Results 1 - 10 of 620
Results 1 - 10 of 620. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Diethylene Triamine (DETA) can be used to extract selectively base metals from hydroxide sludges which are produced in the treatment of acid mine drainage. Solubilized metal concentrations exceeding 40 g/L are obtainable which is in the range where electrowinning is a possibility for metal recovery. Electrowinning experiments were conducted on copper-DETA complexes. The solutions tested contained 8 g/L Cu, 32.5 g/L DETA (ca. 1:2 molar basis), and 5.8 g/L NaCl at pH 12.2 (sodium hydroxide). After several trials stainless steel electrodes were selected. Batch tests showed DETA was not degraded and Cu was electrowon at a current density ca. 200 A/m2, a voltage ca. 2.5 V, and a current efficiency of 100%. The deposits were easily removed but they were brittle. In recycle tests DETA concentration decreased to reach a steady state concentration of ca. 21 g/L. Copper deposit quality also decreased. The proposed process to recover base metals from waste sludge using DETA as a recyclable extractant and electrowinning of the solution appears technically feasible. (author)
[en] The studied site is an old slate quarry in use from the first half of 20th century to 1965 located in Parc Natural de Collserola, in Barcelona. After some restore projects, from 1992 the quarry site has been used as an observatory of natural values of the zone. In this site, in between the slate there are associated minerals like marcasite and pyrite (FeS2 ) which, may be oxidized by water and atmospheric oxygen producing Fe3+ and sulphuric acid. This phenomena is commonly known as acid mine drainage (AMD). As a consequence of the acid leachates, several radionuclides may be extracted from the rocks and be distributed into effluents. In this study, a radiological characterization of soil, sediments and effluents of the aforementioned site are characterized. Total uranium activity in water samples is strongly related with the pluviometry since dilution effect is observed in rainy periods. However, the isotopic ratio 234U/238U in water samples remains constant around 1.2. Regarding soil samples, the concentration of uranium is constant in time but have an important spatial distribution. When you move away from the focus of AMD, the concentration of uranium in soil increase and isotopic ratio 234U/238U decrease.
[es]El emplazamiento estudiado es una antigua cantera de pizarras que se explotó en la primera parte el siglo XX hasta 1965 localizada en el Parc Natural de Collserola, en Barcelona. Desde 1992 el emplazamiento se ha tratado de recuperar convirtiéndolo en un espacio de observación de los valores naturales del parque. Asociadas a las pizarras se encuentran minerales como la pirita y marcasita (FeS2 ) que se oxidan por efecto del oxígeno y el agua dado lugar a iones Fe3+ y ácido sulfúrico causando el proceso conocido como drenaje ácido de mina. Como consecuencia el carácter ácido de los lixiviados, se extraen de la roca distintos radionucleidos que se distribuyen mediante dichos efluentes. En este trabajo se realiza una caracterización radiológica de suelos, sedimentos y efluentes del emplazamiento mencionado. Se ha observado que concentración de uranio en las distintas balsas está estrechamente relacionada con la pluviometría de la zona observándose un efecto de dilución en los periodos más húmedos, sin embargo la relación isotópica 234U/238U permanece constante alrededor de 1.2. Por otra parte, las determinaciones a distintas distancias del foco confirman una distribución espacial variante tanto en lo referente a la concentración de uranio como a la relación isotópica 234U/238U
[en] Uranium in acidic mine drainage from the former Ogoya Mine in Ishikawa Prefecture, Japan, and in neutral surface waters from its surrounding rivers was investigated from the viewpoint of radioactive disequilibrium in the uranium decay series. Water samples were periodically collected from the mine pithead and its surrounding rivers and their U isotopes (238U and 234U) were measured together with chemical components. The 238U concentrations in the water samples varied widely from 0.0036 to 0.78 mBq/L with a factor of about 200. High 238U concentrations were observed in the strongly acidic drainage (pH: around 3.5) from the pithead and the 234U/238U activity ratios showed significant values of as high as 10-15. By taking into account of the measurement of Th isotopes, it appeared that probable processes controlling the high 234U/238U activity ratios in acidic mine drainage were due to that the acidic water flowing from the mine pithead was formed only in the upper water layer of the pits and 234U was preferentially leached in the deeper underground water under the neutral and reducing conditions. (author)
[en] The Escuela Centroamericana de Geologia in conjunction with the, Laboratorio Nacional de Materiales and Modelos Estructurales both of the Universidad de Costa Rica, have carried out qualitative studies on the effects of acid rock drainage (DAR) in the materials used for stabilization and erosion control. on the slopes (km 38 + 600, km 45 + 000, km 47 + 000 and km 48 + 000) on national route No. 27 (RN-27). The present study developed a methodology to recreate and measure the impact that acid drainage has on the rock mass and on the cast concrete of the slopes, through experiments in the laboratory and in the field. The Instituto Costarricense de Electricidad has also carried out an analysis on the effect of acidic waters on concrete. This study is the first in the country focused on highway slopes, which use shotcrete for stabilization. Acid drainage is acidified waters as a consequence of the oxidation of minerals rich in sulfur. These waters, when draining between the materials of the slope, cause physical and mineralogical changes in their original composition and can cause instability. The importance of this study lies in the contribution of a methodology for future work on materials exposed to similar conditions in other national routes and for the support of decision-making corresponding to the stabilization of slopes affected by this process. The hypothesis raised indicates that if the healthy rocks that emerge in the vicinity of the RN-27 and the shotcrete designed and projected with the same acidic specifications that simulate the DAR, then there will be changes in their original characteristics. But if the material used does not have a calcareous component, it will not react with the acid and no changes will be made. This hypothesis was fulfilled and thus from this study, there is enough evidence to justify not using the concrete shot in place where the DAR is given. Five different tests were carried out, three in the laboratory and two in the field, with samples of volcanic breccia, andesite and shotcrete, of which the first two were obtained in the field and the last one was built with the same mixing design as the one placed on site. Changes in mass, dimensions and mineralogical characteristics were analyzed by optical microscopy and X-ray scattering. The results showed that samples exposed to a high level of acidity (pH ≤ 2), have a greater impact on their characteristics, than those that are in contact with a solution of lower acidity (2.0 ≤ pH ≤ 5.5). Shotcrete is the most susceptible material, of all those tested, to attack by acid dissolution, generating gypsum and ettringite as a mineralogical product of the reaction. The volcanic breccia samples are affected only by the dissolution of carbonates in the clasts and veinlets, and the andesite, lacking a calceous component in its composition, did not show alterations in the laboratory. Of the physical properties considered and analyzed, the mass presented the most significant changes while the dimensions did not reflect considerable changes. It was demonstrated, both in the field and in the laboratory, that the exposure of the shotcrete to acid solutions generated changes in its physical and mineralogical properties at the macro and microscopic level. This implies the deterioration in the quality of the concrete and explains the problems of stability and collapse of this material in the RN-27. According to the results in the laboratory and in the field, the accelerated experiment is validated in the laboratory and the working hypothesis is verified. (author)
[es]La Escuela Centroamericana de Geologia en conjunto con el Laboratorio Nacional de Materiales y Modelos Estructurales ambos de la Universidad de Costa Rica, han realizado trabajos cualitativos sobre los efectos de drenaje acido de roca (DAR) en los materiales utilizados para la estabilizacion y control de erosion en los taludes (km 38+600, km 45+000, km 47+000 y el km 48+000) en la ruta nacional No. 27 (RN-27). El presente estudio desarrollo una metodologia para recrear y medir el impacto que tiene el drenaje acido en el macizo rocoso y en el concreto de tipo lanzado de los taludes, mediante experimentos en el laboratorio y en campo. El Instituto Costarricense de Electricidad, ha realizado tambien analisis sobre el efecto de las aguas acidas en el concreto, este estudio es el primero en el pais enfocado en taludes de carretera, que utilizan concreto lanzado para su estabilizacion. El drenaje acido son aguas acidificadas consecuencia de la oxidacion de minerales ricos en azufre. Estas aguas al escurrir entre los materiales del talud, provocan cambios fisicos y mineralogicos en la composicion original de estos y pueden ocasionar inestabilidad. La importancia de este estudio esta en el aporte de una metodologia para futuros trabajos sobre materiales expuestos a condiciones similares en otras rutas nacionales y para el apoyo de la toma de decisiones correspondientes a la estabilizacion de taludes afectados por este proceso. La hipotesis planteada indica que si las rocas sanas que afloran en las inmediaciones de la RN-27 y el concreto lanzado disenado y proyectado con las mismas especificaciones del que fue colocado en los taludes, son expuestas a disoluciones acidas que simulan el DAR, entonces se daran cambios en sus caracteristicas originales. Pero si el material utilizado no tiene componente calcareo este no reaccionara con el acido y no se procuciran cambios. Esta hipotesis si se cumplio y asi a partir de este estudio, existen suficientes evidencias que justifiquen no utilizar el concreto lanzado en sitios donde se da el DAR. Se realizaron cinco ensayos diferentes, tres en laboratorio y dos en campo, con muestras de brecha volcanica, andesita y concreto lanzado, de las cuales las dos primaras fueron obtenidas en campo y el ultimo fue construido con el mismo diseno de mezcla del colocado en el sitio. Se analizaron los cambios de la masa, dimensiones y las caracteristicas mineralogicas mediante microscopia optica y dispersion de rayos X. Los resultados evidenciaron que las muestras expuestas a un algo nivel de acidez (pH ≤ 2), tienen un mayor impacto en sus caracteristicas, que las que estan en contacto con una disolucion de menor acidez (2,0 ≤ pH ≤ 5,5). El concreto lanzado es el material mas susceptible, de todos los ensayados, al ataque de la disolucion acida generando como producto mineralogico de la reaccion, yeso y etringita. Las muestras de brecha volcanica se ven afectadas solamente por la disolucion de los carbonatos en los clastos y vetillas, y la andesita al carecer de componente calcareo en su composicion, no evidencio alteraciones en el laboratorio. De las propiedades fisicas consideradas y analizadas, la masa presento los cambios mas significativos mientras que en las dimensiones no se reflejaron cambios considerables. Se demostro, tanto en campo como en el laboratorio, a que la exposicion del concreto lanzado disoluciones acidas genero cambios en sus propiedades fisicas y mineralogicas a nivel macro y microscopico. Esto implica el deterioro en la calidad del concreto y explica los problemas de estabilidad y colapso de esta material en la RN-27. De acuerdo con los resultados en laboratorio y en campo, se valida el experimento acelerado en laboratorio y se comprueba la hipotesis de trabajo. (autor)
[en] A trace test and computational flow analysis were carried out in order to identify the flow characteristics of mine drainage in an existing oxidation pond. Consequently, despite the need for sufficient retention time of mine drainage to purify the mine drainage, the effective volume of an oxidation pond without any structure is too small and the time for mine drainage required to reach the outlet is also too short. To deal with this problem, computational flow analysis was carried out after systematically arranging the baffles in an oxidation pond. The initial arrival time to the outlet with baffles was more than 360 times compared to the case without baffles. Furthermore, exchange efficiency was also significantly increased from 14.5 to 82.7 %. Thus, adding baffles to an oxidation pond resulted in an increase in the volume of the oxidation pond in the flow range of mine drainage, enhancing the flow efficiency and retention time as well.
[en] Acid Mine Drainage (AMD) is a process that occurs in mining that has sulfide ores. With water and oxygen, several metals are oxidized, an example is uranium. At the mine site of the Osamu Utsumi Mine located at INB - Caldas and in two other mining tailings pile, AMD occurs in an accelerated way and currently, without technological solution. To reduce the amount of water inside the pit, there is a water pumping system for the effluent treatment plant where hydrated lime is added, generating waste water and an alkaline mud called DUCA. The DUCA has a concentration of approximately 0.32% of U3O8, which makes it interesting from the point of view of the metallurgical extraction of that metal. One of the processes that can be used is leaching. The objective of this work was to test the alkaline leaching to extract the uranium present in the DUCA. In order to perform this separation, it was necessary to determine the operating conditions for the process: leaching agent solution (1 mol/L Na2CO3, 1 mol/L NaHCO3, 1 mol/L NaHCO3 with 1 mol/L Na2CO3 and 0.75 mol/L NaHCO3 with 0.25 mol/L Na2CO3), temperature (25 °C, 50 °C, 70 °C and 90 °C) and leaching time (1 hour-6 hours). The parameters were tested with 200 mL pulp and 10% solids. U3O8 solubilization was obtained 80% when using leaching solution with 0.75 mol/L NaHCO3 with 0.25 mol/L Na2CO3, 4 hours reaction and 70 °C temperature. With these optimized parameters, it will be possible to improve the leaching for the largest amount of uranium can be extracted in the sample, to help solve the environmental impact caused by the wastewater from the treatment of acid waters and, in addition, to give an economical destination for this metal that is solubilized in the pit of the mine. (author)
[en] Water is one of the receptors most affected by the impacts caused, especially in the case of mining sulphides and, to a lesser extent, of coal. Acid Mine Drainage (AMD) is the main problem associated with these mining operations, producing extremely high impacts, and in many cases irreversible impacts, until now. A new concept of mining can make this activity compatible with the environmental preservation and also to the recovery of the environment affected by the old mining operations that today are in the process of reopening. This new concept implicates the paradigm of Circular Mining as a derivative of the concept of Circular Economy, considered as a strategy that aims to reduce both the entry of materials and the production of virgin waste, closing the “loops” or economic and ecological flows of resources. The present work discusses the paradigm of Circular Mining, focused on the Iberian Pyrite Belt, one of the most paradigmatic metallogenetic regions in the world. Based on some examples, expeditious calculations show the possibility of recovering base metals as well as strategic elements from acid mine drainage, thus obtaining important economic assets.
[en] Tinto and Odiel rivers (SW of Spain) is an ecosystem of great interest that is seriously affected by acid mine drainage (AMD) from long-term mining activities (pH < 3). Additionally, a large industrial complex is located in the surroundings of this estuary and Huelva town, which includes two phosphate rock processing plants that produce about 3 millions of tons per year of a byproduct called phosphogypsum (PG) containing high U-series radionuclides concentrations. For these reasons, the estuary of Huelva is one of the most heavy metals and radionuclides polluted estuarine systems in Europe with extremely low pH.