Abstract
The importance of gold recovery from low grade ores and flotation tailings is continuously increasing due to raising gold demand and thereby high gold prices. However, due to raising social awareness of the ecological impacts of cyanidic gold extraction and environ-mental specifications, the development and the implementation of alternative hydrometallurgical extraction processes have been a focus for many research institutions in last decades. Present work gives a comparison between compatible extraction reagents, with focus on less harmful processes. The target of this review is to point out the best cyanide-free processes of following methods and reagents: Bioleaching, Chlorination, Aqua Regia, Bromine, Thiocyanate, Thiosulfate and Thiourea leaching. For this propose, the gold leaching reagents are described and discussed in terms of their environmental and economical points of view. As result of this comparison, thiourea stands out as the most promising alternative gold leaching reagent to cyanide.
Highlights
Gold is a rare element with a concentration of just 0.005 ppm in earth crust
The reagents for gold recovery processes are reviewed in the current paper based many valuable works of different scientists
Chlorination, thiocyanate and thiosulfate leaching might be alternatives to cyanide from the point of environmental view but generally the economic issues make hard to replace those processes with cyanidation due to their quite high reagent consumption and high temperature requirements
Summary
Gold is a rare element with a concentration of just 0.005 ppm in earth crust. This low concentration is a big challenge for gold processing due to a need of upgrading by factor of 3000 to 4000 to receive commercial concentrations. All gold concentration and refining processes generate residues with a remaining gold content Those residues arise mainly in tailings from different extraction processes like cyanidation, flotation, amalgamation, etc. A pre-concentration of gold is quite important to enable an effective and economical processing with further chemical treatment methods as leaching, precipitation and refining [5]. The effectiveness of gravity concentration arise from the high difference in the specific density between gold, with a density of 19.3 g/cm, and typical ore which has a density of about 2.6 g/cm.All gravity concentration devices create a gravitational movement between the gold and host rock particles. The minerals with hydrophobic surfaces attach to air bubbles passing through a suspension and float to the surface creating a froth This process is potential to be used for recovery of fine gold as well as other tailings from gravity concentration and leaching. After giving a short overview of the state of the art, description and comparison of gold leaching reagents will follow to determine an alternative reagent to cyanide
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