Corrosion Control in ALS2 Equipment for Chloride-Rich E-Waste Feeds

Recovering precious metals from electronic waste requires equipment that can tolerate changing feed chemistry, suspended solids and repeated wet-process cycles. Chloride-rich material is particularly important because salts can promote localised attack, weaken vulnerable components and accelerate failures where deposits collect around joints, pumps or instruments.

ALS2 acidless separation technology is designed as a cleaner alternative to conventional acid-based refining, yet “acidless” does not mean that corrosion can be disregarded. Electronic scrap may contain chloride salts, residual process chemicals, PVC-derived contaminants and saline moisture. Careful materials selection, process control and inspection are therefore central to reliable operation in a compact precious-metals recovery plant.

Why Chlorides Create A Difficult Operating Environment

Chloride ions are aggressive because they can penetrate or disrupt the passive oxide layer that protects many stainless steels. The result may be pitting, in which small cavities deepen below an apparently sound surface, or crevice corrosion beneath gaskets, clamps, deposits and overlapping components. These forms of attack can remain hidden until a leak or sudden loss of mechanical integrity occurs.

Risk tends to increase when chloride concentration combines with elevated temperature, stagnant conditions or an acidic or strongly oxidising solution. A feed that appears acceptable in bulk can still create severe local conditions inside a dead leg, around a partially blocked screen or beneath settled fines. In a recycling plant, these conditions can change from batch to batch as circuit boards, cables, connectors, batteries and mixed electronic assemblies enter the preparation line.

Corrosion can also be intensified by abrasion. Glass fibres, ceramic particles, metal fragments and shredded housings may wear protective surface films, exposing fresh metal to chloride-bearing liquor. Vibration, thermal cycling and galvanic contact between dissimilar metals add further stress. Equipment performance should therefore be assessed against the combined effects of chemistry, solids loading and mechanical duty rather than chloride concentration alone.

Feed Variability In Australian Recycling Operations

Australian recyclers commonly manage long transport distances between collection points, sorting facilities and downstream processors. A load assembled in Melbourne may have a different moisture and contamination profile from one received in Brisbane or Perth. Storage in an open yard, exposure to coastal air and irregular collection schedules can introduce additional salt, condensation and dirt before the material reaches a recovery plant.

The feed may include equipment from households, offices, telecommunications networks and data centres. Digital consumption spans phones, computers, servers and entertainment products; even online gaming guides sit within a wider digital economy that depends on continually replaced electronic hardware. This variety makes front-end inspection important, especially where lithium batteries, power supplies, plated connectors or chemically contaminated parts are mixed together.

Australian operators must also work within a state and territory regulatory landscape. The Product Stewardship Act 2011 supports national approaches to responsible product recovery, while the National Television and Computer Recycling Scheme covers specified categories of televisions and computers. State environmental licences, waste transport requirements and workplace health and safety duties still apply to the individual facility. A corrosion-resistant design helps protect compliance by reducing leaks, unplanned shutdowns and contaminated wash water, but it does not replace environmental controls.

Selecting Materials For Wet Process Equipment

Stainless steel can be suitable for some ALS2 equipment, but grade selection must follow the actual process envelope. General-purpose grades may be vulnerable to chloride pitting, particularly in warm or stagnant liquor. Higher-alloy stainless steels, duplex grades or nickel-based alloys can offer greater resistance in selected duties, although their performance depends on fabrication quality, weld treatment, surface finish and the combined chemistry of the stream.

Polypropylene, high-density polyethylene, PVC-compatible systems, PVDF, PTFE and fibre-reinforced plastics may be useful for tanks, pipework, linings and selected process components. These materials often provide strong resistance to chloride-bearing solutions, but temperature, pressure, ultraviolet exposure and mechanical impact must be checked. A plastic tank that performs well chemically may still require protection against sharp scrap, forklift damage or distortion under heat.

Small components deserve the same attention as major vessels. Pumps, valves, heat exchangers, screens, level probes and fasteners can become the first points of failure. PTFE-lined valves may suit one service, while elastomers such as EPDM or FKM may be chosen for another after checking temperature, solvent exposure and swelling behaviour. Galvanic couples should be avoided or electrically isolated where dissimilar metals contact a conductive chloride solution.

Designing Out Crevices, Deposits And Leaks

Good corrosion performance begins with geometry. Smooth internal surfaces, continuously drained pipework and accessible inspection points reduce the accumulation of chloride-bearing fines. Welded joints should be finished appropriately for the service, with sharp corners and unnecessary overlaps avoided. Dead legs, unvented high points and low spots that cannot be emptied create stagnant zones where local chemistry can become much harsher than the main stream.

Tanks and vessels should allow complete draining and practical cleaning. Where solids settle, mixing and agitation need to be strong enough to prevent persistent deposits without causing excessive erosion. Pumps should be selected for the particle size and concentration expected from the e-waste feed, while screens and filters require a maintenance arrangement that does not encourage bypassing or prolonged blockage.

External corrosion also matters. In coastal locations such as Sydney, Adelaide or parts of Western Australia, airborne salt can attack supports, cable trays, control cabinets and structural fasteners even when the internal process is well controlled. Enclosures, drainage, protective coatings and suitable mounting details help prevent rainwater and saline dust from turning minor surface damage into a plant-wide maintenance problem.

Monitoring Chloride Exposure During Operation

A corrosion management programme should begin with feed characterisation. Useful measurements may include chloride concentration, pH, temperature, conductivity, oxidation-reduction potential, suspended solids and moisture. Sampling should cover representative batches rather than a single commissioning sample. Changes in supplier, dismantling method or pre-treatment can materially alter the chemical load reaching the ALS2 circuit.

Operators can use trends to identify conditions that precede attack. A rise in conductivity may indicate a saltier feed, while unexpected changes in pH or redox conditions may signal contamination or incorrect dosing. Pressure differences across filters, pump vibration, seepage around seals and unexplained metal content in residues can provide early warning before a vessel or pipe develops a visible leak.

Inspection intervals should reflect the severity and variability of the service. Visual checks can be supported by thickness measurements, dye penetrant testing of selected welds, borescope inspections and examination of removed gaskets or valve parts. Inspection records should identify the component, service conditions, observed damage and corrective action. This creates a practical evidence base for refining material choices as the plant gains operating experience.

Maintenance And Safe Plant Integration

Cleaning should remove chloride-bearing deposits without damaging protective surfaces or creating a new chemical hazard. Rinsing procedures, drain-down practices and control of wash water are especially important after feed campaigns with high salt content. Any cleaning chemical must be compatible with the equipment materials, seals and downstream wastewater treatment system.

Spare parts should be chosen by service duty rather than by appearance or convenience. Substituting a standard fastener, valve trim or elastomer can introduce a weak point into an otherwise robust circuit. Clear tagging and procurement specifications help prevent incompatible components from being installed during a rapid repair, which is valuable when a compact plant is operating with a small maintenance team.

Safe integration also requires separation of clean and contaminated areas, controlled access to wet equipment and effective bunding around tanks and chemical storage. Australian facilities must account for site-specific workplace safety, environmental approval and waste-handling requirements, with extra planning for remote locations where specialist technicians or replacement parts may take longer to arrive. Designing for maintainability reduces both operational risk and the temptation to defer essential inspections.

For operators assessing ALS2 technology, the most useful next step is a process-specific corrosion review covering feed composition, temperature, solids, residence time and cleaning practice. Engage qualified materials and process specialists, test candidate materials against representative chloride-rich samples, and build inspection points into the plant from the beginning. With disciplined design and monitoring, ALS2 equipment can support dependable precious-metals recovery from Australian e-waste while reducing the hazards associated with acid-based refining.