Application of Cotton Stalk As an Adsorbent for Copper(II) Ions in Sustainable Wastewater Treatment

The capacity of untreated cotton stalk to remove and adsorb Cu2+ ions in synthetic and natural aqueous solutions was evaluated. The influence of three sensitive parameters of the adsorption process—solution pH, adsorbent dosage, and contact time—on the percentage of Cu2+ removal in agricultural wastewater, livestock wastewater, and synthetic samples was studied. Physicochemical and morphological properties were studied using thermogravimetry, Fourier infrared spectrophotometry, and scanning electron microscopy. The elemental composition, proximal composition, zero charge point, and acid–base sites were determined. In addition, kinetic studies were performed, and the adsorption equilibrium was analyzed. The optimum conditions for Cu2+ adsorption were the following: solution pH = 5.5, adsorbent dosage of 0.6 g, and contact time of 60 min. Under these conditions, the percentage of Cu2+ removal in synthetic samples was 66.5% when the initial copper concentration was 50 mg/L. The removal percentage in agricultural and livestock wastewater samples was 87.60% and 85.05%, respectively, when the initial copper concentration was 25 mg/L. The adsorption data are consistent with the Freundlich isotherm model, which achieved a quadratic fit of 0.991 compared to 0.5542 for the Langmuir model. The experimental results indicate that the adsorption adequately fits the pseudo-second-order kinetic model. The results suggest that cotton stalks are a promising adsorbent for the ecological and economical removal of Cu2+ in wastewater. This research, therefore, provides relevant information that contributes to the sustainable management of agricultural waste and instills hope for a reduction in water pollution from heavy metals derived from agricultural activities.