Study of cadmium distribution coefficient in acidic and calcareous soils of Iran: Comparison between low and high concentrations

Abstract

Determination of distribution coefficient ( K d ) at part per billion level is essential for evaluating the availability and the fate of cadmium (Cd) added to soil in natural conditions. For this purpose 11 soil samples were selected from different parts of Iran. Subsequently, the effects of chemical and physical characteristics of soil on K d at low (10–800 μ g/l) and high (1–1000 mg/l) concentrations of Cd were investigated. The results demonstrated that acidic soils S 2 , S 1 and S 3 had a lower K d , mean value at both concentrations compared to the calcareous soils. In the samples with low Cd concentration, S 4 (which contained higher amount of calcium carbonate) had the highest K d , mean value (1673.72 l/kg). However, among the samples with high Cd concentrations, S 10 (which contained a higher amount of organic matter compared to other calcareous soils) had the highest K d , mean value (376.05 l/kg). At low initial Cd concentration, K d increased with the increase of Cd concentration. In contrast, when the initial Cd concentration was high, K d gradually decreased with the increase of Cd concentration. It was also observed that sorption isotherms at low Cd concentrations were H-type and did not fit the Langmuir model. Higher values of Freundlich parameters ( K f and n ) indicated the higher affinity of soil for Cd at low concentration.