Greener and safer leaching options

November 26th, 2019

Danielle Hewettby Danielle Thompson-Hewitt

The future of leaching using safer and more sustainable chemistry

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.

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

Hazardous chemicals produce physical and social dangers

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.

Regardless of adherence to these measures, operational risks still remain, including:

  • catastrophic failure with significant environmental impact
  • harm to people, and
  • increased regulatory requirements

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

Diamond and gold ring

Nordhoff Jewellery Couture created this bespoke ring using gold produced using a cyanide- and mercury- free process.

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.

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.

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:

  • 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.

A change in leaching process could bring new life to dwindling or stranded operations.

Gold strike with thiosulfate

Barrick’s Goldstrike operation have been able to unlock the value of their double-refractory stockpiles by using thiosulfate.

This allowed their autoclave facilities to continue operation, preserving jobs, and bringing much needed income to the State of Nevada.

A similar endeavour is happening closer to home, as Clean Mining aim to use their thiosulfate technology to turn Australia’s uneconomic or stranded deposits into opportunity, through the provision of a lower cost, scalable, mobile processing plant.

Explore a greener and safer operation with CSIRO

As I mentioned in last month’s blog, notwithstanding the financial risks to a company, training and education are also huge barriers to the adoption of new technologies.

Introducing new chemistry into an environment that has always operated the same way requires significant change management and investment in people. A new plant and new chemistry requires people who understand how it behaves to ensure its success.

CSIRO invests significant research and training experience in mineral processing and technologies, and providing expert knowledge on:

  • leaching (including alternative chemicals and bioleaching)
  • the types of ore bodies that these different chemistries can be applied to, and
  • the fundamental chemistry that underpins these new processing technologies.

We collaborate with several base- and precious-metal mining companies in Australia and overseas to develop and optimise greener and safer hydrometallurgical processes. Our laboratory-to-pilot scale facilities make it possible for operations to develop and test new, non-hazardous leaching options.

If you’re interested in investigating the advantages of greener leaching processes through research, development and collaboration, we are uniquely positioned to add value to your project.

Contact me on +61 8 9334 8094 or email me at, to discuss how our expertise and experience can help you.

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