The new gold standard: How GreenGold is recycling cyanide and recovering dissolved metals

A GreenGold employee carries out some preliminary test work.

Cyanide gets a bad rap but it’s still mining’s go-to solvent. GreenGold hopes its ReCYN process helps to change the chemical’s image.

Cyanide use in gold leaching has a long history dating back to the late 1880s but its use has not come without controversy.

High profile instances of tailings dam failures have helped to contribute to this, such as the Baia Mare dam disaster in Romania that occurred in 2000 standing as perhaps the most prominent example.

The practice is banned or has moratoriums in place in several countries, including several European nations and states of the United States, several Argentinian provinces and Costa Rica.

Alternative methods have been proposed or implemented in limited capacity, but they do not tend to be as efficient as cyanide. They are, therefore, considered less commercially attractive for mining operations.

According to Malcolm Roy Paterson, the chief executive officer of GreenGold Engineering, cyanide is often misunderstood.

GreenGold has developed the ReCYN Process, which can recover base metals, precious metals and cyanide while detoxifying tailings. It does this in an efficient manner by using an absorbent resin bead that can be imbued with different properties depending on the task at hand.

This can help to reduce cyanide consumption by up to 50 per cent by recycling free cyanide back into the leach circuit.

Paterson, who has over 45 years of experience in the minerals industry, has been continually refining the cyanidation processes that eventually led to ReCYN.

ReCYN works using a resin-based process that offers cost advantages over all other treatment processes that usually involve destruction of cyanide complexes.

Ore slurry flows through several adsorption tanks following the carbon-in-leach (CIL) circuit co-currently with activated resin beads.

This loaded resin is then transferred for metal and cyanide elution (i.e. extraction via solvent washing).

Cyanide recovery involves a process of volatilisation and scrubbing to form a concentrate for return to the leach circuit.

The detoxified slurry is then discharged to the tailings dam.

This recycling process helps to detoxify the tailings stream and allow for the discharge of 100 per cent-compliant clean water. This is not only environmentally beneficial but results in significant cost savings associated with the cyanide reuse and reduced detoxification costs.

“The ReCYN process in detox can recover gold to 0.01 parts per million and silver to less than one part per million,” GreenGold operations director Peter Mellor says.

“A lot of companies are throwing gold out so we can capture that gold that is going to waste.”

With copper soluble ores, ReCYN technology allows for a more innovative approach to a flowsheet that would reduce both operating and capital cost. The inclusion of a ReCYN plant allows higher cyanide levels in the CIL, which keeps the copper off the carbon and allows its subsequent recovery in the ReCYN plant. This therefore turns a traditional detoxification cost into a revenue stream.

GreenGold has two operating plants in Indonesia, with a third on the way. The company has signed agreements with the world’s biggest gold miners to implement the technology.

According to Mellor, reception has been overwhelming. The company provides gratis tailings stream analysis for interested companies in the first instance, to show brownfield improvements.

“If the economics are compelling we will do some preliminary engineering to give them a concept design, provide a site visit to an operational asset in Indonesia, perform lab work on their tailings, and propose a design build on their site,” Mellor says.

“Usually the return on investment is less than 12 months for brownfield projects. For greenfield projects, the costs are similar to a standard detoxification plant.”

This article appears in the February 2019 issue of Australian Mining.

To keep up to date with Australian Mining, subscribe to our free email newsletters delivered straight to your inbox. Click here.