Uranium in phosphate rock and derivates

It is well known that phosphate rock contains a small amount of uranium. During the production of phosphate fertilizers, most uranium present is found in the phosphate fraction. Uranium was determined in the 70–200 ppm range in the phosphate rock and the final products by nuclear and classical methods.     

Effect of temperature and yeast extract on microbial respiration of sediments from a shallow coastal subsurface and vadose zone

Applied Biochemistry and Biotechnology - As a part of our study on microbial heterogeneity in subsurface environments, we have examined the microbial respiration of sediment samples obtained from a...     

A preliminary study on the migration mechanism of heavy metals into the vadose zone of soils of a dismissed industrial site

Within the framework of the site assessment of a dismantled steel-making plant area contaminated by Electric Arc Furnace dust (EAF dust), the actual migration of Cr, Cu, As, Cd, Pb, Zn and Ni (contaminants) from an industrial waste layer towards the vadose zone of the underlying soil has been evaluated. The crystalline phases and contaminant abundance of samples of the industrial waste layer and the surrounding soils were analysed, while the release of contaminants was evaluated by leaching tests. Results indicate the migration of pollutants from the industrial waste layer into the subsurface soil, but the high leachability of soil hides its real degree of contamination, with the consequent possibility of underestimating the hazardous characteristics of the actual situation.     

Crystal structure and thermal behavior of a chromium-piperazinium phosphate

(C₄N₂H₁₂)CrO(H_1.5PO₄)₂·H₂O has been synthesized hydrothermally using piperazine as organic template. Its crystal structure was solved ab initio using synchrotron powder X-ray diffraction data [monoclinic, a = 16.9649(4) Å, b = 9.8609(2) Å, c = 7.14375(14) Å, and β = 94.896(3)°, space group P2₁/a, Z = 4]. 1D structure is composed by isolated infinite anionic chains [CrO(H_1.5PO₄)₂]_n (vertex-sharing {CrO₆} octahedra joined by phosphate moieties). Their 2D plate-like morphology is propitiated by a very strong inter-chain interaction (P–O···H···O–P symmetric hydrogen bonds). KAS isoconversional method was applied to determine the activation energy for both thermal and thermo-oxidative decomposition of (C₄N₂H₁₂)CrO(H_1.5PO₄)₂·H₂O.     

Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides in phosphate rocks and phosphate fertilizers

Uranium, thorium and potassium contents and radioactive equilibrium states of the uranium and thorium series nuclides have been studied for 2 phosphate rocks and 7 phosphate fertilizers. Uranium contents were found to be rather high (39-117 ppm) except for phosphate rock from Kola. The uranium series nuclides were found to be in various equilibration states, which can be grouped into following three categories. Almost in the equilibrium state, 238U approximately 230Th greater than 210Pb greater than 226Ra and 238U greater than 230Th greater than 210Pb greater than 226Ra. Thorium contents were found to be, in general, low and appreciable disequilibrium of the thorium series nuclides was not observed except one sample. Potassium contents were also very low (less than 0.3% K2O) except for complex fertilizers. Based on the present data, discussions were made for the radiation exposure due to phosphate fertilizers.     

Uranium adsorption characteristic and thermodynamic behavior of clinoptilolite zeolite

Summary Natural zeolite, clinoptilolite was tested for its ability to remove uranium from aqueous solutions. Influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficients of uranium on clinoptilolite were measured by batch technique. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. Values of ΔH and ΔS were found as 0.93 and 56.09 J/mole, respectively. It was observed that the adsorption process is endothermic. Kinetics of uranium sorption was investigated at different time intervals at 30 °C. The reaction rate and diffusion constant were calculated.     

Thermal behavior of corn fibers and corn fiber gums prepared in fiber processing to ethanol

In this work, a thorough study of all solid products obtained in corn fiber processing to ethanol has been carried out with thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The thermal behavior of corn fiber, destarched corn fiber, various alkali pretreated fibers and corn fiber gums were compared.It has been established that no significant changes occur in the thermal behavior of the feedstock material as a result of treatment with amylolytic enzymes. On one hand only the concentration of the alkali (NaOH or KOH) seems to be important in determining the chemical composition of the pretreated corn fiber samples. On the other hand, the composition of the corn fiber gums depends on the type and not the concentration of the alkali used in the pretreatment step. The presence of H₂O₂ degrades the structure and alters the composition of the corn fiber to a larger extent. The polymeric hemicellulose which is precipitated after pretreatment with NaOH + H₂O₂ contains less impurities than the corn fiber gum prepared in the absence of hydrogen peroxide.The results indicate that the applied analytical methods are suitable for studying changes in the composition of the variously treated corn fibers. The observed effects of the treatments are in good agreement with data determined with conventional analytical techniques.     

Redox behavior of molybdenum and tungsten in phosphate glasses

In this work, vitreous samples were prepared in the binary system (100 - x)NaPO3-xMO3 with M = Mo and W and x varying from 10 to 60. The transmittance properties in the UV, visible, and near-infrared were monitored as a function of MO3 concentration. In both cases, an increase in the amount of transition metal results in an intense and broad absorption band in the visible and near-infrared attributed to metal reduction under synthesis conditions. It was shown that this large absorption can be partially or totally removed using specific oxidizing agents or by improving synthesis parameters such as melting temperature or cooling rate of the melt. In addition, structural investigations by Raman and X-ray absorption spectroscopy suggest that reduction only occurs when the metal cation is in octahedral geometry and that the transmittance improvement is not related with any structural changes. These results were explained in terms of thermodynamic equilibrium of redox species in the melt and allowed to obtain for the first time transparent and chemically stable glasses containing high concentrations of MO3 with transition metals in octahedral geometry inside the glass network.     

Ce as a probe of the crystal field and the nature of the impurity-ligand bond in borate and phosphate glasses

From the optical absorption spectrum of Ce³⁺ in borate and phosphate glasses, we calculate the nephelauxetic effect in the 4f-5d transition and the crystal field strength in these hosts. Some effects of covalency on the Ce³⁺-ligand bond are discussed and the bond-forming f-orbitals suggested.     

Incorporation of a QM/MM buffer zone in the variational double self-consistent field method

The explicit polarization (X-Pol) potential is an electronic-structure-based polarization force field, designed for molecular dynamics simulations and modeling of biopolymers. In this approach, molecular polarization and charge transfer effects are explicitly treated by a combined quantum mechanical and molecular mechanical (QM/MM) scheme, and the wave function of the entire system is variationally optimized by a double self-consistent field (DSCF) method. In the present article, we introduce a QM buffer zone for a smooth transition from a QM region to an MM region. Instead of using the Mulliken charge approximation for all QM/MM interactions, the Coulombic interactions between the adjacent fragments are determined directly by electronic structure theory. The present method is designed to accelerate the speed of convergence of the total energy and charge density of the system.     

Uranium isotopic analyses by using a sector field inductively coupled plasma mass spectrometer

A sector field mass spectrometer using an inductively coupled plasma as an ion source was used in order to determine the uranium isotopic ratios in reference materials supplied by the National Institute of Standards and Technology (NIST) (NBS 950, 010, 030, 200, 500, 750, and 970). The accuracy obtained for the major isotopes was better than 0.2%.     

Levels and behavior of natural radioactivity in the vicinity of phosphate fertilizer plants

Phosphate rocks are used for phosphoric acid production, which is the basis of agricultural phosphate fertilizers. It is known that phosphate ores contain, due to geological reasons, important amounts of natural radioactivity, mainly U-isotopes and daughters. By studying a specific case in Southwestern Spain, it is shown that the operation of phosphate fertilizer factories clearly enhance the natural radiation levels of its close environment. Levels of U-, Th-isotopes, and other natural radionuclides are given for a wide set of different samples, which support such a conclusion. In addition, the study of isotopic ratios gives information on the environmental behavior of such radionuclides.     

Comparative study of the behavior of ammonium phosphate in fireproofing intumescent formulations

A comparative study of the behavior of ammonium dihydrogen phosphate and partially substituted ammonium polyphosphates in fireproofing formulations based on organic solutions of polymers was made. Differences in the interaction of monomeric and polymeric acidic salts with the surface of a metal being protected were revealed.     

Assembly behavior of iron oxide-capped Janus particles in a magnetic field

Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O(2) atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies.     

赝势平面波计算铀及铀化合物结构研究

Ultrasoft pseudopotential was generated for uranium and the plane waves pseudopotential formalism was used to study its crystal structures at zero temperature as a function of pressure. The alpha phases of uranium were fully relaxed. The zero-pressure zero-temperature equilibrium volumes and bulk moduli are consistent with previous calculations, and in excellent agreement with the experiment. This is also the case for cell parameters and pressure-induced phase transitions. In the calculation of NaCl and CaF2 structure type of compound of uranium, the difference of theoretical lattice constant and the experimental value is less than 3%. For UO2+x the trend of the lattice shinking with the x value increase is in accord with the experiment. For large U2C3 and U2N3 complex cells the difference of theoretical lattice constant and the experimental value is less than 3%, and the difference of coordination of atom is less than 5%.     

Optimization of separation and migration behavior of cephalosporins in capillary zone electrophoresis

The influences of buffer pH, buffer concentration and buffer electrolyte on the migration behavior and separation of 12 cephalosporin antibiotics in capillary zone electrophoresis using three different types of buffer electrolyte, including phosphate, citrate, and 2-(N-morpholino)ethanesulfonate (MES), were investigated. The results indicate that, although buffer pH is a crucial parameter, buffer concentration also plays an important role in the separation of cephalosporins, particularly when cefuroxime and cefazolin, cephalexin and cefaclor, or cefotaxime and cephapirin are present as analytes at the same time. The electrophoretic mobility of cephalosporins and electroosmotic mobility measured in citrate and MES buffers are remarkably different from those measured in phosphate buffer. With citrate buffer, optimum buffer concentration is confined to a small range (35-40 mM), whereas buffer concentrations up to 300 mM can be used with MES buffer. Complete separations of 12 cephalosporins could be satisfactorily achieved with these three buffers under various optimum conditions. However, the separability of 12 cephalosporins with citrate or MES buffer is better than that with phosphate buffer. As a consequence of a greater electrophoretic mobility of cephalosporins than the electroosmotic mobility with citrate buffer at pH below about 5, some cephalosporins are not detectable. The cloudiness of the peak identification and of the magnitudes of the electrophoretic mobility of cefotaxime and cefuroxime reported previously are clarified. In addition, the pKa values of cephradine, cephalexin, cefaclor, and cephapirin attributed to the deprotonation of either an amino group or a pyridinium group are reported, and the migration behavior of these cephalosporins in the pH range studied is quantitatively described.     

Numerical simulation of deformation behavior of droplet in gas under the electric field and flow field coupling

The water droplets in the process of electrostatic coalescence are important when studying electrohydrodynamics. In the present study, the electric field and flow field are coupled through the phase field method based on the Cahn–Hilliard formulation. A numerical simulation model of single droplet deformation under the coupling field was established. It simulated the deformation behavior of the movement of a droplet in the continuous phase and took the impact of droplet deformation into consideration which is affected by two-phase flow velocity, electric field strength, the droplet diameter, and the interfacial tension. The results indicated that under the single action of the flow field, when the flow velocity was lower, the droplet diameter was greater as was the droplet deformation degree. When the flow velocity was increased, the droplet deformation degree of a small-diameter droplet was at its maximum size, the large-diameter droplet had a smaller deformation degree, and the middle-diameter droplet was at a minimum deformation degree. When the flow velocity was further increased, the droplet diameter was smaller, and the droplet deformation degree was greater. Under the coupled effect of the electric field and flow field, the two-phase flow velocity and the electric field strength were greater, and the degree of droplet deformation was greater. While the droplet diameter and interfacial tension were smaller, the degree of droplet deformation was greater. Droplet deformation degree increased along with the two-phase flow velocity. The research results provided a theoretical basis for gas–liquid separation with electrostatic coalescence technology.     

Study of protonic diffusion in hydrogen uranyl phosphate using a pulsed field gradient NMR method

The diffusion of ¹H in the fast protonic conductor H(UO₂PO₄) · 4H₂O has been investigated as a function of temperature by employing pulsed field gradient NMR measurements. In the light of the present diffusion results and published conductivity observations on the same compound, it is likely that protonic diffusion and conductivity in this material occur by the same mechanism. Possible mechanistic processes for the proton motion in this material which are consistent with the activation energy for protonic diffusion found in this study are briefly discussed.