Comparing water consumption in ALS2 and wet chemical recovery

Recovering gold, silver, palladium and other valuable metals from electronic waste can require significant quantities of water. The total depends on the feedstock, equipment, purity target and wastewater controls, but the process route has a major influence. Conventional wet chemical recovery relies on liquid reagents, rinsing and separation stages, while acidless systems are designed to reduce or remove much of that liquid handling.

For recyclers, water consumption is more than a utility bill. Freshwater intake, wastewater treatment, contaminated sludge, chemical storage and discharge permits all affect operating costs and environmental performance. A process that uses less water can also simplify plant design and reduce the risk associated with acidic effluent.

ALS2 is presented through the project technology as an acidless approach for recovering precious metals from electronic waste and WEEE streams. Its potential water advantage should be assessed through a complete site water balance rather than a single headline figure, because ancillary operations still influence the final result.

Why water matters in precious metal recovery

Wet chemical refining uses water as a carrier, reaction medium, washing agent and cooling resource. Printed circuit boards, connectors and other metal-bearing fractions may pass through leaching, filtration, precipitation, rinsing and purification stages. Each operation can create a new liquid stream, even when part of the process water is recycled internally.

Water demand also grows when a plant must meet a high product purity specification. Additional washing can remove residual reagents and soluble impurities, while repeated filtration may require dilution or equipment cleaning. The result is a process with several water-consuming steps rather than a single use point.

The environmental burden extends beyond withdrawal. Acidic or metal-bearing wastewater needs neutralisation and treatment before discharge or reuse. Treatment produces concentrated residues that require controlled management, adding energy and material requirements to the original water demand.

How an acidless route changes the process

ALS2 is intended to separate and recover precious metals without the acid leaching stages associated with many conventional hydrometallurgical routes. Removing those stages can reduce the need for liquid reagent preparation, slurry handling, intermediate rinsing and wastewater neutralisation. The practical benefit is a shorter liquid circuit and fewer opportunities for contaminated water to leave the process.

This does not mean that every ALS2 installation will operate with zero water consumption. Incoming material may need cleaning or conditioning, and water can be used for dust suppression, cooling, floor washing or auxiliary equipment. Some facilities may also use wet separation for a particular feed fraction before the acidless recovery stage.

The meaningful comparison is therefore between total site water demand for equivalent output. A plant should include process water, make-up water, cleaning water, cooling losses and water sent to treatment. When these categories are measured consistently, the reduction created by avoiding acid-based leaching becomes easier to verify.

Where wet chemical recovery uses water

In a conventional wet chemical circuit, water is first used to prepare leaching solutions and bring the feed into contact with the reagent. After dissolution, solids and liquids must be separated. Washing the filter cake or residue is often necessary to recover dissolved metals and reduce chemical carryover, creating additional wastewater.

Downstream recovery can involve precipitation, solvent extraction, ion exchange or electrowinning. These operations may require pH adjustment, rinsing and periodic cleaning. Even when water is recirculated, evaporation, sludge removal and carryover create a need for fresh make-up water.

The quantity varies widely. A closed-loop refinery with advanced filtration may consume far less freshwater than an open or partially recirculating plant. Conversely, a facility processing dirty, mixed or highly variable WEEE may need extra washing to protect equipment and maintain product quality. Comparing only the water used in the leaching vessel would therefore understate the total.

A practical comparison of the two routes

The following comparison describes typical process tendencies rather than fixed consumption figures. Actual performance depends on plant configuration, feed preparation, recirculation, climate and the required metal specification.

Water-use area Wet chemical recovery ALS2 acidless recovery
Main separation stage Uses aqueous reagents and liquid-solid handling Designed to avoid acid leaching and reduce liquid processing
Intermediate washing Often required after leaching, filtration and precipitation Generally reduced, depending on feed preparation and product route
Wastewater generation Acidic or metal-bearing streams are common Lower process-effluent potential, with auxiliary streams still possible
Freshwater make-up Needed for reagent preparation, rinsing and treatment losses Mainly linked to cleaning, cooling, dust control and selected preparation steps
Effluent treatment Neutralisation and metal removal may be required Treatment demand can be lower, but site-specific residues still need control
Water-saving opportunities High recirculation and closed-loop treatment Reduced liquid circuit combined with reuse of necessary auxiliary water

The table shows why “acidless” should be treated as a process distinction, not as an automatic guarantee of a particular litre-per-tonne result. A fair assessment compares the same feedstock, throughput, recovery rate and product quality under equivalent operating conditions.

The variables behind the water balance

Feed composition is one of the strongest variables. Clean, pre-sorted connector scrap may need little preparation, while mixed WEEE can contain dust, plastics, oils, glass and salts. Removing these materials may require washing in one plant, dry classification in another or a combination of methods. Water consumption should be attributed to the full feed preparation route.

Recovery targets also affect demand. Recovering a concentrated precious-metal fraction may involve fewer purification and washing stages than producing separate, high-purity metals. A plant processing copper-rich circuit boards can have a different water profile from one handling mobile phones, plated components or fine shredding residues.

Reuse systems can improve either route. Counter-current rinsing, filtration, rainwater collection, cooling-water recirculation and careful segregation of clean and contaminated streams can reduce freshwater intake. However, recirculation is not free: dissolved salts, suspended solids and chemical residues eventually accumulate and require bleed-off or treatment.

Operational discipline matters as well. Leaks, open washdown practices, poorly controlled spray systems and unnecessary equipment cleaning can add substantial consumption. Metering each major use point allows operators to distinguish unavoidable process demand from preventable losses.

Measuring water consumption fairly

A useful comparison begins with a defined functional unit, such as cubic metres of freshwater consumed per tonne of incoming WEEE or per kilogram of recovered precious metals. Reporting both measures is valuable: feed-based intensity reflects plant throughput, while product-based intensity shows the water associated with actual recovery performance.

The water balance should separate withdrawal from consumption. Water withdrawn from a municipal or local source may be returned after treatment, while evaporated water, moisture leaving with residues and water incorporated into sludge represent consumption. Both indicators should be reported because they describe different environmental pressures.

A complete assessment should record:

Sampling is important when comparing effluent quality. Lower volume does not automatically mean lower environmental risk if the remaining stream is highly concentrated. ALS2 may reduce the volume of chemically contaminated process water by avoiding acid leaching, but every installation still needs controls for dust, residues, cleaning liquids and accidental releases.

Designing for lower consumption

The best water performance usually comes from combining the recovery technology with appropriate plant engineering. Dry handling of suitable feed fractions, enclosed transfer points and efficient dust collection can reduce the need for wet cleaning. Where water is necessary, automated dosing and targeted spray systems are preferable to continuous flow.

Cooling systems deserve special attention. Once-through cooling can dominate a facility’s water demand even when the core recovery process is relatively dry. Closed-loop cooling, heat recovery and monitoring of evaporation can make the difference between a low-water plant and a site with unexpectedly high utility consumption.

Operators evaluating an ALS2 installation can prioritise these actions:

These measures also make comparisons more credible. If ALS2 and a wet chemical route are evaluated at different levels of housekeeping or recirculation, the result may reflect plant management rather than the recovery technology itself.

Turning comparison into an operating decision

A water assessment should be completed during feasibility planning, before equipment selection is finalised. Map every input and output for the proposed ALS2 line, then model the same feed and product specification through the alternative wet chemical route. Include start-up, shutdown, maintenance and emergency conditions, since occasional activities can influence annual consumption.

The result should be reviewed with technical, environmental and financial teams. Lower water demand may reduce treatment equipment, chemical purchases, storage requirements and permitting complexity. It may also improve resilience in regions facing water restrictions or rising utility prices.

ALS2’s acidless design offers a clear basis for reducing the liquid burden associated with precious-metal recovery, particularly where conventional leaching and washing would otherwise dominate the water balance. The strongest business case will come from measured site data, transparent boundaries and a comparison based on equal recovery performance.

Begin by mapping the water flows of your WEEE operation and identify which stages are tied to wet chemistry. Then evaluate how an ALS2-based process could reduce freshwater intake, wastewater generation and treatment requirements while maintaining valuable-metal recovery. A documented water balance can turn the promise of acidless separation into a practical sustainability and operating strategy.