Cadmium desorption behaviour in selected sub-tropical soils: Effects of soil properties

• We studied Cd desorption kinetics of soils with various physicochemical properties.
• Rate of Cd desorption showed two different mechanisms that controlled Cd desorption.
• DTPA could complex with Cd and remove it from external surfaces of adsorbents.
• The soils' pH, CEC, OM, and Feo, had the main effects on Cd desorption and diffusion.

To predict the environmental fate and mobility of contaminants, it is critical to study desorption behaviour of contaminants in soil system. Cadmium (Cd) desorption kinetics studies were conducted in ten sub-tropical soils of the northern part of Iran, with a wide range of physico-chemical properties. Treatments consisted of two levels of cadmium (15 and 30 mg kg− 1 as CdCl2). Soils were incubated at 20% moisture (w/w) level and 25 ± 1 ºC. After weeks, cadmium desorption pattern was investigated by Diethylene Triamine Pentaacetic Acid (DTPA) extraction with equilibration periods from 30 to 960 min. Results showed that two constant rate, parabolic diffusion and simple Elovich equations best described Cd desorption in these soils. The coefficients of kinetic equations had significant correlation with each other. The findings of this investigation indicated that pH, cation exchange capacity, organic matter, and oxalate extractable Fe are the most important soil characteristics in controlling Cd desorption behaviour in sub-tropical soils.