Carp Scales Modified with Cerium Oxide Nanoparticles as a New Bio-Adsorbent for Arsenic and Chromium Separation from Water

Different treatments of fish scales from carps (Cyprinus carpio) (FS)—mechanical milling, modified with cerium dioxide (CeO2) nanoparticles and controlled carbonization of FS and modification with CeO2—were applied to obtain FS, FS-CeO2 and CFS-CeO2 bio-adsorbents. The synthesized adsorbents were used for As(V) and Cr(VI) oxyanion separation from water. Porosity and the amount of CeO2 nanoparticles deposition were controlled using different experimental conditions. Response surface methodology (RSM) was used to select optimal parameters for adsorbent synthesis to obtain the highest adsorption capacity. The structural and surface characteristics of the synthesized adsorbents were examined using FTIR, XRD and SEM techniques. The efficiency of pollutant removal was analyzed in terms of varying experimental conditions: the mass of adsorbent, pH, temperature and contact time. RSM was also used to optimize adsorption and desorption processes. The adsorption data, obtained at 25, 35 and 45 °C, were processed using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm and Van’t Hoff thermodynamic models. The FS-CeO2 bio-adsorbent showed good adsorption capacities of 92.61 and 65.50 mg g−1 for As(V) and Cr(VI) ion removal, respectively, obtained by using the Langmuir model. Thermodynamic parameters proved that adsorption was a viable, spontaneous and endothermic process. The results from kinetic modeling indicated that both adsorbate and surface functional group concentration determine overall kinetic law with the highest participation of intra-particle diffusion resistance to pollutant transport. Exceptional adsorption and desorption performances of FS-CeO2 in conjunction with the bio-based origin of synthesized adsorbents offer valuable alternatives for the remediation of polluted water.