Abstract
Activated carbon adsorbents modified with azo compounds (4-(2-pyridylazo)resorcinol, 1-(2-pyridylazo)-2-naphthol, 4-(2-thiazolylazo)resorcinol), or with allyl and vinylbenzyl derivatives of 4-(2-thiazolylazo)resorcinol, were observed to be highly effective in removing uranium from seawater and providing high loadings. Adsorbents consisting of azo compounds attached to fiber fabrics were prepared using silane coupling to attach azo reagents to silica fibers or mordanting agents such as tannic acid or aluminum acetate to attach them to cellulose fibers. Loadings of 15–45 mg U g−1 adsorbent were obtained. Scanning electron microscopy/energy dispersive X-ray spectroscopy measurements confirmed the presence of high concentrations of uranium on the surface of the silica-based and cellulose-based fibers.
Highlights
In view of the limited resources of uranium available through mining operations on land and the environmental issues associated with uranium mining and ore processing, the feasibility of recovering uranium from the ocean by means of adsorbents or ion exchangers has been explored since the 1960s
Results of measurements of uranium removal from seawater using activated carbon treated with azo dyes
These results show that the relative extent of uranium removal from the seawater was ISOPAN > PAR > PAN > TAR > TAN > Br-PADAP. (ISOPAN was not used in further stages of the study because this item was discontinued by the vendor.)
Summary
In view of the limited resources of uranium available through mining operations on land and the environmental issues associated with uranium mining and ore processing, the feasibility of recovering uranium from the ocean by means of adsorbents or ion exchangers has been explored since the 1960s. In low pH media, a large number of extracting agents have been known for many years to be highly effective in extracting U(VI), which is present in such media in the form of the UO22þ cation. Such agents include, for instance, tri-nbutylphosphate, bis-(2-ethylhexyl)-o-phosphoric acid, tri-n-octylphosphine oxide, and thenoyltrifluoroacetone (Korkisch, 1969). Far fewer extracting agents have been reported to be effective for the anionic complexes that U(VI) forms at high pH, and, in particular, for the neutral Ca2UO2(CO3) complex. Another major problem involves the very low concentration of uranium in seawater. Other nitrogen-based ligands, such as glutarimidoxime (Tian et al, 2012) as well as phosphor-based compounds, such as bis(2-methacryloxyethyl) phosphate (Tissot, 2014), have been proposed as candidates, amidoxime is still the ligand on which most attention is focused
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