LABORATORY STUDY OF THE RESPECTIVE ROLES OF FERRIC-OXIDE AND RELEASEDOR ADDED FERRIC IONS IN THE PHOTODEGRADATION OF OXALIC-ACID IN AERATED LIQUID WATER

These laboratory studies were aimed at distinguishing the relative imp ortance of released or added ferric ions and of ferric oxide particles for the photodegradation of oxalic acid in natural waters. The parame ters whose effects were determined for this purpose included the pH, t he irradiation wavelength, the concentrations of the various species a nd the identity of the ferric oxide sample. In addition, the existence of a potential photocatalytic activity of ferric oxide was establishe d by measurements of the electrical photoconductance of three samples under vacuum and in a dry dioxygen atmosphere. The results show the do minant role of ferric ions. However, the influence of ferric oxide is clearly not attributable to the mere dissolution. Effects due to the p hotoexcitation of surface iron-HC2O4- complexes are confirmed. Photoca talytic events may exist. The relative importance of these various phe nomena depends on the [Fe3+](diss)/[Fe2O3] ratio and on the identity o f the ferric oxide sample; in particular the crystallinity seems to fa vour the photodegradation of oxalic acid.