Abstract
Glycine has recently gained plenty of attention in gold processing as an alternative lixiviant to cyanide due to its non-toxicity, efficiency in metal dissolution as well as selectivity for valuable metals. This paper presents an investigation on the combination of agitated reactor leaching and recovery of gold from mildly refractory ore in cyanide-free alkaline glycine media. Optimal leaching parameters for gold extraction were evaluated using response surface methodology. The investigated parameter range was 0.5–2 M for glycine concentration, pH of 10–12 and temperatures of 23–60 °C, with constant leaching time (24 h) and solid/liquid ratio (100 g/L). Based on the experimental series, a mathematical tool was built to predict gold extraction. It was found that, in the investigated parameter range, glycine concentration did not have a statistically significant effect on gold dissolution. Conversely, both temperature and pH had a substantial role in leaching kinetics. The statistical model suggested that the optimal conditions for gold dissolution were 1.25 M of glycine, pH = 12, and T = 60 °C, corresponding to a predicted 87% gold extraction. The experimental verification showed good reliability of the model with 90% extraction of gold achieved under the predicted optimum conditions. The addition of 15 g/L of activated carbon to the pregnant leach solution (PLS) could provide 100% recovery of gold from solution onto activated carbon, i.e. holistic recovery of 90%. Presence of carbon in leach (CIL) resulted in slightly lower (95%) gold uptake from solution and significantly decreased the holistic gold recovery down to 77%. Additionally, the applicability of direct electrochemical carbon-free recovery method, namely electrodeposition–redox replacement (EDRR), was investigated. In the synthetic solution, a gold recovery as high as 88% was achieved (1247 cycles). However, in the real PLS, only 35% of gold was recovered, which is attributed to different speciation of metals and presence of the other dissolved elements.
Highlights
Continuous demand for gold has resulted in the depletion of primary high grade ores
1.3 New scientific contributions and applications This research contributes to new scientific knowledge of cyanide-free leaching and recovery methods from gold low grade ore and flotation tailings, especially the following: x This study investigated, for the first time, biological pretreatment to increase gold extraction as a pretreatment for chloride leaching from flotation tailings. (Publication I)
The aim of this research was to study the performance of cyanide-free chloride and glycine leaching of gold from low grade flotation tailings and gold ore, which can be integrated with electrochemical metal recovery
Summary
Continuous demand for gold has resulted in the depletion of primary high grade ores. extraction from lower grade ores and industrial process residues (e.g., flotation tailings) as secondary raw materials has attracted attention (Norgate and Jahanshahi, 2010). The noble metal gold “aurum” has attracted humankind since ancient times, due to its bright yellow color, ductility, malleability, exceptionally good electrical conductivity, and resistance to corrosion. These unique properties have led to its use as jewelry and a means of investment, and in electronics, dentistry, and other industrial appliances (Marsden and House, 2006; Renner and Johns, 1997; Syed, 2012). China is followed by Australia, the Russian Federation, the United States, and Canada (World Gold Council, 2020). 10000 tonnes, and the world-wide total amount is approx. The biggest known gold deposits are in Australia with approx. 10000 tonnes, and the world-wide total amount is approx. 50000 tonnes (U.S Geological Survey, 2020)
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