Effects of Anions on the Capacity and Affinity of Copper Adsorption in Two Variable Charge Soils

• Published in: Biogeochemistry 2005-08, Vol.75 (1), p.1-18
• Main Authors: Yu, S, He, Z.L, Huang, C.Y, Chen, G.C, Calvert, D.V
• Format: Article
• Language: English
• Subjects: acetates; Acid soils; Adsorption; Anions; chlorides; clay loam soils; Clay soils; Copper; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; nitrates; Sodic soils; Soil and rock geochemistry; Soil pollution; Soil solution; Soils; sorption isotherms; sulfates; Surficial geology; Variable charge; variable charge soils
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-003-5549-2

Effects of nitrate (NO₃⁻), chloride (Cl⁻), sulfate ($\text{SO}_{4}{}^{2-}$), and acetate (Ac⁻) on$\text{Cu}^{2+}$adsorption and affinity of the adsorbed$\text{Cu}^{2+}$were evaluated in two Fe and Al enriched variable charge soils from Southern China. The maximum adsorption of$\text{Cu}^{2+}$(M, a parameter from the Langmuir isotherm model) in the presence of different anions decreased in the order Cl⁻ &gt Ac⁻ &gt NO₃⁻ &gt$\text{SO}_{4}{}^{2-}$for both soils. The clayey loamy soil (mixed siliceous thermic Typic Dystrochrept, TTD), developed on the Arenaceous rock, adsorbed less$\text{Cu}^{2+}$than the clayey soil (kaolinitic thermic Plinthudults, KTP), derived from the Quaternary red earths, regardless of anion type present in the medium. The affinity of adsorbed$\text{Cu}^{2+}$to both soils could be characterized by the Kd (distribution coefficient) values and successive extraction of the adsorbed$\text{Cu}^{2+}$with 1-mol NH₄Ac$\text{L}^{-1}$. The$\text{log}_{10}K\text{d}$value was smaller for the TTD soil than for the KTP soil and decreased in the order of Cl⁻ &gt NO₃⁻ &gt$\text{SO}_{4}{}^{2-}$&gt Ac⁻ at low initial$\text{Cu}^{2+}$concentrations (≤ 40 mg$\text{Cu}^{2+}$ $\text{L}^{-1}$), whereas at 80 mg$\text{Cu}^{2+}$ $\text{L}^{-1}$, the$\text{log}_{10}Kd$value was similar for NO₃⁻,$\text{SO}_{4}{}^{2-}$, and Ac⁻, but was slightly higher for Cl⁻. Complete extraction of$\text{Cu}^{2+}$adsorbed in the presence of Ac⁻ was achieved. Influence of NO₃⁻ and$\text{SO}_{4}{}^{2-}$on the affinity of adsorbed$\text{Cu}^{2+}$was similar, but the effects of Cl⁻ depended on the initial$\text{Cu}^{2+}$concentrations. The extracted percentage of the adsorbed$\text{Cu}^{2+}$in the presence of NO₃⁻ or$\text{SO}_{4}{}^{2-}$increased with increasing$\text{Cu}^{2+}$adsorption saturation. The presence of Cl⁻, NO₃⁻, or$\text{SO}_{4}{}^{2-}$markedly decreased the equilibrium solution pH for both soils with increasing initial$\text{Cu}^{2+}$concentrations, and the delta pH values at the highest$\text{Cu}^{2+}$level were 0.5, 0.63, and 0.55 U for the TTD soil and 0.79, 0.84, and 0.93 U for the KTP soil, respectively for the three anions. The presence of Ac⁻ had a minimal influence on the equilibrium solution pH because of the buffering nature of the NaAc/HAc medium which buffered the released protons. The effects of anions on$\text{Cu}^{2+}$adsorption and affinity of the adsorbed$\text{Cu}^{2+}$were dependent on anion types and were apparently related to the altered surface p