Stability of iron chelates during photo-Fenton process: The role of pH, hydroxyl radical attack and temperature

Abstract

The stability of some iron-complexes was tested in photo-Fenton process performed at different conditions. Temperatures (298, 303, 308 and 313 K), acidic and alkaline pH and the HO attack in the complexes were investigated. Four iron chelates (CA, EDTA, NTA, OA) were used. The results revealed an increase in performance with increased temperature, both at acidic and neutral pH values. Studies on the stability of the iron chelates to pH show a reduced efficiency at higher pH with very poor performance of CA and OA at pH of 9. The effect of pH on attack of hydroxyl radicals on the chelate was also monitored using total iron reduction, the results show that the complexes are more stable at acidic than at alkaline pH, the suitability of the iron complexes for application at alkaline pH is in the order of EDTA > NTA > OA > Ca. The kinetic and thermodynamic parameters were also computed, judging from the values of coefficient of variation (r2), the contaminant decolorisation followed the pseudo-first-order kinetics at acidic pH, but followed the pseudo-second-order kinetics with the chelate assisted degradation at neutral pH. In each case, the rate constant increased with increasing temperature. The thermodynamic parameters show an endothermic and spontaneous degradation process which does not follow a complex mechanism.