Recovering Silver From Exhaust Gas Sensor Membranes With ALS2
Exhaust gas sensors, sometimes called oxygen sensors or lambda probes, sit inside the exhaust stream of every petrol-powered car and truck. Their job is to measure the oxygen content of gases leaving the combustion chamber and send a continuous signal back to the engine management system. Inside each sensor, a porous ceramic membrane holds a thin metallic layer where silver plays a critical role in conductivity and thermal stability. As the global vehicle fleet ages, these small components are quietly accumulating in workshops, dismantlers, and end-of-life vehicle processing yards.
Spent sensors are usually shredded with the rest of the catalytic converter stream or sent to landfill, even though the silver in their membranes is recoverable. Conventional methods of pulling silver from such parts rely on aqua regia or nitric acid leaching, which works yet creates hazardous wastewater, fume emissions, and licensing hurdles. The ALS2Project, led by Ikoi S.p.A. with support from the European Union's Horizon 2020 research and innovation programme, has developed an acidless separation route aimed at recovering precious metals from electronic waste and WEEE streams in a much cleaner way.
For Australian operators the timing matters. Distances between collection points are huge, vehicle throughput at authorised treatment facilities is uneven, and the country already has deep expertise in precious-metals handling through its long mining history in Western Australia and Queensland. Bringing silver recovery out of acid-based refineries and into compact, modular units opens new options for recyclers in Sydney, Melbourne, Perth, and regional centres such as Wollongong or Townsville.
The sections below explain how sensor membranes are built, how ALS2 changes the chemistry profile of the recovery step, and what the technology could mean for Australian end-of-life vehicle processing under tightening national and state-level e-waste rules.
Exhaust Gas Sensor Membranes and Their Silver Content
A modern narrow-band oxygen sensor uses a zirconia ceramic element coated on each side with a porous platinum electrode, but the lead wires, contact pads, and shielding layers inside the assembly often contain a silver-rich alloy or a silver-loaded ceramic matrix. Silver is favoured for its high electrical conductivity, its resistance to oxidation at exhaust-manifold temperatures, and its ability to bond reliably to ceramic substrates. The result is a sensor weighing only a few hundred grams yet carrying a measurable fraction of a troy ounce of silver per unit when several are processed together.
Because sensors are treated as a wear item, Australian motorists typically replace them every 100,000 kilometres or when a warning light appears. Independent workshops in suburbs such as Parramatta, Footscray, or Osborne Park handle the bulk of these replacements, generating a steady flow of used units. Many are exported as cores, some are stockpiled, and a portion enters general automotive shredder residue, where silver-bearing fines are lost into mixed dust streams.
That loss is what makes membrane-level recovery attractive. Even a modest recovery rate, applied across the millions of vehicles reaching end-of-life in Australia each year, represents a meaningful secondary supply of silver at a time when primary mining grades are declining and refining capacity sits offshore.
How ALS2 Replaces Acid-Based Refining
ALS2 stands for acidless separation. Instead of dissolving sensor membranes in aggressive acids, the process relies on mechanical and electrochemical separation combined with selective dissolution in benign reagents. Membranes are first shredded and classified, then passed through stages that liberate silver-bearing particles without producing chlorine or nitrogen oxide fumes.
The output is a silver-rich concentrate that can be sent directly to a refinery or, in some cases, used as a feedstock for downstream applications. Because the process avoids the most heavily regulated reagents, plants operate under simpler environmental permits and lower occupational health overheads.
A compact skid format means the unit fits inside a standard industrial bay rather than requiring a dedicated chemical hall. For Australian operators facing constrained footprints in suburban industrial estates, this is a meaningful change.
| Criterion | ALS2 Acidless Separation | Traditional Acid-Based Refining |
|---|---|---|
| Primary reagents | Benign leaching solutions, water-based | Aqua regia, nitric acid, hydrochloric acid |
| Wastewater profile | Low-acidity, low-metal effluent | High-acidity effluent requiring neutralisation |
| Air emissions | Minimal fume discharge | NOx and chlorine fumes, scrubber duty |
| Plant footprint | Modular skid, single bay | Multiple tanks, ducting, scrubbers |
| Silver recovery from membrane fractions | High, with low solution losses | High, but losses in solution and sludge |
| Regulatory burden in Australia | Reduced under most state rules | Triggers EPA licensing, dangerous goods storage |
| Operator training | Standard process technician | Specialist chemist or hazardous-materials training |
The shift in reagent profile is the central appeal of ALS2 for operators who want to add silver recovery to an existing line without inheriting the licensing footprint of a traditional refinery.
Silver Yield, Purity, and Process Economics
Yield figures from sensor membrane fractions depend on the grade of feed, the level of pre-sorting, and the recovery plant layout. Pilot work within the ALS2Project has consistently shown recoveries above 90 percent of the silver present in well-characterised membrane feedstocks. Purity levels of the intermediate concentrate have been reported in the high nineties by mass, with remaining impurities largely being base metals that are simple to remove in a downstream refining step.
The economic picture improves sharply when transport and compliance costs are added. Acid-based refiners in Australia are concentrated near Perth and Adelaide, so any feedstock generated in Brisbane, Hobart, or Darwin pays a long-haul freight bill before recovery begins. Distributed compact units close that gap by allowing recovery to happen close to the source of the scrap, reducing both freight and the security risk of moving silver-bearing concentrates over long distances.
For small and mid-tier recyclers, the capital outlay of an ALS2 unit is modest compared with a fully permitted acid refinery, and the operating cost is dominated by electricity, water, and labour rather than reagent consumption. That changes the break-even volume calculation and makes the technology accessible to operators handling as few as a few tonnes of sensor-bearing scrap per year.
Compact Recovery Plants and Modularity
Modularity is one of the design priorities of the ALS2Project. Each stage of the process is built into a skid that can be combined, scaled, or relocated depending on the throughput of the host facility. A workshop that already handles catalytic converter processing can add an ALS2 line alongside, while a regional collection centre can host a smaller configuration that pre-concentrates silver for shipment to a refining partner.
Australia's geography rewards this kind of flexibility. With major population centres separated by thousands of kilometres, and many regional towns hosting small dismantlers, the option of placing compact recovery equipment close to feedstock sources avoids the inefficiencies of centralised processing. A unit commissioned in Townsville or Launceston can serve a catchment radius that would otherwise be uneconomical.
The modular approach also simplifies maintenance and upgrades. When ALS2 is updated with improved separation stages, individual skids can be swapped without taking the entire plant offline, limiting revenue loss for the host operator.
Australian Market Context for End-of-Life Vehicles
Australia's light vehicle fleet runs to more than 20 million registered vehicles, with the heaviest concentrations in Greater Sydney, Greater Melbourne, and South East Queensland. These are also the regions where authorised treatment facilities process the largest volumes of end-of-life vehicles and where the density of exhaust gas sensor replacements is highest. Right-hand-drive vehicles dominate the parc, but a meaningful share of newer arrivals share component platforms with European and Asian models, which means the same sensor designs and silver loadings are common across most vehicles processed locally.
The domestic scrap metal market is well developed, yet precious-metal recovery has historically been the preserve of large operators who can afford the chemistry, the licensing, and the security infrastructure that acid-based refining demands. Smaller dismantlers, including many Indigenous-owned and social-enterprise recyclers in regional areas, have been locked out of that value chain even though they handle a meaningful slice of Australia's end-of-life vehicle throughput.
ALS2 offers a route into that value chain without requiring those operators to take on the regulatory profile of a chemical refinery. For the broader Australian circular-economy conversation, that is a step towards keeping more of the silver generated by vehicle use inside the domestic economy rather than losing it to mixed shredder residue.
Regulatory Landscape Across Australian States
The legal environment for recovering precious metals from electronic waste sits at both federal and state level. The Product Stewardship Act 2011 gives the federal government the power to schedule products and require industry-led stewardship schemes, while state and territory environment protection authorities set the operational rules for handling, transporting, and processing waste electrical and electronic equipment.
Victoria's ban on e-waste to landfill, New South Wales' extended producer responsibility reforms, and Western Australia's controlled waste framework all shape what an operator can and cannot do with sensor-bearing scrap. Because ALS2 avoids the most heavily regulated reagents, the technology generally sits below the licensing thresholds that trigger dangerous goods storage or major hazard facility obligations in most jurisdictions.
The European Union's Waste Electrical and Electronic Equipment Directive, which informs much of the underlying research behind the ALS2Project, has shaped Australian policy thinking over the past decade. Local recyclers preparing for tighter rules around 2026 and beyond are watching technologies like ALS2 as a way to meet upcoming recovery targets without taking on the cost and complexity of acid-based infrastructure.
Working Together on Sensor Recycling in Australia
Australian recyclers, automotive groups, and research partners have a clear opening to pilot ALS2 in real operating conditions. Workshops and authorised treatment facilities in Sydney, Melbourne, Brisbane, and Perth that handle meaningful sensor throughput are well placed to host a demonstration line, and the ALS2Project team is open to discussions with operators, government agencies, and industry bodies interested in evaluating acidless separation for precious-metals recovery.
Operators who want to understand the technology in more detail, run a feedstock assessment, or explore a placement partnership can reach out through the ALS2Project website to begin a conversation about pilot deployment, training pathways, and integration with existing end-of-life vehicle processing capacity.