Kinetics of Fixation of Iron and Zinc Applied as FeEDTA, FeHDDHA and ZnEDTA in the Soil
1975
Lahav, N. | Hochberg, M.
The disappearance of zinc and iron from soil solution after their addition as soluble metal chelates is attributed to adsorption and fixation. The value of the adsorption coefficient, Kd, was estimated from a batch experiment but because of the inaccuracy involved they were evaluated from the breakthrough curves of column experiments using Rehovot sand. FeEDDHA was neither adsorbed nor was its iron fixed by the soil to any significant extent. The fixation of iron applied as FeEDTA was found to be a first order reaction. Assuming that the fixation reaction kinetics is similar in both the solution and the solid phase, then the reaction rate constant can be expressed as k = (k₁θ + k₂ρKd)/(θ + ρKd), where k₁ and k₂ are the reaction rate constants in the liquid and solid phases, respectively. θ is the volumetric water content and ρ is the bulk density. By using 5 different soil/water ratios, the values of k₁ and k₂ were found to be 0.0096 h⁻¹ and 0.087 h⁻¹, respectively. The value of k was also estimated from the breakthrough curve in a column experiment by using the relative effluent concentration under steady state condition (C/Cₒ)ₛ. The adsorption of ZnEDTA was negligible under the present experimental conditions. Thus k = k₁ and is independent of the water content and bulk density. This was shown by comparing the results of the two experimental techniques. The value of k₁ thus found was 0.084 h⁻¹. The first order model of the fixation reaction of zinc applied as ZnEDTA is applicable for time periods up to 8 to 10 hours.
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