The stability of iron chelates in calcareous soils

The stability of Fe-EDTA and Fe-CDTA was investigated in order to evaluate their effectiveness under calcareous soil conditions. To accomplish this evaluation the reaction rate of fixation, K, the adsorption coefficient, K_d, and the retardation factor, S, of the iron chelate were determined through column experiments at pH 7.8 and two ionic strengths, I, of CaCl₂. The results indicated that iron in Fe-EDTA was more fixed than in Fe-CDTA. The fixation increased by increasing the ionic strength. Also it increased linearly with increasing CaCO₃ content of the soil. The values of retardation factor, S, showed that this parameter depended more on the surface area of the soil than on I or CaCO₃ content. The product KS depends on CaCO₃ content, surface area of the soil, ionic strength and chelating agent used. It can be taken as an index for the efficiency of the iron chelate under different conditions. Fe-EDTA was more adsorbed than Fe-CDTA, the adsorption increased with increasing ionic strength and surface area of the soil.