Acid recovery from copper metallurgical process streams polluted with arsenic by diffusion dialysis

Abstract

A copper smelter generates solutions containing H2SO4 (220 ± 10 g/L), non-metals (3.4 ± 0.2 g/L As) and metals (0.5 ± 0.1 g/L Zn, 0.13 ± 0.01 g/L Fe and 0.11 ± 0.01 g/L Cd) that are treated with lime as disposal option. In order to promote circularity, the recovery of H2SO4 by diffusion dialysis (DD) was evaluated with a lab-stack unit containing Anion Exchange Membranes (Neosepta-AFX) that allow the transport of HSO4- and H+, while rejecting metallic species in cationic form. Initially, dialysis coefficients were determined with cycling type experiments, which showed the possibility to purify H2SO4, but As was also transported. Then, dynamic experiments were carried out to study the effect of different variables, such as operational ones (acid and water flow rates) and As speciation (As(V) or As(III)). At the optimum operating conditions (water and acid flow rates of 0.86 L/m2h), Neosepta-AFX proved to allow the transport of H2SO4 (67 ± 2 % of acid was recovered, 146 ± 12 g/L) and rejected the metallic impurities (>85 %) effectively. Nevertheless, As permeated across the membrane (1.26 g/L in the recovered acid) due to its presence as neutral species (H3AsO4/ H3AsO3). In order to overcome it, the use of a solvent extraction step devoted to remove As before the treatment with DD was proposed.