ADSORBABILITY AND PHOTO-FENTON REACTIVITY OF AQUATIC HUMIC SUBSTANCES WITH Fe(III)-TREATED HYDROXYAPATITES IN WATER

Abstract

Fe(III)-treated hydroxyapatite, HAP-300-Fe or HAP-400-Fe, which was prepared by treatment of almost stoichiometric hydroxyapatite HAP-300 or Ca-deficient hydroxyapatite HAP-400 with Fe(III) aqueous solution, was investigated in adsorption of aquatic humic substances, Nordic aquatic humic acid (NHA), Nordic aquatic fulvic acid (NFA), and Suwannee river fulvic acid (SFA), at 25°C for 6 h. HAP-400-Fe indicated higher adsorbability than HAP-300-Fe or the raw hydroxyapatite HAP-400. Further, HAP-400-Fe was investigated as a heterogeneous catalyst in photo-Fenton reaction of NHA, NFA, and SFA at 25°C for 20 h in water. Although all the humic substances were subjected to oxidation or decolorization by catalysis of HAP-400-Fe, the humic substance molecules adsorbed on HAP-400-Fe were slightly degraded and mineralized. This is possibly due to steric hindrance of catalysis by those large adsorbed molecules themselves and/or due to a property to scavenge hydroxyl radicals by Ar-OH groups of those molecules.