Adsorption of arsenic onto films based on chitosan and chitosan/nano-iron oxide

Films made from neat chitosan and chitosan with magnetic nanoparticles (MNPs) were tested as adsorbents of arsenate ions. Sorption equilibrium and sorption kinetics studies are reported, including different models applied to enlighten experimental observations and predict results. The sorption of As (V) was reasonably explained using Freundlich isotherm for neat chitosan film although it was better represented by Langmuir equation for the composite sample. The experimental kinetics results showed that the adsorption of arsenate ions is very fast during the first minutes and then the composite seems to reach saturation, while a slow desorption in the chitosan film was observed and acceptably fitted with a pseudo first order reversible model. The adsorbent containing MNPs presented higher adsorption capacity, which was associated to the additional adsorbent capacity provided by the MNPs and its much more irregular surface area that leads to an enhanced adsorption surface. For instance, at 10 mg/L equilibrium concentration, which corresponds to an initial concentration of As (V) much higher than the normal concentration of arsenate in natural water, chitosan-MNP sample exhibits a removal capacity of 10.4 mg/g that is more than six times higher than the 1.6 mg/g shown by the chitosan film.