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

摘要

As(V) adsorption and desorption were studied on granitic material, coarse andfine mussel shell and granitic material amended with 12 and 24 t ha?1fine shell, investigating the effect of different As(V) concentrations anddifferent 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 shellamendment increased As(V) adsorption on granitic material. Adsorption datacorresponding to the unamended and shell-amended granitic material weresatisfactory fitted to the Langmuir and Freundlich models. Desorption wasalways <19% when the highest As(V) concentration (100 mg L?1)was added. Regarding the effect of pH, the granitic material showed itshighest adsorption (66%) at pH <6, and it was lower as pHincreased. Fine shell presented notable adsorption in the whole pH rangebetween 6 and 12, with a maximum of 83%. The shell-amended graniticmaterial showed high As(V) adsorption, with a maximum (99%) at pH near8, but decreased as pH increased. Desorption varying pH was always<26%. In the granitic material, desorption increased progressivelywhen 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 thesoluble fraction (weakly bound). The granitic material did not show highAs(V) retention capacity, which could facilitate As(V) transfer to watercourses and to the food chain in case of As(V) compounds being applied onthis material; however, the mussel shell amendment increased As(V) retention,making this practice recommendable.