An Enhanced Removal of Pb²⁺ and Cd²⁺ from Maize Flour Mill Wastewater Using Modified Activated Carbon: Adsorption Kinetics and Mechanism

Enhanced Removal of Pb²⁺ and Cd²⁺ from Maize Flour Mill Wastewater Using Modified Activated Carbon: Adsorption Kinetics and Mechanism

Abstract

The use of a cheap and effective adsorption approach based on biomass-activated charcoal to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this study aims at investigating the enhanced removal of Pb²⁺ and Cd²⁺ from maize flour mill wastewater using modified activated carbon. Batch adsorption experiments were conducted to evaluate the influence of contact time, pH, and adsorbent dosage on heavy metal removal efficiency. The results demonstrated that removal efficiency increased with time, reaching 92.2% for Cd²⁺ and 86.4% for Pb²⁺ at 120 minutes, indicating a strong interaction between the metal ions and the modified adsorbent. Adsorption kinetics were analyzed using pseudo-first-order, pseudo-second-order, and Weber-Morris intraparticle diffusion models, with the pseudo-second-order model providing the best fit (R² = 0.9996 for Cd²⁺ and 0.9976 for Pb²⁺), confirming chemisorption as the dominant mechanism. The equilibrium adsorption capacities (Q_e) were 1.4 mg/g for Cd²⁺ and 1.3 mg/g for Pb²⁺, suggesting a high affinity of the modified activated carbon for both metals. The adsorption mechanism was influenced by surface complexation, electrostatic attraction, and ion exchange, as confirmed by the gradual decline in the natural logarithm of residual concentration (LN(Q_e-Q_t)) over time. The study underscores the effectiveness of modified activated carbon in treating heavy metal-contaminated wastewater, offering an environmentally sustainable and cost-effective alternative for industrial wastewater treatment.