| Abstract |
Equilibrium, kinetic, thermodynamic aspects, and mechanism of congo red (CR) adsorption onto rice husk treated with effluent from cotton pre-treatment (ERH) are examined by altering the initial dye concentration (0.1, 0.2, 0.3, 0.4, and 0.5 g/L), contact time (0 to 1440 min), temperature (298, 323, and 343 K), and adsorbent dosage (10, 20 and 40 g/L). When 10 and 20 g/L adsorbent dosages are applied, the treated rice husk adsorbs the CR following the Langmuir model, while at 40 g/L ERH, the adsorption follows the Freundlich model. A maximum of 149 mg CR per gram ERH is adsorbed with 10 g/L ERH at 70 degrees C. This adsorption capacity is one of the better ones found in the literature. The calculated Dubinin-Radushkevich activation energy lower than 8 kJ/mol, indicates the physical nature of CR adsorption. The adsorption kinetic follows a pseudo-second-order kinetic model because R-2 for all tested samples is higher than 0.999. The activation energy (Ea) varies from 0.045 to 40.1 kJ/mol, while the isosteric heat of adsorption (Delta H-X) varies from 1.06 to 36.0 kJ/mol. Ea and Delta H-X lower than 40 kJ/mol and 80 kJ/mol, respectively, confirm the physical adsorption of CR onto ERH. The other thermodynamic analysis indicates spontaneous and endothermic adsorption. These results showed the applicability of the circular economy concept in the effort to obtain an efficient adsorbent without wasting additional chemicals and energy that could be used to create a continuous column-mode process of rice husk modification and purification of colored effluent from the textile industry. |
