Composite of bentonite/CoFe₂O₄/hydroxyapatite for adsorption of Pb (II)

In this contribution, a composite from bentonite (B), CoFe₂O₄ (CF), and hydroxyapatite (HAP) was developed by chemical synthesis route for adsorption of a lead ion, Pb (II) from wastewater. Initially, a composite of B/CF was synthesized by varying the weight ratio of CF, i.e., (1–x)B/(x)CF (x = 0.05, 0.15, 0.25, 0.50), followed by ternary composite synthesis, which was formulated from the sample of (0.85B/0.15CF) and different weight ratios of HAP, i.e., (1–y)[(0.85B/0.15CF)]/yHAP where y = 0.25, 0.35 and 0.45 weight ratios of HAP. The sample of 0.85B/0.15CF was found to be optimal in its adsorption capacity of about 20 mg g⁻¹ from the binary composite samples, while among the ternary composites, a sample with a composition of 0.65[(0.85B/0.15CF)]/0.35HAP revealed an optimum adsorption capacity of about 36 mg g⁻¹, which was then selected for further studies. The adsorption kinetics of Pb (II) by the optimum 0.65[(0.85B/0.15CF)]/0.35HAP sample was studied at different contact times from 30–120 min, where the equilibrium was reached at around 90 min of contact time and the kinetic behavior adopted Pseudo-second order adsorption mechanism. The initial concentration of Pb (II) was also varied from 50–200 mg l⁻¹ to study the adsorption isotherm, which resulted that adsorption capacity of 0.65[(0.85B/0.15CF)]/0.35HAP towards Pb (II) was increased to about 66 mg g⁻¹ and the adsorption isotherm data best fitted with Langmuir adsorption isotherm model. Therefore, the result of this study pinpoints that the present composite material is a potential candidate for the adsorption of Pb (II) ion. (paper)