A Study on the Applicability of Agitated Cyanide Leaching and Thiosulphate Leaching for Gold Extraction in Artisanal and Small-Scale Gold Mining

Abstract

Mercury amalgamation is the method of choice to recover gold in artisanal and small-scale gold mining (ASGM). However, despite the low cost and simplicity of this method, the use of mercury presents serious health and environmental risks, as well as low efficiency in gold extraction. This study investigates the application of cyanide and thiosulphate leaching as alternatives to mercury amalgamation. This investigation was undertaken by conducting leach experiments using cyanide at 1 g/L, 3 g/L, and 5 g/L, and ammonium thiosulphate at 0.1 M and 0.5 M, on three ore samples originating from an artisanal mining area in Zimbabwe. The operating conditions (T = 26 °C, solids loading: 30%, particle size: −300 + 150 µm) were selected to mimic as closely as possible the conditions of artisanal mining processes. It was found that cyanide leaching was the better performing technology compared to thiosulphate leaching, as it achieved gold extractions of 71.6%, 69.7%, and 67.8% for the three ore samples (Sample 1, Sample 2, and Sample 3, respectively), whereas thiosulphate leaching achieved gold extractions of 54.1%, 35.6%, and 38.0% for the three ores, respectively. Both methods outperformed mercury amalgamation, which typically achieves gold recoveries of 30%–50%. Studying the minerology of the ores, using XRF, XRD, QEMSCAN, SEM-EDS, and a diagnostic leach, revealed the presence of sulphide minerals hosting refractory gold which contributed to the low gold extractions observed. Besides achieving higher gold extraction, cyanide leaching proved to be a system that is easier to control compared to thiosulphate leaching, making it much more attractive to artisanal miners.

Una Comparación de Reactivos Alternos al Cianuro como Lixiviantes del Oro: Una revisión

“…Figura 8. Mapa bibliográfico de la lixiviación del oro con cianuro El diagrama anterior muestra que las investigaciones relacionadas con la lixiviación del oro con cianuro van encaminadas a reducir el consumo de cianuro en el proceso de disolución, ya sea adicionando nitrato de plomo como catalizador (Soltani et al, 2020), variando la fuente del reactivo usando cianuro biogénico (Faraji et al, 2021), o al utilizar sistemas de disolución compuestos por cianuro y otro solvente para el oro, como los sistemas cianuro-tiosulfato o el cianuro-glicina (Manzila et al, 2022). Al ser un método ya establecido de disolución, las investigaciones suelen estar relacionadas más a cómo lidiar con los efectos nocivos que tiene este reactivo, es común encontrar artículos hablando de remediación de suelos, descomposición de cianuro o tratamiento de aguas con contenidos de cianuro (Xiong et al, 2021).…”

Investigation of Gold Recovery and Mercury Losses in Whole Ore Amalgamation: Artisanal Gold Mining in Nambija, Ecuador

“…Studies have shown that this activity is economically important for rural communities and reducing poverty [6]. The informal mining practice of amalgamation, as determined by Ecuadorian legislation [7,8], is the predominant method of extracting Au [9]. Amalgamation is one of the oldest processes used in gold recovery [10].…”