Macroscopic and modeling evidence for competitive adsorption of Co(II) and Th(IV) on carbon nanofibers

The competitive adsorption of Co(II) and Th(IV) on carbon nanofibers (CNFs) was investigated by batch and spectroscopic techniques. The batch experiments indicated that the adsorption of Co(II) and Th(IV) on CNFs at single- and bi-solute system decreased with increasing ionic strength at pH 2.0–5.0, whereas the competitive adsorption of Co(II) and Th(IV) was independent of ionic strength at pH > 7.0. However, the decreased extent of Th(IV) adsorption on CNFs was significantly higher than that of Co(II) adsorption at bi-solute systems, indicating that CNFs displayed the stronger chemical affinity for Co(II) compared to Th(IV). The maximum adsorption capacities of CNFs for Co(II) and Th(IV) at single-solute systems were 66.23 and 37.17 mg/g at pH 3.5 and 293 K, respectively. The results of surface complexation modeling, the competitive adsorption of Co(II) and Th(IV) on the CNFs was mainly outer-sphere and inner-sphere surface complexation at pH 5.0, respectively. These findings indicated that CNFs can be used as a promising adsorbent for the high effective enrichments and immobilization of radionuclides in the environmental cleanup.