INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
Complexation at the edges of hydrotalcite: The cases of arsenate and chromate.
M. JOBBÁGY; A.E. REGAZZONI
JOURNAL OF COLLOID AND INTERFACE SCIENCE
ACADEMIC PRESS INC ELSEVIER SCIENCE
Lugar: Amsterdam; Año: 2013 vol. 393 p. 314 - 314
Sorption of CrO42- and HAsO42- by hydrotalcite, in its chloride form, was studied as a function of anion concentration. In both cases, the shape of the isotherms is langmuirian. The maximum uptake of CrO42- equals the ion-exchange capacity of the solid, whereas sorption of HAsO42- saturates at a higher value. Chloride ions inhibit the uptake of both anions, the amount of sorbed CrO42- declining rapidly to zero. The uptake of HAsO42-, however, attains a constant value at high chloride concentrations. The excess of arsenate uptake follows, at constant pH, a langmuirian dependence with equilibrium concentration and decreases with increasing pH, depicting a marked change in slope at pH ≈ pQa3. CrO42- and HAsO42- have notable, albeit different, effects on the electrophoretic behavior of hydrotalcite; the positive particle charge is screened almost completely by CrO42-, whereas sorption of HAsO42- produces charge reversal. These results reflect the formation of inner-sphere arsenate surface complexes at the edges of hydrotalcite particles. The underlying rationale is discussed in terms of the crystal structure of hydrotalcite surfaces.