Comparative Adsorption Affinities of Nano-Metal Oxides Towards Cr(VI): Synthesis, Characterization, Kinetics, Isotherms, Thermodynamic and Techno-Economics Study

We report the preparation and characterization of a series of nano-sized metal oxides namely CuO, NiO, SnO, SnO2 and Zn2SiO4 to adsorb Cr(VI) via batch method. It is the first study that utilizes Zn2SiO4 to adsorb Cr(VI). Metal oxides were characterized using XRD, FTIR and TGA. Operating parameters including pH, contact time, adsorbent dose, Cr(VI) concentration, temperature and interfering ions were studied. The optimum pH values were pH 6 in case of CuO and NiO, pH 7 in case of SnO and SnO2 and pH 4 in case of Zn2SiO4. The pseudo-second-order kinetic model was appropriate to describe the process and Langmuir model was the best fitted isotherm model implying the domination of chemisorption with adsorption capacities 15.5, 7.77, 9.65, 7.06 and 10.95 mg/g for CuO, NiO, SnO and SnO2 and Zn2SiO4, respectively. The intraparticle diffusion model showed a boundary layer control. Cr(VI) adsorption was temperature-dependent and the thermodynamic parameters showed a non-spontaneous process. The ∆H0 values indicated an endothermic adsorption on NiO and SnO and exothermic adsorption on SnO, SnO2 and Zn2SiO4. The practical application for Cr(VI) removal showed 73.2