Two-resistance mass transfer model for the adsorption of the pesticide deltamethrin using acid treated oil shale ash

Adsorption characteristics of the pesticides Deltamethrin were studied in aqueous solutions using acid treated Oil Shale Ash (ATOSA) in a series of batch adsorption experiments. The maximum loading capacity of the adsorbent and the rate of adsorption were found to increase with increasing the pesticide initial concentration, mixing speed and were found to decrease with temperature and particle size. Langmuir as well as Freundlich isotherm models fit the adsorption data with R-2 > 0.97 in all cases. The maximum adsorption capacity for Deltamethrin was 11.4 mg/g. The two-resistance mass transfer model based on the film resistance and homogeneous solid phase diffusion was used to fit the experimental data. A computer program has been developed to estimate the theoretical concentration-time dependent curves and to compare them with the experimental curves by means of the best-fit approach. The model predicts that the external mass transfer coefficient K was affected by varying the initial pesticide concentration, the agitation speed and temperature whereas the diffusion coefficient D was affected by the initial pesticide concentration, and temperature.