Uranium sorption from phosphoric acid solutions using selective ion exchange resins: Part I. Isotherms of extraction and desorption

Experimental measurements have been made of the isotherms for the sorption and desorption of uranium from synthetic phosphoric acid solutions with two types of cation exchange resin. Work was performed with several D2EHPA/TOPO impregnated resins and with one commercially available ion exchange resin containing aminophosphonic acid groups. The effect of Fe²⁺, Fe³⁺ and Ca²⁺ on the effective capacity has been examined. Results show that D2EHPA/TOPO resins are n not affected by the presence of Fe²⁺ or of Ca²⁺. Ferrous ion, whichreduces uranium to the tetravalent oxidation state, prevents uranium sorption. The resin containing aminophosphonic acid groups possesses a higher effective capacity than D2EHPA/TOPO-based resins and was also not affected by the presence of Ca²⁺. Ferric and ferrous ions reduce the effective capacity considerably, though the resin still extracts U(IV).D2EHPA/TOPO-based resins can be eluted with 3 M H₃PO₄ at 40°C or 3 M H₃PO₄ solutions containing Fe²⁺. Ammonium carbonate was found to leach the organic extractants from the resin. The aminophosphonic acid resin can be eluted with (NH₄)₂CO₃ at 20°C producing eluate solutions highly enriched in uranium. A conceptual flowsheet for uranium recovery is proposed.     

Recovery of uranium from phosphoric acid by means of supported liquid membranes

U(VI) was transported at 23 ± 1°C from 5–6 M phosphoric acid solutions through liquid membranes of kerosene solutions of di(2-ethylhexyl) phosphoric acid and trioctyl phosphine oxide (D2EHPA/TOPO) supported on porous polytetrafluoroethylene to a solution of phosphoric acid of equal or greater molarity containing ferrous ion as a reducing agent. The ferrous ion could be omitted when the higher molarity acid was used. The uranium flux was proportional to the U(VI) concentration. The overall resistivity of the membranes to uranium flux had a diffusional component that was proportional to the membrane thickness and an interfacial component that resulted from rate-limiting uranium complexation/decomplexation kinetics. The interfacial component accounted for over 80% of the resistivity of a membrane 75 μm thick. Increasing the temperature to 60°C only slightly diminished the interfacial resistivity. A theoretical model was constructed that accommodated data obtained from uranium transport through the membranes and through quiescent layers of phosphoric acid and D2EHPA/TOPO in kerosene. The average uranium flux from simulated solutions of wet-process phosphoric acid at 90% uranium transfer was estimated to be 1.3 × 10^?11 mol cm^?2 sec^?1, or 0.09 lb ft^?2 yr^?1. The flux was judged to be too low for supported liquid membranes to be competitive with liquid/liquid extraction for recovery of uranium from wet-process phosphoric acid.     

Martensitic Phase Transformation from Non-isothermally Deformed Austenite in High Strength Steel 22SiMn2TiB

Non-isothermal compressive deformation was performed on high strength steel 22SiMn2TiB for the study of martensitic phase transformation from deformed austenite. The transformation start temperature M _s decreased with the increase of deformation from 0 to 50 pct, and the variation of deformation rate (0.1 and 10 s^?1) and the appearance of deformation-induced ferrite and bainite showed no influence on the change of M _s temperature. The deformation at both the rates increased the volume fraction of retained austenite; however, the carbon content of retained austenite decreased at 10 s^?1 and remained basically unchanged at 0.1 s^?1. The yield strength of austenite at M _s temperature and the stored energy in deformed austenite were experimentally obtained, with which the relationships between the change of M _s temperature and the thermodynamic driving force for martensitic phase transformation from deformed austenite were established by the use of the Fisher-ADP–Hsu model. And finally, the transformation kinetics was analyzed by the Magee–Koistinen–Marhurger equation.     

The extraction of hafnium (IV) by some organophosphorus reagents in the presence of two mineral acids

Extraction of hafnium (IV) was studied from solutions of mixtures of perchloric and nitric acids and of perchloric and hydrochloric acids of constant total acidity 2, 4, 6 and 8 M and c_Hf ? 4 × 10^?4mol l^?1. The organic phase consisted of solutions of various acidic or neutral organophosphorus reagents including di-n-butylphosphoric acid, di-n-amylphosphoric acid, di-n-octylphosphoric acid, n-decylphenylphosphonic acid, tri-n-butylphosphine oxide, tri-n-octylphosphine acid (TOPO), tri-n-phenylphosphine oxide, and tri-n-butylphosphate (TBP); or of 2-thenoyltrifluoroacetone, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, or N-benzoyl-N-phenylhydroxylamine in benzene, chloroform, or n-octane. Pronounced synergic extraction of hafnium occurs only with organophosphorus reagents from aqueous phases whose acidity is not lower than 3 M (HClO₄ + HNO₃) or 5 M (HClO₄ + HCl). The synergic effect was not affected markedly by variation of the initial concentration of hafnium in the range 1 × 10^?8 ?4 × 10^?4 mol l^?1, but it decreased with increasing initial concentration of the organophosphorus reagent and decreasing concentration of the H⁺ ions. No synergism was observed for the extraction of hafnium from mixtures of perchloric and sulphuric acids. It is suggested that the hafnium passes into the organic phase in the form of mixed complexes, the salting-out effect of perchloric acid playing an appreciable part.     

A SIMS investigation of impurity diffusion in amorphous Fe40Ni40B20

The diffusion coefficients of Be and Si in the amorphous alloy Fe₄₀Ni₄₀B₂₀ were measured in the temperature range 575–643 K by using the technique of secondary ion mass spectrometry (SIMS). The measurements were carried out on the pre-relaxed alloy specimens and the diffusion coefficients D were found to lie in the range 1.0 × 10⁻²³−2.0 × 10⁻²⁰ m² s⁻¹. The temperature dependence of the measured diffusion coefficients was found to be Arrhenius in nature yielding the values of the activation energy Q as 2.16 ± 0.19 eV atom⁻¹ and 3.39 ± 0.30 eV atom⁻¹ for the diffusion of Be and Si respectively. The corresponding values of the pre-exponential factors (D₀) were 9.4×10^{(−4.0±1.57)}m²s⁻¹ and 7.0 × 10^{5.0 ± 2.42} m² s⁻¹. An overall comparison of all the available data on diffusion in amorphous Fe₄₀Ni₄₀B₂₀ clearly shows that the previously reported correlations for the diffusion coefficient D, the activation energy Q, and the pre-exponential factor D₀ for amorphous alloys are seen in this alloy also. It is suggested that the mechanism of diffusion possibly involves a cooperative movement of a group of atoms.     

Magnetic property recovery in Nd-Fe-B bonded magnet wastes with chemical reaction and physical dissolution

The main difficulty for the recovery of Nd-Fe-B bonded magnet wastes is how to completely remove the epoxy resins. In this study, chemical reaction and physical dissolution were combined to remove the epoxy resins by adding ammonia-water and mixed organic solvents. Ammonia-water can react with the epoxy functional group of epoxy resin to generate polyols. Mixed organic solvents of alcohol, dimethyl formamide (DMF), and tetrahydrofuran (THF) can dissolve the generated polyols and residual epoxy resins. Under the optimum processing conditions, the epoxy resins in the waste magnetic powders are substantially removed. The oxygen and carbon contents in the recycled magnetic powder are reduced from 13500 × 10⁻⁶ to 1600 × 10⁻⁶ and from 19500 × 10⁻⁶ to 2100 × 10⁻⁶ with the reduction ratio of 88.1% and 89.2%, respectively. The recycled magnetic powder presents improved magnetic properties with M_s of 1.306 × 10⁻¹ A∙m²/g, M_r of 0.926 × 10⁻¹ A∙m²/g, H_cj of 1.170 T, and (BH)_max of 125.732 kJ/m³, which reach 99.8%, 99.4%, 95.9%, and 96.9% of the original magnetic powders, respectively.     

Carrier-mediated transport of uranium from phosphoric acid medium across TOPO/n-dodecane-supported liquid membrane

Present studies deals with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium. Tri-n-octyl phosphine oxide (TOPO)/n-dodecane is used as a carrier and ammonium carbonate as a receiving phase for the separation of uranium (VI) from the phosphoric acid medium. Throughout the study PTFE membranes are used as a support. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration and stripping agents. The effect of nitric acid and sodium nitrate in feed is also studied. It is found that there is negligible transport of uranium (VI) from pure phosphoric acid medium but it increases to very significant amount if 2 M nitric acid is added to feed phase. More than 90% uranium (VI) is recovered in 360 min using 0.5 M TOPO/n-dodecane as carrier and 1.89 M ammonium carbonate as stripping phase from the mixture of 0.001 M H₃PO₄ and 2 M of HNO₃ as a feed. The flux and permeability coefficient are found to be 9.21 × 10^− 6 mol/m² s and 18.26 × 10^− 5 m/s, respectively. Lower concentration of phosphoric acid with 2 M HNO₃ and higher concentration of carrier is found to be the most suitable condition for maximum transport of uranium (VI) from its low-level sources like commercial phosphoric acid.     

Extraction and permeation of cadmium ions through supported liquid membrane impregnated with mixtures of D2EHPA and M2EHPA

Abstract

The use of an organic carrier consisting of di-(2-ethylhexyl) phosphoric acid (D2EHPA) and mono-(2-ethylhexyl) phosphoric acid (M2EHPA), diluted in kerosene, for separation of cadmium through a supported liquid membrane (SLM) was investigated. The extraction percentage of cadmium and permeability coefficients rose by increasing M2EHPA and feed phase concentration. By increasing the volume percentage of M2EHPA, the permeability coefficient of cadmium increased to a maximum value of 8 cm s^?1 at 1·5 vol.-% declining at higher volume percentages. The permeability of cadmium ions through the SLM decreased with time. The permeation coefficient increased as the initial cadmium concentration increased.

On a étudié l’utilisation d’un support organique consistant d’acide phosphorique di-(2-éthylhexyle) (D2EHPA) et mono-(2-éthylhexyle) (M2EHPA), dilué dans du kérosène, pour la séparation du cadmium à travers une membrane liquide supportée (SLM). Le pourcentage d’extraction du cadmium et les coefficients de perméabilité s’élevaient avec l’augmentation du M2EHPA et de la concentration de la phase d’alimentation. En augmentant le % de volume de M2EHPA, le coefficient de perméabilité du cadmium augmentait à une valeur maximale de 8 cm s^?1 à un volume de 1·5% et déclinait à des % plus élevés du volume. La perméabilité des ions de cadmium à travers la SLM diminuait avec le temps. Le coefficient de perméation augmentait avec l’augmentation de la concentration initiale de cadmium.     

Grain-boundary diffusion of germanium in copper and Cu-Ge and Cu-Fe alloys

The grain-boundary diffusion (GBD) of germanium in copper and its alloys Cu-2% Ge and Cu-0.5% Fe is investigated in the temperature range of 500?C590°C by means of electron-probe microanalysis. The GBD parameters (triple product P = s??D _GB and effective activation energy E) are found. The temperature dependence of the triple product for germanium GBD in pure copper can be described by equation P = 3 × 10¹⁵exp[?80 kJ mol^?1/(RT)] m³ s^?1. It is shown that the addition of Ge has almost no effect on the GBD parameters in copper, while doping with iron leads to a considerable reduction in the triple product.     

Diffusion studies in the metallic glass Zr61 Ni39 by Auger electron spectroscopy

The diffusion coefficients (D) of Cu and Al in the metallic glass Zr₆₁Ni₃₉ were measured in the temperature range 551–621 K by using the Auger depth profiling technique. The D values for Cu were observed to be higher than the corresponding values for Al by about an order of magnitude in this temperature range. The faster diffusion of Cu was consistent with the observed dependence, in this amorphous alloy, of diffusivity on the atomic size of the diffusing species. The values of the activation energy for diffusion (Q), evaluated on the basis of the observed Arrhenius type temperature dependence of D, were found to be 1.33 ± 0.17 eV for Cu and 1.68 ± 0.13 eV for Al. The corresponding values of the pre-exponential factor (D₀) were 10^{−7.57 ± 1.46} m² s⁻¹ and 10^{−5.35 ± 1.15} m² s⁻¹ respectively. No significant effect of structural relaxation of the glass on diffusivity could be observed from measurements on specimens subjected to a relaxation heat treatment prior to diffusion annealing.     

Dislocation creep controlled superplasticity in the high carbon steel 140NiCr16-6

Superplasticity in the alloyed high carbon-steel 140NiCr16-6 with phosphorus additions and a fine grained microdupiex structure – containing cementite in volume fractions of 22 % (Fe,Cr,Ni)₃C, particle size of about 1 μm and with a medium ferrite grain size of about 2 μm – has been investigated in the temperature regime of 550 to 675°C and in the strain rate range of 10^?5 to 5 · 10^?2 s^?1. Maximum strain rate exponents of m = 0,45 at 675°C with strain rates of the order of 10^?4 s^?1 have been determined. Maximum superplastic elongations of about 700 % were detected. At higher strain rates of 10^?3 s^?1 superplastic elongations of about 570 % were achieved. At relatively low test temperatures of 550°C elongations up to 230 % were recorded. The activation analysis in the temperature regime of 550 to 650°C show an activation energy for superplastic flow of 250 ± 20 kJ/mol. This is in agreement with the activation energy for lattice self diffusion of iron in α-iron. Above 650°C the activation energy decreases to 70 kJ/mol. This is due to a stress induced decrease in the eutectoid α-γ-transformation temperature from 685°C to somewhat lower temperatures during superplastic deformation. The superplastic deformability (m > 0.3) of this steel in a wide strain rate range at relatively low temperatures above 550°C allows near net shape forming of complex parts applying low flow stresses.     

Separation of In3+ and Fe3+ from sulfate solutions using D2EHPA in a laminar microreactor

A microfluidic solvent extraction method is put forward to solve the problems existing in the conventional solvent extraction of indium, such as large waste of extractant, fire hazards, etc. Experiments were performed in a series of microreactors to separate In³⁺ and Fe³⁺ from sulfate solutions using D2EHPA as the extractant. The effect of main parameters such as different contact times, microchannel sizes, interface to volume ratios and pH values on the indium extraction efficiency was investigated. The results show that the smaller the channel size, the more the beneficial diffusion and mass transfer. Specifically, in a microchannel, with a size of 100?μm?×?50?μm?×?120?mm, almost 100% extraction efficiency was reached with contact time about 0·5?s. The mean mass transfer rate can be as high as 0·291?g?m^??2?s^??1, and the ratio of mean mass transfer rate of In³⁺ to that of Fe³⁺ can be as high as 29·76.     

Effect of changing slag composition on spinel inclusion dissolution

Abstract

The rate of MgAl₂O₄ spinel inclusion dissolution in CaO–SiO₂–Al₂O₃ slags at 1504°C has been measured using a laser scanning confocal microscope. It was found that the mechanism of spinel inclusion dissolution was at least in part controlled by mass transfer in the slag phase for the slag compositions used. Evidence in support of this finding was that the calculated diffusion coefficient was inversely proportional to the slag viscosity and that the diffusion coefficients were in reasonable agreement with those obtained in a separate study on alumina dissolution. The diffusion coefficients obtained were in the range of 0·76–2·2 × 10^?10 m² s^?1.     

High-temperature deformation of MnO

Steady-state flow stresses have been measured for {100}-oriented MnO single crystals for temperatures from 900 to 1400°C and strain rates from 2 × 10⁻⁶to 2 × 10⁻³s⁻¹. The crystals were equilibrated in oxygen partial pressures ranging from 10¹¹ to 10²Pa, which induced deviations from stoichiometry of 4 × 10⁻⁴to 9 × 10⁻². Deformation rates are controlled by oxygen diffusion. Pipe diffusion along dislocation cores is predominant for T ≤ 1000°C; volume diffusion is predominant for T ≥ 1200dgC. In general, the primary diffusing oxygen species are singly charged vacancies for low Po₂ and neutral interstitials for high Po₂. At 1400°C, ionization states decrease for the oxygen point defects.     

An Electrochemical Investigation of Fe(II) Dissolved in a Cryolite Melt

Chronopotentiometric studies were made on a cryolite melt containing 3.0 wt pct Al₂O₃ and 0.466 wt pct Fe(II) at 1293 K (1020 °C). The diffusion coefficient calculated from the time of the principal chronopotentiometric transition decreased as the current density was increased, and at the same time, a second subsequent transition appeared. The diffusion coefficient calculated from this second transition was constant at 5.44 × 10^?5 cm² s^?1. The results were interpreted to show that Fe(II) in the solution exists in two forms. Fe is deposited reversibly from an active form; its exchange current density must be >1 A cm^?2. Deposition from the other form is irreversible, and it occurs directly only at high overpotentials, leading to the second transition. The equilibrium constant [active]/[inactive] = 5.4. When the equilibrium is displaced by electrolysis of the active form, the inactive form decomposes to replenish it with a rate constant of 0.9 s^?1. The Tafel curve for the direct deposition of the inactive form shows a slope of 113 mV/decade, which is interpreted as n = 2 and a symmetry factor ≈1. The exchange current density is approximately 0.3 μA cm^?2. The active and inactive forms are identified tentatively as FeF ₃ ^? and FeF ₅ ^3? , respectively.     

The reaction of Cu(II) with LIX 65N in homogeneous solution

The nature of the complexes formed between Cu(II) and LIX 65N (H₂L) in ethanol has been studied by UV-visible spectrophotometry and the kinetics of the reaction between Cu(II) and H₂L by stopped-flow spectrophotometry at 25°C. The major complex, Cu(HL)₂, has a formation constant β₂ = [Cu(HL)₂]/[Cu][HL^?]² of log β₂ = 26.5 l² mol^?2 in 0.04 M NaClO₄. An additional complex, probably Cu(HL)⁺, can be detected in the absence of added NaClO₄. A third complex, identified as Cu₂(HL)₂²⁺, was observed at higher copper concentrations with formation constant K_d = [Cu₂(HL)₂]/[Cu(HL)₂][Cu] 1.7 × 10⁴ l mol^?1 in 0.04 M NaCIO₄. The rate of reaction of Cu(II) with H₂L to form Cu(HL)₂ obeys the rate equation, d[Cu(HL)₂]/d t = K_rate[Cu]¹[H₂L]¹[H⁺]⁰ where K_rate has the value of 2.9 × 10⁴ l mol^?1 s^-1 in the absence of added electrolytes.     

Kinetics of dissolution of synthetic heazlewoodite (Ni3S2) in nitric acid solutions

The dissolution rate of heazlewoodite in nitric acid solution has been determined. The effects of nitric acid concentration, temperature, particle size, stirring intensity and addition of Cu²⁺ ions have been investigated. Solid residues after leaching were examined by SEM, X-ray diffraction and chemical analysis. In the solutions containing less than 2.0 M HNO₃, dissolution was observed to be completely inhibited after 30 min leaching time, and the rate of hydrogen sulphide production was faster than its oxidation to S⁰ and HSO₄^?. In 3 M HNO₃, an abrupt increase in dissolution rate of Ni₃S₂ was found. Two different regions of the dissolution of heazlewoodite were observed below and above 50°C. At temperatures below 50°C, the dissolution rate was very slow, even in 3.0 M HNO₃ solution, and H₂S gas was evolved. Above 50°C, the dissolution rate rapidly increased. Over the temperature interval 60–90°C in 3.0 M HNO₃ dissolution followed a linear rate law, and the activation energy was found to be 42.1 kJ mol^?1. Most of the oxidized sulphide ion was found in the solution as sulphate. The leaching rate was independent of stirring speed. The rate-controlling step of the Ni₃S₂ dissolution is the oxidation of hydrogen sulphide to elemental sulphur or sulphate ions on the Ni₃S₂ surface. Addition of small amounts of Cu²⁺ ions to the nitric acid acted as catalyst for the dissolution of Ni₃S₂. Bubbling air through the leach suspension increased the dissolution rate of Ni₃S₂ in solutions containing less than 2.0 M HNO₃.     

Electrotransport and diffusion of Co,Fe, and Ag in γ-Cerium

Electrotransport mobilities and diffusion coefficients were obtained for radiotracer impurities of Fe, Co, and Ag in Ce. The iron and cobalt moved toward the anode with mobilities of ～10^?3 cm²/v-s in the range of 550° to 650°C. The silver moved to the cathode with mobilities of ～10^?5 cm²/v-s in the range of 600° to 700°C. The, diffusion coefficients obtained fit an Arrhenius equationD=D _o e ^?ΔH/RT with the following parameters: Fe:D _o=3.3×10^?4, ΔH=4.6 kcal/mole Co:D _o=10^?2, ΔH=11 kcal/mole Ag:D _o=1.4, ΔH=28 kcal/mole The results are compared with other rare-earth diffusion data, and the possibility of a substitutional-interstitial diffusion mechanism, is considered.     

The martensite transformation in FeNiC alloys

The effect of austenite defect structure upon the sub-zero martensite burst transformation temperature in FeNiC has been investigated using a combination of optical and electron microscopy, differential scanning calorimetry and microhardness testing. In the absence of a change in composition or dislocation density, the martensite start transformation temperature (M_s) was found to be determined by the grain size of the austenite. Above a grain size of 150 μm, M_s was found to be independent of grain size, but below 150 μm, the transformation temperature was strongly depressed by up to approximately 50 K at a grain size of 10 μm. For any given grain size, an increase in the dislocation density from that typical of a fully recrystallised specimen, i.e. approximately 10¹⁰ lines m⁻², to that of approximately 10¹⁵ lines m⁻² raised M_s by approximately 15 K. The depression of M_s and reduction in the initial burst size of the transformation with decreasing grain size was found to be related to the observation that a fine grain size results in a heterogeneous transformation restricted to a few small pockets of grains. The depression of M_s in the fine grained alloy is consistent with a segregation of active martensite nuclei into a few small grains, a suppression of the autocatalytic stimulation of martensite plates between adjacent grains, and a possible reduction in the number of martensite nuclei.     

Diffusion of copper along the grain boundaries in aluminum

The grain boundary diffusion (GBD) of copper in aluminum is investigated in the range t = 300?400°C. Investigations were performed on a scanning electron microscope equipped with an attachment for electron probe X-ray microanalysis. The triple product sδD _gb (where s is the segregation coefficient, δ is the width of the grain boundary, and D _gb is the GBD coefficient) was calculated by the Fisher criterion using two methods (namely, the copper concentration in the grain boundary, depending on the penetration depth, was determined and the angles in the vertex of the concentration profile was measured using an optical microscope). In the first case, sδD _gb was 5.1 × 10^?11 exp(?102/(RT)) m³/s; in the second case it was 1.4 × 10^?11 exp(?94/(RT)) m³/s. The obtained results are compared with innumerous literature data.