Electrical double layer ion transport with cell voltage-pulse potential coupling circuit for separating dilute lead ions from wastewater

Continuous separation of dilute Pb2+ from wastewater was demonstrated by using a membrane containing highly conductive multiwalled carbon nanotubes (MWCNTs) in an electrochemically switched ion permselective (ESIP) process, with a cell voltage-pulse potential coupling circuit. The membrane with high selectivity for Pb2+ separation was fabricated by pressure filtering MWCNT solution through a polytetrafluoroethylene (PTFE) film. In the separation system, the directional uptake and release of Pb2+ were realized by modulating the positive and negative charge densities on the electrical double layer (EDL) of the membrane, together with the application of an external electric field. The effects of the operating parameters on the flux of Pb2+ and membrane permselectivity were investigated. The highest Pb2+ flux across the membrane occurred with considerable permselectivity at a cell voltage of 0.8 V, a pulse width of 40 s, and a membrane MWCNT content of 30 mg. The system reduced the Pb2+ concentration in the solution from 30 to 0.36 ppm with a current efficiency of 46.1%. Such a novel EDL membrane-based ESIP system could be used for wastewater treatment.