Effects of soil components, solution chemical properties, and temperature on Cu(II) adsorption by alluvial acid soil: a case study in Southwest China

Soil components, solution chemical properties, and temperature are important factors that affect Cu(II) adsorption in soil. However, the research in this area is currently lacking. In this study, the clay fraction was separated from alluvial acid soil. In addition, organic matter, free Fe oxides, and Mn oxides were selectively removed by washing the bulk soil and the clay fraction with H2O2, Na3C6H5O7·2H2O + NaHCO3 + Na2S2O4, and HONH3Cl. Adsorption experiment results indicate that Cu(II) adsorption decreased for bulk soil and clay fractions after removing organic matter and Mn oxides. However, after free Fe oxides were removed, the Cu(II) adsorption increased for bulk soil and clay fractions. The adsorption capacity of the clay fraction for Cu(II) was higher than that of the bulk soil irrespective of the selective chemical extraction treatment. When the initial pH increased from 2 to 3.5, the adsorption capacity increased rapidly; when the pH > 6, the adsorption capacity did not change significantly. When the pH was greater than 6, increased Cu(II) adsorption may occur due to the precipitation of Cu(II). Increased ionic strength can inhibit Cu(II) adsorption. The effects of foreign ions on Cu(II) adsorption were in the order Na+ < K+ < Mg2+ < Ca2+ for cations and NO3− < SO42− ≈ Cl− for anions. The Cu(II) adsorption was an endothermic and spontaneous process under the investigated experimental conditions.