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GREENER AND SAFER LEACHING OPTIONS

 

CSIRO AUSTRALIA

by Danielle Thompson-Hewitt

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Hazardous and toxic chemicals to leach metals have been used for an incredibly long time. In fact, cyanide was first commercially used to recover gold in the late stages of the 19th century. Heavy reliance on these chemicals during leaching means process plants have to be well-designed, constructed, and maintained to prevent the chemicals causing human harm or reaching the environment.

 

This entails significant capital, ongoing operational costs, and strict regulations for mining operations, with no guarantee for 100% safety. However, greener and safer alternatives are now proving successful at commercial scale.

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This delivers an opportunity for both new and established operations to reduce costs, meet environmental, social and governance (ESG) commitments and improve brand perception.

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Most operations respond to the risks of hazardous and toxic chemical use in their operations by ensuring they have appropriate risk and emergency management plans and processes in place. This can be one solution, but it does not completely remove the dangers.

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Regardless of adherence to these measures, operational

risks still remain, including:

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• catastrophic failure with significant environmental impact

• harm to people, and

• increased regulatory requirements

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Furthermore, there is the risk that an incident will result in a loss in business reputation and shareholder value.

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Risk of share value loss aside, consumer pressure is driving a shift to the production of more sustainable resources. Volvo recently joined the Responsible Sourcing Blockchain Network, Tiffany & Co. have their Diamond Source Initiative, and then there is the Aluminium Stewardship Initiative.

 

In Perth, Nordhoff Jewellery Couture has partnered with Clean Mining Limited to sell jewellery made from gold produced using the CSIRO-developed cyanide and mercury-free reagent, and Valcambi offers Green Gold with independently validated source documentation.

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As society continues to become more aware of the availability of greener and safer metal recovery processes, businesses continuing to rely on toxic and hazardous processes (without considering other options), may increase their risk to an operation’s sustainability.

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Greener leaching offers opportunities to new and existing operations. For the large proportion of mining jurisdictions, there have been no recent upgrades in the chemical restrictions that can be used in leaching processes. Yet it is feasible there will come a time when, through either government regulation or community pressure, change may be necessitated.

 

Operators need to be prepared for this. After extensive research, development, and demonstration by numerous parties, industry now has access to a number of viable, greener, and safer options. These include:

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• using non-toxic and non-hazardous chemicals, such as thiosulfate (for gold) and glycine (for copper and other base metals)

• leaching processes which recycle reagents, reducing costs and tailings footprint, e.g. DNi Process™

• bioleaching, using bacteria to leach metals from ores, e.g. BioHeap, and

• bio-oxidation, using bacteria to liberate sulphide-encapsulated gold (in use at Kirkland Lake Gold’s Fosterville operation).

 

Some of these are already in use at commercial scale, offering opportunities to improve operational efficiency, and meet society’s expectations (and regulatory needs) for cleaner processes and cleaner minerals.

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