A Quebec Company Figured Out How to Mine Gold Without the Cyanide

Most gold mining still runs on a chemistry that’s been standard for over a century: cyanide leaching, which dissolves gold out of crushed ore but leaves behind toxic waste that has to be contained, monitored, and treated for years. Part of that containment usually means a tailings pond, essentially a manmade lake holding mine waste, stable enough on a normal day but vulnerable to heavy rain, flooding, or an earthquake.

A Quebec firm called Dundee Sustainable Technologies has spent years building an alternative. Their process swaps cyanide for sodium hypochlorite and sodium hypobromite, common industrial chemicals, run in a closed loop where everything gets recycled for reuse rather than discarded. It also works faster: about two hours of contact time to extract the gold, compared to roughly 36 hours for the cyanide method.

The company’s other piece, a patented process called GlassLock, tackles a separate problem: arsenic, which shows up alongside gold in a lot of ore deposits. Instead of leaving arsenic as toxic waste, GlassLock mixes it with silica, recycled glass, and hematite, and turns it into an inert glass that can be handled and disposed of far more easily than a slurry in a tailings pond.

The clearest evidence that this works at real scale comes from Freegold Ventures, a company developing the Golden Summit project in Alaska, one of the larger undeveloped gold deposits in the Americas. In test work using GlassLock, Freegold recovered 95% of the gold in its ore while isolating 98% of the arsenic as inert glass, cutting the material’s toxicity from 7% down to 0.17%, without using cyanide at all. “The results of this program were extremely positive and encouraging for Freegold as it advances the project through pre-feasibility,” the company said.

None of this makes mining environmentally free. Permitting, land reclamation, and ecosystem protection are still enormous parts of any project. But an option that recovers gold in a fraction of the time, without cyanide, and turns a hazardous byproduct into inert glass is the kind of unglamorous chemistry that could reshape what a “clean” mine looks like, one ore-processing plant at a time.