Recovery of hydrochloric acid and critical raw materials from an effluent of the copper electrorefining process using electromembrane reactors

Abstract

Highly concentrated acids are used to regenerate ion-exchange resins that are applied for the removal of metallic impurities (i.e. antimony, arsenic and bismuth) from spent copper electrorefining baths, thus generating acidic effluents. In this work, the recovery of critical raw materials and HCl from a real effluent is evaluated by electrodeposition using reactors with and without membrane separators. First, four reduction peaks were detected by cyclic voltammetry, and their correspondence to the pairs Cu(II)/Cu(I), As(III)/As, Sb(III)/Sb, Bi(III)/Bi, and Cu(I)/Cu was confirmed by potentiostatic electrodeposition and elemental analysis of the deposits. A high selectivity towards antimony deposition over arsenic and copper was achieved at the least cathodic applied potential (−0.25 VAg/AgCl), obtaining a deposit with 85 wt% of antimony and bismuth as the second most deposited metal. At more cathodic potentials, deposition of copper takes place and the antimony content in the deposits decreases. Galvanostatic electrodeposition tests were carried out using a three-compartment reactor. Results showed that the transport rate of Cl- ions through the anion-exchange membrane is too slow to recover highly concentrated HCl in a separate compartment. However, electrodeposition of the main elements present in the real effluent makes possible obtaining impurity-free HCl (4.8 M) in the cathodic compartment. The complete recovery of antimony (100 %) and almost complete recovery of bismuth (95 %) and copper (90 %) were achieved after 4 h working at −100 mA·cm−2. Tests conducted with a single-compartment reactor confirmed that formation of chlorine gas at the anode causes the redissolution of the metals deposited at the cathode, thus revealing that electromembrane reactors improve the electrodeposition current efficiency.