Adsorption–Desorption Behavior of Copper at Contaminated Levels in Red Soils from China
2002
Yu, S. | He, Z.L. | Huang, C.Y. | Chen, G.C. | Calvert, D.V.
Adsorption–desorption of copper (Cu²⁺) at contaminated levels in two red soils was investigated. The red soil derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult) (REQ) adsorbed more Cu²⁺ than the red soil developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) (RAR). The maximum adsorption values (M A) that are obtained from the simple Langmuir model were 25.90 and 20.17 mmol Cu²⁺ kg⁻¹ soil, respectively, for REQ and RAR. Adsorption of Cu²⁺ decreased soil pH, by 0.8 unit for the REQ soil and 0.6 unit for the RAR soil at the highest loadings. The number of protons released per Cu²⁺ adsorbed increased sigmoidally with increasing initial Cu²⁺ concentration for the RAR soil, but the relationship was almost linear for the REQ soil. The RAR soil released about 2.57 moles of proton per mole of Cu²⁺ adsorbed at the highest Cu²⁺ loading and the corresponding value for the REQ soil was 1.12. The distribution coefficient (K d) decreased exponentially with increasing Cu²⁺ loading. Most of the adsorbed Cu²⁺ in the soils was readily desorbed in the NH₄Ac. After five successive extractions with 1 mol L⁻¹ NH₄Ac (pH 5.0), 61 to 95% of the total adsorbed Cu²⁺ in the RAR soil was desorbed and the corresponding value for the REQ soil was 85 to 92%, indicating that the RAR soil had a greater affinity for Cu²⁺ than the REQ soil at low levels of adsorbed Cu²⁺
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