文摘
The uptake of platinum group elements (PGE) by differentpreparations of estuarine sediment suspended in filteredriver water has been examined. For a given PGE, adsorptiontime courses to untreated sediment and to sedimentwhose hydrous metal oxides or organic matter had beenremoved by appropriate chemical treatments were similar.Adsorption of Rh(III) and Pt(IV) proceeded via a first-order reversible reaction. For Rh, forward rate constantswere 1 order of magnitude greater than reverse rate constants,but for Pt, forward and reverse constants were comparable.Respective system response times, required to attain63% of the new equilibrium, ranged from about 10 to 30 hand 2 to 20 h. In contrast, rapid, initial uptake of Pd(II)was succeeded, in most instances, by a protracted periodof desorption, requiring a more complex mechanisticinterpretation. In all cases, adsorption was reduced followinga period of PGE equilibration with filtered river water,suggesting that complexation with natural organic ligandsexerts a significant control on the adsorption processby, for example, stabilizing PGE in solution. Exchangeabilityof adsorbed PGE, evaluated by ammonium acetateextraction, decreased in the order Pd > Pt > Rh, inqualitative agreement with the proposed or modeledadsorption mechanisms. Experimental results, togetherwith independent assessments of PGE mobility from secondarysources (e.g. road dust), indicate that Pd has the greatestpotential for long-range transport and bioaccumulationin the aquatic environment.
