Removal of Chromate and Nitrate Ions from Aqueous Solutions by Co_xFe_3-xO₄@silica Hybrid Nanoparticles Decorated with Cross-Linked Tragacanth Gum: Experiment, Modeling and Optimization

A hybrid nanocomposite cobalt ferrite and Tragacanth gum, denoted as Co_xFe_3-xO₄@silica@TG was developed and applied in concurrent removal of chromate and nitrate ions from wastewater. The results showed that the presence of Tragacanth gum considerably improved the capability of cobalt ferrite for removing the pollutants. The adsorption properties and surface morphology of the sorbent were compared with those of bare cobalt ferrite, Tragacanth gum, and Tragacanth gum cross-linked copolymer. The properties of the proposed nanocomposite were studied using FT-IR, transmission electron microscopy (TEM), and vibrating-sample magnetometer (VSM) techniques. The effect of different factors including the amount of the adsorbent, sample pH, contact time and initial concentration was also evaluated and optimized through response surface methodology using central composite design. The optimal conditions for the adsorption of both chromate and nitrate ions (30 mg L⁻¹ as the concentration of both of them) were pH=3, an adsorbent dose of 1 mg mL⁻¹ and 22.4 min contact time. The adsorption process was found to follow the pseudo-second order and intra-particle diffusion kinetic models. The equilibrium adsorption data followed the Langmuir isotherm and the highest adsorption capacity was determined to be 44.1 and 30.7 mg g⁻¹ for chromate and nitrate, respectively.