Abstraction of tebuconazole and clomazone pesticide Residues from water by zeolite x: kinetics and Thermodynamics studies
SHIKUKU, Victor Odhiambo
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The presence of pesticide residues in water sources is of great environmental concern due to the detrimental health problems to human and organisms in the aquatic environment '-. associated with pesticide toxicities. Among the widely used pesticides are tebuconazole and clomazone, used in cultivation of numerous crops. Tebuconazole and clomazone have been detected in rivers, streams and lakes at levels exceeding the set safe allowable limits for drinking water. Conventional water treatment technologies that use activated carbon singly have been demonstrated to be insufficient in pesticide removal from wastewater. There is therefore need to evaluate other adsorbents for pesticide remediation from water. Synthetic sodium-type faujasite X (NaX) has been reported to have the capacity to abstract pesticides residues from water. However, the potential of NaX to adsorb tebuconazole and clomazone has not been documented. The objective of this study was to investigate the adsorption behavior of tebuconazole and clomazone pesticides from aqueous solution onto NaX. The effects of pesticide concentration (100 - 1000 ug L- '), contact time (15 - 390 min) and temperature (293 - 323 K) on the adsorption process were investigated using batch shaking sorption experiments using HPLC-DAD and the site of adsorption identified by FT-IR and XRD techniques. Removal efficiency varied significantly (p<0.05) with the initial pesticide concentration for both pesticides. Langmuir and Freundlich models gave the best fit for the experimental data for both pesticides. The maximum adsorption capacity oftebuconazole onto NaX, calculated from Langmuir isotherm, was 500 ug g-i. The adsorption reaction was found to follow pseudosecond order kinetics for both pesticides. The sorption half-life was evaluated and the adsorption rate of tebuconazole (0.0634 h) was faster than that of clomazone (0.1177 h). The calculated thermodynamic parameters indicate that tebuconazole adsorption on NaX is spontaneous (~G=-180.7 J mole") and exothermic (~H=-38.7 kJ mole") while clomazone adsorption was non-spontaneous (~G=5719.6 J mole") and exothermic (~H=- 44.9 kJ mole") under the examined conditions. Intraparticle diffusion model showed that the adsorption oftebuconazole and clomazone onto NaX was multi-mechanistic and was not controlled by pore diffusion. FT-IR and XRD analysis indicated that adsorption of tebuconazole and clomazone onto NaX is an external surface chemisorption process at the single-four-rings (S4R) of the zeolite framework with involvement of the Na+ cations. The results show that NaX is a better adsorbent for tebuconazole removal than clomazone and is valuable for wastewater treatment plants for tebuconazole remediation.