Competitive adsorption of trace elements in calcareous soils of western Iran

Trace elements distribution between the solid and soil solution phases is a key issue in assessing the mobility and retention of trace elements in soils. In a competitive system where soils are contaminated with several trace elements metal adsorption reactions become important. This study was conducted to assess the competitive sorption of cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni) and mangenese (Mn) in surface samples of ten calcareous soils from western Iran. Sorption isotherms were characterized using linear, Freundlich and Langmuir equations. Most sorption isotherms were well described by the Langmuir equation. All soils showed greater sorption capacity and binding strength for Cu than the other trace elements. On the basis of distribution coefficient values for the metal concentration of 25 mg l− 1 (Kd25) and maximum sorption capacity (Q) for each soil and trace element, the selectivity sequence was obtained. The three greatest adsorption sequences found were Cu > Zn > Cd > Ni > Mn, Cu > Ni > Zn > Cd > Mn and Cu > Cd > Zn > Ni > Mn. Copper, Zn and Ni were the trace elements most strongly adsorbed by all soils, whereas Mn and Cd were the least adsorbed in the competitive situation.