Adsorption kinetics of nitrate from aqueous solutions onto modified wheat residue

Adsorption kinetics of nitrate from aqueous solutions onto modified wheat residue was studied. The wheat residue was modified by epichlorohydrin in the presence of pyridine and the adsorption kinetics was investigated in batch experiment. The results showed the modified wheat residue had great anion adsorbing capacity, the zeta potentials of RWR and MWR were −35 mV and +40 mV, the maximum adsorption capacity of RWR and MWR were 0.02 mmol g−1 and 2.08 mmol g−1, respectively. And also, the adsorption can reached equilibrium in 20 min, the adsorption data fit Freundlich isotherm model. The kinetic data were fitted using the pseudo-first-order equation, the pseudo-second-order equation and the intra-particle diffusion model. The results showed that the pseudo-second-order equation and the intra-particle diffusion model generated the best agreement with the experimental data for the adsorption systems. The intra-particle diffusion was the main rate-controlling step. With the increasing initial concentration, the rate constant of pseudo-second-order equation decreased and rate constant of intra-particle diffusion model increased. The adsorption kinetic analyses could be of a great practical value for the technological applications of nitrate removal from aqueous solutions.