PHOTODISSOLUTION OF IRON-OXIDES .3. INTERPLAY OF PHOTOCHEMICAL AND THERMAL-PROCESSES IN MAGHEMITE CARBOXYLIC-ACID SYSTEMS

Irradiation of gamma-Fe2O3 suspensions in the presence of oxalate and EDTA results in a complex interplay between photochemical and thermal electron-transfer reactions. In the thermal dissolution, surface > Fe(III)-L complexes are slowly transferred by acid and reductive pathways until Fe(II)-L buildup in solution produces a strong acceleration. Irradiation accelerates the reaction by producing Fe2+, heterogeneously by photolysis of the oxide surface complexes, and by homogeneous photolysis of aqueous Fem(III)-L. This latter process is responsible for the acceleration in photodissolution rates brought about by the addition of Fe3+aq. Experimental results are reasonably fitted by the analytical solution of the simplified set of kinetic equations.