Sorption-desorption behaviour of arsenic on clay-organic complex (COC) in an Alfisol and Inceptisol of Jharkhand
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Date
2021
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Division of Soil Science and Agricultural Chemistry ICAR-Indian Agricultural Research Institute New Delhi
Abstract
The high concentration of arsenic (As) in soil may pose to potential risk for groundwater contamination and its entry in the food chain. Sorption-desorption of As on different soils especially on clay sized fractions may affect its mobility, toxicity and bioavailability in soil. Therefore, knowledge about arsenic sorption-desorption processes is of relevance in order to predict the behaviour of this element. The interaction of As with soil minerals is greatly influenced by the contents of organic carbon and amorphous Fe-Al-oxides, type of clay minerals as well as soil pH and temperature. Therefore, a laboratory batch experiments were carried out to study the sorption-desorption behaviour of As on soil and clay sized fractions of two different soil orders namely – Alfisol and Inceptisol at varying pH (5.5 and 7.0) and temperature (298 and 308 K). The Alfisol and Inceptisol was dominated with smectite and illite minerals respectively. The contents of organic C was lower and free and amorphous aluminium (Al) and iron (Fe) oxides was higher in Alfisol compared to the Inceptisol. The results showed that the adsorption capacity was higher for soil and clay sized fractions in Alfisol compared to the Inceptisol. The adsorption of As on clay-organic complex was higher at lower pH (5.5) compared to the higher pH in both the soil orders. The adsorption isotherms for both soil orders fitted well to Langmuir and Freundlich models. Among clay sized fractions, high adsorption capacity was found for clay-oxides and clay-organic-complex of Alfisol and Inceptisol, respectively. The thermodynamic results revealed that the sorption reactions were exothermic and favourable at lower temperature (298 K) compared to the higher one (308 K). The desorption data showed that the cumulative desorption was higher in Alfisol but the percentage of As desorbed was higher in Inceptisol. The desorption Index (DI) was higher in Alfisol compared to Inceptisol. Removal of organic matter and Al and Fe oxides decreased the DI in clay for both the soil order. The contents of organic matter, Al-Fe-oxides and type of clay minerals were the major factor to determine the sorption-desorption behavior of As in soil.
Description
T-10615