Selective separation of Pb from hard water by a semi-continuous polymer-enhanced ultrafiltration process (PEUF)

A semi-continuous PEUF process is proposed for the selective recovery of Pb from aqueous effluents in which Ca is present, even in very high concentrations. The proposed process consists of three steps: (1) retention and concentration of Pb and Ca, (2) selective separation of both metal ions and (3) polymer regeneration. Previous experiments carried out in the mode operation of total recirculation proved technical viability of process and established operating pH values at which different stages must be performed. When Pb:Ca molar ratio is 1:1, the concentration stage of the semi-continuous process reaches very high rejection coefficients, which means a permeate stream with less than 0.05 ppm of Pb and 1.5 ppm of Ca. Secondly, in the selective separation stage, Pb concentration remained almost constant while Ca concentration decreased approximately to 25% of its initial value in the reactor. Finally, in the regeneration stage, concentrations of both metals were reduced to 25% of initial concentration, reaching rejection coefficients close to 15%. Moreover, all the results were accurately modelled.