The move away from cyanide in gold processing has been talked of for many years, with words often not followed by actions, yet David Lemieux, President and CEO of Dundee Sustainable Technologies (DST), believes the industry is now starting to get serious about assessing alternative lixiviants.

His assertion comes on the back of one of the biggest gold miners in the world recently making such a move with the help of DST.

Back in December, Newmont signed a Technology Transfer Licensing Agreement with DST to use its cyanide-free gold extraction technology, known as the CLEVR Process™.

The CLEVR Process uses no cyanide, produces no toxic liquid or gaseous effluent and the solid residues are inert, stable and non-acid generating, according to the company. With fast leach kinetics of 1-2 hours, the ability to treat refractory ores and handle base metals, plus a competitive capital/operating expense, the solution has been gaining prominence in the gold market.

Having tested the process out on a variety of ores from various sources, DST is now in the commercialisation phase with CLEVR.

The pact with Newmont follows a successful test work program in the March quarter of this year, after which the gold miner expressed its interest in the execution of such an agreement. This led to Newmont conducting laboratory CLEVR leaching tests in its technical facilities in Englewood, Colorado.

As part of the agreement, DST and Newmont, agreed to:

• A two-year, non-exclusive licence for the use of CLEVR at the laboratory scale in its Colorado technical facilities, with an option to renew for an additional two-year period under the same terms;
• Technology implementation support by DST, including all technology laboratory protocols in addition to technical training sessions to initiate and support the technology transfer and practical operations;
• Ongoing technology support, and for DST to review the laboratory test plans, execution and results conducted by Newmont; and
• Any process scaling-up requirements resulting from positive applications of CLEVR will be conducted jointly with Newmont at DST’s technical facilities in Canada and/or on-site using DST’s technology and engineering group expertise.

Lemieux said the agreement should be viewed as an indication the gold industry is serious about assessing alternative processing approaches.

“DST’s CLEVR Process is a mature and developed novel gold processing technology that allows majors to properly assess how it can be implemented within a given project in terms of environmental benefits, operational efficiency, and operating and capital costs,” he told IM. “Such a level of detail then allows for properly integrated decision making.”

He said there had been increased interest over the years from the industry with regards to alternative processing approaches, which is likely to continue as more jurisdictions target cyanide operations and pressure operators to reduce their dependency on the lixiviant as the main and sole gold recovery mean.

CLEVR is one of two “novel metallurgical processes” DST has in its portfolio, the other being its GlassLock Process™.

GlassLock is a patented process for the sequestration and stabilisation of the arsenic often associated with copper, gold, silver or polymetallic deposits.

In DST’s approach, the arsenic is incorporated into a highly stable and insoluble glass form that can contain up to 20% arsenic, while meeting or exceeding the requirements of the USA EPA’s toxicity characterisation leaching procedure and the Synthetic Precipitation Leaching Procedure, the company said.

Also in the commercialisation phase, GlassLock has been operating at an industrial scale thanks to a demonstration facility built and operated by DST.

According to Lemieux, the increased number of complex orebodies currently being developed means there is likely to be more interest in both CLEVR and GlassLock.

“The chemistry and conditions of the CLEVR process can allow for improved gold recoveries,” he said. “This, combined with DST’s ability to efficiently and permanently stabilise arsenic using GlassLock, is providing good opportunities for DST.”

The Glasslock process, he said, is equally targeting existing operations that have immediate arsenic production and stabilisation needs as well as operations/miners required to address and stabilise legacy arsenical material as part of their permitting requirements.

These abilities were recently recognised by engineering firm Hatch, which entered into a Technology Framework Agreement with DST that could see GlassLock used in combination with Hatch’s fluid bed reactor and arsenic dry scrubbing technologies on gold and arsenopyrite projects.

The objective of the agreement was to “synergise” Hatch’s extensive client base, commercialisation and marketing expertise, fluid bed reactor and arsenic dry scrubbing technologies, and large-scale equipment engineering, supply, procurement, and life cycle services capabilities with DST’s innovative technology to identify and develop potential gold and arsenopyrite projects using GlassLock, the companies said.

While they cannot point to specific results of these two technologies complementing each other, Lemieux said DST has continued and is currently working on testing programs where the roasting and vitrification approach is applied on complex gold concentrates.

“These programs were generated and originate from DST’s own development efforts, but we hope to see more similar opportunities coming from Hatch in the future,” he said.

Lemieux concluded: “Implementing novel metallurgical processes within the industry takes time and DST has progressed greatly, and continues to do so, on the design and operating parameters of specific on-site implementations of GlassLock and/or CLEVR facilities.”