Self-assembly of polyelectrolytes for the removal of metal cations from aqueous solutions

Interactions between polyacrylic acid (PAA) and polyethyleneimine (BPEI) were investigated in the absence and in the presence of metal cations (M) over a large pH-range. These interactions led to the formation of complexes with sizes in the range from colloids to particles. The sizes of the complexes, structures of the resulting media and free metal concentrations were strongly dependent on the way reactants were put into contact. Best conditions for metal separation were obtained when the polycation was used to neutralise the anionic PAA–M complex since it resulted in fast gravity separation of metals and low residual concentrations. A single-step ultrafiltration (UF) treatment was also studied and compared to a two-step treatment made of gravity separation and UF of supernatants in terms of quality and volumetric rates for treated wastewater.