Effect of ionic radius on Ti (IV), Zr (IV), and Hf (IV) adsorption by RB biomass

For the first time, sorption characteristics and mechanisms of group-4 elements were investigated and compared in extremely acidic solutions (4 M HCl) by rice bran (RB) biomass. Numerous instrumental strategies and hard-soft acid-base (HSAB) theory were applied to investigate the sorption features and mechanisms of Ti(IV), Zr(IV), and Hf(IV). The specific surface area of the raw biomass was 4.79 m2.g−1 as determined by Barrett-Emmet-Taller analyzer (BET). Deposition of planned metal ions on the biomass was determined through a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS). The linkage of C=O, O-H, and N-H functional groups of biomass with metal ions became clear with Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum analysis. The role of C=O functional group of ammonium oxalate/ammonium carbonate in metal ions desorption was confirmed by elution experiment. The experiments showed that the high-affinity of rubidium to sorption of zirconium and hafnium (>99%) was owing to their lower hydrated ionic radius. From all the results obtained, exhausting-hard interactions and electrostatic complexation mechanism were diagnosed between hard-functional groups of RB biomass and hard cations of Ti(IV), Zr(IV), and Hf(IV).