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.     

Rare earth extraction from wet process phosphoric acid by emulsion liquid membrane

The recovery of rare earths(RE) during the wet processing of phosphoric acid is very important, the method of emulsion liquid membrane(ELM) with di(2-ethylhexly) phosphate(D2EHPA) as carrier has the high selectivity while cannot provide a satisfactory extraction rate. Here novel method of emulsion liquid membrane(ELM) using Aniline as carrier to extract RE from the feed solution was proposed. The method could increase the extraction rate of RE in the real sample to 93%. The effects of different parameters such as type and concentration of carrier and surfactant, hydrochloric acid concentration, organic to internal phase volume ratio, membrane to external phase volume ratio on extraction of RE~(3+) were investigated. Quantitative extraction(93%) of RE~(3+) was observed with 6 vol.% Aniline and 4 vol.% T154 liquid membrane at external to internal phase volume ratio of 10 for the feed solution. The proposed method of ELM using Aniline as carrier can be expected to provide a practical, efficient, and economical method for extracting RE from phosphate leach solution with high acidity in the industry of wet process phosphoric acid.     

Equilibrium and kinetic studies of the reductive stripping of uranium from DEPA-YOPO reagent into aqueous phosphoric acid

As of mid-1983, over 1000 tons of U₃O₈ per year is being recovered in the U.S.A. from wet-process phosphoric acid using the DEPA-TOPO process developed at Oak Ridge National Laboratory. Another 3000 tons of U₃O₈ per year passes through a number of small phosphate plants unrecovered, because the economics of the process are considered to be marginal at current market conditions. This paper describes equilibrium measurements, studies of uranium reduction kinetics, and uranium(IV) extraction which show how the efficiency of the reductive strip step, a key process operation, can be significantly increased by the use of higher concentrations of H₃PO₄ in the aqueous strip solution. This procedure greatly improves the reduction kinetics allowing decreased retention time in the mixers, use of lower Fe(II) concentration, and smaller process equipment. A model of a mixer-settler unit describes the system over a 5–10 molar H₃PO₄ range.     

Carrier-mediated gamma-aminobutyric acid uptake in human spermatozoa indicating the presence of a high-affinity gamma-aminobutyric acid transport protein

Human spermatozoa are capable of a carrier-mediated gamma-aminobutyric acid (GABA) uptake. The uptake is dependent on the concentration of Cl- and Na+ in the external medium, and the kinetics of the carrier resembles high-affinity GABA transport proteins. The time-dependent uptake of GABA displays large interindividual differences and is not correlated to motility parameters or morphology in the individual sample. Incubation of human spermatozoa with radiolabeled GABA was performed. Swim-up preparations of human spermatozoa were incubated with [3H]GABA, and subsequent GABA uptake was measured at various times by scintillation counting. GABA was accumulated intracellularly, and the uptake could be inhibited by preincubation of the samples in 200 microM nipecotic acid. Addition of aminooxyacetic acid in the medium did not alter the results, indicating that the internalized GABA remained unmetabolized intracellularly throughout the observation period. Kinetic analysis of GABA uptake was performed, and the Km for GABA transport was 14 microM. GABA uptake was reduced by equimolar substitution of NaCl in the capacitating medium by KCl, choline chloride, LiCl, N-methyl-D-glucamine (HCl) or D-glucuronic acid (sodium salt). Maximal reduction of [3H]GABA uptake was observed when the Na+ fraction of the medium was replaced with KCl. The results indicate the presence of a high-affinity GABA transport protein in the plasma membrane of human spermatozoa. GABA uptake was subsequently measured in 30 individual semen samples from men of barren couples. Large interindividual differences in GABA uptake was observed, but GABA uptake was not correlated to motility parameters or to morphology in the individual samples analyzed.     

Synergistic extraction of rare earth by mixtures of 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and di-（2-ethylhexyl） phosphoric acid from sulfuric acid medium

The extraction of Nd^3＋ and Sm^3＋, including the extraction and stripping capability as well as the separation effect of Nd^3＋ or Sm^3＋, from a sulfuric acid medium, by mixtures of di-（2-ethylhexyl） phosphoric acid （HDEHP, H2A2（0）） and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester （HEH/EHP, H2L2（0）） were studied. The distribution ratios and synergistic coefficients of Nd^3＋ and Sm^3＋ in different acidities were also determined. A synergistic extractive effect was found when HDEHP and HEH/EHP were used as mixed extractants for Sm^3＋ or Nd^3＋. The chemical compositions of the extracted complex were determined as Nd.（HA2）2-HL2 and Sm.（HA2）2-HL2. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.     

Recovery of uranium,vanadium, yttrium and rare earths from phosphoric acid by a precipitation method

Commercial procedures for recovery of uranium from phosphoric acid are all based on solvent extraction techniques. Recovery of uranium from phosphoric acid in combination with direct production of concentrated acid is not possible on a commercial scale using solvent extraction. When a dispersion agent such as acetone, and a precipitation reagent - NH₄F - are added, uranium can be precipitated from high concentration (52% P₂O₅), as well as low concentration phosphoric acid (～30% P₂O₅) with 0.6 kg acetone/kg P₂O₅ and 60 g NH₄F/kg P₂O₅. Variation of all parameters, such as uranium valence, phosphoric acid concentration, type and quantity of the dispersion and precipitation agents, has made it possible to develop on a laboratory scale a preferential mode of operation which appears to make uranium recovery from high concentration acid even simpler than recovery from acid of low concentration. This method also enables recovery of ?90% of the yttrium and ?80% of the rare earths contained in the phosphoric acid. To precipitate vanadium much more acetone must be used. The economic calculations presented here show that uranium recovery by the precipitation method is considerably less expensive than recovery by extraction or by other proposed routes: $60/lb at phosphoric acid capacity of 300 kt/a P₂O₅ with solvent extraction and $41/lb yellow cake with the new precipitation route and the same capacity. At present uranium prices ($28/lb yellow cake), the precipitation method does not make uranium recovery by precipitation an economic proposition in the case of plants of moderate phosphoric acid capacities (about 300 kt/a P₂O₅); however, in combination with recovery of yttrium and/or rare earths it appears to become economic - $28/lb yellow cake - at this moderate capacity.     

Extraction of rare earth ions from phosphate leach solution using emulsion liquid membrane in concentrated nitric acid medium

It is very significant to recover rare earths (REs) from wet-process phosphoric acid, in terms of extraction rate and selectivity, the current carrier di(2-ethlhexly) phosphate (D2EHPA) out there is still inferior. Based on this question, our team modified D2EHPA to synthesize new extractants. This paper presents a comprehensive study on the extraction of rare earth ions (RE³⁺) from phosphate leach solution using emulsion liquid membrane (ELM) in concentrated nitric acid medium. The ELM system is made up of (RO)₂P(O)OPh-COOH as carrier, polyisocrotyl succinimide (T154) as surfactant, sulfonated kerosene as diluent, phosphoric acid (H₃PO₄) as stripping solution. Different chemical parameters such as type and concentration of carrier, surfactant, stripping solution, volume ratio of oil phase to internal phase, and volume ratio of emulsion ratio to external phase were analyzed. The extraction of RE³⁺ was evaluated by the yield of extraction. In addition, the demulsification process was also investigated. The proposed method of ELM using (RO)₂P(O)OPh-COOH as carrier can be expected to provide an efficient, simplify operation, and facilitated method for extracting RE³⁺.     

Effect of some operating variables on cobalt(II) transport across a bulk liquid membrane

An experimental study is presented on facilitated transport of cobalt(II) cations through a bulk liquid membrane containing di(2-ethylhexyl)phosphoric acid (D2EHPA). The effects on the kinetics of cobalt(II) transport of stirring rate of the receiving phase and its acidity, mobile carrier (D2EHPA) concentration, emulsifier (Span 80) concentration, initial cobalt concentration, interfacial area, and membrane thickness have been investigated. It has been found that cobalt transport increased with both stirring of the receiving phase and its acidity, while the presence of emulsifier reduced this transport, particularly at the membrane/receiving phase interface. Moreover, the mean cobalt transport rate was practically independent of membrane/feed solution interfacial area (under experimental conditions), while this rate substantially increased with the initial cobalt concentration in aqueous feed solution.     

Carrier-mediated absorption of salicylic acid from hamster cheek pouch mucosa

Previously, we found that monocarboxylic acids undergo carrier-mediated transport in primary cultures of oral mucosal epithelial cells.1 In this study, we investigated whether carrier-mediated absorption of a monocarboxylic acid from the oral mucosa occurs in vivo. Salicylic acid was administered to hamster cheek pouch. At predetermined intervals, the concentration of salicylic acid in the fluid remaining in the cheek pouch lumen and the blood salicylic acid concentration were determined. The absorption of salicylic acid was saturable at high salicylic acid concentrations. Sodium azide, a metabolic inhibitor, and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), a protonophore, significantly inhibited the absorption of salicylic acid but not the absorption of salicylamide from the oral mucosa. Various monocarboxylic acids inhibited the absorption of salicylic acid, whereas dicarboxylic acids had no such effect. Transfer of [14C]salicylic acid from the cheek pouch mucosa to the systemic circulation was observed, and the blood [14C]salicylic acid concentration in the case of coadministration with propionic acid was significantly lower than that in the case of no propionic acid coadministration. These results show that monocarboxylic acids undergo carrier-mediated absorption from the hamster cheek pouch mucosa.     

Okadaic acid and its interaction with sodium, potassium, magnesium and calcium ions: complex formation and transport across a liquid membrane

Okadaic acid, a macrocyclic polyether compound, was shown to mediate the transfer of Na+, K+, Mg2+ and Ca2+ ions from aqueous solution to an organic phase, with a preference for Na+ ions. A kinetic study of the transport of these ions across a liquid membrane showed that the Na+ ion was more rapidly transported than the other ions and that the Na+ ion flux was dependent on the okadaic acid concentration.     

Concentration of europium(III) with supported liquid membrane containing a xylene solution of di-2-ethyihexyl phosphoric acid

The mechanism of europium transport through a supported liquid membrane is presented. The membrane consisted of a Teflon filter membrane with xylene solution of di-2-ethylhexyl phosphoric acid (HDEHP) as a mobile carrier held within the pores by capillary forces. Interposing the liquid membrane between two aqueous solutions of different pH, europium was transported and concentrated from the high pH solution to the low pH solution across the liquid membrane. The experiments were carried out to investigate the effects of the concentration of europium in the aqueous phase and HDEHP concentration in the membrane solution on the permeation rates of europium. The experimental results have been compared with a transport model for concentrating europium across the liquid membrane. The permeation rates of europium can be explained approximately by the diffusion process of the complex formed between europium ion and HDEHP at the membrane interface through the membrane in addition to the diffusion process of europium in the aqueous film adjacent to the membrane interface. Formerly Postdoctoral Fellow, Ames Laboratory, USDOE     

Carrier-mediated transport of monocarboxylate drugs in the pigmented rabbit conjunctiva

PURPOSE: To determine whether an Na+-dependent monocarboxylate transport process exists on the mucosal side of the pigmented rabbit conjunctiva and to evaluate how it may contribute to the absorption of ophthalmic monocarboxylate drugs. METHODS: L-lactate was used as a model substrate. The excised pigmented rabbit conjunctiva was mounted in a modified Ussing chamber for the measurement of short-circuit current (Isc) and 14C-L.-lactate transport. RESULTS: When added to the mucosal side at 37 degrees C and at pH 7.4, applications of as much as 40 mM L- and D-lactate increased Isc in a saturable manner. By contrast, no change in Isc was observed at 4 degrees C or under the mucosal Na+-free condition. 14C-L-lactate transport in the mucosal-to-serosal (m-s) direction at 0.01 mM revealed directionality, temperature dependency, Na+ dependency, and ouabain sensitivity, but not pH dependency. L-lactate transport in the m-s direction consisted of a saturable Na+-dependent process by the transcellular pathway and a nonsaturable process by the paracellular pathway. For the saturable process, the apparent Michaelis-Menten constant was 1.9 mM, the maximum flux was 8.9 nanomoles/cm2 per hour, and the apparent Na+ :L-lactate coupling ratio was 2:1. 14C-L-lactate transport in the m-s direction was significantly inhibited (46% to 83%) by the mucosal presence of various monocarboxylate compounds, but not by dicarboxylate compounds, zwitterionic compound, D-glucose, amino acids, and peptidomimetic antibiotics. Monocarboxylate nonsteroidal anti-inflammatory drugs and the antibacterial fluoroquinolones inhibited 14C-L-lactate transport by 40% to 85%, whereas prostaglandins and cromolyn had no effect. CONCLUSIONS: An Na+-dependent monocarboxylate transport process that may be used by non-steroidal anti-inflammatory and fluoroquinolone antibacterial drugs for transport appears to be present on the mucosal side of the pigmented rabbit conjunctiva. A possible physiologic role for the Na+-dependent monocarboxylate transport process may be to salvage tear lactate.     

Stripping of iron (III) from the D2EHPA + TBP extract produced during uranium recovery from phosphoric acid by oxalic acid

A process employing oxalic acid to separate iron from the organic phase composed of 1.5 M D2EHPA + 0.2 M TBP obtained in the second cycle operation during processing of phosphoric acid for uranium recovery has been developed and tested by bench scale counter-current operations. The process has been studied to optimize various process variables such as equilibration time, temperature, concentration of oxalic acid, iron concentration in organic phase and phase ratio for effective separation of iron. The stripping of iron was found to follow first order kinetics with an activation energy of 77 kJ/mole. Under optimized process parameters, a four stage counter-current stripping of iron has been carried out from an extract comprised of 1.5 M D2EHPA + 0.2 M TBP + 1.12 g/L Fe + 14.8 g/L U₃O₈ with 7.5 wt.% oxalic acid using an organic to aqueous phase ratio (O / A) of 3 at 50 °C. It yields an extract with only traces of iron. From the resulting extract yellow cake exceeding the specification of commercial grade has been produced.     

Modelling of zinc transport through a supported liquid membrane

The transport of zinc (II) from an aqueous solution containing zinc (II), iron (II), calcium (II) and magnesium (II) through supported liquid membrane using di-2-ethylhexyl phosphoric acid dissolved in kerosene as a mobile carrier was studied. The effects of temperature, rate of feed and stripping phase and concentration of stripping phase on the mass transfer coefficients of aqueous boundary layers and membrane were studied. A transport rate model has been derived taking into account diffusion through the feed side aqueous boundary layer, diffusion of carrier–zinc complex through the supported liquid membrane and diffusion through the stripping side aqueous boundary layer as simultaneous controlling factors. The mass transfer coefficient data of the side of the feed phase were correlated in the form of Sh = 0.0047 Re^1.349 Sc^0.3333. This correlation was used to calculate the mass transfer coefficient of the aqueous film at the side of the stripping phase. For some parameters and their levels, the mass transfer coefficients, k_f, k_m and k_s (m s^− 1), were calculated.     

Computing of liquid-liquid equilibria. I. Application of a general chemical model to the extraction of uranium from phosphoric acid by a hydroxyalkyldiphosphonic acid

A microcomputer program - MODEX - has been developed to model equilibrium data for the liquid-liquid extraction of metals, even when redox equilibria and precipitation occur. The calculations, based on chemical interactions, require the total concentrations of the introduced components and the formation constants of the species as parameters. Its flexibility makes it able to treat numerous problems. However, the use of conditional constants, valid in not too different ionic media, restricts its applicability. As an illustration, the program has been applied to the analysis of potentiometric, spectrophotometric and shake-out test data relating to the solvent extraction of uranium from phosphoric acid. The new extractant investigated - a diphosphonic compound R(HO)C-(PO₃H₂)₂ where R is a C-17 alkyl group - was dissolved in a hydrocarbon diluent with octanol as modifier, and various aqueous phase parameters (Fe(II)/Fe(III) ratio, H₃PO₄ concentration) were considered.     

Magnesium transport across the basolateral plasma membrane of the fish enterocyte

The aim of the study was to assess the influence of aortic valve replacement on left ventricular size and muscle hypertrophy according to the type of preexisting valve disease (aortic stenosis, insufficiency or combined disease). The study group consisted of 143 consecutive patients (pts) after aortic valve replacement (109 men, 34 women, mean age 48.1 +/- 10.9 years). Reason for the operation was aortic stenosis in 35 pts, aortic insufficiency in 64 pts and combined disease in 44 pts. Echocardiography was performed before surgery, 1 month and 1 year after operation, and yearly during 5-year follow-up. Transvalvular aortic pressure gradients decreased significantly after valve replacement in all subsets without further changes during follow-up (Pmax (mmHg): from 54.2 +/- 20.7 to 17.9 +/- 9.6 in combined disease pts, from 72.3 +/- 19.9 to 21.6 +/- 14.6 in aortic stenosis and from 34.5 +/- 24.2 to 15.6 +/- 11.3 in aortic insufficiency pts, respectively, P < 0.0005). One year after surgery the diastolic dimension of the left ventricle decreased significantly in all subjects, whereas the systolic dimension only in aortic insufficiency and combined disease pts (from 44 +/- 11.8 to 31.6 +/- 5.4 mm, P < 0.001 and from 41.9 +/- 11.5 to 33 +/- 6.7 mm, P < 0.05, respectively). Further decrease of both diastolic and systolic dimensions was observed only in the aortic insufficiency group. Ejection fraction of left ventricle increased only in combined disease pts (from 51.6 +/- 10% to 56.8 +/- 8.2%, P < 0.05). Wall thickness of the left ventricle decreased 1 year after valve replacement only in the aortic stenosis group and in further follow-up in the aortic stenosis and combined disease group. Normalization of left ventricular size is observed in more than 90% of patients during 5-year follow-up as opposed to left ventricular muscle hypertrophy, regressed only in less than a half of the study population. In patients with aortic valve disease the greatest hemodynamic improvement is observed 1 year after valve replacement. This is expressed by marked reduction of the left ventricular dimensions and wall thickness, without significant improvement of the ejection fraction. Further regression of left ventricle dimensions occurs in patients operated on due to predominant valve insufficiency, whereas regression of left ventricular hypertrophy is observed in patients with preexisting valvular stenosis.     

Fluoride retention in human enamel after a single phosphoric acid and mixed phosphoric acid/SnF2 application in vitro

This paper presents evidence that the Snyder/Pope Visual Memory Technique utilizing the Bender-Gestalt Test is a useful predictor of reading ability for first grade children. Subjects were administered the Bender Visual Memory Technique, the Bender-Gestalt Test, and the Digit Span subtest of the WISC-R at the beginning of first grade. The same children were administered the Reading subtest of the Wide Range Achievement Test at the end of first grade. Category scores of the Visual Memory Technique were correlated with the reading achievement results. One category, Rcc (an error-free recall of an error-free original drawing), correlated significantly with later reading ability (r = .43, p = .01). The Digit Span and reading achievement relationship was not found to be significant. Short-term visual recall is probably highly related to the reading task at Grade 1 and should be assessed when children begin to learn to read. Diagnosticians are encouraged to use the technique with attention to the precision category, Recall correct from correct.     

From membrane to molecule to the third amino acid from the left with a membrane transport protein

The lac permease of E. coli is a paradigm for secondary active transporter proteins that transduce the free energy stored in electrochemical ion gradients into work in the form of a concentration gradient. This hydrophobic, polytopic, cytoplasmic membrane protein catalyses the coupled, stoichiometric translocation of beta-galactosides and H+, and it has been solubilized, purified, reconstituted into artificial phospholipid vesicles and shown to be solely responsible responsible for beta-galactoside transport as a monomer. The lacY gene which encodes the permease has been cloned and sequenced, and all available evidence indicates that the protein has 12 transmembrane domains in alpha-helical configuration that traverse the membrane in zigzag fashion connected by hydrophilic loops with the N and C termini on the cytoplasmic face of the membrane. Extensive use of site-directed and Cys-scanning mutagenesis indicates that very few residues in the permease are directly involved in the transport mechanism, but the permease appears to be a highly flexible protein that undergoes widespread conformational changes during turnover. Based on a variety of site-directed approaches which include second-site suppressor analysis and site-directed mutagenesis, excimer fluorescence, engineered divalent metal binding sites, chemical cleavage, EPR, thiol crosslinking and identification of discontinuous mAb epitopes, a helix packing model has been formulated.A mechanism for the coupled translocate ion of substrate and H+ by the lac permease of E. coli is proposed. Four residues are irreplaceable with respect to coupling, and the residues are paired in the tertiary structure--Arg-302 (helix IX) with Glu-325 (helix 10) and His-322 (helix 10) with Glu-269 (helix VIII). In an adjacent region of the molecule at the interface between helices VIII and V is the substrate translocation pathway in which Glu-126 and Arg-144 appear to play key roles. Because of this arrangement, interfacial changes between helices VIII and V are transmitted to the interface between helices IX and X and vice versa. Upon ligand binding, a structural change at the interface between helices V and VIII disrupts the interaction between Glu-269 and His-322, Glu-269 displaces Glu-325 from Ag-302 and Glu-325 is protonated.Simultaneously, protonated Glu-325 becomes inaccessible to water which drastically increases its pKa. In this configuration, the permease undergoes a freely reversible conformational change that corresponds to translocation of the ternary complex. In order to return to ground state after release of substrate, the Arg-302-Glu-325 interaction must be reestablished which necessitates loss of H+ from Glu-325. The H+ is released into a water-filled crevice between helices IX and X which becomes transiently accessible to both sides of the membrane due to a change in helix tilt, where it is acted upon equally by either the membrane potential or the pH gradient across the membrane. Remarkably few amino-acid residues appear to be critically involved in the transport mechanism of lac permease, suggesting that relatively simple chemistry drives the mechanism. On the other hand, widespread, cooperative conformational changes appear to be involved in turnover. As a whole the data suggest that the 12 helices which comprise the permease are loosely packed with a considerable amount of water in the interstices and that surface contours are important for sliding or tilting motions that occur during turnover. This surmise coupled with the indication that few residues are essential to the mechanism is encouraging in that it suggest that the possibility that a relatively low resolution structure (i.e. helix packing) plus localization of the critical residues and the translocation pathway can provide important insights into the mechanism. (ABSTRACT TRUNCATED)