A scientist onsite at Kalgoorlie Consilidated Gold Mines obtaining data for use in the flowsheeting model.
Meeting of models helps reduce toxic waste
An unfortunate twist of chemistry means that one of the earth’s most beautiful metals requires one of the planet’s most deadly compounds to extract it from an ore body - gold mining relies on the use of cyanide to dissolve gold into solution so it can be recaptured as pure metal.
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22 October 2007 | Updated 14 October 2011
Reducing cyanide discharge
The inevitable by-product of this process is a cyanide-containing slurry that is discharged into specially constructed tailings dams, where the solids settle out and the solution can be reclaimed for reuse.
The recently introduced International Cyanide Code, which sets voluntary guidelines on the quantity and concentration of cyanide being released into tailings dams, recognises the importance of reducing cyanide discharge.
Parker Centre researchers at CSIRO Minerals Division have taken a novel approach to reducing discharge and ultimately meeting new standards.
Using computer modelling, the team investigated a method of reducing cyanide discharge while increasing the amount of water reclaimed and reducing the need for other reagents, such as lime, used in the gold extraction process.
Forecasting water quality and cyanide discharge
Parker Centre Gold Market leader Dr Matthew Jeffrey says his group used a flowsheet package to map out a complete plant with all its different unit operations – in this case the Kalgoorlie Consolidated Gold Mines plant in Kalgoorlie.
The complexity of the model was increased by interfacing the flowsheet model with a thermodynamic package in order to perform the chemical speciation.
'It will calculate the dominant chemical species in the water at each point in the circuit, and by doing that we could use those fundamental calculations in our flowsheeting simulation,' Dr Jeffrey says.
The result is a model that allows researchers to alter the plant’s set-up, tweak various processing steps and then forecast the effects on water quality and cyanide discharge to the tailings dam.
Examining set-up options
Dr Jeffrey and his team looked at a range of different options for altering the processing plant’s set-up, with some more successful than others.
The recently introduced International Cyanide Code recognises the importance of reducing cyanide discharge.
'Once the water goes out to the tailings dam, it’s very difficult to get all of it back, so we were looking at options involving the installation of a tails thickener,' Dr Jeffrey says.
This provides an extra stage where water could be added to wash some of the cyanide out of the tailings slurry and recycle it back into the plant, reducing the amount of cyanide in the waste.
Magnesium as a variable
Another variable in the process was the quality of Kalgoorlie’s water, which has a high magnesium content.
'Magnesium has a large impact on the plant because the amount of lime required is proportional to the magnesium concentration,' Dr Jeffrey says.
The team therefore altered the model so that the water with the higher magnesium content was used to wash the waste slurry in the thickener. This allowed a greater proportion of the better-quality water, with lower magnesium content, to be reclaimed and reused, reducing lime consumption.
Plant set-up proposed
Dr Jeffrey is confident that the proposed plant set-up could assist the company, and other gold processing plants, to meet the cyanide code while potentially reducing water and lime use in the process.
Read more about Flowsheeting and process modelling for gold processors.
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