The behaviour of cadmium adsorption on someEgyptian surface soils

Author(s): Elmetwaly M.Selim, Faiz F.Assaad, Mohamed E.EL-Hefnawy

Adsorption of cadmiumon two different soils fromEgypt (clays and sandy loam soils) was studied. Data on adsorption isotherms, competitive effects and/or inorganic complex formation ofNaCl and Na2SO4 are presented. The adsorptionwas described by a Langmuir or a Frendlich equation. Themaximumadsorption derived fromthe Langmuir equation was taken to measure the adsorption capacity, while the Langmuir parameter was taken to point out the relative degree of affinity or energy at different cadmiumadsorption conditions. In particular, the clay soil had higher adsorption capacities in all cases than the sandy loam soil. The higher clay content, CEC, OM and the surface area of the clay soil may account for the higher capacity. It appears likely that the existence of NaCl decreases the maximumadsorption of cadmium in both soils and also reduces the bonding energy coefficients less than those in presence of Na2SO4 apparently favoring the dissociation of adsorbed Cd complex. Due to this behavior, cadmiumadsorption in case of NaCl salt matrix was about three times less than for Na2SO4. This effect is important since relativelymoderate concentration of Cl in soil solution will greatly reduce the adsorption of Cd on soil surface. Thereby relatively high Cd concentrations in soil solutions will be maintained especially under surface irrigation conditions, which increase the probability for ground water pollutionwith this harmful and toxic metal.

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