Complexation at the edges of hydrotalcite: The cases of arsenate and chromate

[Display omitted] ► Hydrotalcite edges contribute to anion uptake. ► Arsenate forms inner-sphere edge complexes. ► Chromate has a much lesser affinity for edge adsorption sites. ► Stability follows the predictions of the surface complexation concept. Sorption of CrO42- and HAsO42- by hydrotalcite, i...

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Bibliographic Details
Published in:Journal of colloid and interface science 2013-03, Vol.393, p.314-318
Main Authors: Jobbágy, Matías, Regazzoni, Alberto E.
Format: Article
Language:English
Subjects:
Adsorption
Aluminum Hydroxide - chemistry
Anions
Arsenate
Arsenates
Arsenates - chemistry
Chemistry
Chlorides
Chromate
Chromates - chemistry
Crystal structure
electrophoresis
Exact sciences and technology
General and physical chemistry
Hydrogen-Ion Concentration
Hydrotalcite
ion exchange
Isotherms
Layered double hydroxides
Magnesium Hydroxide - chemistry
Solid-liquid interface
Sorption
Surface complexation
Surface physical chemistry
Surface Properties
Uptakes
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Summary:[Display omitted] ► Hydrotalcite edges contribute to anion uptake. ► Arsenate forms inner-sphere edge complexes. ► Chromate has a much lesser affinity for edge adsorption sites. ► Stability follows the predictions of the surface complexation concept. 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.
ISSN:0021-9797
1095-7103
DOI:10.1016/j.jcis.2012.10.069