Geostatistical assessment of solid–liquid distribution coefficients (K d) for Cd, Cu, Pb and Zn in surface soils of Hamedan, Iran

Abstract

This study has applied a geostatistical approach to analyzing and interpreting the distribution coefficient (K d) in soils collected around Hamedan, west of Iran. The samples collected from the agricultural area (about 100 ha) affected by waste water from Shahid Mofatteh power plant. Sorption experiments were carried out using solution of desired concentration of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) (10 and 100 mg l−1). Desorption experiments with CaCl2 0.01 M, were performed immediately following the completion of sorption experiments. Results showed that in all treatments K d100 values is lower than K d10 values. The range of K d10 (l kg−1) were as follows: Cd (253–1656), Cu (545–100000), Pb (1841–100000) and Zn (198–3115). Median K d values showed the following order of decreasing affinity in both 10 and 100 mg l−1 metal concentrations: Pb > Cu > Zn > Cd. Desorption analysis indicated that only trace amounts of heavy metal adsorbed was released. Irreversibility was highest for Pb and Cu, which the K d values were greatest. The resulting variograms of log-transformed K d10 data for Cu indicated the existence of strong spatial dependence. The variograms for K d10 Cd revealed moderate spatial structure and variograms for K d10 Pb and Zn show weak spatial dependence. For K d100, the variogram of Cd show weak spatial dependence and variograms of Cu, Pb and Zn indicate moderate spatial structure.