Separation of Rare-Earth Elements from Nitrate Solutions by Solvent Extraction Using Mixtures of Methyltri-n-octylammonium Nitrate and Tri-n-butyl Phosphate

The article presents data on the solvent extraction separation of rare-earth elements (REEs), such as La(III), Ce(III), Pr(III), and Nd(III), using synergic mixtures of methyltrioctylammonium nitrate (TOMANO₃) with tri-n-butyl phosphate (TBP) from weakly acidic nitrate solutions. Specifically, experimental results on separation of REEs, for the pair Ce(III)/Pr(III) for quaternary mixtures of REEs (La(III), Ce(III), Pr(III), Nd(III)) and for the pair La(III)/Pr(III) for solutions containing La(III), Pr(III), and Nd(III), are presented. It was shown that effective separation for the pair Ce(III)/Pr(III) from a solution containing 219 g Ce(III)/L, 106 g La(III)/L, 20 g Pr(III)/L, 55 g Nd(III)/L, and 0.1 mol/L HNO₃, was achieved using 56 steps of a multistage, counter-current solvent extraction cascade with scrubbing, at an organic-to-aqueous phase volume ratio (O/A) equal to 2/1 on the extraction section and O/A equal to 4/1 on the scrubbing section, using 3.3 mol/L solutions of the mixture TOMANO₃-TBP with molar ratio 0.15:0.85 in dodecane. Separation for the pair La(III)/Pr(III) could be achieved using a solvent extraction cascade with scrubbing in 32 steps at O/A equal to 2/1 on the extraction section and O/A equal to 2.8/1 on the scrubbing section of the solvent extraction cascade from a solution containing 258 g La(III)/L, 58 g Pr(III)/L, 141 g Nd(III)/L, and 0.1 mol/L HNO₃ with 3.0 mol/L solution of the mixture TOMANO₃-TBP with molar ratio 0.2:0.8 in dodecane.     

An effective process for the separation of U(VI), Th(IV) from rare earth elements by using ionic liquid Cyphos IL 104

Separation and recovery of U(VI) and Th(IV) from rare earth minerals is a very challenging work in rare earth industrial production. In the present study, a homemade membrane emulsification circulation (MEC) extractor was used to separate U(VI) and Th(IV) from rare earth elements by using Cyphos IL 104 as an extractant. Batch experiments were carried out using a constant temperature oscillator to investigate the extraction parameters of the single element and the results indicated that Cyphos IL 104 could reach the extraction equilibrium within 30 min for all the three elements, i.e., U(VI), Th(IV), and Eu(III). Besides, the MEC extractor possessed a strong phase separation ability. The extraction efficiencies of U(VI), Th(IV), La(III), Eu(III) and Yb (III) increased with the increase of pH. La(III), Eu(III) and Yb(III) were hardly extracted when pH ≤ 1.50, which was beneficial for effectively separating U(VI) and Th(IV) from La(III), Eu(III) and Yb(III). In the multi-stages stripping experiments, when the stripping stage number was 3, the effective separation could be achieved by using HCl and H₂SO₄, since the stripping efficiency reached 80.0% and 100.0% for Th(IV) and U(VI), respectively. Slope method and FT-IR spectra showed that Cyphos IL 104 reacted with U(VI) and Th(IV) by chelation mechanism. The extraction of multi-elements indicated that U(VI) and Th(IV) could be well separated from the solution which contains all rare earth elements, and the extraction efficiencies of U(VI) and Th(IV) both were close to 100.0%. Based on the above experimental results, a flowchart for efficient separation of U(VI) and Th(IV) from rare earth elements was proposed.     

Solvent extraction behaviour of lanthanum(III), cerium(III), europium(III), thorium(IV) and uranium(VI) with 3-phenyl-4-benzoyl-5-isoxazolone

The extraction behaviour of La(III), Ce(III), Eu(III), Th(IV) and U(VI) with 3-phenyl-4- benzoyl-5-isoxazolone (HPBI) in chloroform has been studied. The mechanism of extraction and the species extracted have been identified. Extraction constants for each system have been calculated. The system has been used to separate Th(IV) from U(VI) and from La(III), Ce(III) and Eu(III). A comparison of the extraction constants with those for the 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) and thenoyltrifluoroacetone (HTTA) systems indicates that HPBI extracts these metal species better than HPMBP and HTTA do.     

Counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) using tris-2-ethyl hexyl phosphate (TEHP)

Evaluation of tris-2-ethyl hexyl phosphate (TEHP) for counter-current extraction and separation of U(VI) from a mixture of U(VI)–Th(IV)–Y(III) from nitric acid medium was carried out under wide experimental conditions. Batch extraction studies were carried out to investigate the effect of nitric acid concentration in feed solution, U(VI)/Th(IV) ratio and extractant concentration and the results were compared with established solvent such as tri-n-butyl phosphate (TBP) for separation of U(VI) from nitric acid medium. McCabe–Thiele diagrams for extraction as well as stripping of U(VI) were constructed under simulated conditions. Based on batch experiments, six stage counter-current extraction studies were conducted under various TEHP concentration and it was observed that 0.1 M TEHP/n-paraffin was most suitable for selective recovery of U(VI) from a mixture of U(VI)–Th(IV). An optimized condition, 0.1 M TEHP/n-paraffin, 2 M HNO₃ in feed and six number of stages was evaluated for selective extraction and stripping of U(VI) from a solution containing mixture of U(VI)–Th(IV)–Y(III) in nitric acid medium. The U(VI) in strip solution was precipitated using 30 % H₂O₂ at pH ~3. Average particle size of the final precipitate was found to be ~33 μm.     

Electrochemical Behavior of Ce(IV)/Ce(III) Couple in N,N-Di(2-ethylhexyl)-n-butanamide (DEHBA), N,N-Di(2-ethylhexyl)-iso-butanamide (DEHiBA), and N,N-Di(2-ethylhexyl)-3,3-dimethyl Butanamide (DEHDMBA)

In this work we report on the electrochemical behavior of Ce(IV)/Ce(III) redox couple in pure N,N-dialkyl amides (N,N-DA), namely N,N-di(2-ethylhexyl)-n-butanamide (DEHBA), N,N-di(2-ethylhexyl)-iso-butanamide (DEHiBA), and N,N-di(2-ethylhexyl)-3,3-dimethyl butanamide (DEHDMBA) equilibrated with nitric aqueous solutions as an entry to the direct electrochemical characterization of plutonium in these extractants. Ce(IV)/Ce(III) redox process was used as a model. Its potential (E_1/2≅1.02 V/SCE) is not affected by the temperature and the nature of the N,N-DA and this clearly indicates that the functionalities of these extractants produce the same relative effect on both +IV and +III oxidation states of the cerium cation. Linear variations of the current intensity of the reduction peak of Ce(IV) with the concentration of Ce(IV)/N,N-DAs/HNO₃(5 M) solutions were obtained from cyclic voltammograms recorded at 25 °C and 40 °C. Due to the poor definition of the voltammograms in DEHiBA and DEHDMBA, such characterization allows only the evaluation of the performances of the chemical extraction of Ce(IV) from aqueous nitric acid solution by the undiluted DEHBA. To our knowledge, the electrochemical behavior of Ce(IV)/Ce(III) in N,N-DAs was not previously studied and our findings will for sure open the door for further investigations in this field.     

Selective extraction of U(VI), Th(IV), and La(III) from acidic matrix solutions and environmental samples using chemically modified Amberlite XAD-16 resin

A new grafted polymer has been developed by the chemical modification of Amberlite XAD-16 (AXAD-16) polymeric matrix with [(2-dihydroxyarsinoylphenylamino)methyl]phosphonic acid (AXAD-16-AsP). The modified polymer was characterized by a combination of ¹³C CPMAS and ³¹P solid-state NMR, Fourier transform-NIR-FIR-Raman spectroscopy, CHNPS elemental analysis, and thermogravimetric analysis (TGA). The distribution studies for the extraction of U(VI), Th(IV), and La(III) from acidic solutions were performed using an AXAD-16-AsP-packed chromatographic column. The influences of various physiochemical parameters on analyte recovery were optimized by both static and dynamic methods. Accordingly, even under high acidities (>4 M), good distribution ratio (D) values (10²–10⁴) were achieved for all the analytes. Metal ion desorption was effective using 1 mol L^–1 (NH₄)₂CO₃. From kinetic studies, a time duration of <15 min was sufficient for complete metal ion saturation of the resin phase. The maximum metal sorption capacities were found to be 0.25, 0.13, and 1.49 mmol g^–1 for U(VI); 0.47, 0.39, and 1.40 mmol g^–1 for Th(IV); and 1.44, 1.48, and 1.12 mmol g^–1 for La(III), in the presence of 2 mol L^–1 HNO₃, 2 mol L^–1 HCl, and under pH conditions, respectively. The analyte selectivity of the grafted polymer was tested in terms of interfering species tolerance studies. The system showed an enrichment factor of 365, 300, and 270 for U(VI), Th(IV), and La(III), and the limit of analyte detection was in the range of 18–23 ng mL^–1. The practical applicability of the polymer was tested with synthetic nuclear spent fuel and seawater mixtures, natural water, and geological samples. The RSD of the total analytical procedure was within 4.9%, thus confirming the reliability of the developed method.     

Extraction of uranium (VI), plutonium (IV) and some fission products by tri-iso-amyl phosphate

The extractive properties of tri-isoamyl-phosphate (TAP), an indigenously prepared extractant, and the loading capacity of extraction solvent containing TAP for U(VI) and Pu(IV) ions in nitric solution have been investigated. The dependence of the distribution ratio on the concentration of nitric acid showed that TAP has an ability to extract these actinides, while the fission product contaminants are poorly extracted. The distribution data revealed a quantitative extraction of both U(VI) and Pu(IV) from moderate nitric acidities in the range 2–7 mol · dm^–3. Slope analysis proved predominant formation of the disolvated organic phase complex of the type UO₂(NO₃). 2TAP and Pu(NO₃)₄·2TAP with U(VI) and PU(IV), respectively. On the contrary, the extraction of fission product contaminants such as¹⁴⁴Ce,¹³⁷Cs,⁹Nb.,¹⁴⁷Pr,¹⁰⁶Ru,⁹⁵Zr was almost negligible even at very high nitric acid concentrations in the aqueous phase indicating its potential application in actinide partitioning. The recovery of TAP from the loaded actinides could be easily accomplished by using a dilute sodium carbonate solution or acidified distiled water (0.01 mol · dm^–3 HNO₃) as the strippant for U(VI) and using uranous nitrate or ferrous sulphamate as that for Pu(IV). Radiation stability of TAP was adequate for most of the process applications.     

Extraction of molybdenum(VI) by 4-(5-nonyl)pyridine in benzene from aqueous mineral acid solutions containing thiocyanate ions

Extraction of Mo(VI) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiocyanate ions has been investigated at room temperature (23±2°C). From mineral acid (HCl, HNO₃, and H₂SO₄) solutions alone Mo(VI) is not extracted quantitatively while the presence of small amounts of KSCN in the system augments the extraction by a large factor. Stoichiometric studies indicate that ion-pair type complexes (NPyH)₂·[MoO₂(SCN)₄] are responsible for the extraction. Separation factors determined at fixed extraction conditions (0.1M Npy/C₆H₆–0.1M acid +0.2M KSCN) reveal that Ag(I), Cu(II), Co(II), Zn(II), Hg(II) and U(VI) are co-extracted while a clean separation from alkali metals, alkaline earths and some transition metals like Ln(III), Zr(IV), Hf(IV), Cr(III), Cr(VI) and Ir(III) is possible. Some of the complexing anions like oxalate, citrate, acetate, thiosulfate or ascorbate do not affect the degree of extraction of Mo(VI) allowing it to be recovered from diverse matrices.     

Extraction kinetics of lanthanum(III), uranyl(VI), and thorium(IV) nitrates from water-salt solutions using a composite based on a polymeric support and tri-n-butyl phosphate at various temperatures

The extraction kinetics of lanthanum(III), uranyl(VI), and thorium(IV) nitrates from water-salt solutions using a composite based on a polymeric support and tri-n-butyl phosphate (TBP) were studied at 293.15–333.15 K. Interfacial diffusion (the film kinetics) is the rate-controlling stage of extraction. Mass transfer coefficients were determined, and their temperature dependence was used to estimate apparent activation energies E _a. The mass transfer coefficients increase in going from lanthanum(III), uranyl(VI), and thorium(IV) nitrate solutions to water-salt solutions containing 2 mol/L sodium nitrate or with rising temperature. E _a is independent of the metal ion and the supporting electrolyte concentration; E _a = 25 ± 1 kJ/mol. At a fixed temperature, the increasing order of the mass transfer coefficients is as follows: thorium(IV) < uranyl(VI) < lanthanum(III).     

LIX 84 as an extractant for throium(IV), uranium(VI) and molybdenum(VI)

The extraction order of Th(IV), U(VI) and Mo(VI) based on pH_0.5 values is Mo(VI)>U(VI)>Th(IV). Quantitative extraction has been observed for U(VI) by mixture of 10% (v/v) LIX 84 and 0.1M dibenzoylmethane at pH 4.2 and by mixture of 10% LIX 84 and 0.05M HTTA in the pH range 5.5–7.3 and for Mo(VI) by 10% LIX 84 from chloride media at pH 1.5. The order of extraction of Mo(VI) from 1N acid solutions is HCl>H₂SO₄>HNO₃>HClO₄ and extraction decreases very rapidly with increase in the concentration of HCl as compared to that from H₂SO₄, HNO₃ and HClO₄ acid solutions. The diluents C₆H₆, CCl₄ and CHCl₂ are found to be superior ton-butyl alcohol and isoamyl alcohol for extraction of Mo(VI). Influence of concentration of different anions on the extraction of U(VI) and Mo(VI) has been studied. Very little extraction has been observed in case of Th(IV) by LIX 84 or its mixtures with other chelating extractants or neutral donors.     

Extraction of thiocyanate complexes of cobalt(II) by diphenyl-2-pyridylmethane in benzene from mineral acid solutions

Extraction of Co(II) by diphenyl-2-pyridylmethane (DPPM) in benzene form mineral acid solutions containing potassium thiocyanate has been studied at room temperature (23±2°C). Its extraction from mineral acids alone is rather poor. Optimal aqueous phase composition for the quantitative extraction of Co(II) by 0.1M DPPM is 0.1M acid+0.2M KSCN. Stoichiometric studies indicate that an ionic type complex, (DPPM·H)₂·Co(SCN)₄, is responsible for extraction. The metal can be back-extracted from the organic phase by aqueous acetate, citrate or oxalate solutions. Separation factors from other metals determined under optimal conditions reveal that Co(II) can be quantitatively separated from CsI), Sr(II), Cr(III), Ln(III), Zr(IV), Hf(IV), Cr(VI) and Tc(VII), Mo(VI), Zn(II), Au(III), Hg(II) and U(VI) are, however, coextracted and hence should be previously removed by other techniques or reagents.     

Synergic extraction of lanthanide(III) ions with 2-thenoyltrifluoroacetone in the presence of 2,2′-bipyridine or pyridine

The synergic extraction of various tervalent lanthanides (Ln), La, Ce, Nd, Sm, Gd, Tb, Yb and Lu, with 2-thenoyltrifluoroacetone (Htta) in the presence of a bidentate heterocyclic amine, 2,2′-bipyridine (bipy), in benzene was investigated. The synergic enhancement was attributed to the formation of the adducts, Ln(tta)₃(bipy). The synergic extraction of La(III), Sm(III) and Lu(III) with Htta and a unidentate amine, pyridine (py), was also studied and the formation of the adducts, Ln(tta)₃py and Ln(tta)₃(py)₂, was observed. The adduct formation constants, β_s,1 and β_s,2, were determined. The β_s,2 values for py decrease with increasing atomic number of Ln(III), but β_s,1 values for bipy increase with increasing atomic number of Ln(III). The synergic extraction constants and the separation factors in the bipy system were also determined.     

Column chromatographic separation of Ce(III) from U(VI) and other elements in hippuric acid medium as an analytical application of poly[dibenzo-18-crown-6]

A simple and efficient column chromatographic method has been developed for the separation of Ce(III) from U(VI) and Ni(II)/Zn(II)/Cd(II)/Co(II)/Ba(II) etc. using poly[dibenzo-18-crown-6] as stationary phase and hippuric acid as a counter ion. HCl and H₂SO₄ were most efficient eluting agents for Ce(III). The capacity of crown polymer for Ce(III) was found to be 0.285 ± 0.01 mmol/g. The tolerance limits of various cations and anions for Ce(III) were determined. Ce(III) was quantitatively separated from U(VI) and Ni(II)/Zn(II)/Cd(II)/Co(II)/Ba(II) in binary as well as multicomponent mixtures. The good separation yields were obtained and had good reproducibility (±2 %). The method incorporated the determination of Ce(III) in real sample. The method was simple, rapid and selective.     

Extraction of U(VI), Zr(IV) and Th(IV) from perchlorate media, by PC-88A

Extraction of U(VI), Zr(IV) and Th(IV) has been investigated from perchlorate media using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) dissolved in toluene. The extraction of U(VI), Zr(IV) and Th(IV) was found to be quantitative in the pH range 1.6 to 3.2, 2.0 to 4.7 and 2.3 to 3.8, respectively, with 3.0^.10^-3, 5.6^.10^-4 and 1.0^.10^-2M PC-88A dissolved in toluene. U(VI) was stripped with 4.0M HCl, Zr(IV) with 2.5M NaF and Th(IV) with 8.0M HCl from the metal loaded organic phase containing PC-88A dissolved in toluene. The probable extracted species have been ascertained by plotting log D vs. log [HR] as UO₂R₂ ^.2HR, ZrR₄ ^.2HR and ThR₄ ^.4HR, respectively. U(VI) was separated from Zr(IV) and Th(IV) and from other associated metals. This method was proved by the determination of U(VI) in some real samples.     

Polarographic analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III)

The analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III) and 1 M H₂SO₄ are investigated using the polarographic technique. The wave corresponding to the reduction of Fe(III) to Fe(II) was found to be completely suppressed by the addition of 1% pyrogallol. Thus, different mixtures of these elements, viz. Hg(II), Cu(II), Cd(II), As(III) and Fe(III)-mixture (A), Cu(II), Cd(II), Sb(III), As(III) and Fe(III)-mixture (B), and Cu(II), Cd(II), Ti(IV), U(VI) and Fe(III)-mixture (C), were quantitatively determined using 1% pyrogallol and 1 M H₂SO₄ as supporting electrolyte. The i₁/c results give excellent correlations in each case, as indicated from the results of leastsquares regression analysis.     

Extraction of U(VI), Pu(IV), Am(III) and some fission products by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester immobilized polyvinyl alcohol hydrogels

Cross-linked hydrogel matrices immobilized with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HA), were prepared to investigate their application in the recovery of radionuclide from acidic waste solutions. Gamma-radiation was used to produce HA immobilized polyvinyl alcohol (PVA) hydrogels (HA-gel). The hydrogels with different characteristics such as: degree of cross-linking (by varying radiation dose) and quantity of extractant immobilized (by starting with aqueous PVA solution containing different amounts of HA), were synthesised. These HA-gels were investigated for solid-liquid phase extraction of U(VI), Pu(IV), Am(III) and some fission products, under various experimental conditions. The concentration of HNO₃ in the aqueous phase was found to play an important role in the extraction of these radionuclei. Extraction of U(VI) was more favourable at lower concentration of HNO₃ (∼0.001 to 0.5M), while at higher concentrations (∼0.5 to 3M HNO₃), more than 90% of Pu(IV) present in the aqueous phase, could be extracted by the HA-gel. The extraction of Am(III) was also found predominant only at lower acidities (at pH∼2 and above). Under optimized conditions, maximum metal loading capacities obtained were 19±0.8 mg, 8±0.4 mg and 11±0.5 mg per gram of swollen HA-gel, for U(VI), Pu(IV) and Am(III), respectively. Under the experimental conditions, extractions of Cs(I) and Sr(II) were observed to be negligible. No leaching out of HA from the HA-gel particles was noted even after its repetitive use for the studied ten cycles of extraction and stripping experiments, as evident from its unchanged extraction efficiency.     

Sorption study of U(VI), Th(IV) and Ce(III) on poly[dibenzo-18-crown-6] in <Emphasis Type="SmallCaps">l</Emphasis>-arginine to develop sequential column chromatographic separation method

A simple and efficient column chromatographic method has been developed for the sequential separation of U(VI), Th(IV) and Ce(III) using poly[dibenzo-18-crown-6] as stationary phase and l-arginine as a counter ion. The different elution patterns with various eluting agents were observed for individual element. The capacity of poly[dibenzo-18-crown-6] for U(VI), Th(IV) and for Ce(III) was found to be 0.96, 0.86 and 1.49 (±0.01) mmol/g of crown polymer, respectively. The method is efficient to separate the elements in multicomponent mixtures and has good recovery. The method is extended to determine the U(VI), Th(IV) and Ce(III) from monazite sand. The method is simple, rapid and selective having good reproducibility (~±2%).     

Spectroscopic,electrochemical, and structural aspects of the Ce(IV)/Ce(III) DOTA redox couple chemistry in aqueous solutions

The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V versus SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)_aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a t_1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same t_1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA^2?) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)_aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S₂O₃^2?. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand.     

Electrometric titrations of Cr(VI), Mn(IV), V(V), Co(III) and U(VI) with a standard iron(II) solution in alkaline media containing hexitols

Direct and indirect potentiometric, bipotentiometric and biamperometric titrations with a standard iron(II) solution are described for some inorganic compounds in alkaline media containing hexitols (mannitol, dulcitol and sorbitol). The optimal conditions for titrations based on the Cr(VI) → Cr(III), Mn(IV) → Mn(III) → Mn(II), V(V) → V(IV), Co(III) → Co(II) and U(VI) → U(IV) systems are discussed. Of the hexitols studied, sorbitol has the greatest effect on the value of the redox potential of the Fe(III)/Fe(II) system; the E_f° value is about —1.10 V vs. SCE.     

Application of the Weisz Ring oven technique to the separation and identification of micro-quantities of some less familiar cations

Summary Use of the ring oven in separation and identification of mixtures of less familiar metal ions has been described. Separation of metal ions from the following mixtures has successfully been carried out: 1. UO₂(II) and Th(IV), 2. Th(IV) and Ce(IV), 3. Pd(II) and Au(III), 4. Pt(IV) and Au(III), 5. Ce(III) and Ce(IV), 6. UO₂(II), Th(IV) and Ti(IV), 7. Th(IV), Ti(IV) and Ce(IV), 8. Th(IV), Ce(IV) and Zr(IV), 9. Ti(IV), V(V) and Zr(IV), 10. Mo(VI), V(V) and W(VI) and 11. Be(II), Al(III) and Mg(II). In the case of binary mixtures, the separation was in the form of a central spot and a concentric ring; in ternary mixtures the metals were precipitated in a central spot and two concentric rings.

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Zusammenfassung Zur Trennung und Identifizierung folgender Gemische seltenerer Metallionen wurde der Ringofen mit Erfolg verwendet: 1. UO₂(II) und Th(IV), 2. Th(IV) und Ce(IV), 3. Pd(II) und Au(III), 4. Pt(IV) und Au(III), 5. Ce(III) und Ce(IV), 6. UO₂(II), Th(IV) und Ti(IV), 7. Th(IV), Ti(IV) und Ce(IV). 8. Th(IV), Ce(IV) und Zr(IV), 9. Ti(IV), V(V) und Zr(IV), 10. Mo(VI), V(V) und W(VI) und 11. Be(II), Al(III) und Mg(II). Bei binären Gemischen erfolgt die Trennung in einen zentralen Fleck und einen Ring, bei ternären Mischungen in einen Fleck und zwei konzentrische Ringe.

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Résumé On a décrit l'utilisation du four annulaire pour la séparation et l'identification de mélanges d'ions métalliques moins courants. On a effectué la séparation des ions métalliques à partir des mélanges suivants: 1. UO₂(II) et Th(IV), 2. Th(IV) et Ce(IV), 3. Pd(II) et Au(III), 4. Pt(IV) et Au(III), 5. Ce(III) et Ce(IV), 6. UO₂(II), Th(IV) et Ti(IV), 7. Th(IV), Ti(IV) et Ce(IV), 8. Th(IV), Ce(IV) et Zr(IV), 9. Ti(IV), V(V) et Zr(IV), 10. Mo(VI), V(V) et W(VI) et 11. Be(II), Al(III) et Mg(II). Dans le cas des mélanges binaires, la séparation se présentait sous forme d'une tache centrale et d'un anneau concentrique; chez les mélanges ternaires, les métaux étaient précipités en une tache centrale et deux anneaux concentriques.