The sequestration of U(VI) on functional β-cyclodextrin-attapulgite nanorods

Effect of water chemistry on Eu(III) biosorption by magnetic bioadsorbent

In this study, magnetic biosorbent was fabricated by chemical co-precipitation of Fe(II) and Fe(III) on the surface Paeclomyces catenlannulatus (P. catenlannulatus) by adding NaOH solution under N2 conditions. The influence of water chemistries (i. e. pH, reaction time, temperature, concentration and ionic strength) on Eu(III) biosorption towards magnetic biosorbent was elucidated by batch technique. The batch experiment showed that Eu(III) biosorption on magnetic biosorbent was independent of ionic strength, suggesting that inner-sphere-surface-complexation predominated Eu(III) biosorption. The biosorption kinetics showed the sorption equilibrium was achieved at reaction time of 24 h, and the maximum biosorption capacity of Eu(III) on magnetic biosorbent calculated by Langmuir model was 69.45 mg/g at pH 3.5 and 298 K. The regeneration experiments showed the slight decrease of biosorption capacity after the fifth recycles. These results suggested that this magnetic biosorbent presented the fast biosorption rate and high biosorption capacity for Eu(III). The results of XPS analysis revealed that various oxygenated function groups (e.g. carboxyl, hydroxyl groups) were responsible for the high effective biosorption of Eu(III). These findings manifested that this magnetic biosorbent could be as a high-effective material for the immobilization and pre-concentration of radionuclides from aqueous solution in environment remediation.

Mechanical investigation of U(VI) on pyrrhotite by batch, EXAFS and modeling techniques

The interaction mechanism of U(VI) on pyrrhotite was demonstrated by batch, spectroscopic and modeling techniques. Pyrite was selected as control group in this study. The removal of U(VI) on pyrite and pyrrhotite significantly decreased with increasing ionic strength from 0.001 to 0.1mol/L at pH 2.0-6.0, whereas the no effect of ionic strength was observed at pH >6.0. The maximum removal capacity of U(VI) on pyrite and pyrrhotite calculated from Langmuir model was 10.20 and 21.34mgg^-1 at pH 4.0 and 333K, respectively. The XPS analysis indicated the U(VI) was primarily adsorbed on pyrrhotite and pyrite and then approximately 15.5 and 9.8% of U(VI) were reduced to U(IV) by pyrrhotite and pyrite after 20 days, respectively. Based on the XANES analysis, the adsorption edge of uranium-containing pyrrhotite located between U^IVO₂(s) and U^VIO₂²⁺ spectra. The EXAFS analysis demonstrated the inner-sphere surface complexation of U(VI) on pyrrhotite due to the occurrence of U-S shell, whereas the U-U shell revealed the reductive co-precipitates of U(VI) on pyrrhotite/pyrite with increasing reaction times. The surface complexation modeling showed that outer- and inner-surface complexation dominated the U(VI) removal at pH<4 and pH>5.0, respectively. The findings presented herein play a crucial role in the removal of radionuclides on iron sulfide in environmental cleanup applications.