MECHANISMS OF CHROMIUM(III) SORPTION ON SILICA .2. EFFECT OF REACTIONCONDITIONS

Metal ion retention on solids present in soils and waters decreases th e risk of these contaminants as they are removed from the mobile aqueo us phase. Determining the stability of the sorbed metal ions and the r eaction conditions which influence the structure of the sorbate are ne cessary to evaluate the environmental risk of the sorbed moieties. In this study, a multitude of molecular level experimental techniques, in cluding diffuse reflectance infrared Fourier transform (DRIFT) spectro scopy and high-resolution transmission electron microscopy (HRTEM), we re employed to ascertain the Cr(III) surface structure on amorphous Si O2 (silica) and reaction conditions (pH, solution Cr concentrations, a nd surface coverage) that affect the sorption mechanism. Chromium(III) formed a monodentate surface complex on silica at surface coverages l ess than 20%, while at greater surface coverages discrete chromium hyd roxide surface clusters were discerned. Only the extent of surface cov erage was observed to influence the atomic structure of Cr(III) on sil ica.