Atmospheric oxidation of pyrite; maximizing the elemental sulphur yield

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This research proposal is about atmospheric pre-treatment and gold recovery of pyrite-refractory ores. The typical method for gold extraction from simple ores is to leach the ore in a dilute cyanide solution. Leaching of the refractory gold ores is more complex than simple ores. Typically, the refractoriness of the gold ores is due to the presence of sulphides, such as pyrite (FeS2). In the refractory ores, fine gold particles are usually encapsulated in the sulphide matrix and are inaccessible to cyanide solution, resulting in poor gold recoveries. Treatment of the refractory gold ores requires one additional step in the process, known as oxidative pre-treatment, to decompose the sulphide structure and liberate the encapsulated gold particles. However, sulphides such as pyrite, are very stable and their decomposition requires strong oxidizing conditions. Roasting and pressure oxidation are two commercially-proven technologies for oxidation of sulphides. However, building a new plant based on these processes can be extremely costly. Additionally, if the feed ore contains penalty elements, such as arsenic, then the roasting process may release these into the environment. Penalty elements are highly toxic and the risk of their release into the environment limits the roasting process application. This proposal will investigate an atmospheric leaching method for pyrite oxidation. The goal is to develop a process with high oxidation kinetics and high elemental sulphur yield. The kinetics of the process should be high to make the economics of the processes justifiable. The high oxidation kinetics will be obtained by application of carbon based catalysts in the process. High yield of elemental sulphur is also important to achieve, in order to eliminate excess sulphuric acid generation. Gold leaching of the oxidized material would be performed in thiosulphate solution by the recently commercialized process by Barrick Gold Corp. Six HQPs (2 PhD and 4 summer students) will be engaged in this project, and will gain extensive knowledge of the extractive metallurgy. The HQPs will be trained to meet the needs of the Canadian mining industry.