Equilibrium and kinetic modelling of the adsorption of Cd ions onto chestnut shell

A study on the removal of Cd²⁺ ions from aqueous solutions by acid formaldehyde pretreated chestnut (Castanea sativa) shell was conducted in batch conditions. The influence of different parameters: adsorption time, temperature (15, 25 and 35 °C) and initial concentration of Cd²⁺ ions (15.3, 50.5 and 87.3 mg L^− 1), on cadmium uptake was analysed. Cadmium free and cadmium loaded chestnut shell were characterized by FTIR spectroscopy, which evidenced the functional groups involved in cadmium uptake. Cadmium adsorption equilibrium could be described by the Freundlich adsorption model at all the temperatures essayed, which predicted shell heterogeneity. The Cd²⁺ adsorption process by chestnut shell followed the pseudo second order kinetic model. Cadmium sorption capacity increased with decreasing temperature at an initial concentration of 15.3 mg L^− 1 and with increasing initial cadmium concentration at a temperature of 25 °C. The second order kinetic constant, which increased with increasing temperature, was used to calculate the energy of adsorption as equal to 19.2 kJ mol^− 1.