Poly(acrylamide) grafts on spherical bead polymers for extremely selective removal of mercuric ions from aqueous solutions

Poly(acrylamide) grafted from solid polymer particles provides a simple solution for extremely selective removal of mercuric ions from aqueous solutions. The grafting of polyacrylamide has been performed, in high yields (164%), by redox initiation from iminoacetic acid groups created on crosslinked spherical beads (210-420 μm) of glycidyl methacrylate/methyl methacrylate/ethylene glycol dimethacrylate terpolymer. In the grafting, homopolymer formation has been reduced greatly (22%) by the treatment of the bead polymer with ceric ammonium nitrate before the addition of acrylamide monomer. The mobility of the graft chains provides nearly homogeneous reaction conditions and rapid mercury binding ability, as for low molecular weight amides [mercury sorption by a 0.105-g polymer sample from 105 mL of a 7.74 × 10^-4 mol L^-1 (∼155 ppm) Hg(II) solution shows first-order kinetics with respect to the Hg(II) concentration, k = 1.1 × 10^-3 s^-1]. The mercury sorption capacity under nonbuffered conditions is around 3.6 mmol g^-1 (i.e., 720 g of mercury/kg) and mostly occurs with the formation of diamido-mercury linkages, which result in the crosslinking of polyacryl-amide brushes outside the spherical beads. The crosslinks can be destroyed by treatment with hot acetic acid, without hydrolysis of the amide groups. This process allows a complete elution of the mercury as mercury acetate, and the overall results is reversible crosslinking of the outer shell by mercuric ions. The material presented is efficient in the removal of mercury at concentrations measured in parts per million, and the mercury sorption is extremely selective over some foreign ions, such as Fe(III), Cd(II), Zn(II), and Pb(II).