Influence of flow rates on the electrogenerative Co2+ recovery at a reticulated vitreous carbon cathode

Reticulated vitreous carbon (RVC) was used as the cathode material in order to recover Co(II) ions. When Zn/ZnSO4 was coupled with Co(II)/RVC, a free energy of −274 ± 2 kJ mol−1 was generated, which in turn recovered Co(II) at the RVC surface spontaneously achieving a current efficiency of 82% when the initial Co(II) was 200 mg L−1. Studies of Co(II) reduction on 100 ppi RVC were accomplished using 500 mg L−1 Co(II) concentration at pH 4.00 and with electrolyte flow rates of 50, 100, 150 and 200 mL min−1. It was shown that poor removal of <75% cobalt was achieved at all flow rates after 8 h of operation. However, without pH adjustment (initial pH 5.44 ± 0.10) using similar test solutions, a shorter time of 7 h was required to remove more than 99% of cobalt at all flow rates. Therefore, this pH condition was selected for evaluating the performance of the system with different cathode porosities. Mass transport characteristics of the system using cathodes of different porosity were also evaluated.

► Cobalt recovery at a reticulated vitreous carbon cathode by an electrogenerative process. ► Current efficiency is 82% with a free energy of −274 ± 2 kJ mol−1 generated. ► pH affects the rate of cobalt removal. ► The mass transport coefficient, km decreased with increasing porosity of the reticulated vitreous carbon cathode.