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-dimen sional carbon-felt cathode and a hydrogen-diffusion anode has been dev eloped. The process is able to cope with effluents coming from lead el ectrowinning processes in fluoroborate baths after the lead has been e lectrolytically removed to approximately 100 mg/L (100 ppm). The lead deposit can be removed from carbon-felt electrodes by chemical or elec trochemical 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 co mparison with that of a dimensionally stable anode (DSA). For a curren t density of 10 mA/cm(2), the energy used for treating a solution cont aining 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 a n HDE anode is used. Approximately 75% of the hydrogen needed for the HDE anode can be partially supplied by the hydrogen evolved at the cat hode during lead deposition. The cathodic reaction has a current effic iency 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.