Comparison of polyethylenimine, polyacrylic acid and poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) in Cu2+ removal from wastewaters by polymer-assisted ultrafiltration

Some results on metal ions removal from wastewaters using water-soluble polymers such as polyethylenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine-co-epichlorohydrin-co-ethylene-diamine) (PDEHED) as chelating agents and the Cu2+ ion as the model in combination with a polymer-assisted ultrafiltration process (PAUF) are reported. In particular, the performances of these polymers in Cu2+ removal from wastewaters were compared. Tests of bonding capacity and best operating conditions of the process showed that complexation conditions depend on pH; indeed, copper ions are complexed by PEI, PAA, PAASS and PDEHED at pHs higher than 6, 4.6, 4.6 and 8, respectively. The decomplexation reactions took place at pH <3. Bonding capacity was 0.333 mg Cu2+/mg polymer, meaning a ratio of polymer/Cu2+ = 3 (w/w) for PEI, PAA and PAASS. For the chelating agent PDEHED, a ratio of PDEHED/Cu2+ = 0.5 (w/w) was determined. UF tests, realized at two transmembrane pressures (2 and 4 bar) by using five different flat-sheet membranes, showed that the PAA polymer and the PAN GKSS HV2/T membrane can be used when the objective of the purification process is to decrease metal concentration not lower than a certain value. The PDEHED polymer is useful if the objective of wastewater treatment is to obtain complete copper removal. Simple washings with tap water were enough for regeneration and reuse of the membranes.