Utilising novel technology for residue management and sustainable mine closure.

Three case studies present the use of new or unconventional technology to improve sustainability and reduce residue management costs at different stages of mine life. The first relates to a US Cu operation closed in the 1970s apart from leaching of a low-grade stockpile; when the declining solution grade made solvent extraction-electrowinning uneconomic, installation in 2004 of a Cu recovery plant using BioteQ's BioSulphide process allowed cost-effective Cu recovery to continue for an additional nine years. The process uses H2S gas generated in a bioreactor to precipitate metals from water. The plant was designed to produce up to 3.8 t/d sulphide by treating up to 12 000 m3/d of leach solution at a design Cu recovery rate of 99%, the treated solution being recycled to the top of the stockpile. The second concerns a Cu smelter in Chile where the As content of Cu concentrate has gradually increased, leading to off-gas As during smelting reporting to water-based scrubbers which then produce highly acidic As-rich liquid blow-down (EPAS). The BioSulphide process was implemented to treat the EPAS solution instead of lime neutralisation. Benefits included a significant reduction in the volume of waste residue generated, the metal sulphide residue with more than 50% w/w As on a dry-weight basis offering an order of magnitude reduction in solids handling and disposal costs. Power and chemical costs are reduced, water recovery is higher, acid contained in EPAS is recovered and the recovery of metals such as Cu, Re and Mo from EPAS becomes a possibility. The third case study involves a large Cu-Au mine currently being permitted in a sensitive watershed area where water treatment is being carefully evaluated with particular regard to Se in the ore body, overburden and waste. A pilot project was undertaken using BioteQ's Selen-IX Se treatment system. A strong-base anion-exchange resin in the sulphate form is used to remove Se selectively from water to concentrations of less than
Three case studies present the use of new or unconventional technology to improve sustainability and reduce residue management costs at different stages of mine life. The first relates to a US Cu operation closed in the 1970s apart from leaching of a low-grade stockpile; when the declining solution grade made solvent extraction-electrowinning uneconomic, installation in 2004 of a Cu recovery plant using BioteQ's BioSulphide process allowed cost-effective Cu recovery to continue for an additional nine years. The process uses H2S gas generated in a bioreactor to precipitate metals from water. The plant was designed to produce up to 3.8 t/d sulphide by treating up to 12 000 m3/d of leach solution at a design Cu recovery rate of 99%, the treated solution being recycled to the top of the stockpile. The second concerns a Cu smelter in Chile where the As content of Cu concentrate has gradually increased, leading to off-gas As during smelting reporting to water-based scrubbers which then produce highly acidic As-rich liquid blow-down (EPAS). The BioSulphide process was implemented to treat the EPAS solution instead of lime neutralisation. Benefits included a significant reduction in the volume of waste residue generated, the metal sulphide residue with more than 50% w/w As on a dry-weight basis offering an order of magnitude reduction in solids handling and disposal costs. Power and chemical costs are reduced, water recovery is higher, acid contained in EPAS is recovered and the recovery of metals such as Cu, Re and Mo from EPAS becomes a possibility. The third case study involves a large Cu-Au mine currently being permitted in a sensitive watershed area where water treatment is being carefully evaluated with particular regard to Se in the ore body, overburden and waste. A pilot project was undertaken using BioteQ's Selen-IX Se treatment system. A strong-base anion-exchange resin in the sulphate form is used to remove Se selectively from water to concentrations of less than