Metals adsorption on solid phase from solution is one of the most important chemical processes controlling their bioavailability in soils. Nickel (Ni) adsorption characteristics in 20 calcareous soils of Iran were investigated in a range from 0.1 to 12.8 mM Ni concentration in solution using adsorption isotherms. The results revealed that Ferundlich, Langmuir and Ridlich-Pterson isotherms well described Ni adsorption on soils. The maximum Ni adsorption (qmax) ranged from 1369 to 5378 mg kg-1 which positively correlated with organic matter, clay content and cation exchange capacity.The coefficient (Kf) of Ferundlich positively correlated with organic matter and clay content while Ridlich-Pterson parameters were not correlated with the soils properties. The results showed that Ni adsorption was not affected by calcium carbonate equivalent (CCE) in these soils. Carbonates exist mostly in the silt and sand fractions with relative low surface area seemed to act as pH modifier rather adsorption sites for metals.

Keywords: adsorption isotherms, calcareous soils, Ridlich-Pterson, Langmuir, Ferundlich