Enhanced sorption capacity of a metal-dye system from water effluents by using activated industrial waste

Activated coal fly ash (FA) treated with NaOH and hexadecyltrimethylammonium bromide (HDTMABr) was used as adsorbent for removal of cadmium(II) ions and rhodamine B (RB) from an aqueous solution. Characterization of fly ash and FA-HDTMABr were done using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The sorption equilibrium in the system was analysed using isotherm models, such as Freundlich, Langmuir, generalized Langmuir-Freundlich, Redlich-Peterson, Jovanović, extended Jovanović, Tóth, Frumkin-Fowler-Guggenheim, Fowler-Guggenheim-Jovanović-Freundlich, Temkin, Dubinin-Radushkevich, Halsey, Brunauer, Emmett and Teller. The evaluation of the fit of the isotherms studied experimentally was carried out by means of the reduced chi-square test and the coefficient of determination. The maximum monolayer adsorption capacity of the FA-HDTMABr was found to be 744 mg·g^-1 and 666 mg·g^-1 for Cd(II) and RB, respectively. The PFO, PSO, Elovich mass transfer, liquid film diffusion and intra-particle diffusion models were analysed. Sorption kinetics data were well fitted by the PSO model. The Elovich and intra-particle model also revealed that there are two separate stages in the sorption process, namely, external diffusion and intra-particle diffusion.