PHASE EQUILIBRIUM STUDY OF THE CAO-MGO-SIO2 SYSTEM AT TEMPERATURES OF 1400?C DAN 1500?C

• Main Author: Abdullah Harahap, Rafiandy
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/85153
• Institution: Institut Teknologi Bandung

Indonesia's nickel resources are primarily composed of laterite nickel ore, estimated at 55 million tons. In 2023, Indonesia's nickel production accounted for 50% of the world's total, reaching 1.8 million tons. One of the key nickel production methods in Indonesia utilizes pyrometallurgy, specifically the Rotary Kiln-Electric Furnace (RKEF) technology, to process saprolite nickel ore. The melting temperature of slag is a critical parameter in nickel ore processing, as the phase equilibrium within the slag influences its characteristics, thereby facilitating the separation of slag from the molten metal. Optimal processing occurs with a SiO2/MgO ratio between 1.6 and 2.2. However, a current challenge is the decreasing availability of nickel ore with a low SiO2/MgO ratio. This study aims to analyze the phase equilibria of slag and solids within the CaO-MgO-SiO2 system across various primary phase regions at temperatures of 1400°C and 1500°C. The experiment began by determining the initial sample composition based on the phase diagram generated by FactSage 8.0 simulations to achieve the desired phase equilibrium. The oxide powders used in the initial mixture were first analyzed for their crystalline water content by heating them to 950°C for 3 hours in a muffle furnace. Once the crystalline water content was known, the oxide powders were weighed, mixed according to the target composition, and placed in a platinum crucible. The samples were melted at 1400°C and 1500°C for 2 hours using a vertical tube furnace (VTF) under inert conditions by flowing argon gas at a rate of 1L/min. Rapid cooling from high temperature to room temperature was achieved by quenching the samples in water. The resulting samples were prepared using conventional metallographic techniques and analyzed using optical microscopy and Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) to identify the types and compositions of the phases formed. The solid phases identified in this experiment include tridymite/cristobalite (SiO2), olivine (Mg2SiO4), wollastonite (CaSiO3), and ?-Ca2SiO4. The liquidus and solidus compositions in the primary phase regions of tridymite/cristobalite (SiO2), olivine (Mg2SiO4), wollastonite (CaSiO3), and ?-Ca2SiO4 were successfully determined at temperatures of 1400°C and 1500°C. The variation in temperature significantly affected the slag melt phase area, with higher temperatures expanding the slag melt phase. The experimental liquidus and solidus compositions were consistent with those predicted by FactSage 8.0 simulations.