Polyacrylamide grafted onto cellulose has been demonstrated to be a very efficient selective sorbent for removal of mercuric ions from aqueous solutions. The mercury-uptake capacity of the graft polymer is as high as 3.55 mmol/g and sorption is also reasonably fast. Thus, 0.2 g of the graft copolymer is able to extract 50 ppm Hg(II) from 50 ml water completely in 8 min. The Hg(II) sorption is selective and no interferences have been observed in the presence of Ni(II), Co(II), Cd(II), Fe(III), Zn(II) ions in 0.1 M concentrations at pH 6. Regeneration of the loaded polymer without losing its original activity can be achieved using hot acetic acid. The graft copolymer described seems very suitable for removal of large amounts of mercury in hydrometallurgical applications and may also be useful for other water treatments.

Graft copolymer of acrylamide onto cellulose as mercury selective sorbent

Polyacrylamide was grafted from N-chlorosulfonamide groups onto crosslinked polystyrene beads using copper-mediated atom transfer radical polymerization (ATRP) methodology. A beaded polymer with a polyacrylamide surface shell was prepared in four steps, starting from styrene–divinylbenzene (10%) copolymer beads of 210–420 mm particle size: chlorosulfonation; sulfamidation with propylamine; N-chlorination with aqueous hypochloride; and grafting using a concentrated aqueous acrylamide solution with a CuBr–tetramethylethylenediamine complex (1:2). The resulting polymer resin with 84 wt% grafted polyacrylamide has been demonstrated to be an efficient mercury-specific sorbent, able to remove Hg(II) from solutions at ppm levels. No interference arises from common metal ions such as Cd(II), Fe(III), Zn(II), and Pb(II). The sorbed mercury can be eluted by repeated treatment with hot acetic acid without hydrolysis of the amide groups.  2002 Elsevier Science B.V. All rights reserved.

Atom transfer radical graft polymerization of acrylamide from N-chlorosulfonamidated polystyrene resin, and use of the resin in selective mercury removal

Polymer-supported pendant urea groups have been demonstrated to be very efficient in selective removal of mercuric ions from aqueous solutions. Methyl methacrylate (0.5 mol)–glycidyl methacrylate (0.4 mol)–divinylbenzene (0.1 mol) terpolymer beads have been prepared by suspension polymerisation. Urea functions have been incorporated into the bead polymer (210–420 μm) via a two-step modification of the epoxy groups involving firstly reaction with excess of triethylenetetramine followed by acidic isocyanate. The resulting polymer resin has a urea group loading of 7.8 mmol g−1 and shows excellent mercury binding capacity >6.7 mmol g−1, even in the presence of excess chloride ions. The mercury sorption is strictly selective and Ca(II), Mg(II), Zn(II), Pb(II), Fe(II) and Cd(II) ions (0.2–0.3 M) do not give rise to any interference. The mercury can be recovered from loaded beads using hot acetic acid thereby regenerating the polymer. Recovered samples can be recycled more than 20 times without loss of activity as a result of the hydrolytic stability of the urea group in acetic acid.

A glycidyl methacrylate-based resin with pendant urea groups as a high capacity mercury specific sorbent

Poly(acrylamide) is grafted onto cross-linked poly (4-vinyl pyridine) (P4-VP) resin “Reillex 425”. Its quaternization with potassium chloroacetate results in cross-linked poly (4-vinyl pyridine) having carboxymethyl pyridinium groups. This resin is grafted with acrylamide after redox initiation through the carboxyl groups with cerium ammonium nitrate. The resulting resin with 111.7 wt% of poly(acrylamide) grafts is a high capacity (3.36 mmol g −1 ) mercury specific sorbent. Experiments performed under identical conditions with some other ions such as Zn(II), Pb(II), Fe(III) and Cd(II) showed that those metal ions are not sorbed by the resin. Flexible graft chains of poly(acrylamide) provide nearly homogeneous reaction conditions in mercury uptake. Regeneration of the mercury loaded polymer can be achieved by acetic acid treatment.

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Poly(acrylamide) grafts on spherical polyvinyl pyridine resin for removal of mercury 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 polyacrylamide 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 result 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). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3068–3078, 2002

Sister Alonza Smith

Papers

Determination of Mercury with s -Diphenylcarbazide