Recovering gold from semiconductor waste with acidless separation
Modern electronics lean on microscopic gold. The hair-fine strands that wire a silicon die to its package are there because nothing else conducts as reliably in those tiny spaces. When those devices reach end-of-life, the gold in their bonding wires does not vanish. It ends up in dross, sweepings, and dusty offcuts from semiconductor back-end lines — what the industry calls wire bonding residue, and one of the most stubborn sources of secondary gold on the planet.
In Australia, the conversation around this material is gaining pace. State-level landfill bans and product stewardship schemes are reshaping how printed circuit boards, integrated circuits, and semiconductor scrap are handled. Recyclers in Sydney, Melbourne, and a growing cluster of regional processors in Queensland now have to think harder about where the value in their feedstock actually sits. For many, the answer is in fractions of a gram — gold trapped in bonding-wire residues that traditional chemistry struggles to recover cleanly.
That is the gap ALS2 is built to close. Developed under Ikoi S.p.A. with backing from the European Union's Horizon 2020 programme, ALS2 is an acidless separation route that pulls precious metals out of complex e-waste streams without aqua regia, cyanide leaching, or the long tail of hazardous waste those processes leave behind. The project positions the technology as a building block for compact, decentralised refining — the kind of footprint that suits a recycler in Perth or a regional player in Townsville as much as a European hub.
What follows is a closer look at how ALS2 actually treats wire bonding residues, what comes out the other end, and why that matters for a market like Australia's, where the gold is small, the regulations are tightening, and the appetite for cleaner refining is growing fast.
Understanding wire bonding residues in semiconductor scrap
Wire bonding joins a chip's contact pads to the lead frame or substrate of its package, typically with gold or copper wire thinner than a human hair. When those packages are scrapped, dismantled, or rejected at quality control, what remains is a mix of metallic fines: sheared wire fragments, spent spools, scrubber dust, etching sludge, and broken substrate pieces. The gold content can run into hundreds of grams per tonne, but it is rarely in a form that responds to a simple smelt.
The trouble is everything that travels with the gold. Bonding residues carry silicon fragments from the die, copper and aluminium from the lead frame and bond pads, organic fluxes, plus traces of platinum group metals that interfere with downstream refining. A recycler who throws bonding residue into a conventional copper- or lead-based smelter often loses gold to slag, struggles with emissions controls, or ends up with a doré bar so contaminated that further refining becomes expensive and slow.
The chemistry gap that traditional methods cannot close
Aqua regia dissolves gold readily but is a poor match for bonding residue. The silicon, copper, and aluminium content consumes huge volumes of acid before the gold reacts, producing a base-metal-laden solution that needs multiple precipitation stages and generates nitrous fumes. Cyanide leaching, common in gold mining towns like Kalgoorlie, is even less practical. Cyanide is highly selective for free gold particles, not the alloyed gold found on bonding wires, and the permitting burden in suburban Australian settings is severe.
Pyrometallurgical routes also run into problems. The fluxes needed to capture gold from bonding residue generate lead- or copper-rich slags that are themselves hazardous waste. Many Australian recyclers operate under strict environment protection authority oversight and would rather avoid adding a smelting step that produces yet another waste stream. The market is asking for a different answer.
| Aspect | Acid-based refining (aqua regia) | Cyanide leaching | ALS2 acidless separation |
|---|---|---|---|
| Main reagents | Nitric acid, hydrochloric acid, SMB | Sodium cyanide, oxygen | Non-acidic leaching media, selective reagents |
| Suitability for bonding residue | Low — high base-metal loading | Very low — alloyed gold resists cyanide | High — designed for complex e-waste matrices |
| Operator safety risk | Fumes, acid burns, NOx handling | Acute toxicity, licence-heavy | Closed-loop, lower chemical hazard |
| Effluent profile | Acidic, metal-laden, requires treatment | Cyanide-bearing, regulated disposal | Reduced hazardous waste volumes |
| Gold recovery from bonding residues | Variable, 70–85% | Below 60% | Targeted above 90% |
| Footprint for small recyclers | Medium to large, ventilated cells | Large, secure bunding | Compact, modular skid format |
What makes the ALS2 process different at its core
ALS2 is built around a non-acidic leaching sequence that targets gold without dragging the rest of the feedstock along. The chemistry leans on selective complexing agents and controlled redox conditions that prefer gold over copper, aluminium, and silicon — the very metals that overwhelm conventional acids. There is no chlorine gas evolution, no nitric vapour, and no cyanide in the loop.
Equally important is the process architecture. The system is a compact, skid-mounted unit with closed-loop reagent recovery, so the leaching medium is regenerated rather than dumped. For an Australian operator watching rising transport costs and tightening landfill levies, the reduction in effluent volume translates directly into a smaller environmental footprint and a lighter compliance load. The Horizon 2020 programme has backed the work because modular, low-impact refining fits the circular economy agenda Australia is moving towards through the National Waste Policy Action Plan.
Step by step through an ALS2 batch
A typical run starts with pre-treatment. Bonding residue is dried, sized, and lightly calcined to burn off organics from the package. The cleaned feedstock enters the main leaching reactor, where the proprietary non-acidic medium dissolves gold selectively over a controlled cycle. Because the medium does not attack silicon or bulk copper the way aqua regia does, far less reagent is consumed per gram of gold recovered.
From the pregnant solution, gold is plated onto a substrate in a recovery cell, leaving a barren liquor that returns to the leaching tank after regeneration. Solid residues leave the system clean enough to enter copper or aluminium recycling streams without further treatment. The cycle is shorter and the mass balance tighter than anything an acid-based refinery can offer on bonding residue.
Recovery rates, purity, and the real value of bonding-residue gold
The numbers are what matter to a recycler running tight margins. Project documentation for ALS2 reports gold recovery from complex e-waste feedstocks in the low- to mid-90 percent range, well above what most aqua regia operations achieve on bonding residue specifically. The recovered metal reaches high purity because the leaching stage simply does not dissolve the metals that would otherwise contaminate the final product.
Purity matters because gold from secondary streams often ends up at the Perth Mint, at specialty refiners in Sydney or Melbourne, or exported for industrial use. Higher purity at the front end means fewer downstream refining steps, fewer assay losses, and a better payability rate. For a Brisbane recycler processing a tonne of mixed semiconductor scrap, the gap between 80 percent and 92 percent recovery is the difference between a marginal job and a profitable one.
Australia's semiconductor waste landscape and what it means for ALS2
Australia does not have a domestic semiconductor foundry industry, but it generates a steady flow of end-of-life chips through datacentre decommissioning, defence electronics disposal, and mining sensor scrappage. Companies such as TES, Cleanaway, and a network of social enterprises already sort and process electronics at scale, with gold traditionally exported as mixed board scrap. State-level regulation is shifting that pattern: New South Wales banned e-waste from landfill in 2019, Victoria followed with its own framework, and other states are tightening collection targets. Researchers at RMIT and the University of New South Wales have highlighted the lost opportunity when bonding-residue gold slips through unrefined.
For Australian operators, ALS2's compact footprint matters. Many recyclers run from suburban industrial estates where councils take a dim view of acid tanks and gas scrubbing stacks, so a modular unit under a standard warehouse roof is a much easier sell at a planning meeting than a traditional refinery hall. The same features suit regional hubs in Kalgoorlie, where the gold heritage runs deep but the workforce is small, and in Hobart, where operators rely on hard yakka and tight community footprints rather than big capital works.
Economics for small and mid-scale e-waste recyclers
Capital cost is the second hurdle after chemistry. The acidless process removes the need for lined acid baths, scrubber stacks sized for NOx, and the bulky effluent treatment plant a conventional refinery demands. Smaller recyclers looking at the unit as part of a circular-economy business case will find the headline equipment price is only part of the story; bigger savings come from lower reagent consumption, smaller waste disposal bills, and faster batch turnaround.
Operating cost in Australia also benefits from reduced heavy logistics. Transporting bonding residue offshore attracts hazardous-waste freight rates and tracking under state environment protection regulations. Treating it locally cuts that leg out, and the recovered gold can be sold in Australian dollars to local bullion dealers or directly into the Perth Mint pipeline. For a 200-kilogram-per-day operation, those savings shorten the payback period. Market signals reinforce the case: the National Waste and Recycling Industry Council has been pushing for greater onshore value recovery, and state procurement policies favour recyclers who demonstrate closed-loop processing under federal product stewardship obligations.
Reach out through the ALS2Project contact page to request the technical datasheet, the recovery-rate benchmarks for bonding residues, and a tailored capex envelope for an Australian installation. A short scoping call is usually enough to map your feedstock, your state-level compliance obligations, and the payback timeline for a skid-mounted ALS2 unit on your site.