Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since ²³⁰Th is part of the ²³⁸U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. The final product was 91.32?±?0.77 mg of thorium with a purity of 99.5?±?1.2 wt%. Of that, 7.65?±?0.10 mg was ²³⁰Th and the remainder ²³²Th. The total yield of ²³⁰Th was 71.1?±?5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

     

Recovery of uranium from phosphate by carbonate solutions

Uranium concentrations were analyzed in the Syrian phosphate deposits. Mean concentrations were found between 50 and 110 ppm. As a consequence, an average phosphate dressing of 22 kg/ha phosphate would charge the soil with 5–20 g/ha uranium when added as a mineral fertilizer. Fine grinding phosphate produced at the Syrian mines was used for uranium recovery by carbonate leaching. The formation of the soluble uranyl tricarbonate anion UO₂(CO₃)₃ ⁴⁻ permits using alkali and sodium bicarbonate salts for the nearly selective dissolution of uranium from phosphate. Separation of iron, aluminum, titanium, etc., from uranium during leaching was carried out. Formation of some small amounts of molybdates, vanadates, phosphates, aluminates, and some complex metals was investigated. This process could be used before the manufacture of Tri-Super Phosphate (TSP) fertilizer, and the final products would contain less uranium quantities.     

Leaching behavior of uranium and vanadium using strong sulfuric acid from Korean black shale ore

The present scientific study focused on leaching behavior of uranium and vanadium from Korean domestic ore. The leaching process experimental conditions optimized for uranium and vanadium metals recovery from Korean domestic ore and developed the basic experimental procedures such as time, particle size, acid influence, temperature effect and pulp density (PD) behavior. Acid influence on leaching process was tested and noted that 2.0 M sulfuric acid concentration is the optimized conditions for present study. The time influence on leaching process was observed and its optimized 2 h for complete leaching process. The temperature influence tested and optimized the 80 °C for complete leaching process and PD is 50 % (wt%). The bench scale experiments developed in a laboratory and tested in pilot level each batch 100 kg of ore sample.     

Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore

In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (µ ^max) and doubling time (t _d) were obtained 0.08 h^?1 and 8.66 h, respectively. Parameters such as Fe²⁺ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 ± 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 °C in 48 h with the particles of d ₈₀ = 100 μm. The optimum concentration of supplementary Fe²⁺ was dependent to the PD. This value was 0 and 10 g of FeSO₄·7H₂O/l at the PD of 5 and 15 %, respectively. The effects of time, pH and PD on the bioleaching process were studied using central composite design. New rate equation was improved for the uranium leaching rate. The rate of leaching is controlled with the concentrations of ferric and ferrous ions in solution. This study shows that uranium bioleaching may be an important process for the Saghand U mine at Yazd (Iran).     

Bioleaching of UO2 2+ ions from a Romanian poor uranium ore

The present paper deals with an experimental study on the bioleaching of a poor uranium ore by means of hydrophytic plants Lemna minor and Riccia fluitans, under various operating conditions. The maximum degree of bioleaching (42%) of the reduced uranium species to U(VI) has been attained for the ore-Lemna minor-alkaline carbonate solution system. The UO₂ ²⁺ ions amount accumulated in the plants is negligible as compared to the dissolved quantity, owing to the ionic competition between uranyl ions and the cations necessary to the mineral nutrition. The X-ray diffraction patterns prove that the uranium species in pyrochlore mineral are completely oxidized to U(VI), while thucolite is only partially turned into UO₂ ²⁺ ions, in the presence of living plants.     

Fractionation of thorium and uranium isotopes in the acid leaching experiments on monazite

A series of leaching experiments with water and gradually harsher acid solutions have been carried out on a monazite.²²⁸Th/²³²Th,²³⁰Th/²³²Th, and²³⁴U/²³⁸U activity ratios in the acid fractions show a common variation pattern: high — low — close to bulk values, which can be explained in terms of preferential solution effect of recoil atoms. Compared with²²⁸Th, the preferential solution effect of²³⁴U is suppressed due to self-annealing of recoil tracks.     

A kinetic model for heap leaching of uranium ore considering variation of model parameters with depth of heap

Many kinetic models for heap leaching of low grade ores have been proposed and the model parameters have been treated as constants. However, some of these model parameters change with the depth of the heap. In the present work an apparatus consisted of six columns with different heights was designed and used to simulate the leaching behavior within a 3-m-high uranium ore heap at a uranium mine in South China. It was found that the model parameters α and ω for heap leaching of the uranium ore varied with the depth of the heap, and that the relationships between α and between ω and the depth of the heap were in the form of the logistic and the quadratic functions, respectively. Furthermore, a kinetic model for heap leaching of the uranium ore considering the variation of the model parameters with the depth of the ore was proposed. The kinetic model gave the fitting precision of more than 95 % and prediction precision of more than 93 %. The present work provided an approach for establishing the kinetic model for heap leaching of low grade uranium ores.     

Determination of hexavalent and tetravalent uranium in phosphate ores through hydrochloric acid selective leaching

The tetravalent and hexavalent uranium content of three Egyptian phosphate type ore samples namely; Sebayia, Abu Tartur and Qatrani have been studied through selective leaching by hydrochloric acid at normal, oxidized and reduced conditions at an amount of hydrochloric acid less than the stoichiometric value i.e. before phosphoric acid production. Oxidizing condition is attained by incorporating 2% of manganese dioxide in the leaching cycle, whereas reducing condition is attained by adding 2% iron powder. The achieved results show that the amount of tetravalent uranium varies between 5 and 95%. As soon as the achieved stoichiometric value of hydrochloric acid is sufficient to produce phosphoric acid both tetravalent and hexavalent uranium dissolve by virtue of phosphoric acid complexing power for uranium. The chemical form of uranium in the ore determines the type of solvent needed to recover it.     

The use of carbonate lixiviants to remove uranium from uranium-contaminated soils

The objective of this research was to design an extraction media and procedure that would selectively remove uranium without adversely affecting the soils' physicochemical characteristics or generating secondary waste forms difficult to manage or dispose of. Investigations centered around determining the best lixiviant and how the various factors such as pH, time, and temperature influenced extraction efficiency. Other factors investigated included the influence of attrition scrubbing, the effect of oxidants and reductants, and the recycling of lixiviants. Experimental data obtained at the bench-and pilot-scale levels indicated 80% to 95% of the uranium could be removed from the uranium-contaminated soils by using a carbonate lixiviant. The best treatment was three successive extractions with 0.25M carbonate-bicarbonate (in presence of KMnO₄ as an oxidant) at 40°C followed with two water rinses.     

Effects of oxidant and particle size on uranium leaching from coal ash

In this paper, uranium leaching efficiency from the coal ash was 45.82% on the condition of 0.3 M H₂SO₄, 1:20 g/L, 60 °C and 12 h. According to the result of Sequential chemical extraction, leaching trials and X-ray diffraction, oxidants promoted the uranium leaching with the generation of baratovite. There were differences between uranium content of leachable states and leaching trials. Although the uranium content bounding with exchangeable, carbonates and Fe–Mn oxides all peaked at particle size fraction 75–150 μm, the highest uranium content in leaching trials peaked at size fraction 48–75 μm.     

Radioactivity of spring and surface waters in the region of the uranium ore deposit at Žirovski vrh

Data are presented on²²²Rn,²²⁶Ra, natural uranium concentrations and gross beta activity of spring and surface waters in the region of the uranium ore deposit at Žirovski vrh. The concentrations were found to be relatively low. There is some increase in the vicinity of the explorative Uranium Mine but is, at least up till now, only of a local character.     

Leaching of El-Missikat low-grade fluoritized uranium ore by sulfuric acid: mechanism and kinetic

A well-characterized low-grade fluoritized uranium samples from new occurrence in Gabal El-Missikat prospect, Eastern Desert, Egypt was subjected to sulfuric acid leaching. The effects of leaching parameters on uranium dissolution mechanism were investigated. The shrinking core model was used to model leaching reactions. The kinetics equations indicates that the reactions appear to be controlled by layer diffusion process. The activation energy for uranium dissolution was evaluated. Low activation energy value (2.54 kJ mol⁻¹) confirm the diffusion layer mechanism. The presence of fluoride ions in the solution increases the dissolution of uranium. The optimum process operating parameters were: sulfuric acid concentration: 1.5 M, solid–liquid ratio: 1:3, contact time 8 h; agitation speed rate 200 rpm; and ore particle size − 75 µm at temperature 60 °C, in the absence of an external oxidant. Under these experimental conditions, the extraction efficiency of uranium was about 91%.

     

A device for uranium series leaching from glass fiber in HEPA filter

For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0?M HNO₃?C0.1?M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution, chemical consecutive chemical leaching by a 4.0?M HNO₃ solution, and repeated chemical leaching by a 4.0?M HNO₃ solution were used to remove the uranium series. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 5?h by the 4.0?M HNO₃?C0.1?M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 36?h by 4.0?M HNO₃?C0.1?M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 8?h by a 0.5?M H₂O₂?C1.0?M Na₂CO₃ solution were 8.9, 0.0, 1.91, and 6.4?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after consecutive leaching for 8?h by the 4.0?M HNO₃ solution were 2.08, 0.12, 1.55, and 2.0?Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after three repetitions of leaching for 3?h by the 4.0?M HNO₃ solution were 0.02, 0.02, 0.29, and 0.26?Bq/g. Meanwhile, the removal efficiencies of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th from the waste solution after its precipitation?Cfiltration treatment with NaOH and alum for reuse of the 4.0?M HNO₃ waste solution were 100, 100, 93.3, and 100%.     

Non-volatile organic analysis of uranium ore concentrates

In support of nuclear safeguards and non-proliferation efforts, Oak Ridge National Laboratory is responsible for characterizing uranium ore concentrate (UOC) samples obtained from two ore mining and milling sites. A sorptive extraction method has been developed for analysis of non-volatile organic compounds that might be used to identify characteristics of the purification process by which uranium was separated from these ores. This method utilizes Gerstel Twister^® stir bars coated with polydimethylsiloxane to extract organic components from aqueous media. A slurry of UOC is extracted with the Twister^® stir bar in 20 % methanol/80 % water containing deuterated internal hydrocarbon standards. Following extraction of non-volatile organics, the Twister^® stir bar is analyzed directly in the inlet of a gas chromatograph fitted with a quadrupole mass spectrometric detector. Results have been consistent and have shown excellent recoveries of internal standards, with the average recovery being 97.5 %. Both qualitative and quantitative differences have been identified between the two sources of UOC utilizing this method. One source contained an increased concentration of amines which commonly are used in the recovery and purification of ores. Amines that were identified in this UOC source include dioctylamine, triisoctylamine, and Alamine^® 336, a common industrial complexant. Also, when comparing both sources, the same UOC source contained various decanol and C20 compounds. Based on the results from this study, non-volatile organic analysis of UOC using sorptive extraction with Twister^® stir bars and GC–MS is a tool that can be used to facilitate sourcing of unknown UOC.     

Mechanism analysis on synergistic leaching of uranium from pyrite oxidized by Acidithiobacillus ferrivorans

Journal of Radioanalytical and Nuclear Chemistry - Low-grade uranium ore, which was challenging to be treated economically by conventional methods, can be treated by uranium leaching by bacteria....     

Heap bioleaching of uranium from low-grade granite-type ore by mixed acidophilic microbes

Journal of Radioanalytical and Nuclear Chemistry - We evaluated uranium bioleaching from low-grade, granite-type uranium ore using mixed acidophilic microbes from uranium mine leachate. A 4854-ton...     

The adsorption of U(VI) by albite during acid in-situ leaching mining of uranium

Journal of Radioanalytical and Nuclear Chemistry - Uranium adsorption experiment was conducted to study the influencing factors and the adsorption mechanisms. The results show that the acidified...