ADSORPTION OF AQUATIC HUMIC SUBSTANCES ON HYDROXYAPATITE IN WATER

Aquatic humic substances, humic acid (Nordic-HA) and fulvic acids (Nordic-FA and Suwannee-FA), were investigated in adsorption on hydroxyapatite (HAP) in water at 25°C for 15 min or 6 h. Adsorbability of HAP to the humic acid was higher than that to the fulvic acids. HAPs calcined at 600°C and 1200°C, HAP-C600 and HAP-C1200, indicated lower adsorbabilities than the raw HAP in the case of adsorption time 6 h. Calcination of HAP resulted in shrinkage of the pores and fusion of the surface, and affected lowering the adsorbability. Actually, judging from evaluation of Freundlich constants, KF and 1/n, we found that the raw HAP has larger adsorption capacity than the calcined HAPs. Although HAP has smaller surface area than charcoal, the KF values of HAP were larger than those of charcoal. In addition, by comparison with adsorption of alizarin red S, we found that Ca sites on HAP surface facilely interact with phenolic OH rather than COOH groups of humic substances.