HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (19) Citing Articles via Google Scholar Google Scholar Articles by Waltham, C. A. Articles by Eick, M. J. Search for Related Content PubMed Articles by Waltham, C. A. Articles by Eick, M. J. GeoRef GeoRef Citation Agricola Articles by Waltham, C. A. Articles by Eick, M. J. Related Collections Soil Kinetics Soil Pollution Soil Chemistry

DIVISION S-2—SOIL CHEMISTRY

Kinetics of Arsenic Adsorption on Goethite in the Presence of Sorbed Silicic Acid

Dep. of Crop, Soil, and Environmental Science, 236 Smyth Hall, Virginia Tech, Blacksburg, VA 24061

* Corresponding author (eick{at}vt.edu)

The potential toxicity and availability of As in the environment is dependent on several factors including redox potential, pH, and the presence of ligands that can compete for adsorption sites on mineral surfaces. Silicic acid is a ligand ubiquitous in natural systems and strongly chemisorbs to Fe oxides. However, there are relatively few studies examining its influence on As adsorption on Fe oxides. This study examined the influence of silicic acid (0.10 and 1.0 mM) on the adsorption kinetics of arsenite and arsenate (0.10 mM) on goethite over a range of common soil pH values (4, 6, and 8). The rate of arsenic (III and V) and silicic acid adsorption was greatest at pH values near their pK₁ value. However, silicic acid sorption was characterized by biphasic kinetics with rapid adsorption followed by a much slower adsorption reaction. The rate and total quantity of arsenite adsorption decreased in the presence of silicic acid at all pH values and concentrations of silicic acid. Approximately 40% less arsenite was adsorbed in the presence of 1.0 mM silicic acid at all pH values. At 0.10 mM, silicic acid had less of an effect on arsenite adsorption. In contrast, only the rate and not the total quantity of arsenate was reduced in the presence of silicic acid. The rate of arsenate adsorption decreased as pH and silicic acid concentration increased. This was attributed to a decrease in the goethite's surface potential upon specific adsorption of silicic acid and deprotonation of the arsenate molecule creating an unfavorable electrostatic field. These results demonstrate the importance of evaluating As speciation, reaction kinetics, and the influence of naturally occurring ligands on the adsorption of As on variable charge surfaces.

Abbreviations: FESEM, field emission scanning electron microscopy • PZC, point of zero charge • TGA, thermal gravimetric analysis • XRD, x-ray diffraction

This article has been cited by other articles:

				T. P. Luxton, C. J. Tadanier, and M. J. Eick Mobilization of Arsenite by Competitive Interaction with Silicic Acid Soil Sci. Soc. Am. J., January 6, 2006; 70(1): 204 - 214. [Abstract] [Full Text] [PDF]

				S. M. Garman, T. P. Luxton, and M. J. Eick Kinetics of Chromate Adsorption on Goethite in the Presence of Sorbed Silicic Acid J. Environ. Qual., September 1, 2004; 33(5): 1703 - 1708. [Abstract] [Full Text] [PDF]