Continuous Liquid-Liquid Extraction of Uranium from Uranium-containing Wastewater Using an Organic Phase-refining-type Emulsion Flow Extractor.

A previously reported emulsion flow (EF) extraction system does not equip the refining device for any used organic phase. Therefore, the processing of large quantities of wastewater by using the EF extractor alone could lead to the accumulation of extracted components into the organic phase, and a lowering of the extraction performance. In the present study, we developed an organic phase-refining-type EF system, which is equipped with a column for refining a used organic phase to prevent accumulation, and successfully applied it for treating uranium-containing wastewater.

Counter current "emulsion flow" extractor for continuous liquid-liquid extraction from suspended solutions.

A single current "emulsion flow" liquid-liquid extraction apparatus has a head with a number of holes from which micrometer-sized droplets of an aqueous phase spout into an organic phase to mix the two liquid phases. For practical use, however, a fatal problem can occur when particulate components in the aqueous phase plug the holes. In the present study, we have succeeded in solving the problem by applying a counter current-type emulsion flow extractor where micrometer-sized droplets of the organic phase are generated.

Reversed-micellar extraction of strontium(II) from model solutions of seawater.

In order to monitor a radioactive nuclide of strontium-90 in seawater around nuclear facilities, a solvent-extraction method for collecting Sr(II) in seawater was examined. A reversed-micellar extraction system containing an anionic surfactant AOT and a molecular extractant N,N,N',N'-tetra(n-octyl)diglycolamide (TODGA) in n-hexane was chosen for the extraction of Sr(II) from model solutions of seawater containing 0.5 M NaCl (1 M = 1 mol dm(-3)), 0.05 M MgCl(2), and/or 0.01 M CaCl(2). The combination of AOT-forming reversed micelles and TODGA coordinating with Sr(II) as an organic ligand (extractant) was found to be efficient for the extraction of Sr(II) from model solutions. The mechanism of the reversed-micellar extraction system was also considered in the present study.

New apparatus for liquid-liquid extraction, "emulsion flow" extractor.

A simple and low-cost apparatus for continuous and efficient liquid-liquid extraction, which does not need continual mechanical forces (stirring, shaking, etc.) other than solution sending, has newly been developed. This apparatus, named "emulsion flow" extractor, is composed of a column part where an emulsified state fluid flow (emulsion flow) is generated by spraying micrometer-sized droplets of an aqueous phase into an organic phase and a phase-separating part where the emulsion flow is destabilized by means of a sudden decrease in its vertical liner velocity due to a drastic increase in cross-section area of the emulsion flow passing through. In the present study, the performance of a desktop emulsion flow extractor in the extraction of Yb(III) and U(VI) from aqueous HNO(3) solutions into isooctane containing bis(2-ethylhexyl) phosphoric acid (D2EHPA) was evaluated. The mixing efficiency of the emulsion flow extractor was found to be comparable with that of a popular liquid-liquid extractor, mixer-settler. Moreover, the emulsion flow extractor proved to have an overwhelming advantage in terms of phase-separating ability.

Solid-solution reactions in As(V) sorption by schwertmannite.

Sorption behavior of As(V) by synthesized schwertmannite was examined under pH 3.3 as a function of As(V) concentration in the initial solution and interpreted in term of solid-solution reactions. Results showed that schwertmannite released 0.62 mmol of SO4(2-) for every 1 mmol of H2AsO4- and 0.24 mmol of OH- that has been sorbed. As(V) replaced SO4 up to half of the total SO4 in schwertmannite. The quantitative relationship among the three chemical compositions indicated that As(V)-sorbed schwertmannite would behave as a solid solution between the As(V) free schwertmannite and schwertmannite containing the maximum level of As(V). The equilibrium constant for the anion exchange in the solid-solution reaction estimated from the reacted solution chemistry depicts the As(V) content found in precipitates formed in acid mine drainage and laboratory experiments. Although schwertmannite is metastable with respect to goethite, the transformation is significantly inhibited by sorption of As(V). The solid-solution reactions also explain the stabilization of schwertmannite by sorption of As(V).

Accumulation and potential dissolution of Chernobyl-derived radionuclides in river bottom sediment.

Areas contaminated with radionuclides from the Chernobyl nuclear accident have been identified in Pripyat River near the Chernobyl Nuclear Power Plant. The river bottom sediment cores contained 137Cs (10(5)-10(6) Bq/m2) within 0-30 cm depth, whose concentration is comparable to that in the ground soil in the vicinity of the nuclear power plant (the Exclusion Zone). The sediment cores also accumulated 90Sr (10(5) Bq/m2), (239,240)Pu (10(4) Bq/m2) and 241Am (10(4)Bq/m2) derived from the accident. Several nuclear fuel particles have been preserved at 20-25 cm depth that is the peak area of the concentrations of the radionuclides. These inventories in the bottom sediments were compared with those of the released radionuclides during the accident. An analysis using a selective sequential extraction technique was applied for the radionuclides in the sediments. Results suggest that the possibility of release of 137Cs and (293,240)Pu from the bottom sediment was low compared with 90Sr. The potential dissolution and subsequent transport of 90Sr from the river bottom sediment should be taken into account with respect to the long-term radiological influence on the aquatic environment.