The recycling of mixed battery streams presents significant challenges in the selective recovery of nickel due to the coexistence of cobalt, lithium, manganese, and other metals. Efficient separation is critical for maximizing resource recovery and minimizing environmental impact. This article examines advanced techniques for nickel separation, including chelation chemistry, ion-exchange resins, and membrane technologies, while addressing contamination risks and comparative efficiencies.
Chelation chemistry leverages selective organic ligands to bind target metals. In nickel recovery, dimethylglyoxime (DMG) forms an insoluble red precipitate with nickel at pH 8–9, while cobalt and lithium remain in solution. Ethylenediaminetetraacetic acid (EDTA) offers broader metal chelation but requires pH adjustment for selectivity. Recent studies show DMG achieves over 95% nickel recovery from synthetic leach solutions, though real-world streams with competing ions may reduce efficiency to 85–90%.
Ion-exchange resins provide another pathway, with iminodiacetic acid (IDA) and aminophosphonic acid (APA) functional groups demonstrating high nickel affinity. IDA resins achieve 90–93% nickel uptake from sulfate solutions at pH 3–4, with cobalt interference below 5%. APA resins show superior selectivity in chloride media, with nickel loading capacities of 1.2–1.5 mmol/g. Competitive adsorption studies indicate manganese reduces nickel uptake by 15–20% due to similar ionic radii, necessitating pretreatment for optimal performance.
Membrane technologies, including nanofiltration and supported liquid membranes (SLMs), enable continuous separation. Nanofiltration membranes with 200–300 Da molecular weight cutoffs reject divalent nickel while allowing monovalent lithium passage. SLMs using di-2-ethylhexyl phosphoric acid (D2EHPA) carriers achieve 85–88% nickel transport across pH 2.5–3.5, though cobalt co-extraction remains a challenge at 10–12%. Electrodialysis with selective ion-exchange membranes can further enhance separation, with nickel purity reaching 98% in optimized configurations.
pH-controlled precipitation remains industrially prevalent due to low operational costs. Nickel hydroxide precipitates at pH 10–11, but cobalt hydroxide co-precipitates above pH 9. Staged precipitation with sodium hydroxide reduces cobalt contamination to 3–5% when maintaining pH below 9.5. Sulfide precipitation using sodium sulfide offers higher selectivity, with nickel sulfide forming at 0.01 M sulfide concentration while cobalt requires 0.1 M. However, sulfide processes generate hazardous H2S, requiring strict containment.
Electrochemical methods, including electrowinning and electrodeposition, provide high-purity nickel recovery. At controlled potentials of -0.7 to -0.8 V vs. SHE, nickel deposits with 99% current efficiency from sulfate electrolytes. Cobalt contamination is limited to 0.5–1% by maintaining potential below -0.9 V. Pulse electrodeposition improves morphology, reducing energy consumption by 15–20% compared to direct current.
Contamination risks arise from aluminum and copper foils in shredded black mass. Aluminum dissolves in acidic leach solutions above pH 2, competing with nickel for chelators and resins. Pre-leaching with NaOH removes 95% aluminum before acid digestion. Copper deposits during electrowinning, requiring ion-exchange pretreatment to reduce concentrations below 50 ppm. Residual electrolytes, particularly LiPF6, generate HF in aqueous systems, necessitating neutralization or solvent extraction prior to metal recovery.
Comparative separation efficiencies for different feedstocks:
Feedstock Type Chelation Ion-Exchange Membrane Sulfide Precipitation
NMC 111 (Ni-rich) 92% 90% 86% 94%
NMC 532 88% 85% 82% 90%
LCO mixtures 85% 80% 78% 88%
Mixed industrial waste 78% 75% 70% 82%
Cost analyses reveal tradeoffs between purity and operational expenses:
Method Capital Cost Operating Cost Nickel Purity
Chelation Medium High 90–95%
Ion-Exchange High Medium 92–96%
Membrane Very High Low 85–90%
Sulfide Precipitation Low Medium 93–97%
Electrowinning High High 98–99%
Process selection depends on feedstock composition and purity requirements. For high-nickel NMC batteries, sulfide precipitation offers optimal balance of cost and efficiency. Mixed streams with significant cobalt may benefit from chelation or ion-exchange for higher selectivity. Membrane systems suit low-volume, high-purity applications despite higher capital costs. Integrated flowsheets combining multiple methods, such as initial sulfide precipitation followed by electrowinning, can achieve 99.5% nickel purity for battery-grade reuse.
Future developments may focus on hybrid systems combining solvent extraction with membrane technologies, or catalytic processes to enhance selectivity. The increasing nickel content in next-generation cathodes will further drive innovations in separation efficiency and cost reduction.