The Chemical Problem at the Core
Emerging Alternatives to Cyanide
Cyanide-Free Commercial Technology
Carbon Emissions and the Energy Shift
Mercury Reduction Efforts
Where the Industry Stands
References and Further Reading
Gold (Au) has been extracted from the earth for thousands of years, and today its environmental legacy carries real weight. The industry generates significant greenhouse gas emissions, relies heavily on toxic chemicals, and remains entangled with mercury pollution in informal mining communities. However, tangible shifts are underway across chemistry, energy, and regulation, pushing gold mining toward a cleaner footprint.
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The Chemical Problem at the Core
For well over a century, cyanide leaching has been the dominant method for dissolving gold from crushed ore. Conventional cyanidation recovers gold effectively, but the process leaves behind highly toxic tailings that threaten soil and water systems. In large-scale operations, cyanide is carefully managed, but spills and seepage have caused documented ecological damage globally.1
The other major chemical hazard is mercury (Hg). Artisanal and small-scale gold mining (ASGM), which supplies roughly 20% of the world's gold and employs about 20 million people across more than 80 countries, accounts for 37% of all global mercury pollution and releases roughly 2000 tons of mercury into the environment every year.2
Mercury does not degrade in the environment and accumulates in food chains, causing irreversible neurological damage in humans and toxic impacts on wildlife.2,3
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A study published in Nature Communications found that intact forests near artisanal gold mining in the Peruvian Amazon are absorbing high concentrations of atmospheric mercury, with the region facing the highest known mercury input of any ecosystem globally.3
Emerging Alternatives to Cyanide
Scientific research has accelerated considerably in the search for non-cyanide leaching reagents. A report published in MDPI's Metals identifies thiosulfate leaching, thiourea leaching, halide leaching, and bioleaching as the leading alternatives to conventional cyanidation. Each offers environmental advantages over cyanide, with thiosulfate systems receiving particular attention because thiosulfate is far less toxic and naturally degradable.1
A practical thiosulfate system combining glycine is gaining traction. Researchers have identified that thiosulfate-glycine leaching enhances gold dissolution stability while reducing reagent consumption, and Swedish pilot trials have already demonstrated gold recovery rates of 54–87% at pilot scale, with further scale-up planned.1,4
The challenge with thiosulfate has historically been reagent degradation and consumption, but new formulations are extending stability and making the process more economically viable. Bioleaching presents another frontier. In this approach, acidophilic microorganisms oxidize sulfide minerals and liberate gold particles without any synthetic chemical lixiviant.1,4
Researchers have demonstrated that bacteria such as Bacillus megaterium can generate biogenic cyanide to recover gold, with one ACS Sustainable Chemistry & Engineering study reporting over 87% gold recovery from low-grade ore via biocyanidation. Bioleaching also fits naturally into circular economy models, since microbial consortia can be cultivated from mining waste streams themselves.5,6
Cyanide-Free Commercial Technology
Beyond academic research, commercial-scale cyanide-free gold extraction technology is now reaching the market. RZOLV Technologies, a Vancouver-based company, has developed a proprietary cyanide-free leaching reagent independently validated by SGS for use in heap, vat, and tank leaching systems. Their system delivers high gold recoveries and fast leach kinetics while using a non-toxic formula designed to protect ecosystems.7
According to RZOLV, their solution also opens up previously uneconomical ore types, including tailings, concentrates, and complex mineralization, where cyanide performs poorly. By reducing environmental risk and simplifying permitting processes, cyanide-free technology like this could help mining companies meet tightening ESG standards while maintaining operational profitability.7
Carbon Emissions and the Energy Shift
Chemical toxicity captures much of the sustainability debate in gold mining, but greenhouse gas emissions tell an equally complex story. Global gold production emitted a total of 50.5 million tonnes of CO2 equivalent in 2023, with Scope 1 and Scope 2 emissions accounting for 30.3 Mt and 20.2 Mt, respectively.8
South Africa alone represents 17% of all emissions associated with gold production, despite producing only 4% of global output, largely because its electricity grid is coal-dominated.8
A recent MDPI Sustainability research paper found that emission intensities across Australian gold mines vary sixfold, from a low of 0.26 t CO2-e/oz at the Agnew mine to 1.71 t CO2-e/oz at Mt Rawdon.9
Underground gold mines consistently outperform open-pit operations on carbon intensity, primarily because higher-grade ore requires less material to be mined and processed. The study concludes that a net-zero global gold industry is achievable if clean energy adoption accelerates alongside operational shifts toward underground methods.9
Leading companies are now committing to binding emission targets. All ten of the world's largest gold mining companies have publicly reported emission reduction plans targeting roughly a 30% reduction in Scope 1 and 2 emissions by 2030 and net-zero by 2050.9
Mercury Reduction Efforts
On the ASGM front, regulatory and technical interventions are making measured progress. A UN Environment Program initiative funded by the Global Environment Facility has already reduced mercury use by nearly 370 tonnes across nine countries and aims to cut an additional 512 tonnes across 15 more nations while improving land management over 1.2 million hectares.2
The Minamata Convention on Mercury, signed by over 130 countries, provides the legal framework, though enforcement remains inconsistent across jurisdictions.2
Mercury-free gold recovery techniques, including retort systems that capture and recycle mercury vapor during amalgam burning and gravity concentration methods that eliminate mercury, have been demonstrated to be technically viable in artisanal settings.2
The EPA's Gold Shop Mercury Capture System represents one low-cost solution designed for small operators. The barrier to adoption in many regions remains economic rather than technical, and UNEP programming continues to address that gap by providing both training and equipment subsidies.2,10
Where the Industry Stands
Gold mining still carries a significant environmental burden. Declining ore grades mean more rock must be processed per ounce of gold produced, raising energy, water, and waste intensity even as absolute emission totals inch downward. Renewables supply only 10% of the sector's electricity globally, and 42 primary gold mines still operate on coal-dominant grids.8,11
The direction of change, however, is clear. Cyanide-free chemistry is moving from laboratory to commercial scale. Bioleaching is closing the efficiency gap with conventional methods. Major producers are investing in electrification and renewable power, and the regulatory environment for mercury in artisanal mining is tightening.
Gold mining is becoming cleaner, but the pace of that change will depend on how quickly the industry converts commitment into capital and chemical innovation into standard practice.1,5,7
References and Further Reading
- Xia, L. et al. (2026). Towards Sustainable Gold Extraction: A Review of Non-Cyanide Hydrometallurgical Processes for Primary and Secondary Resources. Metals, 16(6). https://www.mdpi.com/2075-4701/16/6/569.
- (2023). UN environment agency tackles mercury-tarnished gold mining industry. [Online] UN News. Available at: https://news.un.org/en/story/2023/02/1133587.
- Gerson, J. R. et al. (2022). Amazon forests capture high levels of atmospheric mercury pollution from artisanal gold mining. Nature Communications, 13(1), 559. https://www.nature.com/articles/s41467-022-27997-3.
- Berg, J. et al. (2023). Non-toxic leaching and recovery of gold using thiosulfate based lixviant and Selmext metal separation technology. Swedish Mining Innovations. https://www.swedishmininginnovation.se/wp-content/uploads/2023/10/Chromafora.pdf.
- Faraji, F. et al. (2020). A Green and Sustainable Process for the Recovery of Gold from Low-Grade Sources Using Biogenic Cyanide Generated by Bacillus megaterium: A Comprehensive Study. ACS Sustainable Chem. Eng. 9(1). https://pubs.acs.org/doi/10.1021/acssuschemeng.0c06904.
- Abraham, A. P., and Schopf, S. (2026). Bioleaching as a biotechnological tool for metal recovery: From sewage to space mining. Frontiers in Bioengineering and Biotechnology, 13. https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2025.1712157/full.
- Clean Chemistry for the Future of Metal Extraction: The Dawn of Sustainable Metal Extraction. RZOLV Technologies. https://www.rzolv.com/.
- Suganuma, A. (2024). Largest emission reductions in the gold sector. [Online] SKARN Associates. Available at: https://www.skarnassociates.com/insights/emissions-gold-copper.
- Trench, A., Baur, D., Ulrich, S., and Sykes, J. P. (2024). Gold Production and the Global Energy Transition - A Perspective. Sustainability, 16(14). https://www.mdpi.com/2071-1050/16/14/5951.
- (2026). Reducing Mercury Pollution from Artisanal and Small-Scale Gold Mining. [Online] US EPA. Available at: https://www.epa.gov/international-cooperation/reducing-mercury-pollution-artisanal-and-small-scale-gold-mining.
- (2025). Gold Miners Cut Emissions, but ESG Intensity Worsens Amid Rising Prices. [Online] AI Invest. Available at: https://www.ainvest.com/news/gold-miners-cut-emissions-esg-intensity-worsens-rising-prices-2509/.
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