Using experimental design and response surface methodology (RSM) to optimize gold extraction from refractory sulphidic gold tailings with ionic liquids

Teimouri, S, Mawire, G, Potgieter, JH, Simate, GS, van Dyk, L and Dworzanowski, M (2020) Using experimental design and response surface methodology (RSM) to optimize gold extraction from refractory sulphidic gold tailings with ionic liquids. Journal of the Southern African Institute of Mining and Metallurgy, 120 (7). pp. 415-423. ISSN 2225-6253

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Abstract

© 2020 South African Institute of Mining and Metallurgy. All rights reserved. This work examined the feasibility of gold extraction from a pyrite flotation concentrate sample using an ionic liquid and water mixture as solvent, thiourea complexing agent, and iron(III) sulphate oxidant. A design of experiment (DOE) methodology was used to optimize the process parameters. The purpose of the investigation was to determine how feasible it would be to replace the traditional cyanide extraction process by using an alternative approach, and compare the yield that could be obtained with a less environmentally damaging and hazardous combination of chemicals. Test parameters such as ionic liquid concentration, pulp density, time, and temperature were varied using two imidazolium-based ionic liquids: 1-butyl-3-methylimidazolium hydrogen sulphate [Bmim+HSO4–] and 1-butyl-3-methylimidazolium trifluoromethansulphonate [Bmim+CF3SO3–]. The effects on gold extraction were assessed and screened using a half fractional factorial design (25-1) approach. The ionic liquid concentration, pulp density, and temperature had a statistically significant effect on gold extraction, while the type of ionic liquid and extraction time did not affect the gold extraction as much within the operating range investigated. A high gold extraction was obtained at low ionic liquid concentration, low pulp density, and high temperature. A central composite design in conjunction with response surface methodology were used to create an optimization design with the statistically significant parameters in an attempt to establish the optimal gold extraction conditions. It was found that the optimum concentration of ionic liquid [Bmim+HSO4–] in the aqueous solution was 15% (v/v), pulp density was 15% (w/v), and the temperature 60°C, with a gold extraction of 35.7% under these conditions. This, sadly, was only about half of the yield achieved with the cyanide process. In order to compete with the traditional approach, a way will have to be found to completely destroy the pyrite component in the material, in which a substantial portion of the gold was locked up. This work, and similar studies reported in the literature, indicates that cyanide technology for gold recovery will remain the process of choice in the gold industry for the immediate future.