A complete study on the photocatalytic degradation of ethylenediaminetetraa
cetic acid (EDTA) over TiO2 has been initiated, to establish the influence
of several parameters on the reaction rate, the nature of the intermediates
and the kinetic regime. TiO2 (Degussa P25) suspensions containing EDTA at
pH 3 at different concentrations were irradiated under near UV light. A Lan
gmuirian behavior was observed, from which kinetic constants have been obta
ined. Experiments with 5.0 mM EDTA (zero order kinetic regime) were perform
ed for 3 hours irradiation under different conditions. Under N-2 bubbling,
depletion of EDTA was very low. Under O-2 bubbling, the concentration of ED
TA decreased around 90%. However, the corresponding decrease of TOC ranged
only between 4.5% and 9%. A higher TOC reduction (22% or more) was obtained
by keeping the pH constant by HClO4 addition, or by hydrogen peroxide addi
tion. Addition of 0.5 mM Fe(III) caused a dramatic increase on the initial
rate of EDTA depletion and approximately a 32% TOC decrease. Analysis of th
e filtered solution was performed by ion chromatography and capillary elect
rophoresis to monitor the disappearance of EDTA and the formation of degrad
ation products after different irradiation times. So far, glycine, ethylene
diamine, formic acid, ammonium, iminodiacetic acid, oxalic acid and glyoxyl
ic acid have been identified.