The effect of iron contaminants on thiosulphate leaching of gold.pdf

Minerals Engineering 23 (2010) 399–406Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier .com/locate /minengThe effect of iron contaminants on thiosulphate leaching of gold D. Feng *, J.S.J. van Deventer Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australiaa r t i c l e i n f o Article history: Received 30 August 2009 Accepted 24 November 2009 Keywords: Gold ores Sulphide ores Grinding Leaching Surface modification0892-6875/$ - see front matter  2009 Elsevier Ltd. A doi:10.1016/j.mineng.2009.11.016 * Corresponding author. Tel.: +61 3 fax: E-mail address: dfeng@.au (D. Feng).a b s t r a c t Metallic iron and ferric ions were subjected to wet grinding with a sulphide ore in a ceramic ball mill to simulate the fine grinding process using mild steel, in an attempt to investigate the effect of iron species on the ammoniacal thiosulphate leaching of gold. Metallic iron and ferric ions decreased gold leaching in both kinetics and overall extraction when they were added in the wet grinding of a sulphide ore. This det- rimental effect became more pronounced with the addition of metallic iron and ferric ions at higher con- centrations. Metallic iron retarded the gold leaching more than ferric ions at the same dosage. The decomposition of thiosulphate in the leaching of the sulphide ore increased with the addition of metallic iron and ferric ions in the wet grinding. Thermodynamic analysis indicated that the predominant species for iron was ferric hydroxide under the leaching conditions. Wet grinding at a higher pH of 9 and use of ethylenediaminetetraacetic acid (EDTA) were ineffective in improving the gold leaching with the addition of metallic ions and ferric ions in the wet grinding. Iron oxide and hydroxide slime coatings at the sur- faces of pyrite and pyrrhotite were reduced using carboxymethyl cellulose (CMC) to render the sulphide and slime particle surfaces highl