Solubilization Of Uranium Research Articles

Uranium deposits of Mongolia, their exploration and mine development

Most of the known uranium deposits in Mongolia are related to volcano-tectonic structures of the Late Mesozoic and permeable sandstone aquifers of terrigenous sedimentary rocks in Late Mesozoic-Cenozoic basins. A young uranium deposit has been recently discovered at the surface in Quaternary alluvial sediments. Uranium deposits are classified here according to the International Atomic Energy Agency (IAEA) classification scheme. Beside of supergene and hydrothermal uranium discoveries, uranium mineralization can also be found in the Lower Cretaceous lignite seams, in Mesozoic alkaline intrusive rock related REE, Th, U enriched mineral systems and in metasomatic rocks, as well as in migmatites and pegmatites localized in Precambrian metamorphic rocks. Currently, no uranium can be produced in Mongolian facilities except pilot testing being done first. A pilot test was carried out at the Khairhan and Kharaat deposits in Mongolia and these experiments have demonstrated the ore to be amenable to acid leach (sulphuric acid) with the addition of an oxidizing agent. These tests confirmed that hydraulic control can be maintained and that the uranium solubilization and mobilization can be controlled. The results of the test were encouraging, with the well production rate, uranium concentration in produced solutions, chemical usage, and estimated uranium recovery all within ranges expected for normal commercial operations. There are a number of Mongolian uranium deposits are in the stage of mine development. The Government of Mongolia has approved the agreement of mine development of the Zuuvch ovoo and Dulaan uul deposits. Pilot testing on these deposits is underway and uranium will be extracted by in-situ leaching soon.

Enhancing uranium solubilization in soils by citrate, EDTA, and EDDS chelating amendments

A systematic study was made of the effects of three soil amendments on the solubilization of uranium from a granitic soil. The aim was to optimize solubilization so as to enhance bioavailability for the purposes of remediation. The three amendments tested were with citrate, EDTA, and EDDS as chelating agents. The effects of pH, chelator concentration, and leaching time were studied. The most important factor in uranium solubilization was found to be the pH. In the absence of chelating agents, the greatest solubilization was obtained for alkaline conditions, with values representing about 15% of the total uranium activity in the bulk soil. There were major differences in uranium solubilization between the different amendments. The citrate treatment was the most efficient at acidic pH, particularly with the greatest concentration of citrate tested (50 mmol kg −1) after 6 days of treatment. Under these conditions, the uranium concentration in solution was greater by a factor of 356 than in the control suspension, and represented some 63% of the uranium concentration in the bulk soil. Under alkaline conditions, the EDTA and EDDS treatments gave the greatest uranium activity concentrations in solution, but these concentrations were much lower than those with the citrate amendment, and were not very different from the control results. The uranium extraction yield with EDDS amendment was greater than with EDTA.

Characterization and Dissolution of ZrTh3UO10 and Th3UO8 Ceramics

ABSTRACTThoria-urania-zirconia ceramics were studied in order to investigate the long-term behavior of potential thorium fuels in a repository environment. The ceramics were prepared by coprecipitation of the metal salts. Zirconia was added to determine if further stabilization against dissolution of the thoria-urania system could be achieved. In addition, 0.5 wt% MgO was added to some samples to increase stability and density. The inclusion of Zr in the ceramics did not dramatically decrease the leaching of thorium from the matrix.Material properties of the ceramic were analyzed using electron microscopy techniques such as Energy Dispersive X-ray (EDX) analysis and Electron Energy Loss Spectroscopy (EELS). X-ray diffraction and synchrotron-based x-ray absorption studies including extended xray fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES) were also used to reveal elements of the phase structure and chemistry of the ceramics. X-ray diffraction (XRD) and EDX show that these ceramics separate into a zirconium-based phase and an actinide-based phase with low mutual affinity of thorium and zirconium, as well as partial solubilization of uranium in zirconium. The comparison of EELS spectra collected for the ceramics with spectra collected for UO2 and U3O8 reference materials also allow the assessment of uranium oxidation state independently in the two separate phases. Assessment of the bulk oxidation state using XANES correlated well with the EELS analysis. Interatomic distances and the bulk crystal structure were determined using EXAFS.

The Effect of Acidification and Chelating Agents on the Solubilization of Uranium from Contaminated Soil

AbstractThe role of acidification and chelating agents in the solubilization of uranium (U) from contaminated soil was examined in a series of experiments. Soil acidification and the addition of chelating agents were the two methods compared initially. The results indicated that the addition of citric acid solubilized more U than acidification or the other amendments tested. This increase in U solubility was, however, transitory. A subsequent experiment indicated that citrate concentration had a more dramatic effect on U solubility than did acidification. The greatest soluble U concentration during this experiment (775 mg kg−1 soil, or ∼85% of the total U) was observed after 24 h in the presence of 20 millimoles citrate kg−1 soil at pH 5. The persistence of U solubility over the 96‐h experimental period was primarily a function of pH and citrate degradation. In a separate experiment, in which citric acid rather than citrate was added to contaminated soil, the soluble U concentrations observed were generally lower than those observed in the presence of citrate. Citric acid decreased soil pH to values ≤3.6, and solubilized higher concentrations of Al and Fe than observed in the presence of citrate. Since the maximum solubilization of U was observed at pH 5, the implication of these results is that a combined approach, using both soil acidification and citric acid addition, may be necessary to maximize the phytoextraction of U from soils with a pH > 6.0.

Dissolution of uraninite in acid solutions

The purpose of this work was to assess the oxidative dissolution of uranium from a uraninite-containing rock in acid sulfate solutions under test conditions relevant to uranium leach mines and acid mine waters. Uranium dissolution in acidified mineral salts solution was slow and the predominant carbonate mineral (rhodochrosite) in the rock sample continued to consume acid. Bacterial inoculation (Thiobacillus ferrooxidans) and additional Fe2+ or S0 were tested in efforts to enhance the dissolution. Addition of Fe enhanced the solubilization of uranium, whereas S-addition had little incremental effect on the dissolution with and without bacterial inoculation. © 1998 Society of Chemical Industry

Acid dissolution of uranophane and carnotite

Uranium dissolution from rock samples containing uranophane or carnotite was tested in acid mineral salts solutions in the presence and absence of Fe‐ and S‐oxidizing bacteria (Thiobacillus ferrooxidans) and with FeSO4 or S0 as the substrate. The addition of FeSO4 enhanced the solubilization of uranium from uranophane. S0‐amendment was also effective, because uranium solubilization was enhanced at low pH resulting from the bacterial oxidation of S0. Uranium was readily dissolved from carnotite. However, the carnotite‐containing rock sample was predominantly composed of calcite that excessively consumed acid, increasing the pH and thereby reducing the concentration of uranium dissolved in leach solution.

Investigation of Electrokinetic Decontamination of Concrete

Experiments have been conducted to investigate the capabilities of electrokinetic decontamination of conceret. Batch equilibration studies have determined that the loading of cesium and strontium on concrete may be decreased using electrolyte solutions containing competing cations, while solubilization of uranium and cobalt, that precipitate at high pH, will require lixiviants containing complexing agents. Dynamic electrokinetic experiments showed greater mobility of cesium than strontium, while some positive results were obtained for the transport of cobalt through concrete using EDTA and for uranium using carbonate. *Managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy under contract DE-AC05-96OR22464.

Nutrient requirements for the in-place leaching of uranium by Thiobacillus ferrooxidans

Analyses of the concentrations of the various inorganic metabolites found in naturally occurring acidic drainage from coal waste dumps, uranium tailings or in situ acidic uranium mine drainage suggested that excessive concentrations of nutrients are present in the popular laboratory media utilized in bacterial leaching studies. A new medium was developed and tested for the leaching of uranium in both shake-culture and column leaching studies. Optimal uranium solubilization occurred when the leach liquor contained 0.1 m M K 2HPO 4, 0.5 m M MgSO 4 · 7H 2O and 0.5 m M (NH 4) 2SO 4·2H 2O.

Effect of pH, iron concentration, and pulp density on the solubilization of uranium from ore material in chemical and microbiological acid leach solutions: Regression equation and confidence band analysis

The solubilization of uranium from a finely ground ore material was investigated in leaching tests each lasting for about 24 h. Ferric iron, added as Fe 2(SO 4) 3 or produced by prior microbiological oxidation of FeSO 4, accelerated the rates of uranium leaching, as compared with those obtained with sulfuric acid or acidic ferrous sulfate. Pulp density and initial pH were also test variables. Yields of up to 100% uranium extraction were obtained within 24 h. Quadratic response surfaces were fitted to the experimental leach curves and confidence bands were calculated to assess the significance of the effects of pH, iron concentration, and pulp density on uranium solubilization. The general separation of the confidence bands indicated that each factor had a significant effect.

Solubilization of phosphate, uranium, and iron from apatite- and uranium-containing rock samples in synthetic and microbiologically produced acid leach solutions

The solubilization of phosphate was investigated using apatite and P-containing uranium rock samples in acid solutions. The concentration of soluble phosphate usually increased upon 24-h extraction followed by subsequent precipitation. Uranium solubilization was investigated using leach solutions that contained about 3 g/l ferric iron produced by bacterial oxidation of iron pyrite. 1–94% extraction of uranium was attained within 24h, with the poor recovery associated with a rock sample containing an excessive amount of alkaline material. Reducing equivalents (permanganate-consuming substances) in the acid leach solutions could be oxidized by inoculation with iron-oxidizing thiobacilli (Thiobacillus ferrooxidans). Chemical analysis of iron indicated that most of the iron was in the oxidized form. Stable iron colloids were not present in significant amounts in the leach solutions. Acidic ferric sulfate containing about 6 g/l Fe3+ was also used as a leach solution. Repeated use of the leach solution with rock samples did not decrease the efficiency of the leaching but soluble uranium reached a toxic concentration and thus prevented the bacterial re-oxidation of ferrous iron in the leach solution.

Ferrous iron oxidation and uranium extraction by Thiobacillus ferrooxidans.

The microbiological oxidation of ferrous iron in batch and continuous systems has been investigated in relation to uranium extraction from a low-grade ore by Thiobacillus ferrooxidans. The influence of the parameters, agitation, and aeration on oxygen saturation concentration, rate of oxygen mass transfer, and rate of ferrous iron oxidation was demonstrated. The kinetic values, Vmax and K were determined using an adapted Monod equation for different dilution rates and initial concentrations of ferrous iron. The power requirements for initial leaching conditions were also calculated. Uranium extraction as high as 68% has been realized during nine days of treatment. Regrinding the leach residue and its subsequent leaching yielded 87% uranium solubilization.

Microbiological leaching of a low-grade uranium ore byThiobacillus ferrooxidans

The microbiological leaching of low-grade uranium ore has been investigated using a pure strain ofThiobacillus ferrooxidans. It has been shown that only minute quantities of iron are required to achieve a maximum effect on uranium release. The ore sample contained enough iron (3.23%) to produce this effect, consequently, very little influence has been observed on uranium solubilization by addition of either ferrous sulfate or pyrite to the leach suspensions. The highest uranium extraction rate derived in this study (57.1 mg/l/day) was realized with a 40% pulp density suspension containing 9.0 g/l of ferrous ion. The highest yield (100.0%) was obtained with a 5% pulp density suspension (initial mean particle diameter: 0.64 mm) and without addition of iron after ten days of treatment. The applicability of this method to industrial scale is proposed.

Geology of Felder Uranium Deposit, Live Oak County, Texas: ABSTRACT

The Felder ore deposit is a 5 million-lb uranium deposit in the South Texas coastal plain. It occurs in the basal sandstone of an Oakville Formation (Miocene) alluvial system. The host sandstone is a carbonate-rich arkose which contains virtually no carbonaceous debris and has been reduced by the local introduction of hydrogen sulfide. The ore lies well within the reduced zone and occurs as coffinite and uraninite that fill interstices and coat and replace grains. The overall geometric configuration of the ore is that of a winged, crescentic ore roll. Weak mineralization extends the wings of the ore roll and gives greater expression to the roll character. Departures from the shape are controlled by discontinuities in bedding and by proximity of the ore to the surface. Associated with the uranium is a broad halo of anomalous molybdenum. Subsidiary mineralized trends suggest a preexisting updip position for the main roll. Oxidation from the surface largely destroyed this previous roll by solubilization of uranium. Uranium subsequently migrated into favorably reduced sandstone and reprecipitated at the present roll position. End_of_Article - Last_Page 1393------------