THE SCENARIOS APPROACH TO ATTENUATION-BASED REMEDIES FOR INORGANIC AND RADIONUCLIDE CONTAMINANTS

Guidance materials based on use of conceptual model scenarios were developed to assist evaluation and implementation of attenuation-based remedies for groundwater and vadose zones contaminated with inorganic and radionuclide contaminants. The Scenarios approach is intended to complement the comprehensive information provided in the US EPA's Technical Protocol for Monitored Natural Attenuation (MNA) of Inorganic Contaminants by providing additional information on site conceptual models and extending the evaluation to consideration of Enhanced Attenuation approaches. The conceptual models incorporate the notion of reactive facies, defined as units with hydrogeochemical properties that are different from surrounding units and that react with contaminants in distinct ways. The conceptual models also incorporate consideration of biogeochemical gradients, defined as boundaries between different geochemical conditions that have been induced by waste disposal or other natural phenomena. Gradients can change over time when geochemical conditions from one area migrate into another, potentially affecting contaminant mobility. A recognition of gradients allows the attenuation-affecting conditions of a site to be projected into the future. The Scenarios approach provides a stepwise process to identify an appropriate category of conceptual model and refine it for a specific site. Scenario materials provide links to pertinent sections in the EPA technical protocol and present information about contaminant mobility and important controlling mechanism for attenuation-based remedies based on the categories of conceptual models

Advances in Chalcogenide Crystal Growth

Chalcogenides are the cornerstone of the semiconductor and thermoelectric industries and are up-and-coming materials for superconductors, catalysis, and battery applications. Challenges in the synthesis of those materials emerge from the chalcogen’s volatility and the tendencies of chalcogenide to react with even trace quantities of oxygen. Nonetheless, many techniques have been applied to the growth of chalcogenide single crystals, which are convenient for structure determinations and intrinsic property measurements. This dissertation will detail synthetic strategies applied to the crystal growth of novel chalcogenide materials via molten flux preparation (Chapters 2, 4, and 5), hydrothermal synthesis (Chapter 1 and 3), and single-crystal-to-single crystal (SCSC) modifications (Chapters 1, 2, 3, and 4). The first chapter discusses flux crystal growth coupled with the boron-chalcogen mixture method for synthesizing NaCuNpS3. Moreover, ACuUQ3 (A = Na, K; Q = S, Se) undergoes an SCSC water intercalation process within the layers. In the second chapter, we demonstrated the hydrothermal crystal growth of all-inorganic open-framework chalcogenides A3Ga5S9·xH2O (A = Rb, Cs) and novel post-synthetic oxychalcogenide formation. Flux crystal growth of salt-inclusion chalcogenide family [Cs6X]AGa6Q12 (A = Na, K, Rb; X = Cl, Br; Q = S, Se) is the focus of the third chapter. Additional SCSC ion-exchange reactions were found to yield two compositions: [Cs6F]NaGa6S12 and [Cs6Br]RbGa6S12, inaccessible through the traditional synthetic route. Finally, in the fourth chapter, we considered how flux composition affects the formation of different compositions and polymorphs in the Na–Ga–Q (Q = S, Se) system

The Evolution, Current Status, and Future Prospects of Using Biotechnologies in the Mineral Extraction and Metal Recovery Sectors

The current global demand in terms of both the amounts and range of metals for industrial and domestic use greatly exceeds that at any previous time in human history. Recycling is inadequate to meet these needs and therefore mining primary metal ores will continue to be a major industry in the foreseeable future. The question of how metal mining can develop in a manner which is less demanding of energy and less damaging of the environment in a world whose population is increasingly aware of, and concerned about, the environment, requires urgent redress. Increased application of biotechnologies in the mining sector could go some way in solving this conundrum, yet, biomining (harnessing microorganisms to enhance the recovery of base and precious metals) has remained a niche application since it was first knowingly used in the 1960s. This manuscript reviews the development and current status of biomining applications and highlights their limitations as well as their strengths. New areas of biotechnology that could be applied in the mining sector, and their potential impact in terms of both their potential environmental and economic benefits, are also discussed

Removal of TcO4- from Representative Nuclear Waste Streams with Layered Potassium Metal Sulfide Materials

Many efforts have focused on the sequestration and immobilization of 99Tc because the radionuclide is highly mobile in oxidizing environments and presents serious health risks due to its radiotoxicity and long half-life (t1/2 = 213 000 a). One of the more common methods for Tc removal from solution and immobilization in solids is based on reducing Tc from highly soluble Tc(VII) to sparingly soluble Tc(IV). Here, we report results obtained with two potassium metal sulfides (KMS-2 and KMS-2-SS) that are capable of reducing Tc(VII) to Tc(IV). Batch sorption experiments were performed in both oxic and anoxic conditions for 15 d in both deionized water (DIW) and a highly caustic (pH ∼ 13.6), high ionic strength (8.0 mol L-1), low-activity waste (LAW) stream simulant solution. Tc removal for both materials in DIW is improved in anoxic conditions compared to oxic conditions as a result of a higher solution pH. In DIW and anoxic conditions, KMS-2 is capable of removing ∼45% of Tc, and KMS-2-SS is capable of removing ∼90% of Tc. Both materials perform even better in the LAW simulant and remove more than 90% of available Tc after 15 d of contact in anoxic conditions. Postreaction solids analyses indicate that Tc(VII) is reduced to Tc(IV) and that Tc(IV) is bonded to S atoms in a Tc2S7 complex. Examination of the materials after Tc removal by X-ray diffraction shows that the initially crystalline KMS-2 materials lose much of their initial long-range order. We suggest a Tc removal mechanism wherein the TcO4- enters the interlayer of the KMS-2 materials where it is reduced by sulfide, which results in a distorted crystalline structure and a solid-state Tc2S7 complex

Geo-neutrinos

We review a new interdisciplinary field between Geology and Physics: the study of the Earth's geo-neutrino flux. We describe competing models for the composition of the Earth, present geological insights into the make up of the continental and oceanic crust, those parts of the Earth that concentrate Th and U, the heat producing elements, and provide details of the regional settings in the continents and oceans where operating and planned detectors are sited. Details are presented for the only two operating detectors that are capable of measuring the Earth's geo-neutrinos flux: Borexino and KamLAND; results achieved to date are presented, along with their impacts on geophysical and geochemical models of the Earth. Finally, future planned experiments are highlighted

Guidance for the integrated use of hydrological, geochemical, and isotopic tools in mining operations

This paper summarizes international state-of-the-art applications and opportunities for employing and deploying hydrological, geochemical, and isotopic tools in an integrated manner for investigations of mining operations. It is intended to aid formulation of more integrated approaches for evaluating the overall sustainability of mining projects. The focus is particularly on mine waters, including: environmental water sources, mine water dynamics, and as a source and vector for pollution in the wider environment. The guidance is generic to mining projects and not just reflective of a particular extraction (e.g. coal, metalliferous, uranium) industry. A mine life cycle perspective has been adopted to highlight the potential for more integrated investigations at each stage of a mining operation. Three types of mines have been considered: new (i.e. those in the planning stage), active (i.e. working mines), and historical mines (i.e. inactive and abandoned mines). The practical usage of geochemical analyses and isotopic studies described here emphasise characterisation, dynamics, and process understanding for water quality considerations in tandem with water resource and environmental impact implications. Both environmental (i.e. ambient) and applied (i.e. injected) tracers are considered. This guide is written for scientists (including isotope specialists) who have limited or no mine water experience, environmental managers, planners, consultants, and regulators with key interests in planned, active, and legacy mining projects.The authors thank the IAEA for inviting us to collate an initial report on guidelines from 2018-06-25–28 in Vienna. We thank Chris Gammons for allowing us to use one of his fgures. We especially thank Umaya Doss Saravana Kumar, Lucia Ortega, and Araguás-Araguás from IAEA for assistance, and Andrea Nick for input during the meeting. Special thanks to our reviewers who substantially helped improve the structure and content of this guidance document

EXPERIMENTAL INVESTIGATION OF THE THERMOCHEMICAL REDUCTION OF ARSENITE AND SULFATE: LOW TEMPERATURE HYDROTHERMAL COPPER, NICKEL, AND COBALT ARSENIDE AND SULFIDE ORE FORMATION

Experiments were conducted to determine the relative rates of reduction of aqueous sulfate and aqueous arsenite (As(OH)3,aq) using foils of copper, nickel, or cobalt as the reductant, at temperatures of 150ºC to 300ºC. At the highest temperature of 300°C, very limited sulfate reduction was observed with cobalt foil, but sulfate was reduced to sulfide by copper foil (precipitation of Cu2S (chalcocite)) and partly reduced by nickel foil (precipitation of NiS2 (vaesite) + NiSO4·xH2O). In the 300ºC arsenite reduction experiments, Cu3As (domeykite), Ni5As2, or CoAs (langisite) formed. In experiments where both sulfate and arsenite were present, some produced minerals were sulfarsenides, which contained both sulfide and arsenide, i.e. cobaltite (CoAsS). These experiments also produced large (~10 µm along longest axis) euhedral crystals of metal-sulfide that were either imbedded or grown upon a matrix of fine-grained metal-arsenides, or, in the case of cobalt, metal-sulfarsenide. Some experimental results did not show clear mineral formation, but instead demonstrated metal-arsenic alloying at the foil edges. Below 250ºC in the mixed experiments, reduction of sulfate was not observed, but reduction of arsenite by copper to form domeykite was prominent at temperatures down to at least 150ºC, and reduction of arsenite by nickel to form an un-named mineral, Ni3As, as a crystalline crust occurred as low as 150°C. The implication is that a low temperature fluid carrying both aqueous sulfate and arsenite will quickly precipitate metal-arsenide minerals at a reducing interface, whereas sulfate reduction is much slower, especially at temperatures below 250ºC. This helps to explain the abundance of metal-arsenide minerals and relative lack of metal-sulfide minerals in certain ore deposit types, including unconformity-type U-Ni and “5-element suite” vein deposits

Selective solid phase extraction of uranium using an aminophosphonic acid functionalized composite material

Uranium is an element of interest because it is an abundant source of concentrated energy. In 1948 the US offered money for uranium ore mined in the US, which created a mining boom in the southwest that included the Navajo Reservation. During the late 1960s the demand for uranium decreased and many mining operations shutdown and left behind a legacy of contamination. As a result many Navajo communities have numerous water sources that exceed established maximum contamination levels for uranium and other toxic metals. These contaminations are a direct result of abandoned Cold War uranium mines and mill waste sites as well as the geology of the area. The improper disposal of these wastes has resulted in adverse health and ecological impacts. Groundwater contaminations caused by heavy metal ions remain an environmental concern, despite many years of research on remediation. Traditional solvent extraction methods are expensive, time consuming and pose additional problems with the generation of waste products. The aim of this study is to use solid phase extraction methods to remediate contaminated water sources. An example is Silica Polyamine Composites (SPC), which have been used to filter, isolate and remove unwanted metals by acting as a chelating agent. Given the high valent nature of uranium and the effectiveness of adsorption of metals from wastewaters and mine leachates by SPCs, we hypothesized that a phosphonated SPC will be effective at removing uranyl ions from contaminated water. An aminophosphonic acid functionalized SPC, BPAP, has been applied to uranium adsorption studies. This study has determined BPAP’s ability to be selective for uranium adsorption even in the presence of high concentrations of ions that form complexes with the uranyl cation, such as nitrate and sulfate, using batch capacity studies. Using ICP-OES analysis, we determined BPAPs capacity for uranium in aqueous solutions as 0.42 mmol/g. In addition, we have determined the working capacity of BPAP to be 146 mg/g under flow conditions. Although this result is far from ideal studies are currently underway to minimize the differences and acquire more accurate data. It is ideal to have both the batch capacity and working capacity to be close in value because it demonstrates the potential for a remedial application. One positive aspect of these studies are the recovery of the uranium from the BPAP column with a sodium carbonate gave a solution that was 50 times more concentrated than the feed. Again this shows the ability of SPCs, in general, to not only remediate but to also recover the metal(s) for the intent of reusability. Previous reports have shown that these materials can survive more than 3000 cycles of metal ion extraction, elution and regeneration with less than 10% loss of capacity

Treatment of Arsenic-Bearing Minerals and Fixation of Recovered Arsenic Products: An Updated Review

Mineral processing and extractive metallurgical operations have created and are creating appreciable arsenic bearing wastewater and waste solid products that have to be handled, treated for recycle, or treated for environmentally safe disposal. At present there are intense research and operational activities being conducted to provide the best viable processing procedures to ensure that the mineral processing and extractive metallurgical industries are profitable and environmentally secure. The focus of this presentation is on the element arsenic, even though many other deleterious elements may also be present in ores and concentrates. Numerous base metal resources contain arsenic bearing minerals, especially resources containing mineral sulfides. Information on presently treated metal-bearing resources and potential new resources is voluminous, especially for those containing arsenic mineralization. The influence of elevated arsenic concentrations in the treatment of copper-arsenic sulfides and to a lesser extent the treatment of copper-gold-arsenic sulfides are considered in this presentation. Because of chapter page limitations not all treatment processes are discussed, however, examples are provided to illustrate arsenic problems and industrial solutions. The major emphasis of this presentation has been placed on the present state-of-the-art for arsenic immobilization/fixation and long-term storage considerations

Litsa uranium ore occurrence (Arctic zone of the Fennoscandian Shield): new results of petrophysical and geochemical studies

Mineralogical, petrophysical and geochemical studies have been carried out to determine the sequence and formation conditions of uranium mineralization within the Litsa ore occurrence (Kola Region). Mineralogical studies show the following formation sequence of ore minerals: uraninite – sulfides – uranophane, coffinite, pitchblende. Two stages of uranium mineralization are distinguished: Th-U (1.85-1.75 Ga) and U (400-300 Ma). The distribution of physical properties of rocks in the area is consistent with the presence of two temporal stages in the formation of mineralization with different distribution and form of uranium occurrence in rocks. The factors that reduce rock anisotropy are the processes of migmatization and hydrothermal ore mineralization, which heal pores and cracks. Fluid inclusions in quartz studied by microthermometry and Raman spectroscopy contain gas, gas-liquid and aqueous inclusions of different salinity (1.7-18.4 wt.% NaCl-eq.). According to homogenization temperatures of inclusions in liquid phase, the temperature of the Paleoproterozoic and Paleozoic stages of uranium mineralization at the Litsa ore occurrence is ~ 300 and 200 °С, respectively. Correlations of the spatial distribution of elastic anisotropy index with an elevated radioactive background allow using this petrophysical feature as one of the prognostic criteria for uranium and complex uranium mineralization when carrying out uranium predictive work