“Caption of Hg(II) from acid aqueous solution by immersed poly(N-vinylimidazole) hydrogel particles was studied as a function of pH, counterion, and cation concentration. Fitting parameters to several sorption isotherms have been determined. Their values depend mostly on pH and less, on temperature and counterion, and suggest a large affinity of imidazole groups in the gel and mercury cations. Practically total removal (94.4%) of Hg(II) is achieved at pH = 2, with 10 g of dry gel per liter of solution, when cation concentration was as large as 15,000 ppm (0.075 M). Polymer protonation decreases about fourfold the cation affinity, supporting competitive protonation- complexation mechanisms. By its side, metal uptake decreases polymer protonation. Thermal stability of loaded gels decreases with respect to metal free hydrogels. Scanning electron micrographs reveal no changes in the gel morphology upon cation binding, but Tg increases significantly with the Hg(II) content of loaded gels and swelling decreases moderately, indicating the role of the cation as ionic crosslinker. Practically total elution of Hg(II) is achieved with 1 M HNO3 in consecutive loadingelution cycles.
© 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1467-1475, 2001″

By: M. J. MOLINA,1 M. R. GO´ MEZ-ANTO´ N,1 B. L. RIVAS,2 H. A. MATURANA,2 I. F. PIE´ROLA3

Summary:
Methods of removing heavy metal contamination has been proposed:
Filtration, chemical precipitation, simple and chelation ion exchange, sorption, membrane system.

Search for polymer resins and hydrogels which have electron donor groups have the ability to bind to metal cations.

The use of resin has been proposed in these methods:

1. ion-exchange resins
2. polymer-enhanced ultra filtration
3. precipitation agents

Why Hydrogel?
One reason is that they do not transfer susbtance to the aqueous solution, and can be easily cleaned up indefinately.
Hydrogel used poly(vinylimidazole) hydrogel
(similar to vinylimidazolium sulphobetaine except no sulphate group)
Could sulphate group induce antisceptic properties?

Swelling properties was measured:
4.32g of water per gram of dry gel
(gel made is weighted, mixed with water of x amount. Reweighted difference is minused)

How they measured Hg(II) sorption
Preformed in batch with hydrogel particles suspended in aq solution.
Effective concentration of 10g of dry polymer per 1L of solution.
Equilibrium took 2 days at r.t (20 degrees C)
Concluded that time-dependent retention measurements that 15min was sufficient to reach equilibrium.

Apparatus and Method
Tg was determined.
Thermal stability studied.
SEM micrograph was determined via coating surface with gold.

Potentiometric measurement were performed to determine the degree of protonation α by expression:

α = (10(pH initial) – 10(pH final))/(Hydrogel effective concentration)

Hydrogel effective concentration was deteremined by loading experiements, Hydrogel effective concentration was 10g/L = 0.1M.

The hydrogel was synthesized by a radical crosslinking polymerization.

@ pH = 2 most effective with both sulfuric and hydrochloric acid.
Added 15000ppm final about left 840ppm, 94.4% Asborbed

Experimental capacity of a resin is smaller than the calculated maximum capacity, because part of the ligands is not accessible to the metallic ions.

Describes models used and suggestions for why the models fit or do not fit.

Affinity of the imidazole group is studied and reported that it has a large affinity.

Protons and Hg(II)/metal cation compete to be bound by the imidazole group