Affinity and Selectivity of Immobilized NMethyl-D-glucamine for Mercury(II) Ions

N-Methyl-D-glucamine (NMDG) immobilized onto cross-linked poly(vinylbenzyl chloride) beads is found to have a high affinity and selectivity for Hg(II) from nitric and hydrochloric acid solutions. In HNO3, complexation is >98% from a solution at pH 3, which decreases to 11.2% from 1 M HNO3. Hg(II) is complexed to a greater extent from HCl: 95.4% is complexed from 1 M HCl and >99.5% from solutions at pH 1.0 and greater. Control studies with immobilized sorbitol show that coordination of Hg(II) by the -OH groups is an important component of the mechanism. Complexation by sorbitol is dependent on the pH. Log-log plots of the distribution coefficients versus the hydrogen ion concentration at equilibrium show the importance of the changing nature of the solution species: since ion exchange is not mechanistically possible with sorbitol, the pH dependency reflects the effect of pH on shifting the species in solution from noncoordinating Hg(NO3)42- and HgCl42- to coordinating Hg(NO3)+ and HgCl2. Comparison to results with immobilized diethanolamine and dimethylamine ligands shows that the high Hg(II) affinity of the glucamine may be attributed to cooperation between the tertiary amine and -OH moieties through a N···Hg coordinative interaction. The kinetics is rapid: 98.6% of the complexation occurs within 10 min. The immobilized glucamine has no affinity for other cations (Pb(II), Cd(II), Cu(II), Ni(II), and Zn(II)). The Hg-loaded polymer may be quantitatively regenerated with 4 M HNO3.