Nickel is a valuable transition metal used extensively in various battery chemistries, including nickel-metal hydride (NiMH), nickel-cadmium (NiCd), and nickel-iron (NiFe) systems. While lithium-ion batteries dominate modern energy storage, these nickel-based systems remain in circulation, particularly in industrial, backup power, and legacy applications. Efficient nickel recovery from these batteries is critical for resource sustainability and economic viability, given nickel’s importance in stainless steel, alloys, and emerging battery technologies.

Nickel exists in different forms within these batteries, primarily as metallic nickel foam in NiMH and NiCd cells or as nickel hydroxides/oxyhydroxides in the active electrode materials. The recovery processes differ significantly based on these forms. Metallic nickel foam, used as a conductive substrate in NiMH and NiCd batteries, is relatively straightforward to extract through mechanical separation and pyrometallurgical methods. The foam retains its structural integrity even after battery degradation, allowing for physical separation via crushing, sieving, and magnetic sorting. Once isolated, the nickel foam can be directly melted and refined for reuse in new batteries or other applications.

In contrast, nickel hydroxides and oxyhydroxides, which form the electrochemically active material in these batteries, require more complex processing. These compounds are typically mixed with other elements, such as cadmium in NiCd batteries or rare earth metals in NiMH systems (e.g., lanthanum, cerium in AB5 alloys). Hydrometallurgical methods are commonly employed, involving acid leaching (e.g., sulfuric or hydrochloric acid) to dissolve the nickel compounds, followed by selective precipitation or solvent extraction to isolate nickel from impurities. For NiCd batteries, cadmium must be carefully separated due to its toxicity, often through precipitation as cadmium hydroxide or sulfide. In NiMH systems, rare earth elements pose a challenge due to their similar chemical behavior to nickel, necessitating advanced separation techniques like ion exchange or controlled pH adjustment.

The separation of cadmium from nickel in NiCd batteries is particularly critical from an environmental and regulatory standpoint. Cadmium is a hazardous heavy metal, and its improper handling can lead to significant ecological and health risks. Historically, pyrometallurgical processes were used to volatilize cadmium at high temperatures, leaving behind nickel-rich residues. However, modern hydrometallurgical approaches are preferred for their higher selectivity and lower emissions. These methods typically involve leaching the battery material in acid, followed by selective precipitation or electrodeposition to recover cadmium separately from nickel.

Rare earth elements in NiMH batteries add another layer of complexity. The AB5 alloy (e.g., LaNi5) used in NiMH electrodes contains lanthanum, cerium, neodymium, and praseodymium, which must be separated from nickel during recycling. Solvent extraction using organophosphorus compounds or amine-based extractants has proven effective in partitioning rare earths from nickel in leach solutions. However, the economic viability of rare earth recovery depends on market prices, which have fluctuated significantly over time. In some cases, rare earths are discarded in slag during pyrometallurgical processing due to the high cost of their recovery relative to their market value.

Historically, recycling rates for nickel-based batteries have varied by chemistry and region. NiCd batteries have seen higher recycling rates due to stringent regulations on cadmium disposal, particularly in the European Union under the Battery Directive. NiMH batteries, while less toxic, have been recycled at lower rates due to the lack of similar regulatory pressures and the complexity of rare earth separation. Industrial NiFe batteries, largely used in stationary applications, have had minimal recycling infrastructure due to their long lifespan and niche use. Overall, nickel recovery rates from these systems have been modest compared to lead-acid batteries but higher than early lithium-ion systems due to nickel’s inherent value.

Economic drivers for nickel recovery from these declining battery types are multifaceted. Nickel prices have shown volatility but generally remain high enough to justify recycling, especially as demand grows for stainless steel and lithium-ion battery precursors like nickel sulfate. The value of recovered nickel depends on its purity and form; metallic nickel foam commands a higher price than nickel salts or oxides derived from hydroxide leaching. Additionally, regulatory incentives, such as extended producer responsibility schemes, can improve the economics of recycling by internalizing disposal costs. In regions with limited primary nickel resources, recycling also reduces reliance on imports, enhancing supply chain security.

The environmental benefits of nickel recovery further bolster its economic case. Recycling nickel requires significantly less energy than primary production—up to 90% less in some processes—reducing greenhouse gas emissions and mining impacts. For NiCd and NiMH batteries, proper recycling also mitigates the release of toxic substances, aligning with global trends toward circular economy principles. However, the declining production of these battery types poses a challenge for recyclers, as economies of scale diminish. Future recycling efforts may increasingly focus on mixed feedstock processing, where nickel-based batteries are treated alongside other nickel-bearing waste streams to maintain viability.

In summary, nickel extraction from non-lithium batteries involves distinct processes tailored to the metal’s form—metallic foam or hydroxide compounds. While metallic nickel is simpler to recover, hydroxide-based materials require advanced hydrometallurgical techniques to separate nickel from cadmium or rare earth elements. Historical recycling rates reflect regulatory and economic influences, with NiCd systems leading due to cadmium’s toxicity. The economic rationale for nickel recovery remains strong, driven by commodity prices, regulatory frameworks, and environmental benefits, even as these battery systems phase out in favor of newer technologies. Efficient recycling methods will continue to play a role in sustaining nickel supply chains while minimizing waste and environmental harm.