Study on the treatment of wastewater containing mercury by macromolecular heavy metal flocculant mercaptoacetyl polyethyleneimine.

A novel water-soluble macromolecule heavy metal flocculant mercaptoacetyl polyethyleneimine (MAPEI) was synthesized by reacting polyethyleneimine (PEI) with thioglycolic acid (TGA). The removal of mercury ions (Hg2+) and turbidity from aqueous solutions by MAPEI was investigated. The MAPEI is efficient for the simultaneous removal of Hg2+ and turbidity. The highest removal ratio of mercury ions was above 95%. Factors were studied that could affect the process, such as pH, molecular weight of PEI, co-existing ions, and so on, and the results show that, with the increase in pH or molecular weight of PEI, the removal rate increases; alkali metal and alkaline-earth metal ions and chloride ions (Cl-) and nitrate (NO3-) ions can promote the removal of Hg2+, while sulfate (SO4(2-)) suppresses the process. In the process of treating wastewater containing both turbidity and mercury ions, both have a synergic removal effect with each other. Compared with TGA, MAPEI shows obvious advantages, including higher removal efficiency, larger flocs, and higher floc sedimentation velocity. In addition, compared with PEI, both PEI and MAPEI are almost equally not efficient for turbidity removal, but the presence of mercury ions can improve greatly the efficiency of MAPEI in the removal of turbidity.