Selective recovery of lead and zinc through controlling cathodic potential in a bioelectrochemically-assisted...

Proper treatment of mining wastewaters is critically important to minimize contamination by heavy metals contained in those wastewaters. Herein, a bioelectrochemically-assisted electrodeposition (BES-EDP) system was developed and investigated for selective removal and recovery of Pb and Zn from a mimicked smelting wastewater. It was observed that those two metals were reduced at different cathodic potentials and electrodeposition time. At a cathodic potential of -0.75 V vs. Ag/AgCl, 98.5 ± 1.4 % of Pb was recovered after 10 h of reaction while there was little Zn deposition. Increasing the cathodic potential to -1.2 V could achieve 98.7 ± 0.7 % of Zn with the electrodeposition time of 6 h. The composition of the deposits confirmed the results from solution analysis and metal oxides were also formed during metal reduction. The diffusion impedance was much higher than the charge transfer resistance, suggesting that the diffusion process was a rate limiting step for electrodeposition. The diffusion process was verified by chronoamperometry with a good fit in Cottrell equation. The electrodeposition equilibrium constant k₀ was determined as 3.76 cm s^-1. Those results have demonstrated the feasibility of using bioelectricity to assist with selective metal recovery and warrant further investigation of technologies for sustainable management of mining wastewaters.