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, SnO 2 and Zn 2 SiO 4 to adsorb Cr(VI) via batch method. It is the first study that utilizes Zn 2 SiO 4 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 SnO 2 and pH 4 in case of Zn 2 SiO 4 . 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 SnO 2 and Zn 2 SiO 4 , 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 ∆H 0 values indicated an endothermic adsorption on NiO and SnO and exothermic adsorption on SnO, SnO 2 and Zn 2 SiO 4 . The practical application for Cr(VI) removal showed 73.2% and 99.3% removal on NiO and SnO nanoparticles (NPs) respectively from spiked polluted industrial water and 71.2% and 88.6% of Cr(VI) respectively from spiked drinking water samples. A techno-economics study was performed showing an average cost of 2.3 USD per gram of the prepared nanometal oxides.