Extraction Of Cerium Research Articles

Selective extraction and preconcentration of cerium(IV) in water samples by cloud point extraction and determination by inductively coupled plasma optical emission spectrometry

Cloud point extraction (CPE) was used for the selective extraction and separation of cerium(IV) from aqueous solutions. The method is based on the formation of cerium(IV)-n-p-tolylbenzohydroxamic acid (n-TBHA) complex that is extracted into the micellar phase (Triton X-114) at a temperature above the cloud point temperature (CPT). After phase separation, the surfactant rich phase was diluted up to 1.0 mL and determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). Under the optimum extraction conditions and instrument parameters, by preconcentration of only 10.0 mL of sample in the presence of 0.09% Triton X-114, an enhancement factor of 13.8 was obtained. The analytical curve was linear in the range of 1.5–1200 µg L−1 and the detection limit was 0.4 µg L−1. The method was applied to the determination of Ce(IV) in water samples with satisfactory results.

Leaching Process of Cerium Extraction from Mixture of Cerite-Monazite Mineral

Rare earth oxides have been widely investigated in catalysis as structured and electronic promoters to improve the activity and thermal stability of catalysts. Cerium has an important role in three-way catalysis and fluid catalytic cracking, two significant catalytic processes by their economic relevance and tonnage. Cerium and other rare earths have been studied as possible heterogeneous catalysts at selective oxidation of hydrocarbons. Cerite and monazite are minerals with high concentration of cerium element. Extraction of cerium metal using conventional leaching processes has shown low yields or high costs. The main purpose of this research work is to optimize the parameters in cerium purification stage from this mineral using leaching process. To separate particles with different granulometries, the mineral is ground and fractioned with sieves of 80, 200, 250 and 400 mesh. In order to put off organic components and oxidize cerium(III) to cerium(IV), samples were roasted at 1073K by twenty-four hours. The roasted samples were solubilized by acid attack (leaching) for approximately twenty-four hours; according to the acid used hydrochloric or sulfuric), cerium and other trivalent elements are solubilized as chloride or sulfate solution. Cerium was extracted by selective precipitation at pH~3,4 using ammonium or natrium hydroxide as pH changer. After filtration and drying, the precipitated product was characterized by XRD (x-ray diffraction), and then process efficiency was determined (cerium percentage and the different phases in the powder). Particles granulometry, roasting process (time and temperature), as well as leaching parameters (acid used, time, temperature and concentration of reagents) were the main variables studied.

Kinetics of Cerium(IV) Extraction with DEHEHP From HNO3‐HF Medium Using a Constant Interfacial Cell with Laminar Flow

Studies of the extraction kinetics of cerium(IV) into n‐heptane solutions of di(2‐ethylhexyl)‐2‐ethylhexyl phosphonate DEHEHP from HNO3‐HF solutions have been carried out using a constant interfacial cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo‐first order constants. The effects of the stirring rate, specific interfacial area, and temperature on the extraction rate showed that the most probable reaction zone is in the aqueous homogeneous phase. The results were compared with those of the system without HF. It was concluded that the presence of HF decreases the extraction rate of cerium. The addition of HF increases the activation energy for the forward reaction from 21.2 to 55.3 kJ/mol and for the reverse process from 57.9 to 79.0 kJ/mol. According to the experimental data correlated as a function of the concentration of the relevant species involved in the extraction reaction, the corresponding rate equation was deduced as follows: The kinetic mechanism of the extraction process was proposed taking an aqueous chemical reaction as the rate‐determining step of the overall reaction.

Interfacial behavior of DEHEHP and the kinetics of cerium(IV) extraction in nitrate media

The effects of diluents, temperature, acidity, and ionic strength of the aqueous phase on the interfacial properties of DEHEHP have been extensively investigated using the Du Nouy ring method. In addition, the effect of cerium(IV) concentration loaded in the organic phase on the interfacial tension has also been studied. With the increase of DEHEHP concentration, the value of interfacial tension ( γ) decreases in the studied system, which shows that DEHEHP has interfacial activity as a kind of surfactant. The surface excess at the saturated interface ( Γ max ) and the minimum bulk concentration of the extractant necessary to saturate the interface ( C min ) under the different conditions are calculated according to two adsorption equations such as the Gibbs and Szyszkowski functions to be presented in comprehensive tables and figures. The relationship between the interfacial activity of DEHEHP and cerium(IV) extraction kinetics by DEHEHP has been discussed by considering different factors such as the effects of diluents and temperature. However, the interfacial activity parameter of extractant only is a qualitative parameter, but cannot provide strong enough evidence to quantitatively explain the relationship between extraction kinetics and interfacial properties of an extractant.

Coordination Reactions in the Extraction of Cerium(IV) and Fluorine(I) by DEHEHP from Mixed Nitric Acid and Hydrofluoric Acid Solutions

The coordination reactions during the solvent extraction of cerium(IV) and fluorine(I) from mixed nitric acid and hydrofluoric acid solutions by di‐(2‐ethylhexyl)‐2‐ethylhexylphosphonate, L (DEHEHP) in heptane have been investigated. The extraction data have been analyzed by graphical methods taking into account all plausible species extracted into the organic phase. Different variables influencing the extraction of Ce(IV), such as the concentrations of nitrate ions, hydrofluroric acid, nitric acid, and extractant have been studied. The results demonstrate that DEHEHP can extract not only Ce(NO3)4 as Ce(NO3)4 · 2L and HF as HF · H2O · L, but both together as Ce(HF)(NO3)4 · L. The extraction equilibrium equations are determined according to slope analysis and IR spectra. The equilibrium constants of the extracted complexes have been calculated, taking into account complexation between the metal ion and inorganic ligands in the aqueous phase and all plausible complexes extracted into the organic phase. It is also shown that boric acid, which was added into the mixed solutions to complex with F(I) is not extracted by DEHEHP, and neither does it affect the extraction of cerium(IV) and HF, nor change the extraction mechanism. Finally, the work points out the basis of separating Ce(IV) and recovering F(I) from nitric acid leach liquors of bastnasite.

Liquid–Liquid Extraction of Cerium(IV) from Nitric Acid Media by Di‐(2‐Ethylhexyl) 2‐Ethylhexyl Phosphonate (DEHEHP)

In this paper, the extraction of Ce(IV) from nitric acid solutions is investigated using di‐(2‐ethylhexyl) 2‐ethylhexyl phosphonate (DEHEHP, B) in heptane as extractant. Ce(IV) can be extracted effectively from nitric acid solution, whereas it is poorly extracted from sulfuric acid solution. Compared with some other organophosphorus esters, DEHEHP has moderate extractablity for Ce(IV). The extraction efficiency varies with diluent in the order: aliphatic hydrocarbons > nitrobenzene > aromatic hydrocarbons > carbon tetrachloride > chloroform. Regeneration and loading capacities of DEHEHP have also been examined. Ce(IV) extraction in HNO3 solutions as well as extraction of HNO3 and H2O have been systematically studied. The Ce(IV) extraction increases with an increasing of HNO3 concentration and exhibits the maximum distribution ratio at 1–1.5 mol/L HNO3. Nitric acid, as a source of nitrate ion, enhances the extraction of metal ion. But it also competes with metal ions for extractant molecules by its own extraction under high acidities. The proposed extraction process is described by the following equilibrium equations: The extraction equilibrium constants and infrared spectroscopies of extracted complexes are determined. The extraction thermodynamic parameters are also calculated and the extraction reaction is found to be exothermic. The extracted species are estimated to be HNO3 · H2O · B(o) and Ce(NO3)4 · 2B(o), and then DEHEHP molecule seems to behave as a monodentate ligand while NO3 − ion as a bidentate ligand. In consequence, it is presumed that DEHEHP can be used as a potential extractant for separating Ce(IV) from nitric acid leach liquors of bastnasite.

Liquid–Liquid Extraction, Separation, Preconcentration, and ICP‐AES Determination of Lanthanum and Cerium with N‐Phenyl‐(1,2‐methanofullerene C60)61‐formohydroxamic Acid

A novel method for liquid–liquid extraction, separation, preconcentration, and simultaneous trace determination of cerium(IV) and lanthanum(III) with N‐phenyl‐(1,2‐methanofullerene C60)61‐formohydroxamic acid (PMFFA) is reported. Lanthanum and cerium are extracted at pH 8.5 and 9.5, respectively in chloroform and recovered from monazite sands in the presence of thorium, uranium, and large number of cations and anions in high purity (99.98%). The extraction mechanism is investigated. The influence of PMFFA, pH, diverse ions, and temperature on the distribution constants of lanthanum and cerium was examined. The overall stability constants (log β2 K e) and extraction constants (K ex) for lanthanum(III) are 22.50 and 5.0 × 10−9, respectively and for cerium(IV) are 21.51 and 3.9 × 10−9, respectively. Lanthanum(III) gives a colourless complex with PMFFA which is extracted into chloroform having molar absorptivity 5.5 × 104 L mol−1 cm−1 at 395 nm, and Beer's law 0.12–2.52 µg mL−1, while cerium(IV) forms a red coloured complex, λmax 460 nm, molar absorptivity 1.5 × 104 L mol−1 cm−1, and Beer's law 0.46–9.26 µg mL−1. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry ICP‐AES measurements of lanthanum and cerium which increases the sensitivity 60 folds and obey Beer's law in the range, 2.1–37.5 ng mL−1 for lanthanum and 9.2–186.4 ng mL−1 for cerium. The method is applied for the determination of lanthanum and cerium in real and standard samples, sea water, and environmental samples.

Thermodynamics of cerium(III) extraction with naphthenic acids

Cerium(III) extraction from dilute aqueous solutions with naphthenic acids in decane was studied. The dependence of the distribution ratio on the pH of the equilibrium aqueous phase was determined, and the extraction equilibrium constant and Gibbs energy were calculated.

Thermodynamic study of extraction of cerium(III) and yttrium(III) with tributyl phosphate

To increase the efficiency of hydrometallurgical processing of lean rare-earth raw material, the effect of salt anion and metal cation on the characteristics of Ce(III) and Y(III) recovery from dilute aqueous solutions with tri-n-butyl phosphate was studied on the basis of the thermodynamic theory of extraction.

Extraction and separation of cerium(IV) from nitric acid solutions containing thorium(IV) and rare earths(III) by DEHEHP

The extraction behaviour of Ce(IV), Th(IV) and part of RE(III), viz., La, Ce, Nd and Yb, has been investigated using di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP,B) in heptane as an extractant. Results show that extractability varies in the order: Ce(IV)>Th(IV)⪢RE(III). Therefore, it is possible to find the appropriate conditions under which Ce(IV) can be effectively separated from Th(IV) and RE(III). Furthermore, stripping Ce(IV) from the loaded organic phase can be carried out by dilute H 2SO 4 with an aliquot of H 2O 2. Roasted bastnasite made in Baotou (China) by Na 2CO 3 and leached by HNO 3, there is about 50% Ce mainly as tetravalent nitrate along with other RE(III) and Th(IV) in the leachings. Through fractional extraction, taking nitric acid leachings of roasted Bastnasite as feed and DEHEHP as an extractant, we can obtain the CeO 2 products with high purity of 99.9–99.99%, with a yield of >85%, in which ThO 2/CeO 2<10 −4.

Thermodynamic Analysis of Cerium(III) Extraction from Sulfate Solutions with Salts of Quaternary Ammonium Bases

Cerium(III) distribution between an aqueous sulfate solution and a solution of trialkylbenzylammonium sulfate in xylene was studied. The Ce(III) distribution coefficient grows with increasing pH. The extraction is provided by the formation of cerium mono- and disulfate complexes in the aqueous phase. Schemes of extraction equilibria are proposed and Gibbs energies and equilibrium constants are found.

Kinetics of Cerium(IV) Extraction from H 2SO 4–HF Medium with Cyanex 923

Studies of the extraction kinetics of cerium(IV) from H 2SO 4–HF solutions with Cyanex 923 in n-heptane have been carried out using a constant interfacial area cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The results were compared with those of the system without HF. It was concluded that the addition of HF reduces the activation energy for the forward rate from 46.2 to 36.5 kJ mol −1 while it has an opposite effect on the activation energy for the reverse process(the activation energy increased from 23.3 to 90.8 kJ mol −1). Thus, HF can accelerate the rate of cerium(IV) extraction. At the same time, the extraction rate is controlled by a mixed chemical reaction–diffusion rather than by a chemical reaction alone. A rate equation has also been obtained.

SOLVENT EXTRACTION OF CERIUM(IV) AND FLUORINE(I) FROM SULPHURIC ACID LEACHING OF BASTNASITE BY CYANEX 923

The solvent extraction of cerium(IV) and fluorine(I) from simulated sulphuric acid leaching of bastnasite by Cyanex 923 was studied. The results showed that Cyanex 923 can extract not only Ce(IV) as Ce(HSO4)2 (SO4) · 2(Cyanex 923) and F(I) as HF · (Cyanex 923) respectively but them together. The extraction mechanism of Ce(IV) together with F(I) can be related to the formation of Ce(HF)(HSO4)2 (SO4) · 2(Cyanex 923). It was also showed that boric acid in the leaching liquor which was added to chelate F(I) wasn't extracted alone by Cyanex 923 and didn't influence the Cerium(IV) extraction. Boric acid can enhance the extraction of HF and came into organic phase in form of (HF)(H3BO3) · (Cyanex 923). Hydrofluoric acid was extracted from the bastnasite leaching mainly together with Ce(IV). The results also showed that temperature didn't affect the extraction process. IR spectra of purified Cyanex 923 saturated with Ce(IV), HF and H3BO3 were discussed.

LIQUID -LIQUID EXTRACTION OF CERIUM (in) SALICYLATE WITH TRIS (2-ETHYLHEXYL) PHOSPHATE AND TRIBUTYLPHOSPHINE OXTDE

ABSTRACT Tris (2-ethylhexyl) phosphate (TEHP) and Tributylphosphine oxide (TBPO) are proposed as extractants for the solvent extraction of cerium (III) from salicylate media. A critical study of various experimental parameters such as pH, sodium salicylate concentration, TEHP and TBPO concentration and period of equilibration showed that TBPO is a better extractant, due to its higher basicity. Cerium (III) from organic phase is stripped with distilled water and determined by Arsenazo III. The extraction of cerium (III) with both extractants occurs by solvation mechanism and the extractant dependencies of the extractions suggests that the extracted species are solvated metal salicylate salts, Ce (HSal)3. 3TEHP and Ce (HSal)3. 2TBPO respectively. The method permits separation and determination of cerium from binary and synthetic mixtures of commonly associated elements.

The Solvent Extraction of Cerium from Sulphate Solutions - Mini-Plant Trials

The Solvent Extraction of Cerium from Sulphate Solutions - Mini-Plant Trials

The Recovery of a Mixed Rare-Earth Oxide and the Preparation of Cerium, Europium and Neodymium Oxides from a South African Phosphoric Acid Sludge by Solvent Extraction

A novel process based largely on solvent-extraction methods has been developed for the recovery of rare-earth oxides from waste calcium sulphate sludges obtained during the manufacture of phosphoric acid from a South African apatite ore. A mixed rare-earth oxide (90-98% purity) was first recovered from calcium nitrate leach liquors by extraction with TBP or DBBP, after which it was dissolved in nitric acid to enable pure cerium dioxide (99.98%) to be prepared by selective extraction of cerium(IV) nitrate into TBP. The heavy (yttrium), middle, and light rare-earth fractions were then separated by sequential extraction into D2EHPA at controlled pH values. Pure europium oxide (99.98%) was isolated from the middle fraction by reductive precipitation of europim(II) sulphate, followed by conversion to soluble europium(II) chloride and removal of trivalent rare-earth impurities by extraction with D2EHPA or Versatic 10 acid. Finally, magnet-grade neodymium oxide (95-96%) was obtained from the light rare-earth fraction by extraction of the contained lanthanum, cerium and praseodymium into Aliquat 336 nitrate.

Polymerization and Adduct Formation of Some Lanthanide(III) Decanoates in the Extraction of Lanthanides(III) with Decanoic Acid Using 1-Octanol and Benzene as a Solvent.

The solvent extraction of lanthanum(III), cerium(III), neodymium(III), samarium(III), gadolinium(III), dysprosium(III), erbium(III) and ytterbium(III) with decanoic acid in 1-octanol and benzene was carried out at 25°C and at an aqueous ionic strength of 0.1 mol dm-3 (NaNO3). In extraction systems using 1-octanol as a solvent, all of the lanthanides were found to be extracted as two kinds of monomeric decanoates; in those using benzene, the monomeric, dimeric and tetrameric lanthanide(III) decanoates were proven to be responsible for the extraction, except for gadolinium(III), whose extracted species were the monomeric and dimeric species. The dimerization, tetramerization and adduct formation constants of lanthanide(III) decanoates in the organic phase were estimated. A so-called “gadolinium break” was observed for the polymerization constants of lanthanide(III) decanoates.

In situ electro-oxidation and liquid-liquid extraction of cerium(IV) from nitric acid medium using tributyl phosphate and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate

The process of in situ electro-oxidation of Ce(III) to Ce(IV) followed by its extraction into the organic phase has been investigated for its applicability in the separation of Ce from nitrate medium. Solvent extraction of cerium from nitric acid after its electro-oxidation to fourth valency state was carried out using tributyl phosphate (TBP) and 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate (KSM-17, equivalent to PC-88A). The efficiency of the extractants at different aqueous phase nitric acid concentrations and different electrode potentials were determined. Various reducing agents such as hydroxylamine hydrochloride, sodium nitrite, ferrous sulphate as well as complexing agents like EDTA, oxalic acid etc, were studied as strippants for the back extraction of cerium from the loaded organic phase. The method developed for the extraction of cerium was further extended to the partitioning of cerium from Ce-Am mixture obtained during the KSM-17 based extraction chromatographic elemental fractionation of PUREX High Activity Waste (HAW) solutions. Recovery of Ce obtained in the extraction experiments by batch as well as by continuous flow organic phase was >95% with good radiochemical purity.

The extraction of cerium (III) and lanthanum (III) from chloride solutions with LIX 54

A study has been made of the extraction equilibrium of cerium(III) and lanthanum(III) from NaCl solution with dodecylphenyl-methyl-β-diketone (LIX 54) in n-heptane. It was found that the extraction of both metals depends strongly on pH as well as on the extractant concentration and does not depend on chloride concentration. The extraction of lanthanum is independent of its concentration in the aqueous phase up to 0.05 M but the extraction of cerium diminishes markedly when its concentration exceeds 1.5 m M. Experimental results show that the predominant complexes extracted are CeR 3 and LaR 3 · 3HR. The extraction equilibrium constants are: log K ex = −15.67, for the CeR 3 complex, log K ex = −14.2, for the LaR 3 · 3HR complex, and log K ex = −18.2 when the LaR 3 complex is assumed. The change in enthalpy associated with the extraction for lanthanides is about 7.3 kJ/mol. Cerium is better extracted with LIX 54 than lanthanum. During simultaneous extraction of the metals with 0.1 M LIX 54 the selectivity of their separation is appreciable if the pH range is strongly limited.

Extraction of cerium(III) by polymer gels swollen with bidentate organophosphorus compounds.

The extraction of Ce(III) from aqueous solutions containing Al(NO3)3 was examined by using styrene-divinylbenzene copolymer (SDB) gels swollen with dihexyl-N,N-diethylearbamoylmethylphosphonate (CMP), octyl(phenyl)-N,N-diisobutylcarbanoylmethylphosphine oxide (CMEPO) and an equimolar mixture of CMP and CMPO.The extraction constants (Kex) for the gels with CMIP and CMPO were evaluated. The distribution ratio of Ce(III) for the gel with an equimolar mixture of CMP and CMFO was described as Kd = (KexCMP[CMP]3 +KexCMPO[CMPO] 3)[NO3–]3) by using these extraction constants. The extraction rate was found to be controlled by diffusion of Ce-complex [Ce(NO3)3(CMFO)3 or Ce(NO3)3(CMP)3] through the gel. The diffusion coefficient (Ds) was inversely proportional to the viscosity of extractant (η) and represented by an expression similar to the Stokes-Einstein equation, Dsη/T = constant. A decrease in the viscosity of extractant was effective for increasing the extraction rate.