| Home | << 1 2 >> |
|
Stone, A. E. C., & Edmunds, W. M. (2014). Naturally-high nitrate in unsaturated zone sand dunes above the Stampriet Basin, Namibia. Journal of Arid Environments, 105, 41–51.
Abstract: Elevated groundwater nitrate levels are common in drylands, often in excess of WHO guidelines, with concern for human and animal health. In light of recent attempts to identify nitrate sources in the Kalahari this paper presents the first unsaturated zone (USZ) nitrate profiles and recharge rate estimates for the important transboundary Stampriet Basin, alongside the first rainfall chemistry records. Elevated subsurface nitrate reaches 100–250 and 250–525 mg/L NO3–N, with NO3–N/Cl of 4–12, indicating input above evapotranspiration. Chloride mass balance recharge rates range from 4 to 27 mm/y, indicating a vertical movement of these nitrate pulses toward the water table over multi-decadal timescales. These profiles are sampled from dune crests, away from high concentrations of animals and without termite mounds. Given low-density animal grazing is unlikely to contribute consistent spot-scale nitrate over decades, these profiles give an initial estimate of naturally-produced concentrations. This insight is important for the management of the Stampriet Basin and wider Kalahari groundwater. This study expands our knowledge about elevated nitrate in dryland USZs, demonstrating that it can occur as pulses, probably in response to transient vegetation cover and that it is not limited to long-residence time USZs with very limited downward moisture flux (recharge).
|
|
Alvarado, J. A. C., Balsiger, B., Röllin, S., Jakob, A., & Burger, M. (2014). Radioactive and chemical contamination of the water resources in the former uranium mining and milling sites of Mailuu Suu (Kyrgyzstan). Journal of Environmental Radioactivity, 138, 1–10.
Abstract: An assessment of the radioactive and chemical contamination of the water resources at the former uranium mines and processing sites of Mailuu-Suu, in Kyrgyzstan, was carried out. A large number of water samples were collected from the drinking water distribution system (DWDS), rivers, shallow aquifers and drainage water from the mine tailings. Radionuclides and trace metal contents in water from the DWDS were low in general, but were extremely high for Fe, Al and Mn. These elements were associated with the particle fractions in the water and strongly correlated with high turbidity levels. Overall, these results suggest that water from the DWDS does not represent a serious radiological hazard to the Mailuu Suu population. However, due to the high turbidities and contents of some elements, this water is not good quality drinking water. Water from artesian and dug wells were characterized by elevated levels of U (up to 10 μg/L) and some trace elements (e.g. As, Se, Cr, V and F) and anions (e.g. Cl−, NO3−, SO42−). In two artesian wells, the WHO guideline value of 10 μg/L for As in water was exceeded. As the artesian wells are used as a source of drinking water by a large number of households, special care should be taken in order to stay within the WHO recommended guidelines. Drainage water from the mine tailings was as expected highly contaminated with many chemicals (e.g. As) and radioactive contaminants (e.g. U). The concentrations of U were more than 200 times the WHO guideline value of 30 μg/L for U in drinking water. A large variation in 234U/238U isotopic ratios in water was observed, with values near equilibrium at the mine tailings and far from equilibrium outside this area (reaching ratios of 2.3 in the artesian well). This result highlights the potential use of this ratio as an indicator of the origin of U contamination in Mailuu Suu.
|
|
Tan, K., Li, C., Liu, J., Qu, H., Xia, L., Hu, Y., et al. (2014). A novel method using a complex surfactant for in-situ leaching of low permeable sandstone uranium deposits. Hydrometallurgy, 150, 99–106.
Abstract: Applications of a complex surfactant developed in-house to in-situ leaching of low permeable sandstone uranium deposits are described based on results from agitation leaching, column leaching, resin adsorption, and elution experiments using uranium containing solution from the in-situ leaching site. The results of agitation leaching experiments show that adding surfactant with different concentrations into leaching solution improves the leaching rate of uranium. The maximum leaching rate of uranium from agitation leaching reached 92.6% at an added surfactant concentration of 10mg/l. Result of column leaching experiment shows that adding surfactant with varying concentrations into leaching solutions increased the permeability coefficient of ore-bearing layer by 42.7–86.8%. The leaching rate of uranium from column leaching increased by 58.0% and reached 85.8%. The result of kinetic analysis shows that for the extraction of uranium controlled by diffusion without surfactant the apparent rate constant 0.0023/d changed to 0.0077/d for the extraction with surfactant controlled by both diffusion and surface chemical reactions. Results from resin adsorption and elution experiments show that there was no influence on resin adsorption and elution of uranium with an addition of 50mg/l surfactant to production solution from in-situ leaching. The adsorption curve, sorption capacity of resin, recycling of resin remained the same as without adding any surfactant. Introducing complex surfactant to leaching solution increased the peak concentration of uranium in eluents, reduced the residual uranium content in resin, and promoted the elution efficiency. The method of using a complex surfactant for in-situ leaching is useful for low permeable sandstone uranium deposits.
|
|
Khoury, H. N., salameh, E. M., & Clark, I. D. (2014). Mineralogy and origin of surficial uranium deposits hosted in travertine and calcrete from central Jordan. Applied Geochemistry, 43, 49–65.
Abstract: Secondary uranium encrustations are hosted in thick travertine and calcrete deposits of Pleistocene–Recent age in central Jordan. The central Jordan varicolored marble and travertine are equivalent to the active metamorphic area in Maqarin, north Jordan. More than 100 samples were collected from the outcrops of the varicolored marble, travertine, calcrete, and the yellow uranium encrustations. The secondary yellow encrustations are mainly composed of uranyl vanadate complexes. Tyuyamunite Ca(UO2)2V25+O8·3(H2O)–strelkinite Na2(UO2)2V2O8·6(H2O) solid solution series are the major components and their composition reflects changes in the Ca/Na ratio in solution. Potentially, new vanadium free calcium uranate phases (restricted to the varicolored marble) were identified with CaO:UO3 ratios different from the known mineral vorlanite (CaU6+)O4. Carbon and oxygen isotope data from calcite in the varicolored marble are characterized by Rayleigh-type enrichment in light isotopes associated with release of 13C and 18O enriched CO2 by high temperature decarbonation during combustion of the bituminous marl. Stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values, between decarbonated and normal sedimentary carbonate rocks. The depleted δ13C and δ18O values in the travertine are related to the kinetic reaction of atmospheric CO2 with hyperalkaline Ca(OH)2 water. The gradual enrichment of δ13C and δ18O values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods. Uranium mineralization in central Jordan resulted from the interplay of tectonic, climatic, hydrologic, and depositional events. The large distribution of surficial uranium occurrences hosted in travertine and calcrete deposits is related to the artesian ascending groundwater that formed extensive lakes along NNW–SSE trending depressions. Fresh groundwater moved upward through the highly fractured phosphate, bituminous marl and varicolored marble to form unusual highly alkaline water (hydroxide–sulfate type) enriched with sensitive redox elements among which were U and V.
|
|
Pastukhov, A. M., Rychkov, V. N., Smirnov, A. L., Skripchenko, S. Y., & Poponin, N. A. (2014). Purification of in situ leaching solution for uranium mining by removing solids from suspension. Minerals Engineering, 55, 1–4.
Abstract: This study investigated the process of in situ leaching (ISL) method of uranium mining, and the removal of solid particles from the leaching solution. Investigations were carried out for 4months. The content of firm suspensions in the productive solutions arriving from the well field was up to standard of 3–5mg/l. After keeping in a settler of productive solutions within one hour concentration of suspensions decreases to 2–2.5mg/l. To increase the life of the wells requires more fine purification of the ISL solutions. The best results can be obtained but using filtration. Bag filters were used in experiments carried out at the extraction site. All samples of polypropylene bag filter was produced by the Tamfelt Corporation. The best results were obtained for fabrics S-51M03-L2K4 (pore size 3μm). After three month of trials following indicators of wells work were fixed: on the trial cell decrease in intake capacity did not occur; on the other cells of well field injectability of holes for the same period of time decreased for 15–40%. The results illustrated the high efficiency of this method, which allows injection wells to reach a constant intake capacity, making it possible for technological cells to achieve a constant productivity and balance. Purification of solutions allows to reduce acidulation term of new technological cells from 3–4 to 1.5–2months.
|
|
Haque, N., & Norgate, T. (2014). The greenhouse gas footprint of in-situ leaching of uranium, gold and copper in Australia. Journal of Cleaner Production, 84, 382–390.
Abstract: In-situ leaching (ISL) is a chemical method for recovering useful minerals and metals directly from underground ore bodies which is also referred to as ‘solution mining’. ISL is commonly used for uranium mining, accounting for about 45% of global production. The main benefits are claimed to be a lower environmental impact in terms of visual disturbances, emissions, lower energy use, cost compared with conventional open-cut or underground mining methods, and potential utilisation of lower grade resources. However, there is a lack of reported studies on the assessment of the environmental impacts of ISL, particularly greenhouse gas (GHG) emissions using life cycle assessment (LCA) methodology. The SimaPro LCA software was used to estimate the GHG footprint of the ISL of uranium, gold and copper. The total GHG emissions were estimated to be 38.0 kg CO2-e/kg U3O8 concentrate (yellowcake), 29 t CO2-e/kg gold, and 4.78 kg CO2-e/kg Cu. The GHG footprint of ISL uranium was significantly lower than that of conventional mining, however, the footprints of copper and gold were not much less compared with conventional mining methods. This is due to the lower ore grade of ISL deposits and recovery compared with high ore grades and recovery of conventional technology. Additionally, the use of large amount of electricity for pumping in case of ISL contributes to this result. The electricity consumed in pumping leaching solutions was by far the greatest contributor to the well-field related activities associated with ISL of uranium, gold and copper. The main strategy to reduce the GHG footprint of ISL mining should be to use electricity derived from low emission sources. In particular, renewable sources such as solar would be suitable for ISL as these operations are typically in remote locations with smaller deposits compared with conventional mining sites.
|
|
Martínez-Santos, P., & Martínez-Alfaro, P. E. (2014). A priori mapping of historical water-supply galleries based on archive records and sparse material remains. An application to the Amaniel qanat (Madrid, Spain). Journal of Cultural Heritage, 15(6), 656–664.
Abstract: Engineering heritage refers to a broad variety of items of social, economic, aesthetic or historic relevance, including roads, dams, buildings and supply networks. Due to their utilitarian nature, their heritage value is often overlooked. This occurs even with those infrastructures that have played an essential role in underpinning the daily existence of entire civilizations. Underground water-supply networks provide an excellent example. Although there are exceptions, water networks tend to be functional in design, rather than monumental. Moreover, they present intricate linear layouts that often span several kilometres. This means they are costly to maintain once their operational life is over, and that they are prone to abandonment and destruction. Devising a priori protection strategies is important to preserve these valuable cultural assets. The following pages present a method to map linear structures based on archive records and sparse material remains. The method is illustrated through its application to the Amaniel qanat, a water-supply gallery built in Madrid, Spain, in the early 17th Century. An appraisal of the known remains was carried out first, leading to an inventory of galleries, shafts, shaft caps and deposits. This was followed by a thorough survey of over one thousand handwritten manuscripts, including physical descriptions of the aqueduct, budget accounts or water metering campaigns, among other documents. Known remains and written evidence were matched against original and auxiliary maps to reconstruct the itinerary of the aqueduct. This led to the identification of sectors where it is still possible to find remains in good condition. Thus, a priori mapping is advocated a valuable technique to locate and preserve these remains, as well as to devise non-invasive surveys and establish heritage protection zones.
|