How Particle Size Shapes ALS2 Recovery Rates From Shredded Boards
Electronic waste is accumulating faster than almost any other waste stream in Australia, with the country generating more than 200,000 tonnes of discarded electronics every year. Much of this material, including televisions, computers, and increasingly Internet of Things devices, ends up in the national recycling system under the National Television and Computer Recycling Scheme. Within that stream, printed circuit boards are the most valuable fraction because they concentrate copper, gold, silver, and palladium onto a relatively small mass of material.
The challenge for processors is that the value locked inside these boards is only accessible once the boards are broken apart. Precious metals sit as thin layers, plating, and wire bonds that must be liberated from the underlying fiberglass-reinforced epoxy substrate. The smaller the particles, the more thoroughly those metals are exposed, but the relationship between size and yield is not linear. There is a sweet spot where liberation is high enough for efficient extraction without incurring the processing penalties of ultra-fine dust.
ALS2 is Ikoi S.p.A.’s acidless separation technology, developed to recover precious metals from shredded electronic scrap without the hazards of aqua regia or cyanide leaching. Backed by the European Union’s Horizon 2020 research programme, the system relies on chemical-free reactive media to dissolve and selectively precipitate target metals. Like any hydrometallurgical route, its performance depends on how thoroughly the feed has been prepared, and that preparation starts at the shredder.
The following sections explore how particle size influences recovery rates in the ALS2 process, drawing on the technical parameters relevant to Australian operators working with mixed WEEE streams from Sydney, Melbourne, Perth, and regional collection points.
Why Comminution Matters in Acidless Separation
Comminution is the controlled reduction of a material into smaller pieces, and it is the first physical step that determines what any downstream chemical process can achieve. For acidless separation, the goal of size reduction is not simply to make particles tiny but to expose the metal-rich surfaces that the reactive medium can act upon. A 50-millimetre chunk of laminate hides most of its copper traces beneath a sealed resin layer, while a 2-millimetre flake presents those traces directly to the reaction chamber.
In conventional acid-based refineries, very fine grinding is often used because aggressive reagents can attack metals even when they remain partially occluded. ALS2 operates differently. Its reactive medium works at the surface, where contact between the metal and the solution drives the chemical reaction. If a particle is too large, the reaction cannot reach the metals sealed inside, and recovery falls. If a particle is too small, surface oxidation, losses to filtration, and the cost of shredding all rise without a proportional gain in yield.
The practical implication is that operators must choose a target size range that balances liberation, throughput, and energy use. For mixed consumer boards collected through kerbside drop-off points in Brisbane or from commercial demanufacturing lines in Adelaide, this typically means a controlled two-stage shred rather than a single aggressive grind. The first stage breaks boards into manageable flakes, and the second stage refines the distribution to the window where ALS2 performs best.
Liberation and Surface Exposure at Different Mesh Sizes
Liberation describes the degree to which a target metal is physically separated from the surrounding matrix. In a printed circuit board, gold plating on edge connectors sits as a continuous film, copper traces run as discrete lines, and solder joints form small droplets of a lead-tin alloy. Once the board is shredded, each of these features ends up in a different size fraction depending on how the cutters acted on the material.
Coarse fractions above 8 millimetres tend to retain intact substrate pieces with metal still embedded. These pieces are visible in the field across Australian e-waste facilities, where operators notice that large laminates still show traces of copper when inspected manually. Mid-range fractions between 1 and 4 millimetres typically contain well-liberated flakes, broken traces, and detached connector pins. Fine fractions below 1 millimetre contain the dust, broken plating, and the smallest solder droplets, but they also lose some material to over-handling.
Surface exposure follows a predictable pattern. Each halving of particle size roughly doubles the surface area available for reaction, but only until particles become so small that handling losses start to dominate. This is why ALS2 studies consistently find a recovery peak somewhere in the sub-4-millimetre range, where liberation is high, surface exposure is broad, and dust losses remain manageable. Operators in Western Australia’s gold-focused mining sector will recognise this trade-off, because comminution circuits in gold processing face the same balance between liberation and over-grinding.
Measured Recovery Rates Across Size Fractions
Recovery rates in precious-metals extraction are usually reported as a percentage of the assayed content of the feed. For ALS2, the size fraction fed into the reactor strongly influences what comes out. The table below summarises indicative recovery performance observed across comminution grades for typical mixed-board feeds.
| Particle Size Fraction | Gold Recovery | Silver Recovery | Copper Recovery | Palladium Recovery |
|---|---|---|---|---|
| Greater than 8 mm | 55–65% | 50–60% | 40–50% | 45–55% |
| 4 mm to 8 mm | 78–85% | 75–82% | 70–78% | 76–84% |
| 1 mm to 4 mm | 92–96% | 90–94% | 88–93% | 91–95% |
| 0.25 mm to 1 mm | 95–97% | 93–96% | 92–96% | 94–97% |
| Below 0.25 mm | 90–93% | 88–92% | 89–94% | 87–91% |
The data show a clear pattern. Recovery rises sharply as particle size drops from the coarse range into the 1–4 millimetre window, plateaus across the sub-millimetre range, and then begins to retreat at very fine sizes. The retreat at the smallest fraction reflects material losses through filter cake formation, electrostatic adhesion to ducting, and the tendency of fine metallic flakes to oxidise before they enter the reaction stage.
Copper behaves slightly differently from gold and palladium because so much of it is present as thick traces and vias rather than plating. Its recovery curve rises more gently and falls more gradually, reflecting the broader distribution of copper features across size fractions. Silver, which appears mostly as plating and in solder, tracks closely with gold, while palladium shows the strongest sensitivity to over-grinding because it is concentrated in the smallest components, such as multilayer ceramic capacitors, that shatter into fine dust.
Operational Implications for Australian Plants
Australia’s e-waste processing landscape is shaped by state-level landfill bans, federal product stewardship rules, and a strongly decentralised collection network. New South Wales, Victoria, South Australia, and the Australian Capital Territory have all banned certain categories of e-waste from landfill, which directs more material into formal recovery channels. Plants in Sydney and Melbourne therefore receive relatively well-sorted feeds, while regional facilities in Hobart or Cairns often receive mixed loads that include everything from industrial control boards to consumer gadgets.
The particle size decision interacts directly with how these feeds are handled. A plant receiving well-sorted mobile-phone boards, which are small and rich in gold plating, can run a tighter, finer grind without over-processing losses. A plant receiving mixed consumer boards with large motherboards, such as the desktop towers that arrive in bulk through the NTCRS, benefits from a two-stage process that targets the mid-range fraction where ALS2 peaks. Energy cost per tonne also rises with finer grinding, which matters in a country where industrial electricity prices remain among the highest in the Organisation for Economic Co-operation and Development region.
Local market signals support investment in finer comminution. Australia’s domestic gold refineries and bullion dealers actively seek responsibly sourced secondary gold, and growing scrutiny from investors and regulators around environmental, social, and governance performance is pushing processors towards chemical-free routes such as ALS2. A plant that can demonstrate high recovery from a controlled size fraction has a stronger commercial story than one relying on aggressive chemistry to compensate for poor feed preparation.
Tuning Shredding Equipment for Maximum Yield
Equipment selection is where the theoretical recovery curves meet operational reality. Low-speed, high-torque shredders with cutting screens are well suited to producing the mid-range fraction that ALS2 favours, because they cut rather than smash the laminate. High-speed hammer mills can drive material finer, but they generate heat and dust that can oxidise freshly exposed metal surfaces before they reach the reactor. The choice between them is rarely about one being better than the other and almost always about the downstream target fraction.
Screen aperture is the single most useful operational control. Switching from a 10-millimetre screen to a 4-millimetre screen typically shifts the mass distribution from a coarse-skewed profile to a balanced profile centred on the recovery peak. Below 1 millimetre, the marginal gain in recovery rarely justifies the additional energy, screen wear, and dust management required. Many operators therefore install a secondary screen or air classifier that pulls out the fines and routes them to a separate, slower ALS2 pass.
Process monitoring closes the loop. Inline sensors that measure particle size distribution, combined with periodic assays of feed and residue, allow operators to detect drift before recovery suffers. This is particularly important for plants serving multiple collection regions, because feed character changes between summer holiday intake peaks and quieter periods. Keeping a stable size distribution within the recovery-peak window is what separates a consistent high-yield operation from one chasing batch-to-batch variability.
Australian plants ready to evaluate ALS2 for their own WEEE streams can request a feed-characterisation study through the ALS2Project contact channel, where Ikoi’s engineering team reviews local comminution setups and recommends a target size window tailored to the specific board mix and throughput goals.