaining a typical ore that is suitable for producing ferronickel. One of the parameters of saprolite nickel ore is the SiO2/MgO ratio. The increasing SiO2/MgO ratio has an effect on increasing the liquidus temperature of the slag which has a negative impact on reducing the life of the refractory. The desired characteristics of slag are having the right viscosity and low liquidus temperature to facilitate the pouring process and reduce energy requirements. The addition of additives such as CaO can regulate the properties of the slag, especially the liquidus temperature. Therefore, the focus of this research is to study the effect of adding limestone to the equilibrium oxide phases in the slag from the smelting of saprolite nickel ore. The experiment was started by mixing samples of calcined ore of nickel, lime, and coal according to the ratio. Sample variants were differentiated based on the ratio of SiO2/MgO to saprolite nickel ore, namely 1.46, 1.77, 2.62, 2.85, 3.02, and the addition of 2% and 4% limestone calcine. The mixture is put into platinum foil and then melted in a vertical tube furnace. Melting is performed by isothermal method at 1550?C for 2 hours. After that, the sample was quenched to obtain equilibrium phases at a temperature of 1550?C. The sample is then given resin and the mounting process is carried out. The analysis was carried out by Scanning Electron Microscope-Energy Dispersion Spectroscopy (SEM-EDS) to determine the chemical composition of the sample. The experimental results obtained that the characteristics of the slag's chemical composition are in line with the FactSage simulation results. The solid oxide phases formed at SiO2/MgO less than 2.36 are pyroxene and olivine. Meanwhile, the solid oxide phase formed for SiO2/MgO was more than 2.36, dominated by SiO2. The effect of adding 2% and 4% limestone on the liquidus temperature of the slag as a function of SiO2/MgO in nickel ore is that the liquidus temperature will decrease at low SiO2/MgO less than 2.36, and then increase at high SiO2/MgO more than 2.36. The addition of limestone calcine which is dominated by CaO which is classified as an alkaline oxide can damage the network structure of the olivine and molten slag phases. CaO converts complex silica bonds such as [Si3O9]6- to [SiO4]4-. The disintegration of [SiO4]4- ions in olivine, a solid oxide with a high melting temperature, makes the olivine phase network difficult to form.