Assessing the Sustainability of Solvometallurgy for Black Mass Processing – the LEACH (Low-impact Extraction and Assessment of Chemical Hydrometallurgy) Tool

Abstract

The sustainable recovery of critical raw materials such as cobalt from spent lithium-ion batteries (LIBs) is a pressing challenge, particularly as the demand for electrification accelerates. Solvometallurgy, and in particular the use of deep eutectic solvents (DESs), has emerged as a promising alternative to conventional hydrometallurgical and pyrometallurgical approaches due to its potential for enhanced selectivity, reduced environmental impact, and process modularity. However, the scalability of DES-based leaching remains limited by economic, technical, and safety concerns often overlooked during early-stage research. To address this gap, we present LEACH (Low-impact Extraction and Assessment of Chemical Hydrometallurgy), a modular, penalty-based tool designed to evaluate the sustainability of emerging solvometallurgical processes. Inspired by the EcoScale framework, LEACH incorporates economic, technical, and occupational safety criteria, assigning penalty points that reflect deviations from an ideal process. The tool is structured in three modules—solvent formulation, black mass leaching, and overall process evaluation—allowing for detailed diagnostics and early identification of sustainability bottlenecks. LEACH was applied to two case studies targeting cobalt extraction from black mass using DESs based on choline chloride combined respectively with citric acid or ethylene glycol. While Process 1 (citric acid-based, mild conditions) achieved a higher final score (43.5/100) than Process 2 (ethylene glycol-based, high temperature), both processes were classified as non-ideal (score < 50), underscoring significant limitations in terms of recyclability, toxicity, and regulatory compliance. Notably, safety-related penalties emerged as critical barriers to scale-up, highlighting the importance of integrating occupational hazard assessments from the outset. Overall, LEACH offers a practical, flexible, and safety-conscious approach to guide the design and optimization of sustainable solvometallurgical processes, aligning with Safe-and-Sustainable-by-Design principles and supporting more responsible LIB recycling technologies.