Six surface samples presenting the newly reclaimed soil in Egypt were equilibrated with solutions containing different concentrations of Zn or Cu to test the fitness of adsorption data to three equations namely, Van Huay, Langmiur and Van Bemmelen-Freundlich. Desorption of Zn or cu into soil solution from Zn or Cu pretreated soils were also investigated. Results obtained revealed that soils which contained higher amount of clay and CaCO3 showed higher capacities to adsorb Zn and Cu than the ones lower in their contents of these components. All the investigated equations provided good fitness for Zn and Cu adsorption on all the studied soils except for Langmiur isotherm which failed at the higher concentrations of Zn and Cu in equilibrium solutions of El-Saloum soil. All the parameters calculated from the linear form of Van Huay equation i.e. the affinity constant "n" the theoretical desorbed amount of Zn and its concentration in soil solution were correlated significantly with Zn uptake. Values of max. adsorption of Langmiur equation significantly and negatively correlated with Zn uptake and at the same time correlated significantly but positively with CaCO3 and O.M contents. Also, the emperical parameters of van Bemmelen-Freunlich equation and correlated negatively with Zn uptake but positively with CaCO3 content. Thus, this result supported the previous one about the role of CaCO3 in reducing Zn availability to plant. Most parameters of Van Huay equation significantly correlated with Cu uptake. Also, values of Cu max. adsorption "b" calculated from the linear form of Langmiur equation and the constant " " calculated from van Bemmelen-Freundlich equation were correlated significantly with Cu uptake. Values of desorbed Zn and Cu from Zn or Cu-pretreated soils decreased upon prolonging time of contact between the metal ion and soil. Five and four successive extraction with 0.01 M CaCl2 solution could be considered enough for desorbing most of the retained Zn and Cu, respectively regardless of soil or period of contact between metal ion and soils. |
