Mercury removal and recovery from aqueous solutions by coupled complexation–ultrafiltration and electrolysis

Removal of mercuric ions from wastewater by complexation–ultrafiltration using polyethylenimine (PEI) as complexing agent was previously studied. Conditions for rejection coefficients of mercury higher than 99.7% were obtained. The present work deals with the next operations: recycling of the PEI and recovery of the mercury from the concentrate of the first ultrafiltration. Direct electrodeposition of mercury using a packed bed flow-through (PBFT) cathode was carried out. Influence of operating parameters such as current intensity, pH, PEI and chloride ion concentration was studied. Depletion of mercury from 100 to 20 mg l−1 was achieved with a current efficiency of about 100% when the current density was 1.09 mA g−1 of graphite. A process based on coupled complexation–ultrafiltration and electrodeposition on PBFT cathode was proposed and tested. Design elements of the whole process were given.