ALS2 acidless recovery vs microwave assisted acid digestion in labs
Recovering precious metals from printed circuit boards, mobile phones and other waste electrical and electronic equipment (WEEE) has become a routine ambition for analytical and recycling laboratories across Australia. Researchers in Melbourne, Brisbane and Perth are routinely asked to quantify gold, palladium and platinum content in shredded electronics, leachate streams and black mass samples. Two laboratory methods have become focal points for this work: the acidless separation approach developed under the Horizon 2020 backed ALS2Project by Ikoi S.p.A., and the well-established microwave assisted acid digestion technique used in hundreds of analytical facilities worldwide.
The Australian context matters. The country generated roughly 539,000 tonnes of e-waste in 2019 and is projected to exceed 800,000 tonnes by 2030 according to the National Waste Report. With landfill bans on e-waste in Victoria, the Australian Capital Territory and Tasmania, recovery streams are landing at certified facilities rather than tips, which creates a strong demand for cleaner downstream processing. Australian labs operating under tight Work Health and Safety regulations are searching for techniques that minimise acid handling without compromising analytical precision.
This comparison examines how ALS2 stacks up against microwave digestion for precious metals recovery at lab scale. The goal is to give technical decision makers a balanced view of throughput, environmental footprint, operator safety, recovery yields, capital cost and pathways to scale. Both approaches serve the Australian urban mining sector, but they arrive through markedly different chemistry.
How ALS2 separates precious metals without bulk acids
ALS2 technology centres on a dry, controlled thermal and chemical route that targets precious metals in crushed electronic scrap or e-waste concentrate. The process relies on reactive gas chemistry and selective volatilisation rather than aqua regia, nitric acid or cyanide lixiviants. In lab scale configurations, ALS2 pilots can process tens to a few hundred grams of feedstock per batch, enough to generate representative recovery data without committing to large pilot infrastructure.
From a laboratory workflow perspective, ALS2 skips the lengthy acid digestion step. Sample preparation still requires mechanical size reduction, magnetic separation to remove ferrous fractions and eddy current separation for non-ferrous metals, but the metallurgical step itself takes place in sealed reactors charged with reagent gases. Because the chemistry is gas phase and temperature driven, there is no liquid acid waste stream to neutralise, which simplifies downstream handling and reduces secondary waste. The Horizon 2020 funded development has emphasised modularity, so the same core reaction chamber can be sized down for a university bench in Sydney or Adelaide.
How microwave assisted acid digestion works in laboratories
Microwave assisted acid digestion has been a workhorse in Australian analytical labs for more than three decades. The technique accelerates the breakdown of solid samples by combining concentrated mineral acids such as nitric, hydrochloric and hydrofluoric with microwave heating inside sealed polytetrafluoroethylene or quartz vessels. Temperatures can reach 200 to 260 °C and pressures routinely exceed 30 bar, which drives rapid oxidation of organic matrices and liberation of metals into solution.
Typical runs last 30 to 60 minutes and consume 0.2 to 1 g of sample per vessel. Modern rotor systems hold 16 to 40 vessels simultaneously, allowing respectable throughput for analytical chemists tasked with monitoring recycling streams or characterising geological samples from Western Australia's goldfields. The digested liquor is then analysed by ICP-OES or ICP-MS to quantify precious metals content, and the technique is supported by consumables, certified reference materials and accredited methods documented in National Measurement Institute guidance and CSIRO technical notes.
The dependency on aggressive reagents, high pressure containment and skilled operators does, however, shape its suitability for different laboratory environments. Microwave digestion is fundamentally an analytical tool, and its role in industrial precious metals recovery is therefore indirect: it provides the data that informs process design.
Comparison at a glance
Both methods target the same end goal of recovering gold, palladium and platinum but arrive there through markedly different routes. The summary below captures the most relevant parameters for lab scale decision making.
| Parameter | ALS2 acidless separation | Microwave assisted acid digestion |
|---|---|---|
| Reagent base | Reactive gases, no bulk mineral acids | Concentrated nitric, hydrochloric, hydrofluoric acids |
| Sample size per batch | 50 to 500 g typical | 0.2 to 1 g per vessel, 16 to 40 vessels |
| Cycle time | 2 to 6 hours including heat up | 30 to 60 minutes per run |
| Primary waste stream | Solid metal rich residue, scrubber salts | Acidic liquor requiring neutralisation |
| Recovery for Au, Pd, Pt | Above 90 percent on suitable feed | Above 95 percent when matrix matched |
| Operator skill required | Process engineering, gas handling | Analytical chemistry, pressure systems |
| Capital cost band (AUD) | Higher, custom built | AUD 60,000 to AUD 180,000 |
| Scale up pathway | Modular, designed for industrial scale | Confined to lab and pilot analytical use |
| Fit with Australian e-waste policy | Strong, supports landfill diversion targets | Indirect, supports data and compliance reporting |
Safety profile and environmental footprint
Safety is a defining differentiator. Microwave assisted acid digestion relies on the controlled release of acid fumes from heated vessels, even when sealed, and requires robust fume cupboards, pressure relief pathways and strict operator protocols. Hydrofluoric acid in particular presents severe inhalation and dermal hazards that demand calcium gluconate gel on standby and rigorous training. Australian labs operating under the Work Health and Safety Regulations 2011 must maintain documented risk assessments for these procedures.
ALS2 removes the bulk acid risk profile. The reactive gases used in the process are handled in closed loops with monitoring, and there is no boiling aqua regia to contain. Operators work with gas cylinders, scrubbing columns and high temperature surfaces, but the absence of strong oxidising acids shifts the hazard inventory considerably. Spill response is simplified, and the lab footprint for secondary containment can be smaller.
From an environmental perspective, the two pathways diverge further. Microwave digestion generates acidic waste streams that require neutralisation, often with sodium hydroxide, before disposal through licensed chemical waste contractors. The salt load from neutralisation can be substantial. ALS2 produces a more concentrated, smaller volume of solid residue that can be sent directly to a metals refinery, reducing the burden on effluent treatment infrastructure.
Recovery yields and analytical precision
For pure analytical characterisation, microwave digestion remains a reference method because it produces a homogeneous solution that integrates cleanly with ICP instrumentation. Detection limits for gold, palladium and platinum in the parts per billion range are routine. ALS2 is positioned as a metallurgical recovery method that yields a metal rich phase suitable for refining, and it can be paired with separate analytical assays to verify concentration.
Recovery yields for ALS2 in published Horizon 2020 reporting indicate silver, gold and palladium recoveries above 90 percent for suitable feedstocks, with performance dependent on particle size distribution and the presence of interfering base metals such as copper and nickel. Microwave digestion with appropriate acid mixes can achieve comparable recoveries, but only when feed size is below approximately 200 micrometres and acid ratios are tuned to the matrix. Both methods reward careful sample preparation.
Selectivity is where ALS2 can shine in a recycling context. By tuning gas composition and temperature profile, operators can target precious metals while leaving base metals in a less reactive phase. Microwave digestion is non-selective by design; everything dissolves, which is useful for total elemental analysis but produces a more complex downstream separation challenge. For labs supporting recycling research rather than pure assay work, this distinction carries real weight.
Cost and scalability for Australian laboratories
Capital cost shapes adoption. A modern microwave digestion system with rotor, vessels and sensors typically sits between AUD 60,000 and AUD 180,000 depending on throughput, while ALS2 lab reactors are projected to land in a higher bracket, reflecting the bespoke nature of gas handling and control systems. Australian labs accustomed to standard analytical procurement cycles will need to plan budgets carefully.
Operating cost patterns are equally informative. Microwave digestion consumes substantial volumes of high purity acids, which in Australia carry both supply chain risk and freight costs given domestic manufacturing capacity is limited. ALS2 relies on reagent gases that can be sourced locally in most capital cities, and energy consumption per batch, while not negligible, is concentrated in a short thermal cycle. For high sample volumes, the operating cost ledger can favour ALS2.
The scalability story is critical for Australian recycling operators such as eCycle Solutions in Victoria and Renewd in Western Australia, who are building capacity to process tens of thousands of tonnes per year. Microwave digestion rarely scales beyond tens of grams per batch, while ALS2 is engineered with scale-up in mind. The same chemistry demonstrated at lab scale can be replicated across larger vessels as feedstock volume grows, which means lab scale evaluation feeds directly into commercial procurement decisions.
Fit with Australian circular economy goals
Australia's Product Stewardship Act 2011 and the National Television and Computer Recycling Scheme set the regulatory backdrop for e-waste management. Co funded by manufacturers and importers, the scheme is creating a steady feedstock for accredited recyclers and, by extension, for laboratories that support them. New South Wales has signalled intent to follow Victoria's lead on landfill bans, which will further concentrate e-waste into formal recovery channels.
Within that landscape, both technologies serve legitimate purposes. Microwave digestion will continue to underpin characterisation work at the CSIRO's mineral resources laboratories in Perth and at university research centres including Monash University and the University of Queensland. ALS2 is well matched to demonstration projects funded through the Australian Recycling Investment Fund.
For laboratories weighing the choice, the practical answer is often to use both. Microwave digestion handles routine characterisation and quality control, while ALS2 supports process development, optimisation and scale-up studies. Australian facilities that build capability in both areas position themselves at the centre of a growing circular economy, contributing data and refined metal to a sector that is rapidly moving from niche to mainstream.
Reach out to the ALS2Project team to discuss pilot testing, sample analysis opportunities or collaborative research with Australian laboratories. Partnerships between European innovators and Australian recyclers, universities and state agencies are unlocking the next generation of clean precious metals recovery, and early engagement ensures local priorities shape the next phase of technology development.