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Adsorption of Cadmium or Cadmium-Fulvic Acid Complexes in Soils

2001; Indian Society of Soil Science; Volume: 49; Issue: 1 Linguagem: Inglês

0974-0228

S.B. Pandeya, Abhay Kumar Singh, Singh Dhanesh,

Geochemistry and Geologic Mapping

A laboratory experiment was conducted to study the sorption behaviour of cadmium and Cd-FA complex in three pairs of surface soils collected from sewage sludge disposal area of Patna, Thermal Power Waste disposal area of Barauni and cattleshed waste disposal area of Pusa, along with their respective normal soils. The soils were equilibrated with graded levels of CdSO4 and Cd-FA complex in two sets at 15°C and 35°C, respectively, for 48 hrs. The data on the sorption of Cd2+ and Cd-FA in soils were found to fit the linear form of the Langmuir adsorption isotherm. The values of monolayer adsorption capacity of soils were higher for Cd2+ than those for Cd-FA, probably due to the smaller size of the ion than that of fulvates. Presence of an electrolyte like CaCl2 reduced the adsorption maxima, suggesting competition for sites between Ca2+ and Cd2+ or Cd-FA. The thermodynamics parameters, such as ΔG°, ΔH° and ΔS°, calculated from the data on sorption of Cd2+ and Cd-FA in soils, indicated the interaction processes to be spontaneous in nature. There was a considerable increase in the entropy of the system possibly due to rupture of the water hull present around the adsorbate and adsorbent. The positive value of entropy changes however, indicated stability of the product. Fit of the data on interaction of Cd2+ and Cd-FA with soils to the competitive Langmuir adsorption isotherm with statistically significant values of coefficient of determination suggests that the sorption of Cd2+ or Cd-FA is largely through exchange process. The adsorption of these ions occurs with desorption of Ca2+ and other cations. The same can also be inferred from the observations indicating reduction in adsorption maxima of Cd-FA in presence of CaCl2 in comparison to those in the aqueous phase.