Efficiency of hydrogels based on natural polysaccharides in the removal of Cd2+ ions from aqueous solutions

Hydrogels based on chitosan, maltodextrin and gum arabic with and without magnetite nanoparticles were employed as adsorbents for removing Cd2+ from aqueous solutions. Adsorption kinetics employing the Fickian equation inferred that the diffusion mechanism of water into hydrogels may be conducted by both the diffusion process and macromolecular structure relaxation and may be affected by the presence of magnetite nanoparticles. This effect is related to the increase in reticulation points in the hydrogel network. The following were best parameters for removing Cd2+ from aqueous solutions: pH range from 4.5 to 5.5; initial metal concentration of 200 mg L−1; and dried hydrogel mass of 100 mg. Using non-linearized isotherms described by Langmuir, Freundlich and Redlich–Peterson, it was inferred that there may be a variation in the physiochemical phenomena involving Cd2+ adsorption and the results fit better to the Langmuir or Redlich–Peterson models than the Freundlich model. The present study confirms that magnetic hydrogels and Cd2+ may be recovered after the application of an external magnetic field, unlike hydrogels without magnetic properties, which are generally recovered through the use of a chemical solvent, such as HCl or HNO3.