The Sorption of Technetium and Iodine Radioisotopes by Various Minerals

Removal of radionuclide 99Tc from aqueous solution by various adsorbents: A review

Technetium isotope 99Tc is a main radioactive waste produced in the process of nuclear reaction, which has the characteristics of long half-life and strong environmental mobility, and can be bio-accumulated in organisms, resulting in serious threat to human health and ecosystem. Adsorption method is widely used in the field of removing radionuclides from water due to the advantages of high treatment rate, simple and mature industrial application. In this review paper, the recent advances in research and application of various adsorption materials for 99Tc pollution treatment were summarized and analyzed for the first time, including inorganic adsorbents, such as activated carbon, zero-valent iron, metallic minerals, clay minerals, layered double hydroxides (LDHs), tin-based materials, and sulfur-based materials; organic adsorbents, such as porous organic polymers (POPs), covalent-organic frameworks (COFs), metal-organic frameworks (MOFs), and ion exchange resin; and biological adsorbents, such as biopolymers (chitosan, cellulose, alginate), and microbial cells. The performance characteristics and the adsorption kinetics and isotherms of various adsorption materials were discussed. This review could deepen the understanding of the adsorptive removal of 99Tc from aqueous solution, and provide a reference for the future research in this field.

Removal of CrO42-, a Nonradioactive Surrogate of 99TcO4-, Using LDH-Mo3S13 Nanosheets

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 [Mo^IV₃S₁₃]^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.

Iodine effective diffusion coefficients through volcanic rock: Influence of iodine speciation and rock geochemistry

Accurate prediction of the subsurface transport of iodine species is important for the assessment of long-term nuclear waste repository performance, as well as monitoring compliance with the Comprehensive Nuclear-Test-Ban Treaty, given that radioiodine decays into radioxenon. However, the transport of iodine through intact geologic media is not well understood, compromising our ability to assess risk associated with radioiodine migration. The current study's goal is to quantify the matrix diffusion of iodine species through saturated volcanic rock, with particular attention paid to the redox environment and potential speciation changes. Diffusion experiments were run for iodide through lithophysae-rich lava, lithophysae-poor lava, and welded tuff, whereas iodate diffusion was studied through welded tuff. Iodine transport was compared with a conservative tracer, HDO, and effective diffusion coefficients were calculated. Likely due to a combination of size and anion exclusion effects, iodine species diffused more slowly than the conservative tracer through all rock types tested. Furthermore, oxidation of iodide to iodate was observed in the lithophysae-poor lava, affecting transport. Results provide much needed data for subsurface transport models that predict radioiodine migration from underground sources, and indicate the pressing need for geochemical and redox interactions to be incorporated into these models.

Technetium immobilization by materials through sorption and redox-driven processes: A literature review

The objective of this review is to evaluate materials for use as a barrier or other deployed technology to treat technetium-99 (Tc) in the subsurface. To achieve this, Tc interactions with different materials are considered within the context of remediation strategies. Several naturally occurring materials are considered for Tc immobilization, including iron oxides and low solubility sulfide phases. Synthetic materials are also considered, and include tin-based materials, sorbents (resins, activated carbon, modified clays), layered double hydroxides, metal organic frameworks, cationic polymeric networks and aerogels. All of the materials were evaluated for their potential in-situ and ex-situ performance with respect to long-term Tc uptake and immobilization, environmental impacts and deployability. Other factors such as the technology maturity, cost and availability were also considered. Given the difficulty of evaluating materials under different experimental conditions (e.g., solution chemistry, redox conditions, solution to solid ratio, Tc concentration etc.), a subset of these materials will be selected, on the basis of this review, for subsequent standardized batch loading tests.

Iodine immobilization by materials through sorption and redox-driven processes: A literature review

Radioiodine-129 (¹²⁹I) in the subsurface is mobile and limited information is available on treatment technologies. Scientific literature was reviewed to compile information on materials that could potentially be used to immobilize ¹²⁹I through sorption and redox-driven processes, with an emphasis on ex-situ processes. Candidate materials to immobilize ¹²⁹I include iron minerals, sulfur-based materials, silver-based materials, bismuth-based materials, ion exchange resins, activated carbon, modified clays, and tailored materials (metal organic frameworks (MOFS), layered double hydroxides (LDHs) and aerogels). Where available, compiled information includes material performance in terms of (i) capacity for ¹²⁹I uptake; (ii) long-term performance (i.e., solubility of a precipitated phase); (iii) technology maturity; (iv) cost; (v) available quantity; (vi) environmental impact; (vii) ability to emplace the technology for in situ use at the field-scale; and (viii) ex situ treatment (for media extracted from the subsurface or secondary waste streams). Because it can be difficult to compare materials due to differences in experimental conditions applied in the literature, materials will be selected for subsequent standardized batch loading tests.

In situ reductive dissolution to remove Iodine-129 from aquifer sediments

The use of an aqueous reductant (Na-dithionite) with pH buffer (K-carbonate, pH 12) was evaluated in this laboratory study as a potential remedial approach for removing Fe oxide associated iodine and enhancing pump-and-treat extraction from iodine-contaminated sediments in the unconfined aquifer in the 200 West Area of the Hanford Site. X-ray fluorescence data of untreated sediment indicated that iodine was largely associated with Fe (i.e., potentially incorporated into Fe oxides), but XANES data was inconclusive as to valence state. During groundwater leaching, aqueous and adsorbed iodine was quickly released, then additional iodine was slowly released potentially from slow dissolution of one or more surface phases. The Na-dithionite treatment removed greater iodine mass (2.9x) at a faster rate (1-4 orders of magnitude) compared to leaching with groundwater alone. Iron extractions for untreated and treated sediments showed a decrease in Fe(III)-oxides, which likely released iodine to aqueous solution. Solid phase inorganic carbon and aqueous Ca and Mg analysis further confirmed that significant calcite dissolution did not occur in these experiments meaning these phases did not release significant iodine. Although it was expected that, after treatment, ¹²⁷I concentrations would eventually be lower than untreated sediments, continued, elevated iodine concentrations for treated samples over 750 h were observed for leaching experiments. Stop flow events during 1-D column leaching suggested that some iodide precipitated within the first few pore volumes. Further, batch extraction experiments compared iodine-129/127 removal and showed that iodine-129 was more readily removed than iodine-127 suggesting that the two are present in different phases due to their different origins. Although significantly greater iodine is removed with treatment, the long-term leaching needs to be investigated further as it may limit dithionite treatment at the field scale.

Co-occurrence of geogenic and anthropogenic contaminants in groundwater from Rajasthan, India

Northwest India suffers from severe water scarcity issues due to a combination of over-exploitation and climate effects. Along with concerns over water availability, endemic water quality issues are critical and affect the usability of available water and potential human health risks. Here we present data from 243 groundwater wells, representing nine aquifer lithologies in 4 climate regions that were collected from the Northwestern Indian state of Rajasthan. Rajasthan is India's largest state by area, and has a significant groundwater reliant population due to a general lack of surface water accessibility. We show that the groundwater, including water that is used for drinking without any treatment, contains multiple inorganic contaminants in levels that exceed both Indian and World Health Organization (WHO) drinking water guidelines. The most egregious of these violations were for fluoride, nitrate, and uranium; 76% of all water samples in this study had contaminants levels that exceed the WHO guidelines for at least one of these species. In addition, we show that much of the groundwater contains high concentrations of dissolved organic carbon (DOC) and halides, both of which are risk factors for the formation of disinfectant byproducts in waters that are treated with chemical disinfectants such as chlorine. By using geochemical and isotopic (oxygen, hydrogen, carbon, strontium, and boron isotopes) data, we show that the water quality issues derive from both geogenic (evapotranspiration, water-rock interactions) and anthropogenic (agriculture, domestic sewage) sources, though in some cases anthropogenic activities, such as infiltration of organic- and nitrate-rich water, may contribute to the persistence and enhanced mobilization of geogenic contaminants. The processes affecting Rajasthan's groundwater quality are common in many other worldwide arid areas, and the lessons learned from evaluation of the mechanisms that affect the groundwater quality are universal and should be applied for other parts of the world.

In Situ Spectroscopic Analysis and Quantification of [Tc(CO)3]+ in Hanford Tank Waste

The quantitative conversion of nonpertechnetate [Tc(CO)₃]⁺ species in nuclear waste storage tank 241-AN-102 at the Hanford Site is demonstrated. A waste sample containing the [Tc(CO)₃]⁺ species is added to a developer solution that rapidly converts the nonemissive species into a luminescent complex, which is detected spectroscopically. This method was first demonstrated using a [Tc(CO)₃]⁺ sample of nonwaste containing matrix to determine a detection limit (LOD), resulting in a [Tc(CO)₃]⁺ LOD of 2.20 × 10^-7 M, very near the LOD of the independently synthesized standard (2.10 × 10^-7 M). The method was then used to detect [Tc(CO)₃]⁺ in a simulated waste using the standard addition method, resulting in a [Tc(CO)₃]⁺ concentration of 1.89 × 10^-5 M (within 27.7% of the concentration determined by β liquid scintillation counting). Three samples from 241-AN-102 were tested by the standard addition method: (1) a 5 M Na adjusted fraction, (2) a fraction depleted of ¹³⁷Cs, and (3) an acid-stripped eluate. The concentrations of [Tc(CO)₃]⁺ in these fractions were determined to be 9.90 × 10^-6 M (1), 0 M (2), and 2.46 × 10^-6 M (3), respectively. The concentration of [Tc(CO)₃]⁺ in the as-received AN-102 tank waste supernatant was determined to be 1.84 × 10^-5 M.

In Situ Quantification of [Re(CO)3]+ by Fluorescence Spectroscopy in Simulated Hanford Tank Waste

A pretreatment protocol is presented that allows for the quantitative conversion and subsequent in situ spectroscopic analysis of [Re(CO)₃]⁺ species in simulated Hanford tank waste. In this test case, the nonradioactive metal rhenium is substituted for technetium (Tc-99), a weak beta emitter, to demonstrate proof of concept for a method to measure a nonpertechnetate form of technetium in Hanford tank waste. The protocol encompasses adding a simulated waste sample containing the nonemissive [Re(CO)₃]⁺ species to a developer solution that enables the rapid, quantitative conversion of the nonemissive species to a luminescent species which can then be detected spectroscopically. The [Re(CO)₃]⁺ species concentration in an alkaline, simulated Hanford tank waste supernatant can be quantified by the standard addition method. In a test case, the [Re(CO)₃]⁺ species was measured to be at a concentration of 38.9 μM, which was a difference of 2.01% from the actual concentration of 39.7 μM.

Silver oxide nanocrystals anchored on titanate nanotubes and nanofibers: promising candidates for entrapment of radioactive iodine anions

Iodine radioisotopes are released into the environment by the nuclear industry and medical research institutions using radioactive materials. The (129)I(-) anion is one of the more mobile radioactive species due to a long half-life, and it is a great challenge to design long-term management solutions for such radioactive waste. In this study, a new adsorbent structure with the potential to efficiently remove radioactive iodine anions (I(-)) from water is devised: silver oxide (Ag2O) nanocrystals firmly anchored on the surface of titanate nanotubes and nanofibers via coherent interfaces between Ag2O and titanate phases. I(-) anions in fluids can easily access the Ag2O nanocrystals and be efficiently trapped by forming AgI precipitate that firmly attaches to the adsorbent. Due to their one-dimensional morphology, the new adsorbents can be readily dispersed in liquids and easily separated after purification; and the adsorption beds loaded with the adsorbents can permit high flux. This significantly enhances the adsorption efficiency and reduces the separation costs. The proposed structure reveals a new direction in developing efficient adsorbents for the removal of radioactive anions from wastewater.

Titanate-based adsorbents for radioactive ions entrapment from water

This feature article reviews some titanate-based adsorbents for the removal of radioactive wastes (cations and anions) from water. At the beginning, we discuss the development of the conventional ion-exchangeable titanate powders for the entrapment of radioactive cations, such as crystalline silicotitanate (CST), monosodium titanate (MST), peroxotitanate (PT). Then, we specially emphasize the recent progress in the uptake of radioactive ions by one-dimensional (1D) sodium titanate nanofibers and nanotubes, which includes the synthesis and phase transformation of the 1D nanomaterials, adsorption ability (capacity, selectivity, kinetics, etc.) of radioactive cations and anions, and the structural evolution during the adsorption process.

Removal of radioactive iodine from water using Ag2O grafted titanate nanolamina as efficient adsorbent

Emergency treatment of radioactive material leakage and safety disposal of nuclear waste is a constant concern all along with the development of radioactive materials applications. To provide a solution, titanate with large surface area (143 m(2)g(-1)) and a lamina morphology (the thickness of the lamina is in range of tens of nanometers) was prepared from inorganic titanium compounds by hydrothermal reactions at 433 K. Ag(2)O nanocrystals (5-30 nm) were deposited onto the titanate lamina. The surface of the titanate lamina has crystallographic similarity to that of Ag(2)O nanocrystals. Hence, the deposited Ag(2)O nanocrystals and titanate substrate join together at these surfaces, forming a well-matched phase coherent interface between them. Such coherence between the two phases reduces the overall energy by minimizing surface energy and anchors the Ag(2)O nanocrystals firmly on the external surface of the titanate structure. The composite thus obtained was applied as efficient adsorbent to remove radioactive iodine from water (one gram adsorbent can capture up to 3.4 mmol of I(-) anions). The composite adsorbent can be recovered easily for safe disposal. The structure changes of the titanate lamina and the composite adsorbent were monitored by various techniques. The isotherm and kinetics of iodine adsorption, competitive adsorption and column adsorption using the adsorbent were studied to assess its iodine removal abilities. The adsorbent exhibited a capacity as high as 3.4 mmol of iodine per gram of adsorbent in 1h. Therefore, Ag(2)O deposited titanate lamina is an effective adsorbent for removing radioactive iodine from water.

Migration of Radionuclides in Geologic Media: Fundamental Research Needs

An assessment of the fundamental research needs in understanding and predicting the migration of radionuclides in the subsurface is provided. Emphasis is on the following three technical areas: (1) aqueous speciation of radionuclides, (2) the interaction of radionuclides with substrates, and (3) intermediate-scale interaction studies. This research relates to important issues associated with environmental restoration and remediation of DOE sites contaminated with mixed radionuclide-organic wastes.

XPS and XAS studies of copper(II) sorbed onto a synthetic pyrite surface

Compounds containing copper are likely candidates to delay iodide migration in environmental media through the formation of sparingly soluble phases. Preliminary experiments showed that iodide was neither sorbed onto chalcopyrite nor by a binary system pyrite/copper(II), although significant amounts of copper were present at the pyrite surface. In the present study, spectroscopic studies (XPS, XANES and EXAFS) were thus performed to determine the nature of sorbed copper species. Although introduced as Cu(II), copper was mainly present at the oxidation state (I) on the pyrite surface suggesting a heterogeneous reduction process. Moreover, copper appeared tetrahedrally coordinated to two sulfur and two oxygen atoms onto the pyrite surface, a chemical environment, which seemingly stabilized the metal and made it unreactive towards iodide.

Immobilization of iodide on copper(I) sulfide minerals

In the goal of finding efficient scavengers for radioiodide in conditions (pH, pE) close to those encountered in deep geological sites, sorption of iodide ions on cuprous sulfide minerals (especially roxbyite, Cu(1.75)S) has been studied. Surface analysis by X-ray photoelectron spectroscopy has shown that commercial cuprous sulfides are covered by an oxidized overlayer (mainly in the form of CuSO(4)). Therefore, a synthetic procedure to get roxbyite (typically by mixing Na(2)S with an aqueous suspension of commercial Cu(2)O) was applied to produce pure samples with clean surfaces. Batch equilibration of cuprous sulfide particles suspended in aqueous solutions containing iodide species has revealed significant consumption of iodide. The sorption mechanism involves the formation of a surface complex via the exchange of surface hydroxyl groups by iodide anions, as highlighted by a transient pH increase during the immobilization process. Other copper and mixed copper-iron sulfides (e.g. CuS, CuFeS(2)), which are stable over wide pH and potential ranges are also likely to accumulate iodide species. Because of the specific interaction between iodide and copper(I) centers on the minerals, high distribution coefficients (>1000 ml/g) were observed.