Stability of gold-thiosulphate complexes during gold-thiosulphate leaching process

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The conventional method for gold extraction is to leach gold in a cyanide (CN) solution and the recover the gold-cyanide complex on activated carbon. Finally the gold can be recovered from the activated carbon and refined as highly pure gold.Although the gold extraction with CN (i.e. CN process) is a very efficient process and CN is known to be a highly selective leaching for gold, the toxicity of CN has always been a challenge for the gold industry. CN is one of the most toxic materials known and is extremely toxic for human and animals. The gold industry has been successfully using CN for many years, nonetheless, several accidents of CN spills are reported every year. Another challenge with the use of CN is the cost of its detoxification in the waste waters of the gold extraction plants.To eliminate the use of CN has been a major drive in the gold industry, via development of alternative CN-free processes for gold extraction. Thus far, Barrick Gold Corp., a Canadian gold mining company, is the only company which has developed and commercialized a CN-free process for gold recovery. The process is called CaTS process which uses non-toxic calcium thiosulphate as the gold leaching media. However one significant challenge with this process is the instability of thiosulphate during the gold leaching process. The objective of this study is to understand the fundamental reason behind the thiosulphate oxidation during the leaching process, and develop a solution for this challenge. After successful completion of the project, the reagent cost of the CaTS process will be minimized and the process can be marketed to other Canadian and international gold companies, generating significant revenues for Barrick Gold Corp, and Canada in general.