Abstract
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.
Highlights
Igneous rocks, as granite, have low As concentrations (< 5 mg kg−1), and background levels in soils are between 5 and 10 mg kg−1 (Smedley and Kinniburgh, 2002), As levels are much higher in certain polluted soils
The objectives of this work are (a) to determine As(V) retention/release capacity corresponding to a granitic material, fine mussel shell and coarse mussel shell, as well as to the granitic material amended with 12 or 24 t ha−1 fine mussel shell, for different As(V) concentrations and pH values; (b) to examine fitting of adsorption data to the Langmuir and Freundlich models; and (c) to determine the fractions where the adsorbed As(V) was retained, which is in relation with stability of retention
The granitic material was sampled in a zigzag manner (20 cm depth), with 10 subsamples taken to perform the final one
Summary
As granite, have low As concentrations (< 5 mg kg−1), and background levels in soils are between 5 and 10 mg kg−1 (Smedley and Kinniburgh, 2002), As levels are much higher in certain polluted soils. As indicated in previous works, the use of wood preservative compounds including arsenic or of As-based herbicides could cause arsenic pollution episodes in forest areas (Smith et al, 1998) and cultivation soils (Gur et al, 1979), in both cases increasing risks of soil and water pollution (Clothier et al, 2006). In this way, it is interesting to determine As retention capacity corresponding to solid substrates receiving the spreading of the pollutant, both individually or treated with complementary materials that can affect As retention/release potential.
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