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Schwiede, M.; Duijnisveld, W.H.M.; Böttcher, J. |
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Title |
Investigation of processes leading to nitrate enrichment in soils in the Kalahari Region, Botswana |
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Journal Article |
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2005 |
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Physics and Chemistry of the Earth, Parts A/B/C |
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30 |
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11 |
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712-716 |
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Nitrate, Arenosol soils, Semi-arid, Kalahari, Cattle, Chloride, Travel time |
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Abstract |
In Southern Africa elevated nitrate concentrations are observed in mostly uninhabited semi-arid areas. In the Kalahari of Botswana groundwater locally exhibits concentrations up to 600mg/l. It is assumed, that nitrate found in the groundwater originates mainly from nitrogen input and transformations in the soils. Our investigations in the Kalahari between Serowe and Orapa show that cattle raising is an important source for enhanced nitrate concentrations in the soils (Arenosols). But also in termite mounds very high nitrate stocks were found, and under natural vegetation (acacia trees and shrubs) nitrate concentrations were mostly unexpectedly high. This nitrate enrichment in the soils poses a serious threat to the groundwater quality. However, calculated soil water age distributions in the unsaturated zone clearly show that today’s nitrate pollution of the groundwater below the investigation area could originate from natural sources, but cannot be caused by the current land use for cattle raising. |
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1474-7065 |
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Integrated Water Resources Management (IWRM) and the Millennium Development Goals: Managing Water for Peace and Prosperity |
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THL @ christoph.kuells @ Schwiede2005712 |
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276 |
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Wilson, G.B.; McNeill, G.W. |
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Title |
Noble gas recharge temperatures and the excess air component |
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Year |
1997 |
Publication |
Applied Geochemistry |
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12 |
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6 |
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747-762 |
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The calculation of a groundwater recharge temperature based on the dissolved concentrations of Ne, Ar, Kr and Xe requires a correction for noble gas supersaturation due to excess air entrainment. This entrainment is commonly attributed to the recharge process or to air contamination at the wellhead during sample collection. With the exception of some local studies, most work has concentrated on interpretation of the recharge temperature or quantification of the radiogenic content for palaeoclimatic and dating purposes. The magnitude and source of the excess air is not directly relevant to these studies and so is often ignored. In this work, excess air Ne and other data have been calculated from new and published noble gas data sets for several groundwater systems. For younger groundwaters which have been recharged under one broad climatic regime, the amount of air entrainment increases according to lithology in the order granites, sandstones and limestones respectively. A negative correlation between precipitation and excess air entrainment is identified in at least one aquifer, and some of the mechanisms which may influence the entrainment process are discussed. |
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0883-2927 |
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THL @ christoph.kuells @ Wilson1997747 |
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281 |
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Author |
YI, Z.-ji; LIAN, B.; YANG, Y.-qun; ZOU, J.-ling |
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Title |
Treatment of simulated wastewater from in situ leaching uranium mining by zerovalent iron and sulfate reducing bacteria |
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Journal Article |
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Year |
2009 |
Publication |
Transactions of Nonferrous Metals Society of China |
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19 |
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840 |
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Keywords |
basification, sulfate, sulfate reducing bacteria (SRB), uranium, wastewater, zerovalent iron (ZVI) |
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Abstract |
Batch and column experiments were conducted to determine whether zerovalent iron (ZVI) and sulfate reducing bacteria (SRB) can function synergistically and accelerate pollutant removal. Batch experiments suggest that combining ZVI with SRB can enhance the removal of U(?) synergistically. The removal rate of U(?) in the ZVI+SRB combining system is obviously higher than the total rate of ZVI system and SRB system with a difference of 13.4% at t=2 h and 29.9% at t=4 h. Column experiments indicate that the reactor filled with both ZVI and SRB biofilms is of better performance than the SRB bioreactor in wastewater basification, desulfurization and U(?) fixation. The results imply that the ZVI+SRB permeable reactive barrier may be a promising method for treating subsurface uranium contamination. |
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1003-6326 |
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THL @ christoph.kuells @ yi_treatment_2009 |
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206 |
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Author |
Liesch, T.; Hinrichsen, S.; Goldscheider, N. |
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Title |
Uranium in groundwater — Fertilizers versus geogenic sources |
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Journal Article |
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Year |
2015 |
Publication |
Science of The Total Environment |
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536 |
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981-995 |
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Keywords |
Drinking water, Fertilizer, Geogenic background, Groundwater, Uranium |
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Abstract |
Due to its radiological and toxicological properties even at low concentration levels, uranium is increasingly recognized as relevant contaminant in drinking water from aquifers. Uranium originates from different sources, including natural or geogenic, mining and industrial activities, and fertilizers in agriculture. The goal of this study was to obtain insights into the origin of uranium in groundwater while differentiating between geogenic sources and fertilizers. A literature review concerning the sources and geochemical processes affecting the occurrence and distribution of uranium in the lithosphere, pedosphere and hydrosphere provided the background for the evaluation of data on uranium in groundwater at regional scale. The state of Baden-Württemberg, Germany, was selected for this study, because of its hydrogeological and land-use diversity, and for reasons of data availability. Uranium and other parameters from N=1935 groundwater monitoring sites were analyzed statistically and geospatially. Results show that (i) 1.6% of all water samples exceed the German legal limit for drinking water (10μg/L); (ii) The range and spatial distribution of uranium and occasional peak values seem to be related to geogenic sources; (iii) There is a clear relation between agricultural land-use and low-level uranium concentrations, indicating that fertilizers generate a measurable but low background of uranium in groundwater. |
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0048-9697 |
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Call Number |
THL @ christoph.kuells @ liesch_uranium_2015 |
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145 |
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Author |
Castro, M.C.; Stute, M.; Schlosser, P. |
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Title |
Comparison of 4He ages and 14C ages in simple aquifer systems: implications for groundwater flow and chronologies |
Type |
Journal Article |
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Year |
2000 |
Publication |
Applied Geochemistry |
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Volume |
15 |
Issue |
8 |
Pages |
1137-1167 |
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4He concentrations in excess of the solubility equilibrium with the atmosphere by up to two to three orders of magnitude are observed in the Carrizo Aquifer in Texas, the Ojo Alamo and Nacimiento aquifers in the San Juan Basin, New Mexico, and the Auob Sandstone Aquifer in Namibia. A simple 4He accumulation model is applied to explain these excess 4He concentrations in terms of both in situ production and a crustal flux across the bottom layer of the aquifer. Results from the model simulations suggest variability in the 4He fluxes, ranging from 6×10−6 cm3 STP cm−2 yr−1 for the Auob Sandstone Aquifer to 3.6×10−7 cm3 STP cm−2 yr−1 for the Carrizo aquifer. For the Ojo Alamo and Nacimiento aquifers an intermediate value of 3×10−6 cm3 STP cm−2 yr−1 was estimated. The contribution of in-situ produced 4He to the measured concentrations was also estimated. This contribution is negligible for the Auob Sandstone Aquifer as compared with both the concentrations measured at the top and bottom of the aquifer for most of the pathway. In the Carrizo aquifer, in-situ produced 4He contributes 27.5% and 15.4%, to the total 4He observed at the top and bottom of the aquifer, respectively. For both aquifers of the San Juan Basin in-situ production almost entirely dominates the 4He concentrations at the top of the aquifer for most of the pathway. In contrast, the internal production is negligible as compared with the measured concentrations at the bottom of these aquifers, reaching, at most, 1.1%. The model simulations require an exponential decrease in the horizontal velocity of the water with increasing recharge distance to reproduce the distribution of 4He in these aquifers. For the Auob Sandstone Aquifer the highest range in the velocity values is obtained (25 to 0.4 m yr−1). The simulations for the Carrizo aquifer and both aquifers located in the San Juan Basin require velocities varying from 4 to 0.1 m yr−1, and from 2 to 0.3 m yr−1, respectively. For each aquifer, average permeability values were also estimated. They are generally in agreement with results obtained from pumping tests, hydrodynamic modeling and previous 14C measurements. On the basis of the results obtained by calibrating the model with the measured 4He concentrations, the mean water residence times were estimated. They agree reasonably well with 14C ages. When applied as chronologies for noble gas temperatures in the same aquifers, the calculated 4He ages allow the identification of three different climate periods similar to those previously identified using 14C ages: (1) the Holocene period (0–10 Ka BP), (2) the Last Glacial Maximum (≈18 Ka BP), and (3) the preceeding period (30–150 Ka BP). |
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0883-2927 |
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THL @ christoph.kuells @ castro_comparison_2000 |
Serial |
109 |
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Author |
Zeng, S.; Shen, Y.; Sun, B.; Tan, K.; Zhang, S.; Ye, W. |
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Title |
Fractal kinetic characteristics of uranium leaching from low permeability uranium-bearing sandstone |
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Journal Article |
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Year |
2022 |
Publication |
Nuclear Engineering and Technology |
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54 |
Issue |
4 |
Pages |
1175-1184 |
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Keywords |
Fractal characteristics, In-situ leaching, Leaching kinetics, Pore structure, Uranium mine |
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Abstract |
The pore structure of uranium-bearing sandstone is one of the critical factors that affect the uranium leaching performance. In this article, uranium-bearing sandstone from the Yili Basin, Xinjiang, China, was taken as the research object. The fractal characteristics of the pore structure of the uranium-bearing sandstone were studied using mercury intrusion experiments and fractal theory, and the fractal dimension of the uranium-bearing sandstone was calculated. In addition, the effect of the fractal characteristics of the pore structure of the uranium-bearing sandstone on the uranium leaching kinetics was studied. Then, the kinetics was analyzed using a shrinking nuclear model, and it was determined that the rate of uranium leaching is mainly controlled by the diffusion reaction, and the dissolution rate constant (K) is linearly related to the pore specific surface fractal dimension (DS) and the pore volume fractal dimension (DV). Eventually, fractal kinetic models for predicting the in-situ leaching kinetics were established using the unreacted shrinking core model, and the linear relationship between the fractal dimension of the sample’s pore structure and the dissolution rate during the leaching was fitted. |
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1738-5733 |
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THL @ christoph.kuells @ zeng_fractal_2022 |
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193 |
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Klimkova, S.; Cernik, M.; Lacinova, L.; Filip, J.; Jancik, D.; Zboril, R. |
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Title |
Zero-valent iron nanoparticles in treatment of acid mine water from in situ uranium leaching |
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Journal Article |
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2011 |
Publication |
Chemosphere |
Abbreviated Journal |
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82 |
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8 |
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1178-1184 |
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Acid mine water, Contaminant removal, Surface stabilizing shell, Water treatment, Zero-valent iron nanoparticles |
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Abstract |
Acid mine water from in situ chemical leaching of uranium (Straz pod Ralskem, Czech Republic) was treated in laboratory scale experiments by zero-valent iron nanoparticles (nZVI). For the first time, nZVI were applied for the treatment of the real acid water system containing the miscellaneous mixture of pollutants, where the various removal mechanisms occur simultaneously. Toxicity of the treated saline acid water is caused by major contaminants represented by aluminum and sulphates in a high concentration, as well as by microcontaminants like As, Be, Cd, Cr, Cu, Ni, U, V, and Zn. Laboratory batch experiments proved a significant decrease in concentrations of all the monitored pollutants due to an increase in pH and a decrease in oxidation–reduction potential related to an application of nZVI. The assumed mechanisms of contaminants removal include precipitation of cations in a lower oxidation state, precipitation caused by a simple pH increase and co-precipitation with the formed iron oxyhydroxides. The possibility to control the reaction kinetics through the nature of the surface stabilizing shell (polymer vs. FeO nanolayer) is discussed as an important practical aspect. |
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0045-6535 |
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THL @ christoph.kuells @ klimkova_zero-valent_2011 |
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196 |
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Author |
Robati, A.; Barani, G.A. |
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Modeling of water surface profile in subterranean channel by differential quadrature method (DQM) |
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Journal Article |
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2009 |
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Applied Mathematical Modelling |
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33 |
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3 |
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1295-1305 |
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Subterranean channel, Qanat, Differential quadrature method, Water surface profile, Porous media |
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Abstract |
This study, investigates the hydraulic of flow in a subterranean channel headspring. The continuity and momentum equations of flow in porous media considering real conditions were used and the basic equation of flow in a subterranean channel was resulted. This equation is very similar to the spatially varied flow with increasing discharge. An equation, defining the hydraulic parameters of a subterranean channel section was adopted. Then differential quadrature method (DQM), was applied to the equation of flow in subterranean channel, consequently the water surface profile was resulted. To illustrate the rightness of model, the hydraulic parameters of flow in the Gavgard branch of the Joopar Goharriz Qanat were measured and the water surface profile was determined. This water surface profile was compared to the water surface profile computed by the model, which are in good agreement. |
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0307-904x |
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THL @ christoph.kuells @ Robati20091295 |
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249 |
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Author |
Liu, Z.; Tan, K.; Li, C.; Li, Y.; Zhang, C.; Song, J.; Liu, L. |
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Title |
Geochemical and S isotopic studies of pollutant evolution in groundwater after acid in situ leaching in a uranium mine area in Xinjiang |
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Journal Article |
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Year |
2023 |
Publication |
Nuclear Engineering and Technology |
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Volume |
55 |
Issue |
4 |
Pages |
1476-1484 |
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Acid in situ leaching of uranium, Pollution evolution, Sulfate elimination, Sulfur isotopes analysis |
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Abstract |
Laboratory experiments and point monitoring of reservoir sediments have proven that stable sulfate reduction (SSR) can lower the concentrations of toxic metals and sulfate in acidic groundwater for a long time. Here, we hypothesize that SSR occurred during in situ leaching after uranium mining, which can impact the fate of acid groundwater in an entire region. To test this, we applied a sulfur isotope fractionation method to analyze the mechanism for natural attenuation of contaminated groundwater produced by acid in situ leaching of uranium (Xinjiang, China). The results showed that δ34S increased over time after the cessation of uranium mining, and natural attenuation caused considerable, area-scale immobilization of sulfur corresponding to retention levels of 5.3%–48.3% while simultaneously decreasing the concentration of uranium. Isotopic evidence for SSR in the area, together with evidence for changes of pollutant concentrations, suggest that area-scale SSR is most likely also important at other acid mining sites for uranium, where retention of acid groundwater may be strengthened through natural attenuation. To recapitulate, the sulfur isotope fractionation method constitutes a relatively accurate tool for quantification of spatiotemporal trends for groundwater during migration and transformation resulting from acid in situ leaching of uranium in northern China. |
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1738-5733 |
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THL @ christoph.kuells @ liu_geochemical_2023 |
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192 |
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Author |
Zhao, Y.; Li, X.; Lei, L.; Chen, L.; Luo, Z. |
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Title |
Permeability evolution mechanism and the optimum permeability determination of uranium leaching from low-permeability sandstone treated with low-frequency vibration |
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Journal Article |
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Year |
2023 |
Publication |
Journal of Rock Mechanics and Geotechnical Engineering |
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15 |
Issue |
10 |
Pages |
2597-2610 |
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Chemical reactive rate, Low-frequency vibration, Low-permeability sandstone, Optimum permeability, Permeability evolution mechanism, Uranium migration |
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Abstract |
Low-frequency vibrations can effectively improve natural sandstone permeability, and higher vibration frequency is associated with larger permeability. However, the optimum permeability and permeability evolution mechanism for uranium leaching and the relationship between permeability and the change of chemical reactive rate affecting uranium leaching have not been determined. To solve the above problems, in this study, identical homogeneous sandstone samples were selected to simulate low-permeability sandstone; a permeability evolution model considering the combined action of vibration stress, pore water pressure, water flow impact force, and chemical erosion was established; and vibration leaching experiments were performed to test the model accuracy. Both the permeability and chemical reactions were found to simultaneously restrict U6+ leaching, and the vibration treatment increased the permeability, causing the U6+ leaching reaction to no longer be diffusion-constrained but to be primarily controlled by the reaction rate. Changes of the model calculation parameters were further analyzed to determine the permeability evolution mechanism under the influence of vibration and chemical erosion, to prove the correctness of the mechanism according to the experimental results, and to develop a new method for determining the optimum permeability in uranium leaching. The uranium leaching was found to primarily follow a process consisting of (1) a permeability control stage, (2) achieving the optimum permeability, (3) a chemical reactive rate control stage, and (4) a channel flow stage. The resolution of these problems is of great significance for facilitating the application and promotion of low-frequency vibration in the CO2 + O2 leaching process. |
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1674-7755 |
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THL @ christoph.kuells @ zhao_permeability_2023 |
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198 |
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