Agitation Rate and ALS2 Recovery of Fine Palladium Powder
ALS2Project presents Ikoi S.p.A.’s acidless separation technology as a safer, cleaner route to recovering precious metals from electronic waste and WEEE. Replacing corrosive acid refining can reduce chemical-handling risks and support compact recovery units located closer to feed streams. The technology has also been supported by the European Union’s Horizon 2020 research and innovation programme as it moves toward application-oriented development.
Agitation remains the hidden variable in that work. The influence of agitation rate on ALS2 recovery of fine palladium powder is mainly a mass-transfer question: how readily particles remain wetted, dispersed and in contact with the ALS2 separation medium. A faster impeller may raise extraction, yet it can also increase entrainment or shear. The useful result is therefore not the highest rpm, but a stable operating range that separates metal cleanly without generating new losses.
Why mixing speed changes the separation
Agitation suspends solids, renews liquid-solid interfaces and keeps particle concentration more uniform around the process equipment. For fine powder, weak mixing allows agglomerates to settle or form isolated pockets, so the ALS2 medium sees inconsistent feed. Strong mixing can disperse those agglomerates, but only if the flow pattern provides circulation throughout the vessel rather than a narrow vortex around the impeller.
A useful rate must also suit the next separation step. A stirred suspension can deliver excellent palladium contact while remaining difficult to filter or prone to carrying fine solids into a product phase. Equipment geometry, solids loading and impeller design therefore matter as much as the motor setting. The operating choice should optimise recovery, product purity and residue losses together.
| Mixing condition | Particle behaviour | Likely process outcome | Operating concern |
|---|---|---|---|
| Low mixing | Solids settle or agglomerate | Uneven contact and lower recovery | Wet or caked powder |
| Effective mixing | Powder stays suspended and wetted | Consistent transfer and cleaner separation | Heat, wear and power rise |
| Excessive mixing | Strong shear, foam or emulsion | More entrainment and difficult filtration | Attrition and unstable product |
| Uniform circulation | No persistent dead zones | Reliable basis for scale-up | Requires vessel-specific tuning |
There is no universal agitation value for ALS2. The centre of the comparison describes a process window, not a permanent recipe: particle moisture, feed composition and vessel design can move its edges. Commissioning should verify the window with the actual electronic-waste stream and then record the operating limits in batch instructions.
From impeller speed to mass transfer
The rotation rate of a laboratory mixer is not directly transferable to a full-scale ALS2 unit. Impeller diameter, blade type, baffles, tank proportions, liquid depth and solids loading all change power per unit volume, tip speed and circulation time. Two vessels running at the same rpm can place very different stresses on the powder.
Fine palladium powder has a high surface-to-mass ratio and a low settling velocity. Once wetted, small particles can respond quickly to changes in flow, while dry or damp agglomerates respond slowly and may remain outside the active zone. Measuring mixing time and observing suspension across the vessel often explains more than a single extraction result.
The practical target is adequate solids suspension with the lowest destructive energy that can maintain it. This can be established by measuring torque or motor power, visual suspension, turbidity and the palladium mass balance. Keeping those observations together prevents a laboratory gain from being mistaken for a plant-scale improvement.
Why more agitation is not always better
At the low end of the range, additional mixing usually reduces settling, breaks soft agglomerates and gives the separation medium more uniform access to palladium-bearing particles. That improvement is especially valuable when sampling from one part of the vessel would otherwise be misleading. It also reduces concentration gradients that can slow reaction or capture.
Beyond the useful suspension threshold, extra speed adds shear and circulation energy with little gain in metal transfer. It may break fragile solids, generate fines or foam, and make phase separation and filtration harder. Where an ALS2 configuration uses immiscible liquid phases, agitation can also create an emulsion that delays coalescence.
Recovery percentage alone can hide these effects. A run may show more palladium in one output while losses rise in residues or elsewhere in the mass balance. The best setting therefore balances palladium recovery against solids carryover, product grade, filter-cake permeability, reagent consumption and equipment wear.
Turning test results into plant controls
A convincing trial keeps temperature, reagent concentration, liquid-to-solid ratio, residence time, feed preparation and analytical method constant while changing only the mixing condition. Operators should compare low, intermediate and high settings, include replicate runs and report both palladium recovery and where unrecovered metal remains. Particle-size distribution and moisture deserve special attention because they can change the required agitation between batches.
Feed characterisation is part of this work. Representative lots should be homogenised and assayed for palladium in the feed, recovered fraction and residue. Results should be trended by operator and shift because a drifting feed grade, moisture level or contamination incident can otherwise force operators to compensate with mixing that solves the wrong problem.
Scale-up should preserve the hydrodynamic purpose rather than the motor setting. Power per volume, impeller tip speed, circulation pattern and mixing time are more useful design variables. A compact ALS2 vessel must include enough baffling and working volume to prevent a surface vortex, especially if it receives finely divided electronic-waste residues with variable density.
Variable-speed drives, torque monitoring and simple process measurements make the validated range easier to hold. Trend motor load, turbidity, temperature and separation quality together, then define alarms for high shear, excessive solids carryover or loss of suspension. This turns a laboratory trend into an operating recipe that can be audited across production shifts.
Fit for Australia's recycling market
Australian households in Sydney, Melbourne and Brisbane often keep unused phones, laptops and chargers in drawers or place them in council e-waste bins rather than a dedicated recovery process. Collection events and retailer take-back schemes gather this material, but it then faces long transport distances and mixed feeds. That geography rewards compact ALS2 modules that can treat concentrated streams close to collection or sorting hubs.
The local market values both recovered metal and a credible chain of custody. Electronics imports, a large urban population and established infrastructure for batteries and appliances create a substantial urban-mining feedstock, while Australian industrial buyers increasingly ask for documented environmental performance. An acidless route can reduce hazardous reagent handling, yet water, energy, residues and worker controls still determine its footprint.
Regulation is moving in the same direction. The National Environment Protection (Used Electrical and Electronics Products) Act 2024 provides a national framework, implemented with state and territory arrangements. NSW requires e-waste to be kept out of general waste, and states such as Victoria maintain separate collection and stewardship programs. Any Australian ALS2 deployment must also meet work health and safety, dangerous-goods and environmental obligations through the relevant jurisdiction.
Build mixing control into ALS2 from the start
The best agitation strategy begins during equipment design, not after commissioning. Baffles, a suitable impeller, an effective working volume and a variable-speed drive should be selected together for the expected particle size and solids loading. Feed pumps and discharge valves must deliver the validated suspension without creating a pressure surge or shearing the powder unnecessarily.
Operators also need clear rules for when to raise, hold or reduce mixing. In the same way that a beginner strategy guide illustrates how conservative choices limit exposure, an ALS2 runbook should define conservative responses to changes in torque, turbidity or product quality.
Approach Ikoi S.p.A. or the ALS2Project team with a representative feed sample, your target palladium recovery and available utility limits. The team can scope a controlled agitation trial, compare operating regimes and convert the evidence into an ALS2 operating envelope suitable for an Australian deployment.