Comparing gold conductivity: ALS2 recovery versus electroplating
Gold sits at the top of the conductivity rankings among metals, beaten only by silver and copper on a volume basis but outperforming almost everything when corrosion resistance is added to the equation. That combination explains the metal's enduring presence in connectors, bonding wires, plating baths, and the contact fingers of every printed circuit board made since the 1970s. As global electronics output keeps climbing, the question of where that gold comes from has shifted from purely geological to increasingly circular, and the recovery route chosen has measurable consequences for the metal's downstream performance.
The ALS2 acidless separation process, developed with support from the European Union's Horizon 2020 research and innovation programme, claims a cleaner, safer pathway to high-purity gold from electronic scrap. Its advocates point to lower chemical risk, smaller plant footprints, and the ability to operate close to urban waste streams rather than only next to a sulphuric acid refinery. What matters to engineers, however, is whether the gold that comes out the other end behaves the same way electrically as gold deposited through conventional electroplating, or whether the recovery method leaves a fingerprint on resistivity, contact performance, and long-term reliability.
In Australia, where Kalgoorlie-Boulder still anchors a multi-century gold story and the National Television and Computer Recycling Scheme has been pushing e-waste volumes into formal channels since 2012, the question lands with extra weight. Local refiners in Sydney and Melbourne are handling growing tonnages of end-of-life electronics, and procurement teams from Brisbane to Perth are starting to ask whether secondary gold can genuinely replace primary or electroplated metal in their next generation of products. The answer starts with conductivity.
Why electrical conductivity matters for recovered gold
Conductivity is not just a textbook number. For a contact finish on a high-speed data connector, a one-percent swing in resistivity can change insertion loss budgets, raise operating temperatures, and shorten service life under thermal cycling. Gold's conductivity is normally quoted at around 70 percent of the International Annealed Copper Standard on a volume basis, or roughly 45.2 MS/m, with the exact figure shifting depending on how the sample was prepared.
The way a metal reaches its final form leaves traces in its crystal structure, defect density, residual stress, and impurity profile, and each of those touches the conductivity. Cold-worked gold conducts slightly worse than fully annealed gold. Gold with trapped organics from a plating bath conducts differently than gold that was simply melted and solidified under clean conditions. Gold sourced from a hydrometallurgical route using aqua regia will contain trace chloride complexes if the washing step is rushed, and those traces matter at the contact interface.
For buyers of recovered metal in Australia, the shorthand is often a fire assay purity number, but conductivity is what actually decides whether a recovered bar can be drawn into bonding wire, rolled into ribbon, or evaporated onto a wafer. Engineers in the electronics manufacturing belt around western Sydney, where a sizeable share of Australian contract assemblers operate, routinely request resistivity data rather than just assay certificates.
How the ALS2 acidless separation process works
The ALS2 route sidesteps the aqua regia and cyanide leaching stages that have dominated precious-metals refining for more than a century. Instead, the feedstock is sized, thermally pre-conditioned, and then processed to liberate metals without aggressive acid baths. The chemistry leans on selective leaching media and physical separation steps that recover copper, silver, palladium, and gold in sequence.
What that means for the gold fraction is significant. With no aqua regia, there is no chloride entrapment in the gold grains. With no cyanide, there is no residual alkaline film that has to be boiled off before the metal can be re-melted. The recovered gold tends to come out of the process as a relatively clean granular or sponge form that, after a standard melting and annealing cycle, ends up with grain sizes and textures close to those of conventionally refined primary metal.
The Horizon 2020 backing has also pushed the ALS2 consortium to publish process data on the recovery yields and downstream purity that their compact plants can hit. Reported purities for the gold stream consistently land in the 99.99 percent range for printed circuit board feedstocks, with resistivity measurements reported within a band that sits within one or two percent of the IACS reference.
The structure of electroplated gold layers
Electroplating does not produce a bulk metal. It produces a coating, typically two to thirty microinches thick, laid down over a nickel or copper underplate on a connector, lead frame, or circuit board pad. The gold in that coating is rarely pure 24-carat; most commercial hard gold deposits run around 99.7 to 99.9 percent gold with small additions of cobalt, nickel, or iron that suppress grain growth and harden the finish.
The grain structure of electroplated gold is columnar, with grains that grow perpendicular to the substrate. That grain shape, combined with the embedded hardening elements and the inevitable micro-porosity that lets the underplate peek through, lowers the effective conductivity of the deposit well below that of bulk annealed gold. Hard gold typically measures between 30 and 45 percent IACS depending on thickness and bath chemistry, while pure soft gold used in semiconductor applications can climb back toward the bulk value when deposited carefully.
The practical upshot is that an electroplated gold contact is not a gold conductor in the metallurgical sense. It is a gold-faced nickel or copper conductor, and its conductivity is dominated by the underplate, the contact geometry, and the thickness of the gold skin. Comparing it to a bulk recovered metal is not quite apples to apples, which is why procurement engineers in places like Adelaide's electronics cluster or the manufacturing corridors around Melbourne's outer south-east have to ask careful questions about form factor before they swap one for the other.
Side by side: ALS2 recovered gold compared to electroplated gold
When recovered metal from the ALS2 route is melted, annealed, and drawn into a wire or rolled into a strip, it approaches the conductivity of conventionally refined primary gold. The acidless route avoids the chloride and cyanide residues that can show up in the grain boundaries of gold recovered through traditional leaching, so the as-cast metal has fewer trapped impurities and a cleaner anneal response. After a standard 650 to 700 degree Celsius anneal in a protective atmosphere, ALS2 recovered gold consistently measures within striking distance of the 45.2 MS/m reference.
Electroplated gold sits in a different category. Even the softest, purest deposits are thin films over dissimilar underplates, with conductivity shaped as much by skin effect, porosity, and contact normal force as by the gold itself. In high-frequency applications, only the gold near the surface carries the current, which is why gold plating works at all. In bulk applications, electroplated gold is essentially irrelevant, because there is no bulk.
The numbers below summarise how the two materials compare for typical engineering uses. They reflect published ALS2 process data, industry-standard electroplating specifications, and the kind of values a procurement engineer in Perth, Brisbane, or Hobart would put into a spreadsheet when weighing a switch to secondary metal.
| Property | ALS2 recovered gold (bulk, annealed) | Electroplated hard gold (on Ni underplate) |
|---|---|---|
| Typical form | Ingot, granule, drawn wire, rolled strip | Thin coating, 2–30 microinches over Ni or Cu |
| Purity | Up to 99.99% Au | 99.7–99.9% Au with Co, Ni, or Fe hardeners |
| Volume resistivity | ~2.2 × 10⁻⁸ Ω·m (near pure Au) | Higher, dominated by underplate and porosity |
| IACS conductivity | ~70% (bulk reference) | ~30–45% effective in deposit |
| Grain structure | Equiaxed after anneal | Columnar, normal to substrate |
| Typical thickness | Millimetres (bulk) | 0.05–0.75 micrometres |
| Best fit for | Bulk contacts, bonding wire, ribbon, sputtering targets | Surface finish on connectors, PCB pads, lead frames |
| Residue concerns | Low, no chloride or cyanide entrapment | Bath organics, hardening elements in matrix |
The takeaway for engineers is straightforward. If a design calls for a bulk gold conductor, an alloy addition, or a wire bond, ALS2 recovered metal slots in with minimal performance penalty and meaningful sustainability upside. If a design calls for a corrosion-resistant surface finish on a contact, electroplating remains the standard, and the conductivity of the underlying stack matters more than the gold skin.
What this means for Australian manufacturers and recyclers
Australia's e-waste volumes are growing faster than its population, and the country's two largest schemes under the national product stewardship framework, covering televisions and computers, are pushing more end-of-life equipment through accredited recyclers every year. A growing share of that stream contains gold-bearing boards, edge connectors, and plating residues, and local processors are eyeing the ALS2 compact plant format as a way to capture value on shore rather than shipping concentrates offshore.
For an assembler in the western suburbs of Melbourne weighing a switch to secondary gold, the conductivity question usually reduces to one of fit-for-purpose. Bonding wire for a sensor package can be drawn from ALS2 recovered metal with no real loss in performance. A connector finish still calls for plating, and the recovered metal simply feeds the bath rather than competing with it. The two technologies end up complementing one another, with ALS2 feeding the front end of the plating line and electroplating handling the surface engineering. Australian engineers tend to give any new approach a fair go when the data holds up, and the conductivity numbers above are exactly the kind of evidence that wins them over.
There is also a softer benefit. Australian manufacturers can talk to procurement and customers in plain language about local recovery, lower transport emissions, and avoidance of acid-heavy refining. In a market where customers increasingly ask where their components came from, having a credible domestic source of high-purity gold that performs on the test bench is worth more than a small cost saving from imported metal. No worries, as the local saying goes, when the numbers line up like this.
The ALS2 project team welcomes technical enquiries from Australian recyclers, refiners, and electronics manufacturers interested in pilot deployments, conductivity data, or integration with existing plating operations. Reach out through the project contact page to discuss feedstock samples, plant sizing, and the path to a circular supply of high-purity gold.