Kinetic modeling of antimony(V) adsorption–desorption and transport in soils

Abstract

h i g h l i g h t sSb(V) sorption on soils were timedependent and irreversible. Retention mechanisms were different for acidic red soil and calcareous soil. Sb(V) transport in soils dominated by non-equilibrium reactions. Kinetic reversible-irreversible MRM formulation well described experiment results. Antimonate [Sb(V)] adsorption-desorption and transport in an acidic red soil (Yingtan) and a calcareous soil (Huanjiang) was investigated using kinetic batch and miscible displacement experiments. Different formulations of a multi-reaction model (MRM) were evaluated for their capabilities of describing the retention and transport mechanisms of Sb(V) in soils. The experimental results showed that adsorption of Sb(V) by two soils was kinetically controlled and largely irreversible. The Sb(V) adsorption capacity and kinetic rate of the acidic red soil was much higher than that of the calcareous soil. The asymmetrical breakthrough curves indicated the strong dominance of non-equilibrium retention of Sb(V). A four step sequential extraction procedure provided evidence that majority of applied Sb(V) was irreversibly retained. A formulation of MRM with two kinetic sorption sites (reversible and irreversible) successfully described Sb(V) adsorption-desorption data. The use of kinetic batch rate coefficients for predictions of breakthrough curves (BTCs) underestimated Sb(V) retention and overestimated its mobility. In an inverse mode with optimized rate coefficients, the MRM formulation was capable of simulating Sb(V) transport in soil columns.

Kinetic modeling of antimony(III) oxidation and sorption in soils

“…Extensive retention and low mobility of Sb(III) was found in the two soils before 100 pore volumes of Yingtan soil and 150 pore volumes of Huanjiang soil. This result was different with the result of Sb(V) study by Zhang et al [28] in the same two soils. In their study Sb(V) can easily breakthrough the soil column of Huanjiang soil, while for Yingtan soil Sb(V) was extensive retention.…”

“…The adsorption isotherms of Sb tot in Fig. 2 was different from Sb(V) adsorption results from our previous study [28], which showed that the adsorption of Sb(V) in Yingtan soil was much higher than in Huanjiang soil. This is because that Sb(V) adsorption was dramatically influenced by solution pH while Sb(III) can be adsorbed in a wide range of pH [35].…”

“…After 200 pore volumes of KCl input, most of the Sb leached out was Sb(V). In calcareous Huanjiang soil Sb(V) showed a non-equilibrium transport process as the extensive tailing and slow release during leaching [28]. In our experiment the extensive tailing and slow release of Sb(V) was more significantly due to the oxidation rate of Sb(III) and abundant of Sb(III) adsorbed before leaching.…”

“…The peak Sb tot concentration in the effluent of Huanjiang soil column was only about 15% of the applied concentration after applying approximately 300 pore volumes of Sb solution. This is contrary to the transport behavior of Sb(V) in the same two soils [28]. It means that Sb(III) has strong mobility in acidic Yingtan soil with colloid of Fe-oxides, while on the contrary Sb(V) was more easily transport in calcareous Huanjiang soil.…”

“…However, to our knowledge the redox chemistry of Sb in natural soil-water systems is still unclear. Furthermore, although Zhang et al [28] have proven numerical models incorporating kinetic reactions and transport processes was capable of simulating Sb(V) transport in soil columns, their capability in simulating the retention and transport of Sb(III) in soils has not been evaluated.…”