Effect of common ions on copper sorption behavior in dryland calcareous soils in Iran

Abstract

This study assessed the effect of common ions on the sorption behavior of copper (Cu) in 10 calcareous top soils from western Iran. Six 10-mM electrolyte background solutions were employed in the study [KCl, KNO₃, KH₂PO₄, Ca(NO₃)₂, NaNO₃ and NH₄NO₃]. The use of NH₄NO₃ increased Cu retention in soils, whereas the use of Ca(NO₃)₂ decreased Cu retention in all soils. Both Na⁺ and K⁺ affected Cu sorption equally. Copper sorption was decreased by H₂PO, as opposed to NO or Cl^–. The Freundlich distribution coefficient (K _F) decreased in the order Cl^– > H₂PO > NO. Saturation indices indicated that at low and high concentrations, Cu solubility is controlled by adsorption and mineral precipitation reactions, and common minerals in all background solutions (except KH₂PO₄) are azurite, brochanite, malachite and tenorite. In the KH₂PO₄ background, the solutions in all soils were saturated with respect to Cu₃(PO₄)₂. Clay content, cation-exchange capacity and Cu-DTPA appeared to be the most important soil properties influencing K _F. The results suggested that the risk of Cu leaching to groundwater is greater in the presence of NO and Ca²⁺  than in the presence of other studied cations and anions.

Keywords:

• copper sorption
• distribution coefficient
• calcareous soils
• ions