Distribution coefficients of cadmium and zinc in different soils in mono‐metal and competitive sorption systems

We aimed to investigate the distribution coefficients ( K d ) of Cd and Zn in different soils in mono‐metal (MS) and competitive sorption (CS) systems. Eleven surface soil samples varying widely in their origin and properties were collected in Egypt and Greece. Sorption isotherms were determined and K d derived. Clayey Entisols showed a higher affinity for Zn, while a Histosol showed a higher affinity for Cd. In MS the K d of Zn was higher than the K d of Cd in the studied soils, except for an Aridisol and acidic Alfisols. In case of CS the K d of Zn was higher than the K d of Cd in the soils. The K d of Cd decreased in CS compared to MS. The decreasing percentage of K d ‐Cd ranged from 6.5% in the Histosol to 81.8% in the sandy Entisols. K d ‐Zn in CS decreased in the Entisols, Alfisols, and Histosol, but increased in the Aridisol, Vertisol, and Mollisol compared to MS. This suggests that upon co‐addition of the two metals to the soil Zn became preferentially sorbed at the expense of Cd. Permanent charge clayey soils with relatively low Fe‐, Al‐ and Mn‐oxides content sorbed more Cd and Zn than the variable charge red soils with a higher content of these oxides. Cation exchange capacity (CEC), soil organic matter, Al d , Fe d , Fe o , Al o and total carbonates are important for the sorption of Cd, whereas clay, CEC, Si d , Si o and Al o content determine the sorption of Zn.