Cadmium removal by macro algae Caulerpa fastigiata: Characterization, kinetic, isotherm and thermodynamic studies

The removal of cadmium from aqueous solution by biosorption on a new biosorbent Caulerpa fastigiata (Macro algae) was studied as a function of initial metal ion concentration, pH, temperature, sorbent dosage and biomass particle size. The maximum biosorption was found to be 92.01% for C. fastigiata at 25 °C, at the initial pH value of 5.5 in 60 min and at the initial cadmium (II) ion concentration of 30.29 mg L−1 and beyond pH 5.5, Cd2+ ions removal rapidly declined. Uptake kinetics followed the pseudo-second-order model and equilibrium was well described by Freundlich model. Isotherms had been used to determine thermodynamic parameters of the process, viz., free energy change, enthalpy change and entropy change. The thermodynamic data represent exothermic process and free energy change (ΔG°) with negative sign reflects the feasibility and spontaneous nature of the process. The SEM studies showed Cd2+ biosorption on selective grains of both biosorbents. The FTIR spectra indicated that the functional groups predominantly involved in the biosorption were OH, COO−, CH, CC, CS and CC groups. The XRD pattern of the biosorbent was found to be mostly amorphous in nature.