Rapid Physisorption of Cr(VI) Using Cassava Peel Biosorbents: Kinetics, Isotherm Analysis and Mechanistic Insights

Increasing environmental concerns and strict discharge regulations have driven the need for efficient and low-cost treatment methods for industrial effluents. Chromium, particularly in its hexavalent form [Cr(VI)], is one of the most hazardous pollutants present in wastewater due to its high toxicity and carcinogenic nature. This study explores the potential of cassava peels (Manihot esculenta), an abundant agricultural byproduct, as a biosorbent for the rapid removal of Cr(VI) from aqueous solutions. Batch adsorption experiments were conducted to assess the influence of various parameters, including adsorbent dosage, initial Cr(VI) concentration, pH, and contact time. Optimal removal was observed at pH 2, with a contact time of just 5 min and an adsorbent dosage of 16 g.L-1, achieving a maximum removal efficiency of 99.53 %. Adsorption equilibrium data were evaluated using Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. Among these, the Langmuir model provided the best fit, indicating monolayer adsorption, with a maximum adsorption capacity of 5.076 mg.g-1. The mean adsorption energy calculated from the Dubinin-Radushkevich model (E = 0.997 kJ.mol-1) confirmed that the process was dominated by physisorption. Kinetic analysis showed a strong correlation with the pseudo-second-order model (R² = 1.0), suggesting that the rate-limiting step involves surface interaction between the Cr(VI) ions and functional groups on the cassava peel surface. These findings highlight cassava peels as a promising, renewable, and cost-effective material for the rapid removal of Cr(VI) from industrial wastewater, particularly under acidic conditions.