The tiny West Australian town of Menzies is the setting for a gold processing demonstration plant that aims to reinvigorate small gold miners with a cost-effective and environmentally-friendly alternative to cyanide. TONY HESELEV reports

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Demonstrating a golden opportunity in environmentally-friendly processing

A low cost demonstration plant for technology that can overcome the environmental risks and regulatory barriers associated with the use of cyanide in gold recovery, could hold the key to unlocking stranded Australian deposits.

The demonstration plant, which will open in 2018, is at the centre of a collaboration between CSIRO and small producer Nu-Fortune Gold.

The plant is being built in the West Australian goldfields at Menzies, 130 kilometres north of Kalgoorlie, where Nu-Fortune Gold leases the old stamp battery site from Perth Mint and currently produces small-scale gold bars with a mill and gravity circuit.

Demonstration plant for thiosulfate gold recovery process

The plant will demonstrate CSIRO’s thiosulfate-based recovery process – a non-toxic reagent to dissolve the fine gold out of ores (the gold that is not recovered by gravity) and its application – in the next stage towards its commercialisation.

The method has undergone intensive testing in the laboratory to understand its leaching performance in association with reagent recovery and recycle. Results indicate that it can be applied to a range of ore types, as opposed to a highly specific alternative to cyanide developed by Barrick Gold together with CSIRO at its Goldstrike mine in Nevada in 2014.

The demonstration plant aims to prove at scale that the reagent (or lixiviant) can economically recover gold in an alternative process to techniques using cyanide, overcoming a range of health, safety and environmental risks and associated regulatory obstacles.

Cyanide-free gold processing

Nu-Fortune Gold director, Paul Hanna, says the company believes there is a risk that within the next few years many countries will ban cyanide in gold production. It has already been banned in some states in the USA and parts of Europe.

“It piqued our interest because we were searching high and low for an alternative to cyanide at our battery,” Mr Hanna says.

“We’re an entrepreneurial company, and the fact that we could be market leaders in the application of this technology is very appealing to us. Also appealing is the relatively low capital expenditure requirement, which essentially gives us a low cost entry into being able to treat our own gold.”

CSIRO and Nu-Fortune Gold envisage the plant being used as a gold processing research hub. This would provide opportunities for the research organisation to demonstrate the method on a greater range of ore types from other gold miners, enable equipment suppliers to trial and develop customer-driven solutions in collaboration with industry and researchers, and provide opportunities for research and training of metallurgical students.

Processing infrastructure is being built out of modular components and the Menzies site is expected to be used for ongoing research and development for several years.

The longer-term vision is for mobile processing facilities that can unlock gold deposits stranded by factors such as resource size and transport costs.

“It works for us because we’ve got the infrastructure there and we get first look at any new technologies developed,” Mr Hanna says.

Having gone through the CSIRO-managed national science and technology accelerator program, ON, the team has gone beyond the science to look at the whole process and its economics. Through ON, they interviewed potential customers to identify opportunities where the thiosulphate could be applied and examined “investment readiness”, such as business and equity models, funding options and founder agreements.

Mining opportunities for smaller gold deposits

The team identified a lack of opportunities for miners with smaller deposits that did not fit into the large-scale economics of gold processing plants using cyanidation.

CSIRO team leader, Paul Breuer, says they started by taking a step back and looking at the miners with gold deposits who can’t use cyanide or can’t afford the capital expenditure of a typical processing plant (costing about $30 million).

“We asked ourselves whether we could come up with a solution for these miners, in this case a novel processing plant costing $1 million or $2 million that could be used without having all the regulatory hurdles to jump over.

“We realised we could knock down a lot of those hurdles.”

Dr Breuer says that gold recovery rates would be very similar with the alternative reagent. However, higher concentrations were needed than with cyanidation, meaning that initiatives such as dry tails stacking and nanofiltration were required to recover and recycle the reagent and minimise water use to make the process economic.

Customisable for other ores

While more components are needed in the new process and the configuration is unfamiliar to the industry, it is not complex because standard off-the-shelf equipment is used. The plant can also be customised to deal with different ore types. 

“One of the main challenges of the new process is overcoming the perceived risk of adopting a new technology that is unproven at scale,” Dr Breuer says.

“The best way of proving this is with a demonstration plant. We could have built a pilot plant at CSIRO but we wanted to get operator/end user involvement early so that we make sure the developed process is robust and practical.

“These plants need a little bit more intuition and control around the chemistry and we’re working to make it as simple as possible so that it can be adopted as widely as possible.”

The $2.1 million project to construct, commission and operate the demonstration plant in 2017-18 is being supported by an $860,000 grant from the Science and Industry Endowment Fund.

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