Photo of Barrick Gold's Cowal gold mine.

New analytical methods have helped the Cowal gold mine become the first operation in Australia to comply with the gold industry's International Cyanide Management Code.

Single analysis solution tracks cyanide

New CSIRO-developed analytical methods have helped the Cowal Gold Mine become the first operation in Australia to comply with the gold industry’s International Cyanide Management Code.

  • 17 March 2010 | Updated 14 October 2011

Method will help meet International Cyanide Management Code

Analytical methods developed by the Minerals Down Under Flagship have helped the Cowal Gold Mine in central New South Wales (NSW), Australia, meet stringent environmental conditions set by the NSW Government to become the first operation in Australia to comply with the gold industry’s International Cyanide Management Code.

The new methods use high performance liquid chromatography (HPLC) to provide accurate quantitative determinations of the chemical composition of samples taken along the course of the ore treatment process. They allow the mine operator, Barrick Gold Corporation, to track and manage both the cyanide employed to leach the gold from its ore and the reagents subsequently added to destroy residual cyanide before discharge into the tailings dam.

Senior Metallurgist at the Cowal mine Simone Painter says the relationship with CSIRO has not only helped the company meet all its environmental standards, but to do it in a way that increases efficiency and saves on reagent costs.

All the different cyanide species can be detected, identified and their concentrations measured.

The project was undertaken by researchers working through the Parker Cooperative Research Centre (CRC) for Integrated Hydrometallurgy Solutions.

Cyanide is needed in gold recovery

Cyanide has been used to recover gold since the late 19th century. It forms a stable chemical complex with gold in alkaline solution.

At Cowal the gold–cyanide complex is then adsorbed onto activated carbon, from which the gold is recovered by desorption with hot caustic cyanide solution and electrowinning it from the resulting solution. Any cyanide remaining in the tailings stream - either free or complexed with other metals - is destroyed by reacting it with peroxysulfuric acid, also known as Caro’s acid.

The NSW Government’s environmental consent conditions for the mine are based around tailings levels of weak acid dissociable (WAD) cyanide - hydrogen cyanide, cyanide ions and the cyanide liberated from metal complexes at a moderately acid pH of about 4.5.

They stipulate less than 20 milligrams per litre (mg/L), 90 per cent of the time and never above 30 mg/L. In response, Barrick Gold has set the mine’s target at below 15 mg/L all the time.

HPLC might provide a single analysis answer

The mine is equipped with laboratory facilities to make relatively simple determinations of free cyanide and WAD cyanide using standard chemical techniques. But during commissioning the company recognised that in order to track and manage the cyanide in its system, it needed to monitor all the potential species and derivatives, such as the sulfurous form known as thiocyanate.

It asked CSIRO for assistance, and members of the Parker Centre’s environmental management project (led by Dr Paul Breuer) recognised that HPLC might provide a single analysis answer.

Chemical species in solution pumped through a column packed with an ion exchanger will separate out according to the strength of the physical interactions between them, the solvent and an ion exchange material. Each species takes a characteristic length of time – its residency time – to travel through the column and emerge at the other end.

All the different species can be detected, identified and their concentrations measured either using their characteristic absorption of ultraviolet light or through their capacity to conduct electricity in a cell.

Tracking the generation and destruction of cyanide species

Dr Breuer’s research team was able to determine appropriate solvents, ion exchange materials and detection methods for precise discrimination and measurements of the chemical species in samples taken throughout the ore treatment process.

The data provided by the HPLC analysis not only calibrates on-site chemical monitoring, ensuring environmental consent conditions are met, but also enables the company to track the generation and destruction of all cyanide species at the mine, and to minimise the amounts of reagents used to achieve optimum performance.

Read about CSIRO's capabilities in Precious and base metals hydrometallurgy.

  • Article originally appeared in Process magazine February 2009.