The use of low-cost, locally available and eco-friendly adsorbents has been investigated as an ideal method of controlling waste. In this paper,activated Delonix regia leaves(DRL), Delonix regia tree bark(DRB) and combined Delonix regia leaves and bark (DRBL) have been used as biosorbents for the removal of Chromium (VI) from aqueous solutions. The biosorption studies were carried out using each biosorbent singly and the combination of the two in equimolar proportions respectively. The concentrations of the metal ions uptook were determined by atomic absorption spectroscopic (AAS) method. Biosorption experiments were performed as a function of pH, contact time, particle size, biosorbent dosage, temperature, initial concentration of the biosorbate. The maximum removal of chromium(VI) was obtained at pH 2 after two hours. Kinetics data obtained in this study fitted satisfactorily to the pseudo-first-order rate equation for all the biosorbents, suggesting that the biosorption process is chemisorption. The experimental equilibrium data were tested for Langmuir and Freundlich models, and the Freundlich model fitted better for all the biosorbents with correlation coefficient (R2) ranges 0.997 – 0.999. Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy evaluated from experimental data predict the nature of the uptake, revealed that uptake of Chromium (VI) was endothermic at 25 0 C. The results show that a large proportion of Chromium (VI) was uptook at higher percentage when the combined form of the biosorbents was used as compared to when the biosorbents were used singly.
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