Gold sits inside almost every electronic device we use. A single tonne of printed circuit boards from discarded computers can hold far more gold than a tonne of typical ore, yet most of that value is lost when e-waste is burned or dumped. The challenge has always been how to get the gold out safely. For decades, the default answer in many parts of the world was mercury, a metal so toxic that its use in gold recovery is now one of the largest sources of mercury pollution on the planet. That is finally changing. A mercury-free process, developed by researchers and validated in peer-reviewed studies, now makes it possible to reclaim gold from circuit boards without the health and environmental costs that once came with it.
Why mercury became the problem
Mercury has been used in small-scale gold recovery for a simple reason: it binds to gold particles and forms an amalgam that can be separated from everything else. The trouble starts when the amalgam is heated to drive off the mercury and leave the gold behind. The vapours released are highly toxic, and they do not stay in one place. Studies cited in the research indicate that up to a third of artisanal miners working with mercury show signs of moderate metallic mercury vapour intoxication. Globally, artisanal and small-scale gold mining is estimated to generate around 37% of all mercury pollution, roughly 838 tonnes a year, more than any other single sector.
The scale of the problem is growing because the waste itself is growing. In 2022 the world produced an estimated 62 million tonnes of electronic waste, and only about 22% of it was formally collected and recycled. The rest ends up in landfills, informal dumps, or backyard recovery operations where mercury and open burning are still common. For anyone running a professional recycling operation, this is both a responsibility and an opportunity: the same boards that are hazardous when handled badly are a genuine source of recoverable value when processed correctly.
The mercury-free breakthrough
The new approach, published in the journal Nature Sustainability by a team at Flinders University, replaces mercury with a combination of two much safer ingredients. The first is trichloroisocyanuric acid, a low-cost compound already widely used in water sanitation and pool disinfection. When it is activated with salt water, it dissolves gold from the surface of circuit boards at room temperature and normal pressure. No cyanide, no mercury, no acid fumes, and no need to heat the mixture to dangerous temperatures.
The second ingredient is a sulfur-rich polymer that acts as a selective sorbent. Once the gold has dissolved into the water, this polymer binds only the gold, even when the solution also contains copper, nickel, tin, and other metals from the boards. After the gold is recovered, the polymer can be triggered to break back down into its monomer form, which means it can be recycled and reused in the next batch. The result is a closed-loop process that recovers high-purity gold while keeping the chemistry benign and the reagent reusable.
How to reclaim gold from circuit boards step by step
The chemistry is only one part of the story. In a real recycling plant, gold recovery happens in stages, and each stage needs the right equipment. Here is how a mercury-free workflow fits together from start to finish.
Step 1: Shred the boards to expose the metals
Gold sits on the surface of circuit boards as thin plating on contacts, connectors, and component leads. To make it accessible, the boards first need to be reduced to a manageable size. A four-shaft shredder or a twin-shaft pre-chopper breaks the boards down while keeping the material loose enough for the next stage. This step also frees the components, which is where much of the precious metal is concentrated.
Step 2: Separate the metal fraction
After shredding, the material is a mix of metal and non-metal. Air separation and vibrating screens separate the heavier metal fraction from the plastic and fibreglass, while electrostatic separation can further concentrate the metallic content. This is the same physical separation used in a circuit board recycling plant, and it does two jobs at once: it concentrates the gold-bearing fraction so that less chemical is needed later, and it recovers the copper, which is itself a valuable output. Copper powder purity of 96-98% is achievable with modern dry separation lines.
Step 3: Leach the gold with the mercury-free reagent
The concentrated metal fraction is then treated with the trichloroisocyanuric acid and salt water solution. The gold dissolves selectively into the liquid at ambient temperature. Because the reagent is mild, the operator is not exposed to cyanide gas or mercury vapour, and the waste stream is far easier to manage than the residues left by traditional methods.
Step 4: Capture the gold with the polymer sorbent
The dissolved gold is recovered by passing the solution through the sulfur-rich polymer, which binds the gold and leaves the other dissolved metals behind. Once the polymer is loaded, the gold is stripped from it and the polymer is regenerated for the next cycle. This selective step is what makes the process economical on mixed boards, because it avoids the need to refine a large volume of mixed metal.
Step 5: Melt and cast the gold
The recovered gold is finally melted and cast into bars. A medium frequency induction furnace is well suited to this job, since it melts small batches of precious metal quickly and cleanly without the fuel handling and emissions of a gas-fired furnace. The same furnace can also be used to melt the copper recovered from the boards, so one piece of equipment serves the whole plant.
What this means for recyclers
For a professional e-waste recycler, the shift to mercury-free gold recovery changes the economics in three ways. First, it removes a serious health and liability risk from the operation, which matters more as environmental regulations tighten. Second, it turns a hazardous waste stream into a controlled chemical process with a reusable reagent, cutting both consumable costs and disposal costs. Third, it lets a plant sell a cleaner story to customers and regulators, which is increasingly a requirement for winning contracts in developed markets.
None of this requires exotic machinery. The physical side of the process, shredding, air separation, electrostatic separation, and melting, is exactly what a well-equipped circuit board recycling plant already does. The chemical side is an add-on that fits into the same workflow. That is why the most practical path for most operators is to build the mercury-free chemistry on top of proven mechanical separation equipment, rather than trying to reinvent the whole line.
Building a mercury-free gold recovery line
If you are planning a circuit board recycling operation, the equipment choices you make at the front of the line determine how well the chemistry works at the back. A plant that produces a clean, well-separated metal fraction will use less reagent, recover more gold, and produce a higher-purity output than one that feeds mixed material into the leach step. San Lan Technologies Co., Ltd, a manufacturer of e-waste recycling machinery based in Ganzhou, China, supplies the full range of circuit board recycling equipment needed for this workflow, from shredders and pre-choppers to air separation and electrostatic separation lines, with capacities from 300 kg/hour up to 2000 kg/hour and copper powder purity of 96-98%.
The company also supplies the medium frequency induction furnace used to melt recovered gold and copper into ingots, and its engineers provide custom plant design, installation, and commissioning support for complete recycling lines. For operators who want to move away from mercury without giving up yield, combining proven mechanical separation with the new mercury-free leaching chemistry is the most realistic route to a safer, more profitable plant.
Reclaiming gold from circuit boards no longer has to mean choosing between profit and safety. The science is published, the chemistry is mild, and the equipment to do it at scale already exists. The plants that adopt this approach early will be the ones that set the standard for the rest of the industry.
