keywords: Adsorption, bentonite, phenol, cadmium, kinetic, thermodynamic
In this study, Raw Bentonite (RB), Carbonized Bentonites(CB), Hydroxyiron (III) bentonite- composite (HBC), have been used for the adsorption of phenol and cadmium from aqueous solution. Effect of initial pH of adsorbates was carried out at pH 2-11 and adsorbent dosage from 0.5 to 2.5 g with 50 mL adsorbate solution. Adsorption thermodynamics were developed for 5-25 mg/L and 10-50 mg/L of phenol and cadmium solutions for 1 h. Adsorption experiments were performed for 1 h. RB, CB and HBC showed the following physicochemical characteristics: pH 7.38, 7.26 and 7.20; pHpzc: 11.00, 10.50 and 10.10; Conductivity (2μ/m):1.656, 1.660 and 1.657; Bulky density (g/cm3):1.186, 1.111 and 1.214; Attrition (%): 17.49, 26.53 and 27.21, respectively. Adsorbent features were determined using XRF, FTIR and SEM techniques. The presence of hydroxyl, carboxylic, hydrogen bonding and aldehyde group showed that adsorbents bonds phenol and cadmium. At equilibrium, the maximum adsorption efficiencies for phenol: RB (52.020%), CB (63.468%), HBC (79.952%) and cadmium: RB (41.980%), CB (48.398%), HBC (65.830%) respectively were achieved for contact time. Adsorption capacities were found to increase with increase in contact time, temperature and concentration. The equilibrium adsorption data fitted better into the Langmuir than the Freundlich model. Thermodynamic parameters – Gibbs energy, enthalpy and entropy change indicated that adsorption was endothermic, meaning that chemisorption dominates physisorption. Adsorption kinetics was better explained by the Blanchard pseudo-second order kinetic model than the Lagergren first order. Overall, the adsorption of phenol was more favourable than for cadmium for all adsorbents.
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