Kinetics of cadmium desorption from some soils of Iran

Cadmium (Cd) is highly toxic and therefore represents a potential threat to the environment and human health. To improve predictions of the toxicity and threat from Cd contaminated soil, knowledge of timedependent desorption behavior of these soils is crucial. Kinetics of Cd desorption from 15 Cd-spiked surface soil samples (0-30 cm) from the northern part of Iran with a wide range of physical and chemical properties, were studied. Treatments consisted of two levels of Cd (15 and 30 mg/kg as CdCl2) with two replications. Samples were incubated under 20% w/w moisture content and 25ᰃ. After 3 and 6 weeks, Cd desorption pattern was investigated by DTPA (Diethylne-Triamine-Pentaacetic-Acid) extraction with shaking times from 30 to 960 min. Results showed that two-constant-rate, parabolic-diffusion and simple Elovich equations were the best fitted equations among five kinetic models used. The coefficients of kinetic equations had significant correlation with each other. Stepwise multiple regression equations indicated that pH and CEC (cation exchange capacity) were the most important soil characteristics for predicting the rate constants of the kinetic models.