OPTIMIZATION OF EFFECTIVE DISPERSION COEFFICIENT OF THE METHYLENE BLUE ON DIFFERENT SAND-BENTONITE MIXTURES

This work was devoted to modeling the Fickian Dispersion Advection Equation (FDAE) transport and optimizing the effective dispersion coefficient of methylene blue through different sand-bentonite mixtures. First, we carried out several experiments to determine the parameters of the methylene blue adsorption isotherms on each sand-bentonite mixture used in this study (0%, 2%, 4% and 6% bentonite). Then, we injected the adsorption isotherm parameters obtained for each mixture into the FDAE and optimized the effective dispersion coefficient of the methylene blue. In this respect, the methylene blue solution (C0= 100 mg/l) was injected at a fixed flow rate of 1 ml/min in fixed bed columns (L=3.5 cm, D=1.2 cm) saturated with CaCl2 saline solution (0.01M). The results obtained show that the adsorption is otherm of methylene blue in sand-bentonite mixtures are described by the freundlich model. The effective dispersion coefficients of methylene blue obtained for heterogeneous media are identical with an average value equal to 10.435 cm2/min and as expected, they are lower than the dispersion coefficient of the medium purely sandy (0% bentonite). On the other hand, the Peclet number is more less sensitive to the heterogeneity of the environment, this is attributed to the variation of the convective flow in function of the bentonite fraction. In fact, the more the fraction of the bentonite increases the more the porosity of the porous medium decreases and consequently the speed flow increases. Keywords - Optimization, Effective dispersion coefficient, methylene blue, sand/ bentonite mixtures.