Dissolution of ferronickel slag in the hydrothermal process using NaOH solution followed by water leaching: The effect of particle size

The aim of this study is to determine the effect of particle size of ferronickel slag to elements dissolution in the hydrothermal process using NaOH solution followed by water leaching. Ferronickel slag with various particle size were prepared and mixed with NaOH solution in the PTFE reactor. It was then roasted at 220°C for 2 hours in the carbolite muffle furnace. The roasted product was then leached with demineralized water and filtered therefore, filtrate and residue were generated. In this study, characterizations were performed by XRF (X-ray fluorescence), ICP-OES (Inductively coupled plasma-optical emission spectroscopy), SEM-EDS (Scanning electron microscope-energy dispersive spectroscopy) and XRD (X-ray diffraction). Initial element content of the ferronickel slag influences its extraction percentage in relation to the particle size in the hydrothermal process. Particle size significantly affects extraction percentage when its initial element content was low, and otherwise. The dissolution of rare earth elements (REEs) in the hydrothermal process of ferronickel slag using NaOH solution were significantly affected by particle size, especially for Nb that reached extraction percentage up to 99.54%. However, the extraction percentage of Al, Ce, Fe, Mg and Si are likely not affected substantially by particle size of ferronickel slag used. Moreover, reactions that occurred in the hydrothermal process followed by water leaching caused morphology and phase transformations.