Interaction of europium with humic acid covalently bound to silica beads

The uptake of Eu3+ (a trivalent actinide homolog) by Aldrich humic acid cov alently bonded to an inorganic support is examined. Two types of covalent l inkages are used and the synthetic routes to produce the resins are discuss ed. The use of these resins excludes having to account for humic acid desor ption from the surface, yields a well characterized system, and allows the experiment to focus on and account for the role of humic acid in the sorpti on of Eu. The proton exchange capacity of the resins is examined by titrati on and the differences observed are traced to the resin synthesis. Europium sorption experiments are performed at pH 4 and pH 6 in 0.1 M NaClO4. Kinet ic experiments show equilibrium is reached in 24 hours. The kinetic data ar e used to evaluate the loading capacity, with results similar to equilibriu m experiments. The complexation results are evaluated based on the metal io n charge neutralization model. For the resins an effect of pH and resin syn thesis route on the Eu uptake is observed. The uptake increases with pH for both resins. The resin HA-Epo (Epoxy linkage) has a higher metal binding a t pH 4, while the resin HA-HAB (2-hydroxylazobenzene linkage) had more prot on exchange sites occupied by metal ions at pH 6. Overall, more Eu is bound to HA-Epo at pH 6 since its proton exchange capacity is higher. The evalua ted stability constants vary slightly and show a dependence on the linkage group but are similar to Literature values that examined complexation by aq uatic humic acid analyzed with the same model. This result supports the uti lity of the metal ion charge neutralization model and the applicability of the resulting stability constants.