Preparation of Nd(III) carbonate by precipitation stripping of Nd(III)-loaded VA10

The preparation of fine particles of Nd(III) carbonate from kerosene solution, from which Nd(III) was extracted with versatic acid 10 (VA10) by a precipitation stripping technique using an aqueous NH₃-(NH₄)₂CO₃ solution as stripping medium, was studied. In preliminary experiments, we were unable to recover simple Nd(III) carbonate from Nd(III)-loaded VA10 by CO₂ gas bubbling, when water, (NH₄)₂CO₃, NH₄HCO₃, NaHCO₃, or NA₂CO₃ solution saturated with CO₂ was used as the stripping solution. To obtain simple Nd(III) carbonate, it is necessary to use more than the stoichiometric amount of NH₃ compared to VA10 and about 10 times as much (NH₄)₂CO₃ as Nd(III). The solution mixture of NH₃-(NH₄)₂)CO₃ acts as a pH buffer, an adductor for VA10, and a CO ₃ ²⁻ ion source. Although it was concluded that the precipitates are Nd₂(CO₃)₃·xH₂O (x⊧4), their X-ray pattern does not coincide with that quoted by JCPDS. By heating these precipitates, cubic Nd₂O₃ was obtained at 823 K, while, at 973 K, hexagonal Nd₂O₃ was formed. Since the stripping solution consisting of NH₃-(NH₄)₂CO₃ was highly alkaline, VA10 was also stripped in the aqueous phase. To use a closed-circuit system for the precipitation stripping of Nd(III) carbonate from Nd(III)-loaded VA10, it is important to regenerate VA10 in the organic phase. For this purpose, evaporation of NH₃ by air bubbling was studied. By bubbling air into a stripping solution warmed at 333 K, almost all the VA10 can be transferred to the organic phase.     

Recovery of Al(III) and Fe(III) from mixed chloride solutions containing platinum(IV)

The sorption of Fe(III), Al(III) and Pt(IV) from the individual and mixed chloride solution was investigated by using PC88A resin. With the increase of HCl concentration to 5 M, the distribution coefficient of Fe decreased slowly, while that of Al decreased rapidly and the distribution coefficient of Pt was nearly zero in our experimental range. Batch experiments showed that it was possible to extract both Fe and Al simultaneously by adjusting HCl and PC88A resin concentrations. However, continuous extraction chromatographic experiments indicated that simultaneous sorption of Al as well as Fe was difficult in our experimental range. Two extraction chromatographic steps would extract most of Fe and 90% of Al from the mixed solution, while Pt was not extracted. Extraction chromatography of the mixed chloride solution with PC88A resin was found to be fast and simple.     

Leaching of Cu2O with aqueous solution of sulfur dioxide

Leaching of Cu₂O with aqueous SO₂ solution is significant, since during the dissolution process, precipitation of copper as Chevreul’s salt also takes place under appropriate conditions. The dissolution is controlled by surface reactions and proceeds through both aqueous SO₂ and acid dissolution paths. An overall rate equation based on the above premise has been found to agree well with the experimental data. At pH values higher than 1.8, precipitation of copper as Chevreul’s salt takes place after about 10 minutes of leaching. The extent of the precipitation depends upon the pH, SO₂ concentration, initial Cu²⁺ concentration, and sulfate concentration in the leaching solution.     

The coprecipitation behavior of Co(II) and Ni(II) with Fe(III), Cr(III) and Al(III) from aqueous ammoniacal solutions

The coprecipitation of cobalt(II) and nickel(II) with iron(III), chromium(III) and aluminum(III) from ammoniacal solutions has been investigated. The coprecipitation behavior was found to be very sensitive to the solution pH and total ammonia concentration. Co(II) and Ni(II) can be precipitated from low ammonia concentration solutions but are readily redissolved at higher ammonia concentrations. The coprecipitate of divalent and trivalent species was found to contain very large amounts of the divalent metals (up to a mole ratio M M(II)/M(III) of 2.5) when aluminum was the trivalent species, whereas with iron(III) or chromium(III), the ratio was only 0.5.     

Reduction of arsenic acid with aqueous sulfur dioxide

The reduction of arsenic acid with aqueous sulfur dioxide in sulfuric acid solutions is presented. First order kinetics with respect to arsenic acid and sulfur dioxide concentrations are observed. Appreciable reduction occurs only when tetravalent sulfur is present as sulfur dioxide. The protonation of arsenic acid in strong sulfuric acid solutions decreases the rate of pentavalent arsenic reduction.     

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.     

Separation of praseodymium(III) from aqueous solutions by nanofiltration

Abstract

The increased demand for rare earth elements in commercial products is increasing their production, which in turn increases public exposure to rare earth elements. The objective of the present work is to study the separation of praseodymium from aqueous solutions by a commercial nanofiltration membrane (NF-300) at various operating conditions. The permeate and feed samples were analysed with inductively coupled plasma atomic emission spectrometry (ICPAES) to find praseodymium [Pr(III)] concentration. The results indicated that the separation of Pr(III) ions increased with increase in applied pressure (2–10 bar) and cross flowrate (4–16 L min^?1); and decreased with increase in feed concentration (10 mg L^?1 PrCl₃ – 100 mg L^?1 PrCl₃). The highest observed separation of the Pr(III) was found to be 89·07 and 84·20% for an initial feed concentration of 10 and 100 mg L^?1 PrCl₃ respectively. It was also observed that separation of Pr(III) increases to 99·28 and 99·30% in complexation step by using ethylene diamine tetra aceticacid (EDTA) and diethylene triamine penta aceticacid (DTPA) respectively, as the chelating agent has generally influenced by pH (2 –10).

La demande accrue d’éléments de terres rares dans les produits commerciaux augmente leur production, ce qui, à son tour, augmente l’exposition du public aux éléments de terres rares. Le but de ce travail est d’étudier la séparation du praséodyme à partir de solutions aqueuses au moyen d’une membrane commerciale de nanofiltration (NF-300) sous diverses conditions d’utilisation. On a analysé les échantillons de perméat et d’apport au moyen de la spectroscopie d’émission atomique avec plasma induit par haute fréquence (ICPAES) afin de déterminer la concentration du praséodyme [Pr(111)]. Les résultats indiquaient que la séparation d’ions de Pr(111) augmentait avec une augmentation de la pression appliquée (2–10 bar) et de la vitesse de l’écoulement transversal (4–16 L min^?1) et diminuait avec une augmentation de la concentration de l’apport (10 mg L^?1 PrCl₃ – 100 mg L^?1 PrCl₃). On a trouvé que la valeur la plus élevée de séparation observée pour le Pr(111) était de 89·07 ou de 84·20% pour une concentration initiale de l’apport de 10 ou de 100 mg L^?1 de PrCl₃, respectivement. On a également observé que la séparation du Pr(111) augmentait jusqu’à 99·28 ou 99·30% dans une étape de complexation en utilisant de l’acide éthylènediaminetétracétique (EDTA) ou de l’acide diéthylènetriamino-pentaacétique (DTPA), respectivement, comme agent chélateur, influencé généralement par le pH (2–10).     

The extraction of Fe(III) from ammonium chloride solutions with capric acid

Extraction equilibria in the FeCl₃NH₄Clcapric acidCCl₄ system were investigated. Using slope analysis the results were interpreted in terms of the formation of the binuclear species [Fe(OH)R₂]₂ and [Fe(OH)₂R·HR]₂ in the organic phase. From calculations of the complex formation function and the experimental data it was shown that the effect of Fe(III) hydrolysis in the aqueous phase on metal extraction may be neglected.     

Stability of chromium (III) sulfate in atmospheres containing oxygen and sulfur

The stability of chromium (III) sulfate in the temperature range from 880 to 1040 K was determined by employing a dynamic gas-solid equilibration technique. The solid chromium sulfate was equilibrated in a gas stream of controlled SO₃ potential. Thermogravimetric and differential thermal analyses were used to follow the decomposition of chromium sulfate. Over the temperature range studied, the change in the Gibbs’ free energy of formation of chromium sulfate Cr₂O₃(s) + 3SO₃(g) → Cr₂(SO₄)₃(s) can be expressed as ΔG⁰ = •143,078 + 129.6T (±300) cal mole^•1 ΔG⁰ = •598,350 + 542T (±1250) J mole^•1. X-ray diffraction analysis indicated that the decomposition product was crystalline Cr₂O₃ and that the mutual solubility between Cr₂(SO₄)₃ and Cr₂O₃ was negligible. Over the temperature range investigated, the decomposition pressures were significantly high so that chromium sulfate is not expected to form on commercial alloys containing chromium when exposed to gaseous environments containing oxygen and sulfur (such as those encountered in coal gasification).     

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.     

Removal of SO2 with oxygen in the presence of Fe(III)

A laboratory study of the aqueous oxidation of SO₂ in the presence of Fe(III) and Fe(II) has been conducted. The SO₂ concentration was 3930 ppm (3.93 × 10⁻³ atm or 398 Pa) in a gas stream with nitrogen and oxygen. The oxygen pressure was varied from 0 to 0.203 atmosphere. The initial concentration of Fe(III) ranged from 10⁻³ to 5-10⁻³ molar while that of Fe(II) was 5 × 10⁻³ molar. The temperatures were 298, 309.2, and 317.5 K. The solution pH was 1.83. The oxidation of SO₂ is intensive and yields from 90 to 97 pct recovery of incoming SO₂ when 5 × 10⁻³ molar Fe(III) and an oxygen pressure above 0.057 atmosphere are applied at 298 K. The reaction mechanism has been explained by determining the rate constants of the oxidation reactions from a kinetic model. The rate constants show that SO₂ is mostly oxidized by oxygen through formation of ferric-sulfite complex and that regeneration of ferric ion is possible under a normal oxygen pressure. The activation energy of the oxidation has been determined and has been found to be 13.5 Kcal/mole.     

Adsorption of erbium(III) on D113-III resin from aqueous solutions: batch and column studies

The adsorption and desorption behaviors of Er(III) ion on D113-III resin were investigated. Batch adsorption studies were carried out with various Er(III) ion concentrations, pH, contact time and temperature, indicating that D113-III resin could adsorb Er(III) ion effectively from aqueous solution. The loading of Er(III) ion onto D113-III resin increased with increasing the initial concentration. The adsorption was strongly dependent on pH of the medium with enhanced adsorption as the pH turned from 3.45 to 6.75. In the batch system, the D113-III resin exhibited the highest Er(III) ion uptake as 250 mg/g at 298 K, at an initial pH value of 6.04, calculated from the Langmuir isotherm model. The adsorption kinetics was in agreement with Lagergren-first-order kinetics among the Lagergren-first-order model, pseudo-second-order model, liquid film diffusion model and intraparticle diffusion model. The adsorption data gave good fits with Langmuir isotherms. The thermodynamic parameters such as ΔG, which were all negative, indicated that the adsorption of Er(III) ion onto D113-III resin was spontaneous and the positive value of ΔH showed that the adsorption was endothermic in nature. Thomas model was applied to experimental column data to determine the characteristic parameters of column useful for process design. Er(III) ion could be eluted by using the 4.0 mol/L HCl solution. The characterization of both before and after adsorption of Er(III) ion on D113-III resin was undertaken with IR spectroscopic technique. Moreover, the surface characterization of D113-III resin was described by scanning electron micrographs (SEM).     

Precipitation of nanosized titanium dioxide from aqueous titanium(IV) chloride solutions by neutralization with MgO

Aqueous titanium (IV) chloride solutions were neutralized to different terminal pH (2.5 to 6.0) with magnesium oxide as base at 95 °C and were found to yield nanosized titanium dioxide. The produced materials were compared to those obtained by simple forced hydrolysis. The techniques of XRD, TGA–DTA, FT-IR, BET, SEM and TEM were applied for the characterization of the produced materials. Honeycomb-shaped uniform nanosized crystalline TiO₂ powders with aggregate particle size of about 50 nm were successfully obtained by neutralization with magnesium oxide. Phase-pure rutile or mixed rutile and anatase crystalline TiO₂ powders were precipitated with proper selection of conditions. It was found that forced hydrolysis at 95 °C favors the formation of rutile TiO₂. Rutile TiO₂ powders with different crystallite sizes between 11 and 18 nm were obtained from aqueous TiCl₄ solutions with Ti concentration ranging from 0.5 mol/L to 2.0 mol/L. Neutralization with MgO at 95 °C, on the other hand, favored the formation of mixed anatase and rutile materials. The anatase fraction (ranging from 0 to 70%) increased with pH elevation (from 2.5 to 6.0). The neutralization method yielded much higher titanium precipitation efficiency (up to 100%) than simple forced hydrolysis. The magnesium content in the TiO₂ products was found to increase with a rise in the final pH due to partial hydrolysis of magnesium. It was less than 0.1% when the final pH was kept at or below 3.3.     

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.     

Mixed solvent systems for the extraction and stripping of iron(III) from concentrated acid chloride solutions

The extraction of concentrated iron(III) from acid chloride solutions has been investigated with methyl isobutyl ketone (MIBK), tri-n-butyl phosphate (TBP), di(2-ethylhexyl) phosphoric acid (D2EHPA), and their mixtures in various proportions, at different acid concentrations. On comparing the extraction of iron(III) with mixed and individual extractant, it was found that both D2EHPA-MIBK and D2EHPA-TBP mixtures exhibit synergism, the latter having better extraction ability. The synergistic coefficients, at different initial acid concentrations for each mixed extractant system, were evaluated and compared. An increase in the concentration of MIBK and TBP in the mixed organic resulted in higher synergistic coefficient. The stripping of iron(III) from loaded D2EHPA was found to increase with the strip feed acid concentration, while from loaded organic mixtures, it initially increased and then decreased. Stripping of iron(III) from D2EHPA-MIBK loaded solvent is better then D2EHPA-TBP. The extracted iron species formed and the stripping reactions have been proposed. Ultraviolet visible spectra of the stripped organic phase support the result and the proposed mechanisms.     

Rates of extraction of cobalt from an aqueous solution to D2EHPA in a growing drop cell

A technique has been developed to study the rate of extraction of cobalt from an aqueous phase into a growing drop of heptane containing di(2-ethylhexyl) phosphoric acid (D2EHPA). The hydrodynamics of the growing drop are accounted for. Experiments have been carried out at the single temperature of 25 ± 0.1°C Sphere the pH, aqueous cobalt concentration and the organic D2EHPA concentration have been varied. A mathematical model is given which is based upon the control of rate by mass transfer with chemical reaction. The model fits the experimental data well considering the experimental errors and the complexity of the transfer of solute where fresh surfaces are continually produced by the growing drop.     

Preparation of ammonium chloroplatinate by a precipitation stripping of Pt(IV)-loaded alamine 336 or TBP

The possibility of preparing ammonium chloroplatinate powders by precipitation stripping from Pt-loaded Alamine 336 or TBP was investigated experimentally. A similar examination was done for the precipitation stripping of Pd(II). Furthermore, the possible separation of Pt(IV) from Alamine 336, loaded with both Pt(IV) and Pd(II), was studied. Precipitation stripping of (NH₄)₂PtCl₆ from Pt(IV)-loaded Alamine 336 was possible using an aqueous NH₃ solution and aqueous mixed solutions of NH₃-NH₄Cl or NH₄Cl-HClO₄. It was found that the use of 0.2 kmol m⁻³ HClO₄-2 kmol m⁻³ NH₄Cl as a stripping solution was most effective. The precipitation of (NH₄)₂PtCl₆ from Pt(IV)-loaded TBP was almost completely achieved using an aqueous NH₃ solution concentrated above 2 kmol m⁻³. Pt(IV) can be efficiently separated as (NH₄)₂PtCl₆ precipitates from both Pt(IV) and Pd(II)-loaded Alamine 336, using 0.2 kmol m⁻³ HClO₄-4 k mol m⁻³ NH₄Cl, with soluble Pd(II) remaining in both the aqueous and organic phases.     

Extraction of Fe(III) from hydrochloric acid solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921)

Ferric ions were efficiently removed from HCl solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921). Iron was removed under the form HFeCl₄ through direct binding on the resin or by extraction with Cyanex 921 involving a solvation mechanism. High concentrations of HCl and intermediary extractant loadings were required for maximum sorption efficiency and rationale use of the extractant. At intermediary extractant loading (in the range 300–450 mg Cyanex 921 g^− 1) the maximum sorption capacity increased with extractant loading. Maximum sorption capacity slightly increased with temperature, the reaction is endothermic and the enthalpy change was found close to − 30.8 kJ mol^− 1. Sorption isotherms were fitted with the Langmuir equation and maximum sorption capacity reached values as high as 20–22 mg Fe g^− 1 in 3 M HCl solutions. Despite the good fit of experimental data with the pseudo second-order rate equation, sorption kinetics was controlled by the resistance to intraparticle diffusion. The intraparticle diffusion coefficient (D_e) varying in the range 1.2 × 10^− 11–4.7 × 10^− 10 m² min^− 1 was found to increase with metal concentration and with temperature, while varying the extractant loading it reached a maximum at a loading close to 453 mg Cyanex 921 g^− 1. The desorption of Fe(III) can be achieved using 0.1 M solutions of nitric acid, sulfuric acid, sodium sulfate and even water, maintaining high efficiencies for sorption and desorption for at least 5 cycles.     

Efficient extraction and stripping of Nd(III), Eu(III) and Er(III) by membrane dispersion micro-extractors

The extraction of low concentration rare earth elements at high phase ratio was investigated. The traditional extraction set-up, such as mixer-settler, have drawbacks of easy emulsification, difficult separation and low efficiency if operated at the above condition. Membrane dispersion micro-extractor, owing to its well-dispersed, high surface-to-volume ratio and fast mass transfer rate, was employed in our work. Nd(III), Eu(III), Er(III) were chosen to represent light, medium, heavy rare earth elements (REEs). The extraction process of REEs with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) was investigated by membrane dispersion micro-extractors. Firstly, the extraction equilibrium of these three elements was explored in the stirred conical flasks, and it is indicated that the extraction efficiencies can be 0.95, 0.97 and 0.98, respectively within 40 min at phase ratio of 100:1. Then the effects of operational conditions such as the residence time, organic and aqueous flow rates on extraction efficiency were also explored in micro-extractors. The results indicate that the efficiency decreases and then increases if increasing aqueous phase flow rate, residence time and droplets' diameter are the key factors of this process. Increasing the phase ratio reduces the extraction efficiency significantly. When the REEs solution has an initial pH of 4.00, the flow rates of continuous and dispersed phase are 40 and 1.6 mL/min, respectively, and 90 mg/L Nd (III), Eu(III) and Er(III) is extracted by 1 mol/L P507 at the out-let length of 8 m. The extraction efficiencies are 0.978, 0.983 and 0.991, respectively. Finally the stripping process was also studied with the micro-extractor. The stripping efficiencies of Nd(III), Eu(III) and Er(III) can reach 0.99, 0.96 and 0.91, respectively when the out-let length is 8 m and the concentration of hydrochloric acid is 1 mol/L. The developed approach offers a novel and simple strategy on the fast extraction and enrichment of low concentration rare earth elements from waste water.