Decarbonizing NdFeB sludge recycling: carbon footprint analysis of hydrometallurgy and calcium thermal reduction pathways

Sintered NdFeB sludge represents a critical, high-abundance secondary resource whose effective recycling is imperative for the sustainable development of the rare earth industry. To clarify green recycling pathways, this study develops a comparative Life Cycle Assessment (LCA) framework to evaluate conventional hydrometallurgy with calcium thermal reduction diffusion (Ca-RD) routes. The assessment was conducted using empirical data from industrial and pilot-scale operations. Following ReCiPe 2016 and IPCC 2013 methodologies, a functional unit of 10 kg of regenerated sintered NdFeB magnets was defined. The results indicate that the hydrometallurgy process is 297%, 248%, and 177% higher than those of the Ca-RD process in terms of damage to human health (HH), damage to ecosystem (ED), and resource depletion (RA), respectively. Furthermore, Ca-RD achieves a 71.64% reduction in carbon footprint (68.38 kg CO₂eq per 10 kg magnets) compared to the hydrometallurgy process (241.09 kg CO₂eq). Process-level analysis identifies extraction (29.28%), sintering (14.85%), and electrolysis (14.14%) as primary emission contributors in hydrometallurgy, while the emissions of Ca-RD are predominantly driven by the sintering stage (52.35%). These quantitative findings highlight the potential of Ca-RD in reducing the environmental burden of rare earth magnet manufacturing.