How feedstock pre-drying changes ALS2 energy costs
Electronic waste rarely arrives at a precious-metals recovery plant in a perfectly uniform condition. Printed circuit boards, connectors, mobile phones, cables and mixed WEEE may carry rainwater, wash water, oils, dust or moisture absorbed during storage. That water has no recoverable metal value, yet it can have a meaningful effect on the energy required to process each tonne.
For an ALS2 acidless separation plant, feed preparation is therefore an important operating decision. Pre-drying can improve consistency, reduce the amount of water entering downstream stages and support stable separation conditions. However, drying itself consumes heat or electricity, and the energy balance depends on the feedstock, local climate, equipment design and available waste heat.
This question is especially relevant in Australia, where collection networks may move material from regional areas to facilities around Sydney, Melbourne, Brisbane or Perth. Long transport routes, outdoor storage and seasonal humidity can change the moisture profile before the feed reaches a compact precious-metals recovery plant.
The right objective is not to remove every gram of water. It is to control moisture at the lowest practical energy cost while preserving valuable metal-bearing fractions and maintaining the safety advantages of acidless refining.
Why moisture matters in electronic waste
Moisture adds mass without adding recoverable value. If a tonne of incoming material contains 10 per cent water, approximately 100 kilograms must be heated, evaporated and removed before that portion of the feed is effectively dry. The energy required includes sensible heat to raise the water temperature and latent heat to convert liquid water into vapour.
The theoretical latent heat of evaporation is substantial, commonly estimated at about 2.3 megajoules per kilogram near typical drying temperatures. Real plants use more because of heat losses, air movement, equipment inefficiency and the need to warm the solids. A simple energy estimate is therefore useful, but it should not be mistaken for a guaranteed plant consumption figure.
Water can also affect handling. Damp shredded boards may agglomerate, reducing screening efficiency and making size classification less precise. Sticky dust can foul conveyors or filters, while wet material may create inconsistent residence times. These effects can raise energy use indirectly through reprocessing, stoppages and reduced throughput.
How pre-drying affects ALS2 performance
ALS2 technology is designed around acidless separation and recovery of precious metals from suitable electronic waste streams. Stable feed preparation helps the process receive a more predictable material mix. With less free water, downstream equipment may operate closer to its intended temperature, concentration and loading conditions.
Pre-drying can also reduce dilution. Where water accompanies the feed into a process stage, additional energy may be needed to heat that water or manage it through separation and recovery steps. Removing excess moisture before treatment can reduce this burden and support more consistent gold, silver, palladium and other precious-metal recovery conditions.
The benefit is feed-specific. Clean, dry printed circuit boards may need little or no thermal drying, while mixed WEEE stored outdoors can require substantial conditioning. A plant should measure moisture by batch, product category and season instead of applying one fixed drying target to every delivery.
The energy balance behind drying
A basic calculation starts with the moisture removed. For example, reducing one tonne of feed from 12 per cent moisture to 5 per cent removes roughly 74 kilograms of water, assuming the figures are expressed on a wet basis. At an idealised evaporation requirement of around 2.3 megajoules per kilogram, the latent heat alone is approximately 170 megajoules.
Actual energy demand will be higher. Industrial dryers may require electrical energy for fans, conveyors and controls, along with thermal energy for hot air, steam, thermal oil or direct heating. Depending on the equipment and insulation, total energy could be materially above the theoretical minimum. This is why a site-specific heat and mass balance matters more than a generic drying benchmark.
The avoided energy must be counted as well. If the ALS2 process would otherwise heat or carry the same water through later stages, pre-drying may transfer energy use from the main process to the dryer rather than eliminate it. The strongest business case occurs when drying uses low-cost waste heat and also prevents operational losses such as blockages, unstable feed rates or repeated treatment.
Choosing the right drying method
Mechanical dewatering is often the first option where free water is present. Draining, screening, centrifuging or pressing can remove liquid water with far less energy than evaporation. These methods are particularly relevant after wet collection, washing or exposure to rain. Removing free water before thermal drying can significantly reduce the thermal load.
Thermal systems may include low-temperature belt dryers, rotary dryers, cabinet dryers or controlled hot-air units. The preferred design depends on particle size, dust characteristics, throughput and the sensitivity of plastics and electronic components to heat. Excessive temperature can damage polymers, create unwanted fumes or alter the physical properties needed for separation.
Waste heat integration can change the calculation. Warm air from motors, compressors or other plant equipment may be recovered, while heat from a nearby industrial process can supply part of the dryer duty. In Australia, a facility with rooftop solar may reduce the electricity cost of fans and controls during daylight, but solar generation does not automatically solve a high-temperature heat requirement.
Australian operating conditions
Moisture risk varies widely across Australia. A recycler in Brisbane or coastal Queensland may receive feed exposed to high humidity and intense summer rainfall, while a Melbourne facility may face damp winter storage conditions. Perth’s dry climate can reduce ambient moisture in some periods, although outdoor exposure and transport practices still matter.
Local logistics are equally important. E-waste collected through council drop-off sites in Melbourne, Sydney or Adelaide may be stored for weeks before consolidation. Material arriving from remote Western Australia, regional Queensland or the Northern Territory can spend longer in transport and may be covered, uncovered or exposed to condensation at different points in the chain.
Regulation and community expectations also shape feed preparation. Victoria’s landfill ban for e-waste has encouraged separate collection and diversion, while the National Television and Computer Recycling Scheme has increased the movement of regulated electronics through formal recycling channels. These streams can differ greatly from informal mixed loads, so moisture specifications should be linked to procurement and acceptance procedures.
Electricity pricing is another local consideration. Demand charges, time-of-use tariffs and network constraints can make electrically heated drying expensive during peak periods. A plant near Sydney or Melbourne may therefore benefit from scheduling drying when power is cheaper, using stored heat, or prioritising mechanical dewatering before electrical conditioning.
Measuring moisture before investing
A moisture management programme should begin with representative sampling. Surface moisture alone can be misleading because shredded boards, dust and porous packaging may retain water internally. Samples should be taken from different parts of a delivery and tested using a consistent method, with separate records for supplier, material type and storage duration.
Useful data includes wet mass, dry mass, ambient conditions, drying time, energy input and throughput. Operators can then identify a practical target range rather than pursuing an unnecessarily low moisture level. The target should support safe feeding and stable ALS2 operation while avoiding energy expenditure that produces no measurable recovery or reliability benefit.
A simple trial can compare untreated feed, mechanically dewatered feed and thermally pre-dried feed. Key measures include kilowatt-hours per tonne, thermal energy per tonne, dryer capacity, dust emissions, downtime, particle classification and precious-metal recovery. The most economical option may be partial drying, particularly when the final few percentage points of moisture require disproportionate energy.
Designing a lower-cost preparation strategy
The most efficient sequence is usually to prevent water entering the system, remove free water mechanically and use thermal drying only where it creates a clear process benefit. Covered storage, sealed transfer points and rapid drainage after wet collection can reduce the starting moisture before any energy is purchased.
Supplier specifications can support this approach. Contracts may define acceptable moisture ranges, packaging requirements and procedures for loads affected by rain or wash water. A rejection or surcharge policy should be applied carefully, since overly strict limits could reduce access to valuable regional feedstock. It may be better to price loads according to measured moisture and treatment cost.
Dryer controls should respond to actual feed conditions. Variable-speed fans, adjustable residence time and temperature control can prevent overdrying light loads. Heat recovery, insulation and air recirculation can further reduce losses, while dust collection must be designed for fine electronic-waste particles and potential combustible dust hazards.
The energy model should include capital cost, maintenance, labour, throughput and lost production during cleaning. A dryer that saves energy per tonne but becomes a bottleneck may increase total operating cost. In a compact ALS2 plant, footprint and integration are particularly important because every additional preparation stage must justify its space and complexity.
| Feed condition or operating choice | Likely energy effect | Main operational implication |
|---|---|---|
| Dry, covered printed circuit boards | Low drying demand | Focus on screening and consistent feed sizing |
| Damp mixed WEEE | Moderate to high demand | Measure moisture and separate wet fractions |
| Free water removed mechanically first | Lower thermal demand | Add drainage, pressing or centrifuging capacity |
| Thermal drying to a very low moisture target | Potentially high demand | Check whether the extra dryness improves recovery |
| Dryer using recovered waste heat | Lower purchased energy | Requires compatible heat source and controls |
| Drying during peak electricity periods | Higher operating cost | Consider scheduling or thermal storage |
| Outdoor storage in humid or rainy conditions | Higher and more variable demand | Improve covers, drainage and stock rotation |
Turning moisture control into a process advantage
Feedstock pre-drying should be treated as part of ALS2 plant design rather than an isolated utility decision. The relevant comparison is the total energy and operating cost of the preparation route against the energy, reliability and recovery benefits delivered downstream.
A staged approach reduces risk. Begin with moisture testing and a short production trial, then establish a material-specific target. If the data shows that drying improves throughput or recovery, integrate mechanical dewatering, heat recovery and automated control before expanding thermal capacity.
For Australian recyclers, this approach also improves resilience. It can accommodate seasonal rainfall, long-distance logistics and variations between council, commercial and industrial collection streams. Better feed control supports a cleaner, safer precious-metals recovery operation while preserving the central advantage of acidless separation: reducing dependence on conventional acid-based refining chemistry.
ALS2Project provides a foundation for evaluating these decisions through the broader goals of resource efficiency, WEEE recycling and cleaner recovery technology. Operators, technology partners and recyclers can use measured moisture data to assess where pre-drying creates genuine value and where simple storage or mechanical handling changes are the better investment. Contact the ALS2Project team to discuss feed characterisation, energy modelling and the integration of efficient preparation into a compact precious-metals recovery plant.