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<p>The adsorption-desorption characteristics of arsenic (As) in soil may affect its mobility, bioavailability, and potential toxicity. While As adsorption behaviour in soil has been thoroughly studied, very little is known about the interactions of As with clay-sized fractions present in soils, including clay-organic complexes (COC), <i>clay-oxides</i>, and <i>clay</i>. In this study, we investigated the adsorption and desorption behaviour of As on clay-sized fractions as a function of As concentration, pH, and temperature in two different soil orders, namely Alfisol and Inceptisol. Naturally occurring COC were isolated from bulk soil using density fractionation, while <i>clay–oxides</i> and <i>clay</i> fractions were obtained through selective chemical dissolution methods. Batch adsorption–desorption experiments of As were then conducted under controlled laboratory conditions. The adsorption data exhibited a strong fit to both the Langmuir (<i>r</i> = 0.95–0.99) and Freundlich (<i>r</i> = 0.97–0.99) isotherm models. The adsorption of As on the clay-sized fractions from both Alfisol and Inceptisol was exothermic (-<b>∆</b>H° = 13.7 to 34.3&#xa0;kJ mol<sup>− 1</sup>) and spontaneous. Between the two soil orders, Alfisol had better As retention at the acidic pH (5.5) at 298&#xa0;K. Among the clay-sized fractions, clay–oxides in Alfisol and COC in Inceptisol exhibited the highest As adsorption capacities (<i>q</i><sub><i>max</i></sub>) i.e., 588 and 344&#xa0;µg g<sup>− 1</sup>, respectively. The Al-Fe oxides played a dominant role in As adsorption–desorption in Alfisol, whereas organic matter was more influential in Inceptisol. The desorption efficiency was higher in Inceptisol and the desorption index (DI) revealed comparatively higher hysteresis (DI &gt; 1) for COC in Alfisol and Inceptisol and <i>clay-oxides</i> in Alfisol. These findings enhance understanding of the contrasting roles of Al–Fe oxides and organic matter to regulate As retention and desorption at varying temperature and pH, providing valuable insight for predicting As mobility and developing soil-specific management strategies to ensure environmental safety and sustainable agricultural production.</p>

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Adsorption-desorption behaviour of arsenic on naturally occurring clay-organic complexes in an Alfisol and Inceptisol

  • 期刊论文

  • 发表日期：

    2025年9月9日

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  • Deepak,
  • Ruma Das,
  • Debasis Golui,
  • Nayan Ahmed,
  • Ram Swaroop Bana,
  • Amrit Kumar Jha,
  • Siba Prasad Datta

摘要

The adsorption-desorption characteristics of arsenic (As) in soil may affect its mobility, bioavailability, and potential toxicity. While As adsorption behaviour in soil has been thoroughly studied, very little is known about the interactions of As with clay-sized fractions present in soils, including clay-organic complexes (COC), clay-oxides, and clay. In this study, we investigated the adsorption and desorption behaviour of As on clay-sized fractions as a function of As concentration, pH, and temperature in two different soil orders, namely Alfisol and Inceptisol. Naturally occurring COC were isolated from bulk soil using density fractionation, while clay–oxides and clay fractions were obtained through selective chemical dissolution methods. Batch adsorption–desorption experiments of As were then conducted under controlled laboratory conditions. The adsorption data exhibited a strong fit to both the Langmuir (r = 0.95–0.99) and Freundlich (r = 0.97–0.99) isotherm models. The adsorption of As on the clay-sized fractions from both Alfisol and Inceptisol was exothermic (-∆H° = 13.7 to 34.3 kJ mol− 1) and spontaneous. Between the two soil orders, Alfisol had better As retention at the acidic pH (5.5) at 298 K. Among the clay-sized fractions, clay–oxides in Alfisol and COC in Inceptisol exhibited the highest As adsorption capacities (qmax) i.e., 588 and 344 µg g− 1, respectively. The Al-Fe oxides played a dominant role in As adsorption–desorption in Alfisol, whereas organic matter was more influential in Inceptisol. The desorption efficiency was higher in Inceptisol and the desorption index (DI) revealed comparatively higher hysteresis (DI > 1) for COC in Alfisol and Inceptisol and clay-oxides in Alfisol. These findings enhance understanding of the contrasting roles of Al–Fe oxides and organic matter to regulate As retention and desorption at varying temperature and pH, providing valuable insight for predicting As mobility and developing soil-specific management strategies to ensure environmental safety and sustainable agricultural production.