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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.

The biosorption of Eu(III) and U(VI) on Bacillus subtilis ( B. subtilis ) as a function of reaction time, pH, ionic strength, temperature was investigated by macroscopic and modeling techniques. The macroscopic experiments indicated that the biosorption kinetics and isotherms of Eu(III) and U(VI) on B. subtilis can be satisfactorily fitted by pseudo-second-order kinetic model and Langmuir model, respectively. No effect of ionic strength revealed that the inner-sphere surface complexation dominated the biosorption of Eu(III) and U(VI) onto B. subtilis . The maximum sorption capacity of B. subtilis calculated from Langmuir model at pH 4.5 and 298 K was 58.80 and 90.91 mg/g for Eu(III) and U(VI), respectively. According to the surface complexation modeling, the biosorption of Eu(III) and U(VI) on B. subtilis can be simulated by diffuse layer modeling with three inner-sphere surface complexation sites such as phosphoryl, carboxyl and hydroxyl groups. The findings presented herein suggested that B. subtilis is a promising bio-adsorbent for the preconcentration and retardation of radionuclides in the environmental remediation strategy such as permeable reactive barrier.

The sulfonated graphene oxide (GO-OSO 3 H) was synthesized by the oxidation of GO under concentrated H 2 SO 4 conditions. It is demonstrated based on characterization results that sulfonated groups was satisfactorily grafted on the surface of GO. Macroscopic investigation indicated that the adsorption of Eu(III) on GO-OSO 3 H can be better fitted by pseudo-second-order kinetic model with high correlation coefficient (R 2 > 0.999) compared to pseudo-first-order kinetic model (R 2 3 H was independent of ionic strength, revealing that inner-sphere surface complexation dominated the Eu(III) adsorption at pH from 2.0 to 11.0. The maximum adsorption capacity of GO-OSO 3 H for Eu(III) calculated from Langmuir model was 125.0 mg/g at pH 5.5 and T = 293 K conditions. The calculation of thermodynamic parameters showed that the adsorption of Eu(III) on GO-OSO 3 H was an exothermal and spontaneous processes. According to fitting of surface complexation modeling, the adsorption of Eu(III) on GO-OSO 3 H can be satisfactorily simulated by diffuse layer model with monodentate and mononuclear complexes (SOEu 2 + species) and bidentate and mononuclear complexes ((SO) 2 Eu (OH) 3 − species) at pH 2.0–11.0 conditions.