Atmospheric oxidation of pyrite with a novel catalyst and ultra-high elemental sulphur yield

- An atmospheric oxidation process of pyrite is investigated.
- The effect of two carbon based catalysts on oxidation is presented.
- Without a catalyst oxidation of pyrite reached 60% with a maximum 28% S0 yield.
- With AF 5 addition 96% oxidation was achieved with a maximum 74% S0 yield.
- Activated carbon addition lead to 100% oxidation with a maximum 64% S0 yield.

The effectiveness of two different carbon based catalysts, Lewatit® AF 5 (AF 5) a new microporous carbonaceous bead, and a granular coconut shell based activated carbon, in aiding atmospheric oxidation of a gold-bearing pyrite concentrate was tested. Oxidation in ferric sulphate media unassisted by a catalyst was incomplete after 96 h and resulted in only 60% pyrite oxidation, with an elemental sulphur yield ranging between 16% and 28%. Under the same test conditions, oxidation tests assisted by AF 5 saw approximately 96% pyrite oxidation with elemental sulphur yields ranging between 65% and 74%, while activated carbon assisted oxidation reached 100% pyrite oxidation with elemental sulphur yields between 63% and 64%. Testwork indicated that not only were pyrite oxidation kinetics greatly enhanced by the addition of carbon based catalysts leading to almost if not complete oxidation, but drastic increases in elemental sulphur yields and thus reductions in sulphate yields were also experienced.It is shown that the AF 5 catalyst adsorbs all of the elemental sulphur produced on its surface. The AF 5 beads are large enough (approximately 0.5 mm) that after the leach process they can be screened out of the slurry, resulting in negligible elemental sulphur within the residue after solid/liquid separation. AF 5 also showed much stronger mechanical properties than the activated carbon, resulting in only approximately 0.40% AF 5 loss to fines compared to approximately 21.5% activated carbon loss to fines.

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