Use of a hydrogen-diffusion electrode in the electrochemical removal of lead from effluents of lead electrowinning processes

An electrochemical process for the removal of lead using a three-dimensional carbon-felt cathode and a hydrogen-diffusion anode has been developed. The process is able to cope with effluents coming from lead electrowinning processes in fluoroborate baths after the lead has been electrolytically removed to approximately 100 mg/L (100 ppm). The lead deposit can be removed from carbon-felt electrodes by chemical or electrochemical stripping, yielding a lead-containing solution that can be reused in the electrowinning process. The use of a hydrogen-diffusion electrode (HDE) significantly decreases the cost of the process in comparison with that of a dimensionally stable anode (DSA). For a current density of 10 mA/cm(2), the energy used for treating a solution containing 120 mg/L (120 ppm) of lead is approximately 990 kJ/m(3) (275 Pi h/m(3)) when a DSA is used, but only 166 kJ/m(3) (46 W h/m(3)) when an HDE anode is used. Approximately 75% of the hydrogen needed for the HDE anode can be partially supplied by the hydrogen evolved at the cathode during lead deposition. The cathodic reaction has a current efficiency of 25%. The required electrodic area for the removal process is 1.5 m(2)/m(3).h for an effluent containing 120 mg/L (120 ppm) of lead.