Thiosulfate Gold Leaching by Chromafora – High Yield and Low Costs Confirmed in Pilot
Chromafora’s pilot project for a non-cyanide gold extraction process has recently been formally reported to and fully approved by Sweden’s innovation agency and co-funder Vinnova. The results demonstrate a groundbreaking method with high yeild—so far up to 92 percent—combined with competitive economic outlook.
Cyanide leaching is the conventional method for gold leaching, but it poses significant risks to both humans and the environment. Therefore, Chromafora has modernized thiosulfate leaching and combined it with its unique metal separation technique SELMEXT™. The result is cyanide- and toxin-free gold extraction from electronic waste, mining waste, and other residues.
The Swedish impact company Chromafora has successfully developed a pioneering gold extraction process. The method is cost-efficient and entirely non-toxic and has the potential to become the first profitable alternative to conventional and hazardous cyanide leaching.
“Our method eliminates the toxic risks associated with cyanide and makes it possible to refine the ore and gold concentrates directly at the mine site instead of transporting them elsewhere. This benefits local communities and reduces transportation needs”
Johan Berg, application manager at Chromafora.
High gold prices have increased interest in gold recovery from both primary mining operations and secondary streams such as end-of-life electronics. Many countries have already banned cyanide leaching, creating a strong demand for a competitive and environmentally friendly alternative.
The objective of the pilot project was to further develop the combination of a thiosulfate-based lixiviant and Chromafora’s metal separation technology, Selmext, and to demonstrate its economic and environmental potential. The test was conducted in collaboration with a mining company between 1 March 2022 and 30 March 2025. Pilot-scale leaching yields ranged from 53–92 percent, while laboratory yields were between 80–86 percent. In addition, recovery of the Selmext and catalytic reagents showed that up to 96 percent recycling is possible. This results contributes to economic competitiveness.
“When we assess a hypothetical full-scale plant with a capacity requirement of processing 15,000 tonnes of gold concentrate per year, the total operating cost of Chromafora’s gold leaching process is comparable to that of conventional cyanide leaching”
Johan Berg
The gold leaching work is now entering a new phase. A demonstration plant is currently being commissioned, and the door is open to new collaborations, with the goal of becoming the a commercial alternative to cyanide leaching.
Advantages of Chromafora’s Gold Leaching Method
- Non-toxic and based on a limited number of well-known chemicals
- A cost-efficient thiosulfate based method
- Enables internal, direct recycling of almost all process chemicals
- Suitable for on-site leaching and gold recovery at the mine, benefiting local communities and reducing transportation
About Chromafora’s Gold Leaching Method
Chromafora’s gold leaching method is a cyanide-free hydrometallurgical gold extraction process in which a thiosulfate-based lixiviant is combined with Chromafora’s metal separation technology, Selmext. Selmext addresses a key limitation of the well-known but deficient thiosulfate leaching method by efficiently separating metal impurities from the gold-enriched lixiviant solution, and thereby enabling effective final gold extraction.
The project was divided into research and pilot phases. Pre-treatment and leaching were primarily carried out by Luleå University of Technology, Sweden, while the pilot was conducted by Chromafora in collaboration with the Björkdalsgruvan mine, a gold mine in northern Sweden.
Chromafora is seeking more partners in recycling, metallurgy, technology, and the mining industry. Interested in learning more? Contact Johan Berg at johan.berg@chromafora.com.
Published articles:
Mining Magazine
Bergsmannen (in Swedish)
