Effective Humic Acid Removal Using Zn/Al Layered Double Hydroxide Anionic Clay

Abstract

A new effective removal of dissolved humic acid in aqueous medium has been performed by mean of adsorption onto Zn/Al layered double hydroxide (Zn/Al LDH). Zn/Al LDH was synthesized by direct precipitation method through the addition of 0.5 M NaOH solution to a mixed solution containing Zn(NO3)2 and Al(NO3)3 with molar ratio 0.1 : 0.05 until the acidity of the mixed solution reached pH 7.0. The removal of humic acid was based on adsorption process where the negatively charged humic acid would be adsorbed to the positively charged Zn/Al LDH surface. The optimum humic acid adsorption on Zn/Al LDH was observed at pH 5 with the first order rate constant, capacity, and energy of adsorption were 2.17 x 10-3 min-1, 0.194 mmol g-1 (115 mg g-1), and 33.89 kJ mol-1, respectively. Literature survey showed that Zn/Al LDH is more than 6 times more effective than carbon as the most effective adsorbent of humic acid in the market.