U(VI) removal efficiency and mechanism of biochars derived from sewage sludge at two pyrolysis temperatures

Dual Effect of Acetic Acid Efficiently Enhances Sludge-Based Biochar to Recover Uranium From Aqueous Solution

Excess sludge (ES) treatment and that related to the uranium recovery from uranium-containing wastewater (UCW) are two hot topics in the field of environmental engineering. Sludge-based biochar (SBB) prepared from ES was used to recover uranium from UCW. Excellent effects were achieved when SBB was modified by acetic acid. Compared with SBB, acetic acid-modified SBB (ASBB) has shown three characteristics deserving interest: 1) high sorption efficiency, in which the sorption ratio of U(VI) was increased by as high as 35.0%; 2) fast sorption rate, as the equilibrium could be achieved within 5.0 min; 3) satisfied sorption/desorption behavior; as a matter of fact, the sorption rate of U(VI) could still be maintained at 93.0% during the test cycles. In addition, based on the test conditions and various characterization results, it emerged as a dual effect of acetic acid on the surface of SBB, i.e., to increase the porosity and add (−COOH) groups. It was revealed that U(VI) and −COO− combined in the surface aperture of ASBB via single-dentate coordination. Altogether, a new utilization mode for SBB is here proposed, as a means of efficient uranium sorption from UCW.

The effects of pH on U(VI)/Th(IV) and Ra(II)/Ba(II) adsorption by polystyrene-nano manganese dioxide composites: Fourier Transform Infra-Red spectroscopic analysis

Fourier Transform Infra-Red (FTIR) spectroscopy provides structural information of prime importance to understand ions coordination to adsorbents. This consequently aids in the design of improved ion exchange materials and help in deriving the optimum adsorption conditions. In the present work, the adsorption mechanism of both U(VI)/Th(IV) and Ra(II)/Ba(II) radionuclides couples onto polystyrene-nano manganese dioxide (PS-NMO) composite is reported in relation to the effect of working solution pH. The separation of each radionuclide couple; i.e. U(VI)/Th(IV) and Ra(II)/Ba(II); could be effectively achieved at pH = 3 and pH = 1 respectively. The pH values not only determine the species of the respected elements that are mainly present in aqueous solution before applying the adsorbent, but it also alters the structure of the composite adsorbent. FTIR spectroscopy showed that Th(IV) formed inner sphere complexes and occupied the A site in the dioxide layer, while U(VI) formed outer sphere complexes on the surface of the composite. Spectra subtraction showed that some aromatic bands and vinyl C-H bands were split or shifted to lower wavenumbers with the loading of Ba(II). This was attributed to changes in the composite stereochemistry to accommodate Ba(II). The working solution pH could be the key in the separation process of both U(VI)/Th(IV) and Ra(II)/Ba(II) from their mixture, and FTIR spectroscopy stands as a useful technique to explain the difference between metal ions responses to adsorbants.