Graduate Thesis Or Dissertation
 

Theoretical and experimental evaluation of transfer of 2, 4-dichlorophenoxyacetic acid in porous media

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  • Experiments were conducted to study the effect of pore size distribution on the diffusion of 2, 4-Dichlorophenoxyacetic acid (carbon- 14) through water saturated porous media. Eight size fractions of glass beads were used representing the porous media. It was found that as the average particle radius, and hence pore radius, increased, the value of the diffusion coefficient also increased. A relation was obtained between pore radius and the ratio of porous material diffusion coefficient and free chemical diffusion coefficient. Results indicate that the diffusion coefficients of various chemicals can be obtained from self-diffusion coefficients. Two methods were used to measure self-diffusion coefficients. The agar method consisted of bringing two columns of agar media together having the same concentration of the ion under investigation, but one column having the ion labelled. Agar media of various concentrations were used and the value of the self-diffusion coefficient was determined by extrapolating the values of self-diffusion coefficients to zero concentration of agar. This method did not give reliable results of the self-diffusion coefficients for 2,4-Dichlorophenoxyacetic acid (carbon-14) and. Calcium Chloride (calcium-45). The cell diffusion method was then used and the values of the self-diffusion coefficients were obtained. This method involved the immersion of a short capillary tube filled with a solution containing a labelled ion in a bath containing a solution of the same concentration, but not labelled. It was found that cell diffusion method yielded reliable estimates of the self-diffusion coefficients of the chemicals considered. Experiments were designed to evaluate theoretical dispersion models proposed by Lindstrom et al. (1967) and Lindstrom and Boersma (1971) for non-sorbing as well as sorbing porous materials. As the average particle radius, and hence pore radius, increased, the shape of the experimental curve varied indicating that pore size dis tribution effects the movement of the chemicals. The experimental and theoretical curves were compared and found in agreement within the experimental error. The results indicated that the mathematical theory well describes the movement of chemicals. Theoretical and experimental curves for sorbing media were compared and found to be in agreement within the experimental error as well. This suggests that the proposed dispersion models may be used to predict the effects of pore size distribution and adsorption on the transport of chemicals.
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