Recovery of copper(II) from aqueous solutions by means of supported liquid membranes

Relatively stable liquid membranes were easily and reproducibly prepared by impregnating commercial porous polytetrafluoroethylene or polypropylene membranes with solutions of commercial chelating extractants. When such membranes were placed between aqueous solutions of copper(II) sulfate at pH 1–4 and of sulfuric acid at pH 0.5, transfer of copper(II) ion from the less acidic to the more acidic solution took place simultaneously with an equivalent proton transfer in the opposite direction. The copper(II) ion moved selectively with respect to iron(III) ion and against a twenty-fold concentration gradient. The mechanistic and practical implications of these results are discussed.     

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.     

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.     

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.     

Recovery of uranium from lignites

There is a renewed interest in lignites as a source of fuel and for the possible by-product recovery of uranium. This paper summarizes the experimental work carried out at Oak Ridge National Laboratory during 1952 to 1954 that deals with the sulfuric acid leaching of lignite ash for uranium recovery. A discussion of the possible utilization of sulfur dioxides in flue gases should be of value to those companies planning to process lignites.     

Facilitated transport of vanadium (V) by supported liquid membranes

A systematic study of the flux of complex vanadium anions through hydrophobic supported liquid membranes is carried out in sulphate media to determine the feasibility of this technique for the removal/recovery of this metal from diluted effluents. Preliminary batch experiments guide us to use mixtures of tertiary amine Alamine 336 and phosphine oxide Cyanex 923 as carrier, dissolved in aromatic diluents. The models previously derived to explain this process in transition state have proven not to be valid for this system due to the slow stripping kinetics of the process and the complex mechanism of the extraction process. Values for the permeability of vanadium in these conditions were obtained in order to have a basis for comparison with other metals. An empirical fit of these data is obtained, which can serve us as a first approach in the design of continuous processes for the recovery of this metal with supported membranes.     

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     

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.     

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.     

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.     

Separation of molybdenum from tungsten by di-2-ethylhexyl phosphoric acid extractant

The efficiency of extracting molybdenum(VI) from a weakly acidic solution containing a large amount of tungsten and a small amount of molybdenum using di-2-ethylhexyl phosphoric acid (D2EHPA) is low. However, when ethylenediaminetetraacetic acid (EDTA) complexing agent is present, the efficiency of molybdenum extraction is significantly increased. In this paper the effect of various factors (including the D2EHPA and EDTA concentration, pH of the feed solution, contact time, phase ratio) on molybdenum extraction has been studied. The effect of the composition of the strip solution on stripping molybdenum from the organic phase is reported. Counter-current extraction has also been investigated. The results of multiple-stage extraction show that molybdenum can be satisfactorily separated from sodium tungstate solution obtained by leaching tungsten ore, with little loss of tungsten. A possible mechanism of the extraction of molybdenum in the presence of EDTA is discussed. The reaction for extracting molybdenum is:

     

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.     

Liquid scintillation counting as a means of measuring uranium leached from low-grade ores by Thiobacillus ferrooxidans

Studies of U₃O₈ leaching by Thiobacillus ferrooxidans in pulverized uranium ore samples usually involve fluorimetry or X-ray fluorescence to determine the concentration of U₃O₈. As these analyses could not be performed routinely in our laboratory, we sought an alternative means of estimating the U₃O₈ generated in our leach experiments. Initial experiments indicated that liquid scintillation counting could be used to measure U₃O₈, for a given batch of pulverized ore, in conjunction with a standard curve relating counts per minute to U₃O₈ concentration measured fluorimetrically or by X-ray fluorescence. This relationship (U₃O₈ concentration vs. counts per minute) was shown to be true for a number of pulverized ore samples of different uranium grades. Moreover, the results indicated that a single standard curve consisting of the data from all of the different ores could be used, in spite of the ores containing different proportions of uranium and other radioactive emitters. An examination of a linear and two non-linear regression models showed that a power function gave the best fit to the data.     

Recovery of copper from chalcocite by means of the pyridine and chloride ion donor systems

Recovery of copper from natural chalcocite by means of pyridine—hydrochloric acid mixtures and pyridine solutions of pyridine hydrochloride is described. The systems were found to be effective media for leaching of chalcocite. Total copper recovery is reached after 15 minutes at 60°C.     

Arachidonic acid release from diacyl phosphatidylethanolamine by human platelet membranes

Sixty-one full-term, appropriate-weight black newborns had higher heart rates, replicating a racial heart rate difference, but did not differ significantly in systolic blood pressure from 71 white newborns. Systolic blood pressure in the newborn is related both to the total number of feedings from birth and to the total fluid intake.     

The extraction of iron(III) from aqueous acid solutions by di(2-ethylhexyl)phosphoric acid

The extraction of iron(III) from aqueous solutions containing sulphuric, hydrochloric and nitric acids by di(2-ethylhexyl)phosphoric acid (DEHPA) in kerosene has been investigated under different conditions. As a result, it is found that although extraction is dominated by an ion-exchange reaction, the rate of iron(III) extraction from sulphuric acid solutions to reach equilibrium is relatively slow in comparison with that from hydrochloric or nitric acid solutions. In the extraction from aqueous solutions containing hydrochloric or nitric acid, however, the DEHPA combines with iron(III) according to the solvating reaction at higher aqueous acidity. From studies on the rate of the extraction from sulphuric acid solutions, examined under non-equilibrium, it is confirmed that dependencies of extraction rate on hydrogen ion and DEHPA concentrations are in the first and inverse first orders, respectively. The hydrolyzed species is considered to interpret the extraction mechanism in this system.     

液膜萃取法回收废胶体钯活化液中的钯

传统钯回收方法存在成本高、分离效率低,适合高含量钯回收等问题,试验采用液膜萃取法回收废胶体钯活化液中的钯,并考察了内相试剂用量、流动载体用量、表面活性剂用量、油内比、乳水比、外相酸碱度等因素对钯萃取率的影响.结果表明:以9％N503、4％Span80、2％液体石蜡、85％磺化煤油组成膜相,内相试剂EDTA溶液浓度为0....     

从硫酸烧渣中回收铅的试验研究

进行了H2SO4+NaCI溶液浸出低品位硫酸烧渣回收铅的试验研究.考察了氯盐浓度、酸度、液固比对铅漫出率的影响.在氯盐浓度300g/L、[H+]=1mol/L、液固比5:1的条件下,铅的浸出率迭97.28%.以CaO调节漫出后液pH值为9,沉淀中铅的品位达到60%.     

Solvent extraction of uranium(VI) from industrial and analytical grade phosphoric acid using organic extractants in kerosene with variable content of aromatic hydrocarbons

The distribution ratio of U(VI) between phosphoric acid, industrial and analytical grade, and kerosene solutions of D2EHPA-TOPO extractants with variable amount of aromatic hydrocarbons has been studied. Under these conditions it was observed that the content of aromatic hydrocarbons in the diluent as well as other ions present in industrial phosphoric acid play a significant role in the extraction of uranium(VI).