ADSORPTION OF HUMIC ACID ON HYDROXYAPATITES

Abstract

Adsorption of humic acid (commercially available) on hydroxyapatites (HAP-100, HAP-200, HAP-300, HAP-400) was investigated in water at 25°C for 6h. Among the apatites, HAP-300, which has the largest specific surface area, indicated the highest adsorbability. Adsorption with HAP-300 within 15 min indicated higher adsorbability than that with charcoal. The isothermic curves according to Langmuir and Freundlich equations revealed that adsorbability of HAP-300 was higher than that of charcoal in the case of low concentration of humic acid (less than 6.56 mg/L). Since the adsorption was improved in NaOH solution than in water, we consider that humic acid is electrostatically adsorbed on Ca sites of hydroxyapatite surface unlike charcoal, which shows physical adsorption into its micro pores. The hydroxyapatite may be applied to an adsorbent alternative for charcoal in water purification plants.