RESUMEN
The presence of citric acid in decontamination waste can cause complexation of the radioactive cations resulting in interferences in their removal by various treatment processes such as chemical precipitation, ion-exchange, etc., which are employed for the removal of radioactivity and may cause potential danger to the environment. Mesoporous Al-MCM-41 (Si/Al=30, 51, 72 and 97) and Si-MCM-41 molecular sieves were synthesized hydrothermally and characterized by XRD, BET (surface area) and FT-IR to evaluate the removal of citric acid through an adsorption process. Adsorption of citric acid over Al-MCM-41 shows the applicability of Freundlich and Langmuir isotherm and follows first order kinetics. The effects of contact time, concentration of citric acid, adsorbents (various Si/Al ratios of Al-MCM-41, Si-MCM-41, Hbeta zeolite and commercial carbon) and pH have been investigated. It has been found that the amount of citric acid adsorbed per unit gram of catalyst followed the order Al-MCM-41 (Si/Al=30)>Al-MCM-41 (Si/Al=51)>activated charcoal>Al-MCM-41 (Si/Al=72)>Al-MCM-41 (Si/Al=97)>Si-MCM-41>Hbeta zeolite.
Asunto(s)
Aluminio/química , Quelantes/aislamiento & purificación , Ácido Cítrico/aislamiento & purificación , Purificación del Agua/métodos , Zeolitas/química , Adsorción , Catálisis , Carbón Orgánico/química , Quelantes/química , Ácido Cítrico/química , Porosidad , Silicio/química , Espectroscopía Infrarroja por Transformada de Fourier , Difracción de Rayos XRESUMEN
INTRODUCTION: In the nuclear industry 1,4-dioxane is used as a solvent in liquid scintillation technique for measuring low-energy beta-emitters such as ³H or C¹4 in aqueous media. Improper disposal of 1,4-dioxane can contaminate the ground and surface waters. Conventional wastewater treatment processes like chemical treatment, air stripping, carbon adsorption, and biological treatment are ineffective for the degradation of 1,4-dioxane. METHODS: In the present study, the kinetics of degradation of 1,4-dioxane using advanced oxidation processes viz., H2O2 alone, Fe(II) + H2O2, UV (15 W) + H2O2, UV (15 W) + Fe(II) + H2O2, US (130 KHz) + Fe(II) + H2O2, and sunlight + Fe(II) + H2O2 at pH 3.0 was investigated. The optimization of Fe (II) for the processes using Fe (II) + H2O2 was carried out. CONCLUSIONS: The kinetics of degradation using sunlight + Fe (II) + H2O2 was found to be fastest when compared to the other processes. The degradation was found to follow first-order kinetics. Formation of acidic intermediates was suspected from the observed pH changes during the degradation processes.