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:: Together Two Compounds Answer Gold Recovery Woes
An elution process that combines the benefits of chloride and sulfite is showing it has the potential to be a key step in a new gold thiosulfate leaching and recovery system.
The process uses both chloride and sulfite in a synergistic mixture to elute (or strip) the gold thiosulfate complex from the resin used to adsorb the gold after it is leached from its ore using the cyanide alternative - thiosulfate.
Traditionally, cyanide is used to recover gold from ores, and then activated carbon is used to recover the precious metal from the ensuing cyanide solution. However, many refractory ore types do not respond well to this process and as regulations on using cyanide become stricter, industry may need to look for other recovery methods.
Although thiosulfate offers an alternative means of dissolving gold from ore, there is a crux: activated carbon does not work well in recovering the gold from the thiosulfate leach solution.
This is where the new Minerals Down Under Flagship’s elution process, which also sees the eluant and resin recycled, could help. Lead researcher CSIRO’s Dr Matthew Jeffrey, working through the Parker CRC for Integrated Hydrometallurgy Solutions, says a small-scale pilot has validated the work. “It ran for 40 days with continuous loading of the resin, followed by elution and resin recycling, and then gold recovery by electrowinning. There was no decline in performance of either the adsorption or elution circuits over this period," he says.
Dr Jeffrey says that many operations have refractory ore types that do not respond well to the traditional cyanidation process. “These ores contain carbonaceous material that ‘steals’ the gold from the cyanide solution. This phenomena is known as preg-robbing."
The gold ‘stolen’ by the carbonaceous material is lost as recovery moves to the next step. This is because it is finer than the screens used to recover the activated carbon pellets.
Thiosulfate leaching coupled with resin adsorption and elution is one of the potential technologies for processing these ore types.
“An alternative step in the gold recovery process would offer companies a solution for these preg-robbing ores. And with environmental regulations often changing the way cyanide can be used, industry is on the look-out for alternatives to use with a range of different ore types, not just for the preg-robbing ores," Dr Jeffrey says.
This article originally appeared in the February 2010 issue of CSIRO’s Process magazine.
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