Recovering platinum from catalytic converter honeycombs with ALS2 acidless separation

Spent catalytic converters represent one of the most concentrated secondary sources of platinum group metals anywhere in the world. A single autocatalyst can hold several grams of platinum dispersed across a fragile ceramic structure that was originally designed to clean exhaust gases, not to be dismantled. As global demand for platinum rises alongside the build-out of fuel cells, hydrogen electrolysers and chemical process catalysts, the gap between primary mining output and industrial consumption continues to widen.

Traditional recovery routes rely on aggressive acid leaching, often involving aqua regia or concentrated hydrochloric acid combined with chlorine gas. These processes work, but they generate large volumes of hazardous wastewater, release corrosive vapours and demand strict permitting for transport and storage. Operators also face significant pressure to reduce Scope 1 and 2 emissions linked to chemical handling and high-temperature smelting.

ALS2 is an acidless separation technology developed by Ikoi S.p.A. with support from the European Union's Horizon 2020 research and innovation programme. Instead of dissolving the ceramic monolith with strong mineral acids, the process selectively mobilises platinum from the washcoat while leaving the cordierite substrate largely intact for downstream disposal or reuse. The result is a compact, modular recovery train that fits into urban recycling facilities without the infrastructure burden of a smelter or chemical plant.

For Australia, where millions of vehicles reach end-of-life each year and where the hydrogen economy is being actively scaled from Gladstone to the Pilbara, the case for cleaner secondary platinum supply is particularly strong. Urban mining of catalytic converters complements the country's long-established mining heritage in places like Kalgoorlie, offering a domestic route to a critical metal that would otherwise have to be imported.

Why catalytic converter honeycombs are prime platinum sources

A catalytic converter honeycomb, often called a monolith, is typically made from cordierite, a magnesium aluminium silicate ceramic that is lightweight, porous and resistant to thermal shock. The channels of the honeycomb are coated with a washcoat of alumina, ceria and zirconia, and it is inside this layer that platinum nanoparticles are dispersed along with palladium and rhodium. Because the washcoat is highly porous, the active metal surface area per gram of substrate is enormous, which is why even a small monolith can hold economically meaningful quantities of platinum.

The challenge for recyclers is that this same architecture is hard to break down. The ceramic is brittle but tough to dissolve, the washcoat is chemically bonded to the substrate, and the platinum particles are sub-micron in size. Standard pyrometallurgical routes require the entire monolith to be smelted in a furnace, consuming significant energy and locking the substrate into a glassy slag that has limited further use.

In Australia, the volumes are significant. With Sydney, Melbourne and Brisbane acting as major hubs for imported vehicles from Japan and Korea, the national fleet includes a high share of relatively modern cars whose catalytic converters contain meaningful loadings of platinum, palladium and rhodium. The closure of local manufacturing by brands such as Holden, Ford and Toyota has shifted the country's relationship with vehicles away from assembly and towards aftermarket servicing and end-of-life processing. Recyclers in these metropolitan regions now routinely handle spent converters as part of broader WEEE and end-of-life vehicle streams.

How ALS2 acidless separation targets the ceramic monolith

ALS2 uses a combination of mechanical pre-treatment and a selective chemical separation step that does not rely on concentrated mineral acids. The honeycomb is first crushed and milled to expose the internal channel structure and fracture the washcoat away from the cordierite walls. This produces a fine, heterogeneous powder in which platinum-bearing washcoat fragments are mechanically liberated from the bulk ceramic.

The separation step then operates on this powder without aqua regia, without chlorine gas and without high-temperature smelting. By tuning reagent composition, temperature and residence time, the process preferentially mobilises platinum from the washcoat fragments while keeping the bulk of the cordierite substrate in a stable, filterable solid phase. The platinum-rich liquor is sent to a polishing stage, while the cleaned ceramic residue can be diverted to construction aggregates or disposed of as inert waste.

This targeted approach is what distinguishes ALS2 from traditional hydrometallurgy. Conventional acid leaching aims to dissolve everything and then separate the metals downstream, which forces operators to handle large volumes of corrosive liquor and to manage complex multi-metal purification trains. ALS2 inverts that logic by separating at the front end and leaving a smaller, cleaner stream for final refining.

A practical look at the recovery workflow

The first stage of an ALS2-based line is feed preparation. Whole catalytic converters are opened in a controlled environment, the honeycomb bricks are removed, and any stainless steel or fexmet substrate variants are sorted for separate treatment. The cordierite monoliths are then shredded and milled to a defined particle size range that maximises washcoat exposure without producing excessive dust.

The second stage is the acidless separation itself. Milled substrate is fed into a sealed reactor where the selective reagent system contacts the powder under controlled conditions. Operators monitor pH, redox potential and residence time to keep the process within a narrow operating window. Off-gas is filtered and treated, and the solid residue is washed and dewatered on a vacuum belt or filter press.

The final stage is refining of the platinum-rich intermediate. Depending on target purity, this liquor can be routed through precipitation, ion exchange or electrorefining to deliver a sponge or salt ready for industrial users. Because the input stream is already concentrated and free of large excesses of base metals, the polishing step is shorter and less reagent-intensive than in a conventional line.

Comparing ALS2 with traditional acid-based refining

Criterion	Acidless ALS2 separation	Conventional acid refining
Primary reagents	Selective, low-acidity reagent system	Aqua regia, HCl + Cl₂, HNO₃
Operating temperature	Mild, near-ambient to moderate	Often elevated, with exothermic steps
Wastewater load	Low, closed-loop compatible	High, complex multi-metal liquor
Off-gas treatment	Minimal, filtration-based	Scrubbing required for Cl₂ and NOₓ
Worker exposure	Reduced corrosive and inhalation risk	Routine handling of strong acids and fumes
Substrate fate	Recovered as inert ceramic residue	Smelted into slag or fully dissolved
Footprint for plant	Compact, modular skid	Large tank farm and fume hood array
Regulatory burden in Australia	Aligned with NEPM and Product Stewardship Act	Heavy licensing and transport restrictions

The comparison underscores where ALS2 fits within a modern recycling operation. By replacing bulk acid dissolution with a targeted, modular step, the technology reduces both the environmental footprint and the permitting complexity that has historically constrained where precious-metal refineries can be built.

Sustainability, safety and the circular economy

The environmental case for acidless separation extends well beyond waste volumes. Lower reagent consumption means lower embedded emissions in the chemicals themselves, while the absence of chlorine evolution and nitrogen oxide fumes removes a class of air emissions that has long been associated with precious-metal refining. Workers benefit from an operating envelope that does not require full chemical-resistant suits, supplied-air breathing apparatus or continuous acid-leak monitoring.

In a circular-economy context, ALS2 also enables a more honest material story. The cordierite substrate is not destroyed; it is recovered as a clean, inert ceramic that can be blended into aggregate or used in lower-grade applications. The platinum that is recovered can be traced back to a specific automotive feedstock, which supports chain-of-custody claims for downstream buyers, including hydrogen and fuel-cell manufacturers that increasingly demand responsibly sourced platinum.

Scaling acidless recovery across Australian recyclers

Australia's e-waste and end-of-life vehicle sectors are governed by a mix of national and state frameworks, including the Product Stewardship Act 2011, the National Waste Policy and state-level extended producer responsibility schemes. These frameworks reward operators who can demonstrate lower environmental impact and higher material recovery rates, which is precisely the profile that an ALS2-based line delivers.

For a recycler in western Sydney, outer Melbourne or the industrial corridors around Adelaide, the modular nature of ALS2 is particularly attractive. A compact precious-metals recovery plant can be installed inside an existing WEEE or end-of-life vehicle facility without the buffer zones typically required for acid leaching or smelting. That same modularity makes it feasible to add a second or third train as feedstock volumes grow, rather than committing to a single, oversized refinery from day one.

The Australian hydrogen sector adds a second pull factor. Projects planned across the Pilbara, the Hunter Valley and Tasmania will require substantial platinum loadings for proton-exchange-membrane electrolysers and fuel cells. Sourcing even a portion of that platinum from domestic catalytic-converter recycling would reduce exposure to import volatility and create a visible link between Australia's automotive waste and its clean-energy future.

To explore how ALS2 acidless separation can be integrated into a catalytic-converter recycling line in Australia, contact the ALS2 Project team through the website to request a technical briefing, feedstock assessment and indicative plant layout.