A study of AVR sediment leaching with copper-bearing cyanide effluent and electrowinning recovery of copper

Abstract

In this paper, we proposed a combined leaching-electrowinning approach to recover Cu from AVR sediment. Firstly, speciation diagrams of the metal-cyanide (Cu, Zn and Fe) system were constructed using thermodynamic calculations. Afterward, leaching-electrowinning experiments were systematically conducted. The speciation calculations showed that CuSCN was converted into Cu-CN compounds when the CNT/Cu mole ratio exceeded 1.71. The cyanide ions complexed with Zn2+ were completely captured by Cu+ when the Cu/Zn mole ratio reached 5.0, yielding the formation of zinc hexacyanoferrate composite or Zn(OH)2 precipitation. Corresponding leaching results indicated that the selective Cu leaching from AVR sediment was realized with the leaching efficiency of 99%, forming Na2Zn3[Fe(CN)6]2 as the main ingredient of the residue at the optimal leaching conditions. Cyclic voltammetry tests suggested that cuprocyanide complexes were dominantly presented as [Cu(CN)2]− complexes in the leachate (5680 mg/L, CNT/Cu mole ratio of 2.18), exhibiting much higher current density than that of [Cu(CN)3]2− in the cyanide effluent. However, during the electrowinning process, [Cu(CN)2]− were gradually converted into higher-order complexes, and the cathodic current efficiency decreased correspondingly. Ultimately, the Cu recovery of 92% was achieved with a current efficiency of 57% and energy consumption of 1.91 kW·h/kg Cu.