Optimization of direct smelting for mercury-free gold recovery in artisanal and small-scale gold mining

Abstract

Artisanal and small-scale gold mining (ASGM) faces challenges in accessing capital, technology, and responsible practices, hindering sustainable operations and contributing to environmental and health impacts from mercury use. This study evaluated optimizing direct smelting of gold concentrates as an alternative to mercury amalgamation for efficient and responsible production. 50 kg of ore from Nholi mine was concentrated using a Knelson concentrator and analyzed (XRF, fire assay with AAS, XRD). Response surface methodology with a face-centered composite design investigated smelting temperature (1100–1400 °C), duration (30–90 min), and concentrates-to-flux ratio (1:1–3:1) effects. The impact of sulfide concentration (pyrite varied 6.7–48%) on gold recovery was explored. Low-sulfide concentrates associated with pyrite and sphalerite yielded best recovery (>80%) at 1250 °C for 90 min with 2:1 concentrates-to-flux ratio. Direct smelting with ≤6.7% sulfide enabled over 87% gold recovery, facilitating responsible ASGM production.