Isotherm and kinetic modeling of sorption of Cadmium onto a novel red algal sorbent, Hypnea musciformis

Abstract

In this work, sorption of cadmium from aqueous solution using a novel sorbent, Hypnea musciformis, was carried out. In order to optimize the operating variables namely, pH (3–6), sorbent dosage (0.5–2.5 g/L) and agitation speed (60–100 rpm), Box–Behnken Design was employed. The optimum conditions for the maximum cadmium percentage removal was 4.6, 1.67 g/L and 81 rpm for pH, sorbent dosage and agitation speed, respectively. At the optimal operating conditions, studies were carried out for effects with respect to various concentrations of cadmium and temperature for isotherm, kinetics and thermodynamic studies. The data obtained have been analysed by isotherm models such as Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherms. The most fitted equation for describing the isotherm profile was the Langmuir model (R2 = 0.9990) with the maximum sorption capacity of 105.49 mg/g. The kinetics studies exposed that the process of sorption of cadmium onto red algae has been satisfactorily described for pseudo-second order. The calculated thermodynamic parameters such as ∆G , ∆H and ∆S showed that the sorption of cadmium onto red algae was feasible, spontaneous and endothermic.