Characterization and Reprocessing of Artisanal and Small-Scale Gold Mine Tailings

Abstract

Millions of tons of solid waste are generated by artisanal and small-scale gold mining in several regions of the world. This study focused on the tailings from the Abu Hamad artisanal gold mine located in northeastern Sudan. The results of the analyses carried out showed that this amalgam waste contained on average 5.5 g/ton of gold, 50 g/ton of mercury, 3.3 g/ton of silver, and 191 g/ton of copper. The particle size distribution was between - 10 and + 300 mu m, and the average grain size was about 65 mu m. Metal distributions showed that gold and mercury grades increased in fine-grained size fractions. X-ray diffraction analyses showed that quartz is the main constituent mineral phase of these residues. The presence of gold, mercury, and other accessory minerals such as sulfide and oxide minerals was revealed by the SEM-EDS. Microscopic analysis showed that majority of gold particles in these tailings are free while few others were occluded in quartz. The gravity tests carried out showed that the best gold recovery result was 47.18%. Bench scale stirred cyanide leaching tests showed that gold, mercury, copper, and silver can be recovered at 90%, 71%, 32%, and 22%, respectively, in 24 h. These high gold recoveries show that these tailings offer a possible commercial secondary resource for gold mining. These wastes contain high mercury grades, which can cause various environmental and public health problems, that is why new environmentally friendly treatment techniques should be developed to recover gold and mercury from these tailings.