OpenCOSMO-RS-Guided Development of Deep Eutectic Solvents for Zinc Extraction from Tyre-Derived Carbon Black

Pyrolysis of end-of-life tyres produces recovered carbon black with potential for high-value reuse. However, its application is limited by residual inorganic components, particularly zinc-containing species originating from tyre vulcanisation. Zinc removal could therefore improve the quality of the recovered carbon while enabling metal recovery. Conventional demineralisation commonly relies on corrosive mineral acids, creating environmental and safety concerns. This study investigates deep eutectic solvents (DESs) as a green and tunable medium for the selective extraction of zinc from tyre-derived carbon black. OpenCOSMO-RS calculations were first employed to screen candidate formulations to rationally down-select the most promising systems for experimental evaluation. Molecular COSMO files generated from ORCA calculations were used to estimate activity coefficients for zinc-containing probe species and rank solvent systems before experimental preparation. Binary and ternary choline chloride-based DESs containing urea, ethylene glycol, glycerol, and oxalic acid were subsequently prepared and tested. Among the evaluated formulations, the ternary choline chloride–glycerol–oxalic acid (CGO) system exhibited the highest leaching performance, reaching 86.81% ± 8.94%. FTIR analysis confirmed the formation of the DES, while zinc extraction was quantified using flame atomic absorption spectroscopy. No Ni, Pb, Cr, or Cu were detected in the leachates under the investigated conditions, suggesting preferential zinc extraction. Further work will evaluate the physicochemical properties of the treated carbon black and the regeneration and reuse of the DES. The findings demonstrate the potential of rationally designed DESs for zinc recovery from tyre-derived carbon black. This approach may support both metal recovery and the upgrading of waste-derived carbon materials within a more circular tyre-recycling process.