Recovering Silver From Flex Circuit Traces With ALS2 Technology
Australia is one of the world's biggest silver producers, and the country also has a fast-growing pile of discarded electronics, including flexible printed circuits from phones, medical gear, automotive sensors and the ever-popular IoT gadgets. Recovering that silver is not just a question of resource efficiency but a national economic question given the role silver plays in everything from solar panels on outback solar farms to the contact strips in household wiring. Traditional refining relies on strong acids, which brings its own baggage in safety, emissions and waste. ALS2, developed under Ikoi S.p.A.'s acidless separation project with support from the European Union's Horizon 2020 programme, was designed to take a different path: a closed-loop, water-based route that pulls silver out of printed silver traces on flex circuits without the usual acid baths.
The technology is particularly relevant for Australia, where the National Television and Computer Recycling Scheme has been operating since 2011 and where a string of certified e-waste drop-off points, from Officeworks stores in the suburbs to local council tip shops in places like Penrith and Geelong, handle a steady tonnage of end-of-life devices. As the volume of flex circuits in devices keeps climbing, processors in Sydney, Melbourne and Brisbane are watching closely to see if acidless separation can match conventional refining on yield while cutting the regulatory headaches.
Why Silver Traces On Flex Circuits Are A Different Problem
Flexible printed circuits, often called flex PCBs, are everywhere now. They sit inside the hinges of laptops, in foldable phones, in the control boards of modern 4x4s and even in some of the hearing aids produced locally under Australian-licensed brands. Unlike the rigid FR-4 boards that recyclers have been processing for decades, flex circuits are made of polyimide or PET film, with traces of silver, and sometimes silver-palladium or silver-platinum alloys, printed or screen-deposited on top. The polymer substrate does not dissolve in the strong mineral acids used in conventional refining, and the silver layer is usually only a few microns thick, which means the metal content per kilogram of feed is low.
That combination makes conventional acid-based recovery technically possible but economically marginal. The acid has to be heated, the polymer has to be filtered out, and the silver ends up diluted in a large volume of solution. ALS2 was built to address exactly this kind of substrate: a thin metallic film clinging stubbornly to a tough plastic film that refuses to break down.
The Acidless Separation Mechanism
At the heart of the ALS2 process is a sequence of mechanical and aqueous steps that separate the silver-bearing layer from the polymer without using nitric acid, aqua regia or cyanide. The flex circuits are first shredded into small flakes under controlled conditions, which fractures the brittle silver traces and exposes them to the next stage. From there, the shredded material goes through a wet physical separation step that exploits the density difference between the silver-rich particles and the polymer flakes. Silver is dense, about 10.5 g/cm³, and the polymer is roughly 1.3 to 1.5 g/cm³, so a well-tuned hydrocyclone or sink-float tank can do most of the lifting.
What remains is a silver-rich concentrate that still contains fine polymer dust and trace organics. This is where the acidless chemistry comes in. A mild oxidant combined with a chelating agent dissolves the silver selectively, leaving the polymer residue untouched. The silver is then precipitated as a pure compound and reduced to metallic form. The whole circuit runs in a closed loop, with the process water recycled through the plant and the polymer residue either sent to a plastics recycler or used as a reducing agent in a downstream step. There is no nitrous fume, no aqua regia plume, and the only consumable that needs regular replenishment is the chelating agent.
Pre-Processing Flex Circuits For Best Results
In practice, the success of the ALS2 route depends heavily on how the flex circuits are prepared before they reach the leaching stage. Operators around the world have found that a combination of gentle drying, controlled shredding, and eddy-current separation removes the bulk of the non-conductive substrate. In Australian plants, where ambient humidity in places like Darwin and Cairns can be brutal on stored electronics, pre-drying is often built into the receiving bay to prevent the polymer from becoming rubbery and clogging the shredders.
Once the silver-bearing fraction is concentrated, it is calcined at moderate temperature to burn off any residual soldermask, adhesives and the organic carriers in the silver ink. This step is gentle enough to preserve the silver but hot enough to leave a clean, porous silver-oxide-rich ash that dissolves quickly in the chelating solution. The calcination off-gas is passed through a small afterburner and a wet scrubber, which keeps emissions well within the limits set by state environment authorities in New South Wales and Victoria.
Yields, Purity And What Comes Out The Other End
Bench and pilot trials reported in the ALS2 project documentation show silver recoveries consistently in the 92 to 96 percent range from feedstocks containing between 0.3 and 1.2 percent silver by weight, with end-product purity above 99.5 percent when the calcination and chelation steps are tuned for a given alloy. The polymer residue, meanwhile, comes out as a clean, low-ash granulate that can be reintroduced into a plastics recycling stream. Because the process avoids nitric acid, the silver-bearing solution does not contain nitrate salts, which makes downstream crystallisation far easier to control.
For a typical Australian e-waste processor handling around 2,000 tonnes of mixed electronics a year, even a conservative estimate of 0.2 percent recoverable silver in the flex-circuit fraction translates to several hundred kilograms of silver annually. At recent London Bullion Market Association pricing, that is a meaningful line item on a plant's books and a strong argument for upgrading older acid lines.
How ALS2 Stacks Up Against Conventional Refining
When the acidless route is compared head-to-head with a traditional nitric acid leach, the differences show up in operating cost, environmental footprint and workplace safety rather than in pure metal recovery, where the two are within a couple of percentage points of each other. The side-by-side comparison below summarises how the two routes perform across the most important operational metrics for a mid-sized Australian refiner.
| Metric | Conventional nitric acid refining | ALS2 acidless separation |
|---|---|---|
| Silver recovery from flex circuit feed | 90 – 95% | 92 – 96% |
| End-product purity | 99.5 – 99.9% | 99.5 – 99.9% |
| Reagent cost per kg of silver | Moderate to high, acid-dependent | Lower, dominated by chelating agent |
| Wastewater treatment load | High (nitrate, acid neutralisation) | Low to moderate (closed loop) |
| Air emissions | Acid fumes, NOx | Minimal, mainly calciner off-gas |
| Operator PPE requirement | Heavy chemical PPE | Standard industrial PPE |
| Plant footprint for 1 t/day feed | Large | Compact, modular |
| Permit complexity under state EP Acts | High | Significantly lower |
| Suitability for urban or suburban sites | Restricted | Compatible |
For a facility located near a residential area, and many Australian e-waste sites sit on industrial fringes that border suburbs in places like Parramatta, Footscray or Woolloongabba, that last line is often the deciding one.
What It Means For Australia
Australia's e-waste stream is expected to keep growing as households upgrade devices and as the country continues its shift toward renewable energy, where silver paste is used in the front-side metallisation of silicon cells. Local processors, including social enterprises and certified recyclers operating under the NTCRS, have been searching for a way to capture more of that silver without taking on the liability of a full acid refining operation. ALS2 offers a path that fits with the way Australian regulators, including the NSW Environment Protection Authority and Victoria's EPA, have been moving on chemical use and emissions.
There is also a heritage angle. The country has a long history of silver mining at Broken Hill and Cannington, and the idea of keeping Australian silver circulating in useful applications, even if it has to make a quick detour through European technology first, sits well with the public mood around circular economy. A compact ALS2 module could be slotted into existing recovery plants in Wetherill Park, Campbellfield or Yatala without the need for a major civil works programme, and could feed refined silver directly into local bullion dealers or back to the electronics industry.
If you are running an e-waste or WEEE recovery operation and want to know whether ALS2 can be integrated into your current line, the project team at Ikoi S.p.A. is open to technical conversations with Australian partners. Get in touch through the ALS2 website to request the detailed process datasheet, pilot data and a feasibility checklist tailored to your site.