PHASE EQUILIBRIA OF SIO2-CAO-MGO-AL2O3 SYSTEM IN TRIDYMITE AND OLIVINE PRIMARY PHASE FIELD AREA AT TEMPERATURES 1400°C AND 1450°C WITH AL2O3 CONTENT OF 5% AND 10%

• Main Author: Ghazi Algifari, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82239
• Institution: Institut Teknologi Bandung

Nickel resources in Indonesia are generally in the form of laterite nickel ore, estimated at 55 million tons, with production in 2023 reaching 50% of world nickel production, amounting to 1.8 million tons. One of the nickel production processes in Indonesia is carried out through the pyrometallurgical process using a Rotary Kiln-Electric Furnace (RKEF) which uses saprolite nickel ore. The melting temperature of the slag is a critical parameter in nickel ore processing. The phase equilibrium in the slag determines the characteristics of the slag to facilitate its separation from the molten metal. This process can operate optimally with a SiO2/MgO ratio ranging from 1.6 to 2.1. The current problem is the decreasing availability of nickel ore with a low SiO2/MgO ratio. This study aims to analyze the slag phase equilibrium with the SiO2-CaO-MgO-Al2O3 system and the metal phase for smelting in the primary solid phase area of tridymite and olivine, to study the effect of smelting temperature on the solid phase area, and to study the effect of Al2O3 content in slag on the slag liquidus temperature. The experiment began with determining the initial sample weight composition that results in smelting in the desired solid area, calculated using FactSage 8.0. Then, the crystal water content was determined in the initial sample using a muffle furnace at 950°C for 3 hours. Next, the sample was weighed and mixed according to its composition and placed in a graphite crucible. The sample was then melted using a vertical tube furnace (VTF) with temperature variations of 1400°C and 1450°C and Al2O3 content variations of 5% and 10% with an argon gas flow of 1L/min to maintain an inert condition. The sample then underwent rapid cooling using water. The melting results were subsequently observed and analyzed using an optical microscope and Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) to determine the composition of the formed phases. The liquidus composition in the primary tridymite and olivine phase areas was successfully obtained under the condition of 5% and 10% Al2O3 composition in the slag and temperature variations of 1400°C and 1450°C. The slag liquidus composition at equilibrium from the experiment matched the FactSage 8.0 simulation. The metal phase formed had main components of iron, nickel, and silicon, which melted in each experiment. Increasing the Al2O3 composition in the slag increased the silicon content in the metal. Temperature variations affected the equilibrium phase area of the slag melt, with higher temperatures expanding the equilibrium phase area. The increase in Al2O3 composition in the slag also broadened the equilibrium phase area of the slag melt, and the expansion due to Al2O3 composition was more significant compared to the temperature effect.