Batch Adsorption Performance of a KOH-Activated Corn Cob Carbon–Calcined Fly Ash Composite for Multi-Pollutant Removal

Abstract

The discharge of dye and heavy metal-containing wastewater remains a major environmental challenge, highlighting the need for low-cost, effective adsorbents. This study evaluated the batch adsorption performance of a composite adsorbent KOH-activated corn cob carbon combined with calcined coal fly ash toward methylene blue (MB), cadmium (Cd²⁺), and hexavalent chromium (Cr(VI)). Corn cob carbon was prepared via carbonization and KOH activation, while fly ash was calcined before composite preparation. SEM-EDS and BET analyses characterized the adsorbent’s physicochemical properties. KOH activation raised the corn cob carbon’s surface area from 8.80 to 40.88 m²/g, while calcination increased the fly ash’s surface area from 0.32 to 1.65 m²/g, indicating improved surface development. Under optimum conditions (5:1 fly ash-to-carbon ratio, 90-mesh particle size), the composite achieved removal efficiencies of 99.39% for MB (0.40 mg/g) and 99.56% for Cd²⁺ (1.659 mg/g), showing strong performance toward cationic pollutants. Cr(VI) removal, however, reached only 25.37% (1.723 mg/g), likely due to unfavorable electrostatic interactions between the adsorbent surface and anionic chromium species under the tested conditions. Overall, the composite showed promising adsorption performance for cationic contaminants, while further modification is needed to improve its effectiveness against anionic pollutants like Cr(VI).