Circular economy approach for rice husk modification: Equilibrium, kinetic, thermodynamic aspects and mechanism of Congo red adsorption

Abstract

Equilibrium, kinetic, thermodynamic aspects and mechanism of Congo red adsorption onto rice husk treated with effluent from cotton pre-treatment are examined by altering the initial dye concentration, contact time, temperature, and adsorbent mass. When a lower mass is applied, the treated rice husk adsorbs the Congo red following the Langmuir model, while at a higher mass, the adsorption follows the Freundlich model. А maximum of 149.1 mg/g Congo red is adsorbed with 10 g/L rice husk at 70oC. This capacity of the chemically modified rice husk is one of the better ones found in the literature. The calculated Dubinin–Radushkevich activation energy indicates the physical nature of Congo red adsorption adsorbed under the pseudo-second-order kinetic model. The thermodynamic analysis confirmed spontaneous and endothermic adsorption with physically created Congo red-rice husk bonds. 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.