Heavy metal flocculation by phosphonomethylated-polyethyleneimine and calcium ions

Removal of various heavy metal ions such as Cu2+, Co2+, Zn2+, Ni2+, and Pb2+ from aqueous solutions by induced flocculation of phosphonomethylated-polyethyleneimine (PPEI)-heavy metal complex with Ca2+ ions was studied. Considerable floc formation accompanying metal sequestration was demonstrated, even at low initial concentration of the target metals. The PPEI-Ca2+ flocculant system was also effective for heavy metal scavenging purposes. Applications in actual waste streams, particularly in the treatment of wastewaters, such as rinse solutions from electroless Ni plating, which contain competing complexing species such as EDTA, highlighted some of the advantages of the process over traditional alkali precipitation methods. The ability of spent PPEI flocculant to be regenerated by 2 N HCl has also been confirmed with slight effect on its metal sequestration ability.