Optimization of Nigerian zircon sand partial decomposition using response surface methodology for foundry applications

Abstract

The purification of zircon sand for industrial applications, particularly in the foundry industry, requires the removal of impurities such as Fe, Al, U, and Th to meet stringent quality and safety standards. Nigerian zircon sands, often sourced from cassiterite tailings, pose challenges due to their high impurity levels, including radioactive elements. This study aimed to optimize the partial decomposition process to enhance the reactivity of Nigerian zircon sands for subsequent acid treatments while avoiding fine milling, which is costly and poses health risks from radioactive dust. A sub-stoichiometric amount of NaOH was used to selectively decompose the metamict regions of zircon, exploiting their higher chemical reactivity. Optimization using Response Surface Methodology (RSM) with Central Composite Design (CCD) determined optimal conditions of 409°C, 49 minutes reaction time, and 0.8 times the stoichiometric NaOH. Under these conditions, significant decomposition of the metamict regions was achieved. XRD analysis revealed a reduction in zircon content from 89% to 75%, monazite from 5% to 1%, and quartz from 3% to 1%, along with the formation of 20% sodium zirconate, indicating successful partial decomposition. XRF analysis confirmed the reduction of impurities, including Fe, Al, U, and Th, while SEM imaging showed the elimination of surface contaminants. Particle size analysis indicated a slight reduction from 218 µm to 214 µm, demonstrating that the process achieved significant chemical changes without substantial physical alteration of the sand. These findings highlight an effective and practical approach for preparing Nigerian zircon sand to meet foundry industry requirements.