Sulphate sorption at high equilibrium concentration in Andosols
(2006) Geoderma — Vol. 136, n° 3-4, p. 716-722 (2006)
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- The main process by which inorganic SO42- inputs are retained in soils is through adsorption on soil colloids. However, in soils subject to intense SO42- addition, precipitation of Al-x(SO4)(y)(OH)(z) minerals also may contribute to SO42- sorption. While direct observation of Al-x (SO4)(y)(OH)(z) precipitate in soil has been reported only recently, sorption isotherms experiments have been rarely performed to distinguish between adsorption and precipitation processes. Traditionally, SO42- sorption experiments have involved relatively low SO42- concentrations in the range 0-5 mM. However, for SO42- precipitation to occur, higher concentrations may be needed. Here, we evaluated SO42- sorption in four contrasting Andosols samples by measuring sorption isotherms with SO42- concentrations ranging from 0.1 to 15 mM and under low pH conditions (pH 4). A 1 h sorption lowest equilibration time was precipitation at high dissolvedallowed. A sorption isotherms showed a distinct biphasic shape. In the lowest SO42- concentration range (< 5 mM), SO42- sorption obeyed a Langumir isotherm, whereas at higher SO42- concentrations (> 6 mM), SO42- sorption could be described by a linear isotherm. The transition between a Langmuir-type and a linear-type isotherm also corresponded to the transition point where the solution was oversaturated with respect to Al-x(OH)(y)(SO4)(z) minerals, according to thermodynamic calculations. We interpreted these results in terms of initial SO42- adsorption onto the surface of soil constituents at lower dissolved SO42- concentrations followed by SO42- precipitation at high dissolved SO42- concentrations. (c) 2006 Elsevier B.V. All rights reserved.
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Delfosse, T., Delmelle, P., & Delvaux, B. (2006). Sulphate sorption at high equilibrium concentration in Andosols. Geoderma, 136(3-4), 716-722. https://doi.org/10.1016/j.geoderma.2006.05.009 (Original work published 2006)