SELECTIVE ELECTROEXTRACTION OF BASE METALS FROM LEACHING SOLUTIONS OBTAINED DURING THE RECYCLING OF WASTE PRINTED CIRCUIT BOARDS. III. PRELIMINARY TESTS FOR IRON, NICKEL AND ZINC ELECTROEXTRACTION

This paper presents the results of our research concerning the feasibility of the Fe, Ni and Zn electroextraction from partially treated spent leaching solutions resulting from the waste printed circuit boards recycling process using the bromine/bromide system. The first tests, performed in a real sample of spent leaching solution and using a Pt Fisher type cathode, led to inacceptable results due to the intensive hydrogen evolution. To find a feasible industrial solution, systematic preliminary tests were performed by hydrodynamic cyclic voltammetry in synthetic solutions using small diameter (3 mm) rotating disk electrodes (RDEs) of carbon paste (CP) and 304 type stainless steel (304 SS), resulting in theoretical current efficiencies of up to 95.8%. Further, to prove the feasibility of the pure Zn and Zn alloys electroextraction, long duration (0.15÷8 h) experiments were done by potentiostatic chronoamwperometry using RDEs on CP and 304 SS of large diameters (38 and 29 mm, respectively). The obtained results proved that, depending on the electrolyte’s composition and pH, and on the imposed potential, high purity Zn (over 98%) or Zn-Fe-Ni alloy deposits can be obtained at current efficiencies between 20 and 96% and specific energy consumptions between 2 and 17 kWh/kg of alloy.