Kinetic, Isothermal, and Thermodynamic Analyses of Adsorption of Humic Acid on Quaternized Porous Cellulose Beads

Porous cellulose beads were quaternized with glycidyltrimethylammonium chloride (GTMAC), and the potential use of the quaternized cellulose beads as an adsorbent was explored for the removal of humic acid (HA) from aqueous media. The introduction of quaternary ammonium groups was verified by FT-IR and XPS analyses, and their content increased to 0.524 mmol/g-Qcell by increasing the GTMAC concentration. The adsorption capacity of the HA increased with decreasing initial pH value and/or increasing content of quaternary ammonium groups, and a maximum adsorption capacity of 575 mg/g-Qcell was obtained for the quaternized cellulose beads with a content of quaternary ammonium groups of 0.380 mmol/g-Qcell. The removal % value increased with increasing dose of quaternized cellulose beads, and HA was highly removed at higher quaternary ammonium groups. The kinetics of the HA adsorption in this study followed a pseudo-second-order equation, and the process exhibited a better fit to the Langmuir isotherm. In addition, the k2 value increased with increasing temperature. These results emphasize that HA adsorption is limited by chemical sorption or chemisorption. The quaternized cellulose beads were repetitively used for the adsorption of HA without appreciable loss in the adsorption capacity. The empirical, equilibrium, and kinetic aspects obtained in this study support that the quaternized cellulose beads can be applied to the removal of HA.