The recovery of cobalt and nickel from spent lithium-ion batteries is a critical step in enabling a sustainable battery supply chain. Traditional hydrometallurgical and pyrometallurgical methods dominate industrial-scale recycling, but emerging approaches are looking to adapt techniques from other industries to improve efficiency and selectivity. One such area of interest is the repurposing of catalyst recycling methodologies, particularly those developed for petrochemical refining, to enhance metal recovery from battery waste.
Catalyst recycling in the petrochemical industry focuses on recovering precious metals like platinum, palladium, and rhodium from spent catalytic converters and chemical processing catalysts. These processes often involve leaching, precipitation, and solvent extraction steps that share similarities with battery material recovery. However, key differences in feedstock composition, target metals, and impurity profiles necessitate modifications to ensure effective adaptation.
A major overlap between the two domains is the reliance on acid leaching to dissolve metal components. In petrochemical catalyst recycling, strong acids such as hydrochloric or nitric acid are used to solubilize platinum group metals. Similarly, battery recycling employs sulfuric acid or a mix of acids to leach cobalt, nickel, and lithium from cathode materials like NMC (nickel-manganese-cobalt) or NCA (nickel-cobalt-aluminum). The leaching kinetics, however, differ due to the distinct chemical structures—battery cathodes are typically layered oxides, while petrochemical catalysts often consist of metals supported on alumina or zeolites.
Selective precipitation is another shared technique. In petrochemical catalyst recovery, pH adjustment and reducing agents are used to isolate specific metals from leach solutions. For example, ammonium chloride is added to precipitate platinum as ammonium hexachloroplatinate. In battery recycling, hydroxide or carbonate precipitation is commonly employed to recover nickel and cobalt separately. The challenge lies in the co-dissolution of lithium and other impurities, which requires additional purification steps not always present in catalyst recycling.
Solvent extraction, widely used in both fields, demonstrates both parallels and divergences. Petrochemical catalyst recycling often employs solvents like tri-butyl phosphate (TBP) or Cyanex extractants to separate platinum group metals. Battery recyclers use similar extractants—such as di-(2-ethylhexyl) phosphoric acid (D2EHPA) for cobalt and nickel—but must account for lithium co-extraction, which is not a concern in catalyst processing. The presence of aluminum and manganese in battery waste further complicates the extraction chemistry, requiring tailored solvent formulations.
One notable difference is the treatment of carbonaceous residues. Spent petrochemical catalysts often contain coke deposits that must be removed through calcination before leaching. Battery electrodes, in contrast, have polymeric binders and conductive carbon that require alternative pretreatment, such as pyrolysis or mechanical separation. The organic components in battery waste can interfere with leaching efficiency if not adequately removed, whereas coke in catalysts is more straightforward to address.
Thermal processing also presents contrasts. Pyrometallurgical methods for petrochemical catalysts typically involve smelting at high temperatures to form metal alloys, followed by leaching. In battery recycling, smelting is used but must account for the volatility of lithium, which is lost in slag unless captured separately. The lower melting points of battery metals compared to platinum group metals influence furnace design and energy consumption.
The adaptation of catalyst recycling techniques to battery waste must also consider economic factors. Petrochemical catalysts contain high-value metals in relatively low quantities, justifying energy-intensive processes. Battery materials, while valuable, are present in larger volumes but at lower individual metal prices. This shifts the optimization focus toward throughput and cost reduction rather than maximum metal recovery per unit mass.
Environmental and regulatory considerations further shape process design. Catalyst recycling often deals with highly toxic compounds like cyanide complexes used in precious metal refining. Battery recycling, while less hazardous in some aspects, must manage fluorine from PVDF binders and organic electrolytes, requiring different waste treatment approaches. Regulatory frameworks for battery recycling are also evolving rapidly, unlike the well-established standards for catalyst recovery.
Innovations from petrochemical catalyst recycling that could benefit battery material recovery include advanced membrane filtration for selective metal separation and electrochemical recovery methods. Membrane technologies, such as polymer inclusion membranes, have been explored for platinum group metal separation and could be adapted for cobalt and nickel purification. Similarly, electrochemical deposition techniques optimized for precious metals may improve the recovery efficiency of battery-derived metals.
Process automation and real-time monitoring tools developed for catalyst recycling could also enhance battery recycling operations. Continuous flow systems with inline sensors for metal concentration analysis are standard in catalyst plants but are only beginning to be applied in battery recycling facilities. Implementing these technologies could reduce downtime and improve yield consistency.
Despite the potential synergies, several challenges remain in fully integrating catalyst recycling methods into battery material recovery. The scalability of adapted processes must be validated, particularly for the high-volume nature of battery waste streams. Additionally, the variability in battery chemistries—ranging from LFP (lithium iron phosphate) to high-nickel NMC—demands flexible approaches that can handle diverse inputs without extensive reconfiguration.
In summary, the crossover between petrochemical catalyst recycling and battery material recovery offers promising avenues for improving metal reclamation efficiency. Shared principles in leaching, precipitation, and solvent extraction provide a foundation for adaptation, while differences in feedstock composition and economic drivers necessitate tailored modifications. By leveraging proven techniques from catalyst recycling and addressing battery-specific challenges, the industry can advance toward more sustainable and cost-effective recovery of cobalt, nickel, and other critical materials. Future research should focus on hybrid processes that combine the strengths of both fields while mitigating their respective limitations.