Study of Fe(III)-NTA chelates stability for applicability in photo-Fenton at neutral pH

Abstract

The stability of ferric nitrilotriacetate chelates (Fe(III)-NTA) was studied under thermal, oxidative and photochemical stress. The knowledge of chelate stability is fundamental to correctly implement the management system of wastewater treatment plant for application of chelates as catalyst in photo-Fenton process at neutral pH. Fe(III)-NTA solution stability was monitored under different temperature conditions (T=10–30°C), in presence and absence of UV-A irradiation and by adding three different concentrations of H2O2. The additional effect on chelate stability caused by different irradiation source (UV-A, UV-C and Xenon lamps) was also evaluated. Although the complexes were stable under the temperature test range, temperature control is crucial when stressing the solution by irradiation or by adding hydrogen peroxide. The solution was kept stable during two hours of reaction under UV-A irradiation only when temperature was set at 10–15°C while in presence of hydroxyl radicals (HO) the temperature control could only reduce the chelates decomposition. Fe(III)-NTA solution mineralization could be obtained under irradiation and radical strain. Thus, the production of organic radical from free ligands was also demonstrated. Finally, the suitableness of UV-C lamps as light source for the process application was questioned since they caused a strong degradation of the chelate solution. Indeed, only 30min of UV-C irradiation by adding 0.59mM of hydrogen peroxide caused almost 90% reduction of the chelate content in the solution.