Articles | Volume 6, issue 1
Research article
17 Mar 2015
Research article |  | 17 Mar 2015

Adsorption, desorption and fractionation of As(V) on untreated and mussel shell-treated granitic material

N. Seco-Reigosa, L. Cutillas-Barreiro, J. C. Nóvoa-Muñoz, M. Arias-Estévez, E. Álvarez-Rodríguez, M. J. Fernández-Sanjurjo, and A. Núñez-Delgado

Abstract. As(V) adsorption and desorption were studied on granitic material, coarse and fine mussel shell and granitic material amended with 12 and 24 t ha−1 fine shell, investigating the effect of different As(V) concentrations and different pH as well as the fractions where the adsorbed As(V) was retained. As(V) adsorption was higher on fine than on coarse shell. Mussel shell amendment increased As(V) adsorption on granitic material. Adsorption data corresponding to the unamended and shell-amended granitic material were satisfactory fitted to the Langmuir and Freundlich models. Desorption was always <19% when the highest As(V) concentration (100 mg L−1) was added. Regarding the effect of pH, the granitic material showed its highest adsorption (66%) at pH <6, and it was lower as pH increased. Fine shell presented notable adsorption in the whole pH range between 6 and 12, with a maximum of 83%. The shell-amended granitic material showed high As(V) adsorption, with a maximum (99%) at pH near 8, but decreased as pH increased. Desorption varying pH was always <26%. In the granitic material, desorption increased progressively when pH increased from 4 to 6, contrary to what happened to mussel shell. Regarding the fractionation of the adsorbed As(V), most of it was in the soluble fraction (weakly bound). The granitic material did not show high As(V) retention capacity, which could facilitate As(V) transfer to water courses and to the food chain in case of As(V) compounds being applied on this material; however, the mussel shell amendment increased As(V) retention, making this practice recommendable.

Short summary
The granitic material presented lower As(V) adsorption capacity than the mussel shell studied. Fine shell showed moderate As(V) retention (higher than coarse shell). The amendment of 12 and 24 t ha-1 fine shell on the granitic material increased As(V) retention. Most of the adsorbed As(V) did not desorb in a wide range of pH. The adsorbed As(V) was retained mainly on the soluble fraction, with weak bindings, also facilitating release and transfer to water, plants and the food chain.