Kinetic Investigation and Dissolution Behavior of Cyanide Alternative Gold Leaching Reagents

Abstract

Raising social awareness and environmental specifications on cyanide application force gold industry to search for alternative leaching reagents. Therefore, researchers worldwide investigate cyanide alternatives for gold recovery since several decades. Often the research activities cannot be compared directly, since different input materials and experimental conditions are used. Over the course of this study, different promising cyanide alternative reagents were investigated in terms of their capability of pure gold dissolution at different temperatures. All experiments took place under identical conditions by using uniform samples of 99.99% gold disks, to enable a comparability. Thiosulfate as one of the most promising reagent thiosulfate according to literature revealed an insufficient leaching behavior. The gold dissolution was hindered due to the formation of a sulfide passive layer. Also in the thiourea trials, a surface precipitation took place, though gold dissolution did not stop. The halogens iodine, bromine and the well-known gold solvent aqua regia dissolved gold very fast (up to ~1,000 mg·h −1 ·cm −2 ). Methanosulfonic acid (MSA) was not capable to extract any gold. The experiments were compared with cyanide trials at identical conditions. The average dissolution rate of investigated reagents at 25 °C shows following order: aqua regia > iodine > bromine > cyanide > thiourea > thiosulfate > MSA.

Low-cost synthesis of AuNPs through ultrasonic spray pyrolysis

“…In previous decades, the extraction of gold was performed from gold ores by using cyanide leaching [42,43]. Due to the environmental issues of cyanide, of halides, aqua regia, thiosulfate and thiourea are now used as alternative materials [44].…”

Leaching Behavior of Gold and Silver from Concentrated Sulfide Ore Using Ammonium Thiosulfate

“…Metals 2020, 10, x FOR PEER REVIEW 2 of 9 investigated in terms of leaching mechanism and kinetics [14][15][16][17]. Lampinen et al investigated the ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate [18].…”

“…Aylmore and Muir conducted a thermodynamic analysis to provide a range of pH and Eh conditions for reagent concentrations [13]. In addition, the thiosulfate leaching process for Au extraction has 2 of 9 been investigated in terms of leaching mechanism and kinetics [14][15][16][17]. Lampinen et al investigated the ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate [18].…”

Selective recovery of precious metals through photocatalysis

“…The recovery process of precious metal is divided into two steps: firstly, dissolve PM 0 into PM x+ from electronic wastes; then reduce PM x+ to PM 0 from the leachate. In the process of dissolving PM 0 to PM x+ , dissolution methods in the industry involving the use of corrosive and toxic aqua regia and cyanidation endanger the environment and characterized of high chemical consumption [14][15][16][17][18] . In view of the toxicity of aqua regia and cyanide, scientists have developed non-toxic leaching agents such as thiourea, thiosulfate and iodine to treat the dissolution of gold, but they are ineffective for the dissolution of platinum group precious metals and the operation steps are complicated (Extended Data Table 1) [18][19][20][21][22][23] .…”