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

Abstract

As(V) adsorption and desorption were studied ongranitic material, coarse and fine mussel shell and graniticmaterial amended with 12 and 24 t ha−1fine shell, investi-gating the effect of different As(V) concentrations and dif-ferent pH as well as the fractions where the adsorbed As(V)was retained. As(V) adsorption was higher on fine than oncoarse shell. Mussel shell amendment increased As(V) ad-sorption on granitic material. Adsorption data correspond-ing to the unamended and shell-amended granitic materialwere satisfactory fitted to the Langmuir and Freundlich mod-els. Desorption was always<19 % when the highest As(V)concentration (100 mg L−1) was added. Regarding the effectof pH, the granitic material showed its highest adsorption(66 %) at pH<6, and it was lower as pH increased. Fineshell presented notable adsorption in the whole pH rangebetween 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 pHincreased. Desorption varying pH was always<26 %. In thegranitic material, desorption increased progressively whenpH increased from 4 to 6, contrary to what happened to mus-sel shell. Regarding the fractionation of the adsorbed As(V),most of it was in the soluble fraction (weakly bound). Thegranitic material did not show high As(V) retention capacity,which could facilitate As(V) transfer to water courses and tothe food chain in case of As(V) compounds being appliedon this material; however, the mussel shell amendment in-creased As(V) retention, making this practice recommend-able