Removal and recovery of copper from wastewater by a complexation–ultrafiltration process

Carboxyl methyl cellulose (CMC) as a water-soluble metal-binding polymer in combination with ultrafiltration (UF) was used in a hybrid approach for selective removal and recovery of copper from water. In the complexation–UF process the cationic forms of heavy metals were first complexed by a macro ligand in order to increase their molecular weight to having a size larger than the pores of the selected membrane that can be retained and flow out in the retentate whereas permeate water was purified to a certain extent from heavy metals. The complexation of Cu 2+, Pb2+, Fe2+ and Mn2+ by CMC from synthetic solutions and real wastewater followed by UF filtration used as a complex separation step was studied. The aim was to recover water-soluble polymers and to obtain a heavy metal concentrate; attempts were also made to destroy the Me:CMC complexes by a pH decrease. The decomplexation procedure was followed by a second step of UF. The results obtained show that a low mole Cu:CMC ratio favors both ultrafiltrate permeability during the first stage of the process and the separation following the next step of complex destruction at a lower pH. The comparative experiments with (1)synthetic water containing copper as a single heavy metal; (2)copper containing a solution with addition of ferrous iron, manganese and lead; and (3) drainage mine water contaminated with copper, ferrous iron, manganese and lead show a selectivity for Cu during the first stage of UF approaching 99% in these three cases. However, the destruction of complexes of heavy metals from the real wastewater was limited — up to 80%.

C It has been shown that UF assisted by complexation can be successfully applied for removal of heavy metals using CMC as a complexation agent. C Regarding the transient permeate flux during the membrane separation of complexes, some of the data obtained indicate that, while at low heavy metal concentration, the optimal metal: CMC mole ratio is 1:6; at higher metal concentrations (over 200 mg/L), a lower mole ratio, 1:2 or 1:1, is preferable. C Several experimental results show that the rejection of metal–CMC complexes is improved in treatment of drainage mine water compared to synthetic water with the same heavy metal concentration. C The high effect of decomplexation of metal: CMC complexes was proved at pH 2. Almost complete separation of metal (Cu) from the mixture was performed at this pH using a second UF unit. However, a rapid permeate flux decay at high metal concentration has to be considered. C The overall results related to the two-step process of metal (copper) complexation/UF separation — decomplexation/UF separation could be of technological interest as an opportunity for metal (copper) recovery.