Optimization by RSM of the degradation of three phenolic compounds - hydroquinone, resorcinol and catechol - on Fe-modified clays

A Fenton-type wastewater treatment, using clay catalysts (montmorillonite and kaolinite), was prepared and used to degrade three phenolic compounds: hydroquinone, resorcinol and catechol. The operating conditions of the degradation of these compounds are optimized by the response surface methodology (RSM) which is an experimental design used in process optimization studies. The results obtained by the catalytic tests and analyses performed by different techniques (X-ray diffraction, volumetric adsorption, atomic absorption spectroscopy and high performance liquid chromatography (HPLC)) showed that the modified montmorillonites have very interesting catalytic, structural and textural properties; they are more effective for the catalytic phenolic compound degradation, they present the highest specific surface and they may support iron ions. We also determined the optimal degradation conditions by tracing the response surfaces of each compound; for example, for the catechol, the optimal conditions of degradation at pH 4 are obtained after 120 min at a concentration of H2O2 equal to 0.3 M. Of the three phenolic compounds, the kinetic degradation study revealed that the hydroquinone is the most degraded compound in the least amount of time. Finally, the rate of the catalyst iron ions release in the reaction is lower when the Fe-modified montmorillonites are used.