Safer aromatic process diluents for solvent extraction of critical metals from spent batteries

Journal article, 2026

This paper presents the demonstration of two aromatic compounds 1,4-di-tert-pentylbenzene and 1-methyl-4-(tert-pentyl)benzene as safer alternative process diluents in the application of critical metal recovery. Recycling of batteries is needed, and within the hydrometallurgy recycling route, solvent extraction (SX) offers a highly efficient, highly selective and low energy separation technique. Besides available options for sustainable, aliphatic diluents like HVO100, aromatic alternatives, suitable for both laboratory and industrial use, are deficient. Synthesis and characterization (NMR and GC-MS) are provided and important process parameters (boiling point, flash point, viscosity, solubility, density, surface tension and inter-surface tension) were measured. Eligibility of the aromatic diluent candidates was investigated by solvent extraction using Aliquat 336, DEHPA and Cyanex 272 as extractants with various experimental conditions and metal compositions of typical battery metals like nickel (Ni), copper (Cu), cobalt (Co), manganese (Mn) and rare earth elements (REEs). Performance was compared with that of commercially used diluents.