Mineralogical characterization of gold and mercury found in amalgamation waste

The aim of this study was to characterize gold (Au) and mercury (Hg) in amalgam tailings generated from small-scale gold mining (ASGM) activities in Mauritania. Metal contents were determined by applying density and size distribution analysis and chemical analysis methods to the samples; and mineralogical phases were examined by characterization tests. Dissolution tests were also conducted for gold recovery and mercury removal. Samples taken from the field were determined to have a grade of 14.41 g/t gold and 179.4 g/t mercury, while they also contained 1 g/t silver and 364.8 g/t copper. The size distribution of the tailings was determined to be between 150 and 74 microns, but the grades of gold and mercury were higher in the finer sizes. The SiO2 content in the sample was 89.57%, with very low percentages of 2.6% Al2O3 and 2.46% Fe2O3. In heavy media separation, gold recovery rates increased with increasing size, but varied between 23.49% and 70.67%. The heavy product, which was recovered at 0.34-1.90%, contained gold grades ranging from 300 to 2543.8 g/t, and mercury grades ranging from 2082 to 8700 g/t. It was observed that the tailings were primarily composed of quartz mineral, with the gold largely present in free form. With 24-hour cyanide leaching, 90% of the gold, 22% of the silver, and 71% of the mercury were dissolved. Increases in recovery yield were observed in samples reduced to finer particle sizes by grinding. With glycine leaching, 94.8% gold, 92.9% silver, 49.2% mercury, and 6.1% copper solubilities were obtained after 12 hours. It was determined that the low dissolution efficiency of mercury was due to the presence of cinnabar. The findings indicate that glycine, an friendly alternative, not only provides high gold and silver recovery but also allows for high levels of mercury removal. This is a significant advantage over cyanide leaching, a toxic reagent.