Abstract
In this work the tannic acid adsorption efficiencies for fly ash (FA), NaOH treated fly ash (NaFA) and Chitosan modified NaOH treated fly ash (Chitosan/NaOH/fly ash composite) were compared. Chitosan/NaOH/fly ash composite presented higher tannic acid adsorption efficiency than FA and NaFA. This may be attributed to the H-bonding imparted by Chitosan molecules on the surface of NaFA, consequently leading to organic partioning. The adsorption of tannic acid onto Chitosan/NaOH/fly ash composite as a function of initial tannic acid concentration, contact time, adsorbent dosage, temperature, ionic strength and solution pH were investigated for their optimization. The adsorbents were characterized by XRD, FE-SEM, surface area – porosity measurement and FT-IR spectroscopy. The adsorption kinetics of tannic acid followed a pseudo-second order model. The equilibrium adsorption data were best fitted by Redlich-Peterson isotherm models. The tannic acid adsorption slightly decreased with increasing ionic strength adjusted by NaCl. The adsorption was relatively high at pH 5.5–7.0 and decreased above pH 7.0. The value of ΔG°, ΔS° and ΔH° indicated spontaneous and exothermic process.
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