A regenerable precipitant-solvent system for CO2 mitigation and metals recovery

This work describes a new resource engineering process for greenhouse gas control and metals recovery, and reports initial progress in its development. Central to this process is a regenerable solvent-precipitant system that enables pH-swing via a change in operational temperatures. In this particular contribution, various liquid-phase aliphatic tertiary amines and acids were examined to identify the suitable components that afford pH control between 10 and 2, deemed necessary for metal hydroxide precipitation and leaching metals from magnesium-bearing solids, respectively. Within the desired operational constraints (Tmax ≤ 110 °C, Pmax ≤ 1 bar, tmax ≤ 2 h), we found the triethylamine-sulphuric acid aqueous system (Et3N-H2SO4-H2O) has sufficiently covered the pH regimes of interest, affording a pH swing (at 25 °C) between 10.5 and 1.9. Triethylamine (Et3N) provided the highest acid neutralising capacity of 7 mol H+ L−1 Et3N, capable of aqueous alkalisation to pH > 10.5 (25 °C, 1 bar), and recoverable at ≤105 °C (1.0 bar) via fractional distillation. As for the acid component, H2SO4 allows for the formation of an acidic aqueous solution (pH 1.9, 25 °C, 1 bar) resulting from the partial liberation of Et3N from the acid-bound Et3N·H+ and HSO4− counter anion dissociation.