Enhancing Gold Assaying Crucibles in Ghana: Optimizing Fosu Clay Grog with Sintered Mullite for Improved Performance

Abstract

Due to material and structural issues, fire-assaying crucibles used for analyzing precious metals in ores have encountered challenges related to poor thermal cycling in Ghana’s sub-Saharan region. This study aimed to enhance the crucibles by analyzing aluminosilicate minerals' multiphase development using X-ray diffraction and understanding the effects of composition determined by X-ray fluorescence on thermal behavior and water absorption observed through optical microscopy. The improved crucible design exhibited enhanced thermal cycling stability and lower permeability to the assay charge. Analysis showed that Fosu Clay (FC) demonstrated promise with a favorable Al2O3:SiO2 ratio and low impurities; mullite was identified as the primary phase formed at high temperatures, with quartz and cristobalite also present. Introducing 6% CSM dopant to FC increased the mullite content while supporting the transformation from quartz to cristobalite. The optimal crucible sample included coarse and fine-doped grog with an FC-clay binder, demonstrating excellent thermal stability, adequate porosity, and water absorption. Adjusting the percentage of doped grog further increased mullite content while reducing silica content; this suggests that locally produced improved crucibles are feasible through sintering commercial clay with mullite doping and precise composition adjustments.