Carbon assisted atmospheric pyrite oxidation to enhance reaction kinetics and elemental sulphur yield

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Date
Authors
Cowan, Denver
Keyword
Atmospheric oxidation , Pyrite , Elemental sulphur , Sulphuric acid , Activated carbon , Ferric sulphate
Abstract
Pyrite is an important mineral due to its ability to contain high concentrations of gold. Unfortunately, pyrite does not typically allow for conventional gold leaching, and often an oxidative pre-treatment process must be applied in order to recover the refractory gold. Oxidative pre-treatments exist in a variety of forms categorized under either pyrometallurgical or hydrometallurgical processes. Further hydrometallurgical pre-treatment methods must be investigated in order to meet the current demands of the industry due to the ever changing types of gold deposits. This study investigates the effectiveness of two carbon-based oxidation rate enhancing additives, Lewatit® AF 5, a micro/mesoporous carbonaceous bead, and granular coconut shell activated carbon in the atmospheric oxidation of pyrite and their ability to promote elemental sulphur generation rather than sulphuric acid. Pyrite oxidation in the absence of the carbon additives was 60% after 96 h, with elemental sulphur yields ranging between 16% and 28%. Under the same test conditions, oxidation tests assisted by AF 5 resulted in approximately 96% pyrite oxidation with elemental sulphur yields ranging between 54% and 63%, while activated carbon assisted oxidation reached virtually 100% pyrite oxidation with elemental sulphur yields between 53% and 54%. AF 5 indicated superior mechanical properties and elemental sulphur retention when compared to activated carbon, resulting in its choice for an additional parameters study. Characterization of the two carbon additives indicated the presence of amino acid group L-cystine on AF 5, absent from activated carbon, which was believed to promote the sulphur retention observed with AF 5. Parameters testing indicated that AF 5 was a versatile additive to atmospheric pyrite oxidation as elemental sulphur yield and oxidation was not greatly impacted by varying parameters when AF 5 was present. The highest oxidation and elemental sulphur yields were achieved at a concentrate to carbon additive ratio of 1:2 and a temperature of 90 oC, however. A final study conducted using polyethylene terephthalate (PET) and high-density polyethylene (HDPE) doped with L-cystine did indicate that L-cystine did enhance elemental sulphur retention, and helps to explain AF 5’s sulphur retention.
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