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Detection of radioactive isotopes of polonium is important for understanding natural processes, management and assessment of radioactive waste, and nuclear forensics applications. Further, the most common methods for preparation of polonium samples for alpha spectrometry are electrodeposition and spontaneous deposition which are time consuming. Here, we compare three approaches utilizing rapid microprecipitation from bismuth phosphate, copper sulfide, or tellurium alongside traditional spontaneous deposition methods. From these experiments, results show that copper sulfide microprecipitation recoveries are similar to spontaneous deposition on silver and less time consuming with an approximate five-fold decrease in preparation time, including in the presence of complex matricesmore » like seawater.« less

The primary approach to assessing monitored natural attenuation (MNA) is currently based on a conceptual model utilizing the total contaminant concentrations, assuming a single aqueous species. However, many contaminants, such as metals and radionuclide - including iodine, can exist in multiple species that behave chemically differently in the environment and can exist simultaneously. For example, radioiodine often occurs concurrently as three major aqueous species: iodide (I^-), iodate (IO₃^-), and organo-I, which undergo distinct attenuation pathways and exhibit markedly different mobility and geochemical behavior. Here, current literature is reviewed with the objective to: 1) demonstrate differences in iodine species’ geochemical behaviormore » and natural attenuation mechanisms; 2) show that a species-specific (or multi-species) approach provides greater details on contaminant migration and attenuation; and (3) discuss the logistics of a species-specific approach to developing conceptual models for assessing overall contaminant mobility. The species-specific approach results in a more accurate assessment of mass flux and maximum groundwater concentrations; and, therefore, a more defensible risk evaluation to support short- or long-term remediation and/or natural attenuation strategies. Although iodine is the focus of this paper, this methodology could be applied to other risk-driving contaminants such as mercury and uranium, which have even more complex aqueous speciation than iodine, or technetium and chromium, which have complex solid phase speciation and natural attenuation reaction networks. Accounting for species-specific geochemical behavior, while implementing MNA strategies can greatly reduce uncertainty, and, therefore, remedial costs required to ultimately achieve remediation regulatory objectives.« less

Two studies in the early 1980s described the leaching behavior of americium (Am) disposed as part of acidic high-salt processing wastes from the Hanford Site’s Plutonium Finishing Plant to nearby ground sediments. Here these batch leach experiments showed that the Am concentrations followed a linear log [Am] versus pH relationship with a slope of –1. Column leach experiments in the second study, however, did not follow this relationship and only ~30% of the americium desorbed even after extensive column leaching. Here, the 1980s research is re-examined along with previously unpublished information and, in light of recent published work, a plausiblemore » mechanism is proposed to explain these phenomena. Amorphous silica in the contaminated sediments is postulated to be the substrate responsible for both the exchangeable Am available for leaching and the retained low-leachable Am made evident in the column leach experiments. The exchangeable Am³⁺ in the contaminated sediment leach experiments behaves with pH dependence similar to that observed for uptake onto amorphous silica of sodium (Na⁺), calcium (Ca²⁺), barium (Ba²⁺), cadmium (Cd²⁺), uranyl (UO₂²⁺), ferric (Fe³⁺), chromic (Cr³⁺), cupric (Cu²⁺), plumbous (Pb²⁺), uranium(IV) (U⁴⁺), plutonium(IV) (Pu⁴⁺), zirconium (Zr⁴⁺), analogue lanthanide (gadolinium, Gd³⁺, europium, Eu³⁺, and lutetium, Lu³⁺) and curium (Cm³⁺) ions as well as other studies with Am³⁺. Correspondingly, the residual low-leachable Am³⁺ revealed in the column leach experiments is attributed to incorporation of Am³⁺ within amorphous silica by dynamic Am³⁺ sorption and silica precipitation processes.« less

Enhanced TcO ₄ ⁻ reduction by metallic Fe ⁰ in the presence of particulate and structural Si. Rhythmical precipitation of dissolved iron leads to formation of layered structures related to geological phenomena such as orbicular rocks and Liesegang rings.

The phenomenon of sequestration of metal ions into the crystal structure of minerals is common in nature. To date, incorporation of technetium(IV) into iron minerals has been studied predominantly for systems under carefully controlled anaerobic conditions, employing syntheses with iron(II) solutions or using pre-synthesized iron oxides/oxyhydroxides. Mechanisms of the transformation of iron phases leading to incorporation of technetium(IV) under aerobic conditions remain poorly understood. We investigate granular metallic iron for reductive sequestration of technetium(VII) at elevated concentrations under ambient conditions. Here we report the retarded transformation of ferrihydrite to magnetite in the presence of technetium. We observe that quantitative reductionmore » of pertechnetate with a fraction of technetium(IV) structurally incorporated into non-stoichiometric magnetite benefits from concomitant zero valent iron oxidative transformation. An in-depth profile of iron oxide reveals clusters of the incorporated technetium(IV), which account for 32% of the total retained technetium estimated via X-ray absorption and X-ray photoelectron spectroscopies. This corresponds to 1.86 wt.% technetium in magnetite, providing the experimental evidence to theoretical postulations on thermodynamically stable technetium(IV) being incorporated into magnetite under spontaneous aerobic redox conditions.« less

Zero valent iron (ZVI) is a promising material for reductive removal of technetium from industrial waste streams. An example application of this method could be to treatment of low activity aqueous waste that is currently stored in tanks at the Hanford site. However, there is still a lack of understanding of the useful lifetime of ZVI for treatment and the changes in reductive removal of Tc over time. In this research, we studied the reductive removal of Tc from aqueous solutions by ZVI aged with up to 30 days by contact with 0.08 M NaCl solutions. These results show thatmore » ZVI could be used to remove Tc(VII) from aqueous solutions by its reduction to the less soluble and relatively immobile Tc(IV) with greater than 99% removal in three hours. Still, greater than 90% of Tc is removed with ZVI aging up to one week. However, after 10 days of aging of zero valent iron, a significant decrease in removal of Tc occurs (55% removal at three hours) followed by negligible removal after aging for two weeks or more which is consistent with formation of iron oxides on the surface. Further, these results correlate with XRD and FTIR analysis showing an increase in magnetite followed by maghemite and goethite with aging time.« less