Uranium is a chemically toxic and radioactive heavy metal. Depleted uranium (DU) is the byproduct of the uranium enrichment process, with a majority of U as uranium-238, and a lower content of the fissile isotope uranium-235 than natural uranium. Uranium-235 is mainly used in nuclear reactors and in the manufacture of nuclear weapons. Exposure is likely to have an impact on humans or the ecosystem where military operations have used DU. Yuma Proving Ground in Arizona, USA has been using depleted uranium ballistics for 36 years. At a contaminated site in the Proving Grounds, soil samples were collected from the flat, open field and lower elevated trenches that typically collect summer runoff. Spatial distribution and fractionation of uranium in the fields were analyzed with total acid digestion and selective sequential dissolution with eight operationally defined solid-phase fractions. In addition to uranium, other trace elements (As, Ba, Co, Cr, Cu, Hg, Mo, Nb, Pd, Pb, V, Zn, Zr) were also assessed. Results show that the trench area in the testing site had a higher accumulation of total U (12.4%) compared to the open-field soil with 279 mg/kg U. Among the eight solid-phase components in the open-field samples, U demonstrated stronger affinities for the amorphous iron-oxide bound, followed by the carbonate bound, and the residual fractions. However, U in the trench area had a stronger binding to the easily reducible oxide bound fraction, followed by the carbonate-bound and amorphous iron-oxide-bound fractions. Among other trace elements, Nb, As, and Zr exhibited the strongest correlations with U distribution among solid-phase components. This study indicates a significant spatial variation of U distribution in the shooting range site. Fe/Mn oxides and carbonate were the major solid-phase components for binding U in the weapon test site.

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Removal of chromate (CrO4 2–) and pertechnetate (TcO4 –) from the Hanford Low Activity Waste (LAW) is beneficial as it impacts the cost, life cycle, operational complexity of the Waste Treatment and Immobilization Plant (WTP), and integrity of vitrified glass for nuclear waste disposal. Here, we report the application of [MoIV 3S13]2– intercalated layer double hydroxides (LDH–Mo3S13) for the removal of CrO4 2– as a surrogate for TcO4 –, from ppm to ppb levels from water and a simulated LAW off-gas condensate of Hanford’s WTP. LDH–Mo3S13 removes CrO4 2– from the LAW condensate stream, having a pH of 7.5, from ppm (∼9.086 × 104 ppb of Cr6+) to below 1 ppb levels with distribution constant (K d) values of up to ∼107 mL/g. Analysis of postadsorbed solids indicates that CrO4 2– removal mainly proceeds by reduction of Cr6+ to Cr3+. This study sets the first example of a metal sulfide intercalated LDH for the removal of CrO4 2–, as relevant to TcO4 –, from the simulated off-gas condensate streams of Hanford’s LAW melter which contains highly concentrated competitive anions, namely F–, Cl–, CO3 2–, NO3 –, BO3 3–, NO2 –, SO4 2–, and B4O7 2–. LDH–Mo3S13’s remarkable removal efficiency makes it a promising sorbent to remediate CrO4 2–/TcO4 – from surface water and an off-gas condensate of nuclear waste.

In this paper, we examined three different sequential coprecipitation schemes based on Mg(OH) and CaF precipitation using triethylamine (TEA) and hydrofluoric acid (HF), respectively, for determination of cadmium (Cd) impurities from multivitamin/mineral (MVM) supplements by isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP-MS). The schemes involved three-step coprecipitation with either TEA alone or in combination with HF and are designated as Scheme 1 (TEA-TEA-TEA), Scheme 2 (TEA-HF-TEA) and Scheme 3 (HF-TEA-TEA) according to the addition sequence of each reagent. Experiments were carried out with MVM solutions spiked with 60 μg L Cd from a multielement standard solution. All schemes provided quantitative separation of Cd from MVM matrix. Scheme 1 was the least effective in removal of interfering concomitant elements, molybdenum (Mo) and tin (Sn). Scheme 2 performed better for Sn, but failed in eliminating Mo. Scheme 3 was the most effective in eliminating both Mo and Sn. Mo levels in test MVM solutions reduced from 4.3 μg mL to as low as 0.014 μg mL while that for Sn decreased from 0.5 μg mL to 0.018 μg mL allowing interference-free determination of Cd to be achieved. Salt-matrix due to Mg, Ca, P and K along with the essential elements (Mn, Fe, Cu and Zn) levels was also reduced significantly. Reagent blanks from HF and TEA were insignificant (0.008 μg L) allowing a limit of detection of 0.004 μg L or 0.26 ng g Cd to be achieved (3σ, n = 6). The performance of the coprecipitation method (Scheme 3) was validated by determination of Cd in multivitamin/multielement tablets certified reference material (SRM 3280) by ID-ICP-MS. Experimental results (ng g) and recoveries were 78.8 ± 4.7 (98.5%), 77.9 ± 5.2 (97.4%) and 76.5 ± 4.8 (95.6%) for Cd,Cd and Cd isotopes, respectively. Several commercial MVM supplements were analyzed using the method. Mean Cd concentration ranged from 21.4 ng g to 93.3 ng g. These values are much lower than those reported to date for various MVM supplements by ICP-MS determinations without chemical separation.

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Technetium (99Tc) is a long-live radionuclide, and its removal from legacy nuclear waste is problematic mainly because of its persistence as highly soluble pertechnetate (99TcO4 –) ions. Here, we report the application of [Sn2S6]4– anion intercalated layered double hydroxides, LDH-[Sn2S6] for the removal of perrhenate (ReO4 –), a nonradioactive surrogate of 99TcO4 –. In acidic and neutral media, LDH-[Sn2S6] can remove over 98 and 96% of ReO4 –, respectively, from a 1000 ppb spiked solution in 48 h, and the removal of ReO4 – remains beyond 87% even after 15 days of interaction with the solution. Moreover, in the presence of other metal ions, for instance, Cu2+, ReO4 – removal increases to about 99.9%, leaving the residual concentration of <1 ppb with K d ∼ 5.00 × 107 mL/g. LDH-[Sn2S6] also exhibits large sorption capacities for ReO4 – at 9.3 × 104 μg/g at pH ∼ 2. Evidenced by XRD, SEM, HRTEM, EDS, and XPS, we further demonstrate the removal of ReO4 – occurs by ion-exchange and precipitation. Overall, the roles of 3d transition metal ions and the pH-driven sorption mechanisms introduce remarkable insights into metal sulfides intercalated LDH to remove 99TcO4 –.

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