Replacing mercury & cyanide in gold mining

The scale of the problem

Roughly 15 to 20 million artisanal and small-scale gold miners work across Sub-Saharan Africa, South America, and Southeast Asia. They produce about 20% of the world’s gold — and roughly 37% of all global anthropogenic mercury emissions, about 2,200 tons a year, the single largest source. Mercury used in amalgamation evaporates during smelting, settles into rivers and oceans, and bacteria convert it to methylmercury, which bioaccumulates in the fish hundreds of millions of poor people eat. This is the exact mechanism that produced Minamata disease. Cyanide leaching, used in larger operations, occasionally fails and releases toxic concentrations straight into drinking-water rivers.

Our stance is that miners are not adversaries. They are people doing dangerous, low-margin work to feed their families — and the most durable fix is the one that pays them to adopt it.

Mercury → borax and retorts

The mercury problem has a persuasive answer because the alternative simply recovers more gold.

Borax smelting (the replacement)

Crushed gold-bearing ore is concentrated by gravity — panning, sluicing, or a centrifuge — down to a heavy mineral fraction, then melted with borax flux, which lowers the melting point and dissolves silicate impurities, leaving pure gold behind. No mercury enters the process, so none escapes into the watershed.

Read the top two rows together: the miner who switches to borax roughly doubles their gold yield while eliminating mercury entirely. That is the whole persuasion. Once the math is shown, the conversion is voluntary, permanent, and faster than any enforcement could achieve. The economic argument is the lock.

Mercury retorts (an occupational safeguard)

A retort is a cheap device that condenses and recaptures mercury vapor when amalgam is burned, instead of letting it drift into the air and the miner’s lungs. It reduces mercury released and protects the person doing the burning. But it is important to be precise about what it is: a retort is occupational protection for miners still using mercury, not a replacement for mercury. The goal is always to move to borax; the retort reduces harm while that transition happens.

Cyanide → a thiosulfate process

Cyanide is harder, because there is no drop-in that simply out-earns it the way borax out-earns mercury. Clean Water Help’s Baguio Gold research replaces cyanide leaching with a two-stage thiosulfate-based process:

The sequence matters. First, persulfate advanced oxidation (AOP) at low pH conditions the solution and breaks down residual organics. Then a copper-ammonium thiosulfate system at higher pH, paired with an anionic resin, recovers the gold — removing cyanide from the process entirely and precipitating heavy metals out of the stream. The result is a discharge with sharply lower toxicity than conventional cyanide leaching: no persistent cyanide salts, and the heavy metals that would otherwise disperse into the watershed are captured as precipitate instead.

The cost is complexity. The process requires careful control of the AOP and thiosulfate stages and the copper-ammonium reagent balance, which is why it fits operations where cyanide is already in use and a supervised chemistry transition is feasible.

Where each fits

You don’t win this by banning the chemical. You win it by handing the miner a process that recovers more gold and happens to poison no one.

The economic case

Stopping a toxin at the source costs a fraction of chasing it downstream. It costs roughly $1,500 to prevent a kilogram of mercury from entering a river by helping a miner switch to safer chemistry — and roughly $50,000 to remove that same kilogram once it has dispersed into sediment, fish, and people. Mercury and lead source control show ROIs above 100:1 in the public health literature. That asymmetry — high upfront leverage, long payoff, some research variance — is exactly the profile foundations and sustainable-development funders are built to carry, which is why this work is partner-funded rather than small-donor-funded.

Clean Water Help in the field

This brief is grounded in our Baguio Gold project in the Philippines, where the thiosulfate research is being developed, and in Ghana’s artisanal gold-mining belt, where our sequence is filters first, then behavior change: deploy heavy-metal treatment so exposure drops immediately, then work with miners to reduce and ultimately replace mercury at the source. If you fund this kind of work, we have validated proposals ready.

Sources & notes

• Chemistry, costs, and recovery figures: Clean Water Help field research (Baguio Gold), summarized in the detoxifying-communities solution table, cross-checked with UNEP Global Mercury Assessment and Minamata Convention reporting.
• Field examples: Baguio Gold research and Ghana mining-belt program.
• The thiosulfate cyanide-replacement is research-stage; borax and retort routes are established ASGM practice. Figures are approximate and context-dependent.

Common questions

Money. Borax recovers ~80% of fine gold versus mercury’s 30–40%. More gold per gram of ore, no mercury — once the economics are shown, the conversion is voluntary and durable.

A cheap device that condenses and recaptures mercury vapor when amalgam is burned. It cuts exposure but is an occupational safeguard for miners still using mercury — not a replacement for mercury.

Our Baguio Gold thiosulfate process: persulfate AOP at low pH, then a copper-ammonium thiosulfate system with an anionic resin at higher pH — removing cyanide, precipitating heavy metals, and cutting discharge toxicity.

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