Equilibrium and kinetic studies of adsorption of Cd(II) from aqueous solution using modified corn stalk

This paper describes the adsorption of cadmium ions from aqueous solution using acrylonitrile (AN)-modified corn stalk (AMCS). AMCS was characterized by elemental analysis, scanning electron microscopy, surface area and porosity analyzer, Fourier transform infrared and solid-state CP/MAS 13C NMR spectra, and then used to evaluate the adsorption capacity in different pH values, adsorption isotherm, kinetics and thermodynamics in batch experiments. The results showed that AMCS is found to be an effective adsorbent because of its pore size and functional groups (-CN). The pH of 7.0 was an optimal pH for removal of Cd(II) ion and the Langmuir model provides a better fit to the equilibrium data than the Freundlich model, showing a maximum uptake of 12.73 mg g−1, compared to raw corn stalk (RCS) (3.39 mg g−1). Analysis indicated that pseudo-second-order kinetics controlled the adsorption rate. The activation energy (Ea) was 9.43 kJ mol−1. Thermodynamic parameters such as ΔG, ΔH and ΔS were also evaluated to predict the nature of adsorption process.