Mixed Rare Earth Oxides Research Articles

Recovery of metal values from spent nickel–metal hydride rechargeable batteries

Abstract A hydrometallurgical process is developed for the separation and recovery of metal values such as nickel, cobalt and rare earths from spent nickel–metal hydride (Ni–MH) rechargeable batteries. After removal of the external case, the electrode materials are dissolved in 2 M sulfuric acid solution at 95°C. The resulting liquor contains typically (g l−1), 10.6 Ni, 0.85 Co, 1.70 Fe, 0.36 Zn, 0.21 Al, 0.54 Mn, 1.73 La, 0.10 Ce, 0.33 Pr, 1.10 Nd and 0.032 Sm. The pH is around 0.4. The rare earth values are recovered from the liquor by means of a solvent extraction circuit with 25% bis(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene, followed by precipitation with oxalic acid. A mixed rare earth oxide of about 99.8% purity is obtained after calcination of the precipitate. The total yield of rare earths approaches 93.6%. The cobalt and nickel in the raffinate are effectively separated by solvent extraction with 20% bis(2,4,4-tri-methylpenthyl) phosphinic acid (Cyanex 272) in kerosene. The individual cobalt and nickel are then recovered as oxalates by the addition of oxalic acid. Cobalt and nickel oxalates with purities close to 99.6% and 99.8%, respectively, are obtained. The overall recoveries are over 96% for both cobalt and nickel. A total flowsheet of the process for recovery of rare earths, cobalt and nickel from spent Ni–MH batteries is proposed.

Characterisation of LaGdO 3 by X-ray powder diffraction and raman spectroscopy

LaGdO 3 is prepared via a reverse-strike coprecipitation method and sintered at temperatures of 1350–1450°C for 6 h. Raman spectroscopy of the sintered materials revealed profiles similar to that observed for pure B-type Gd 2O 3. Low temperature (−196°C) Raman spectra showed a total of 18 bands of a possible 21 allowed modes predicted for the monoclinic B-type mixed rare earth oxide with C2/ m space group. These bands were assigned to modes in comparison to the band assignments for Gd 2O 3 as follows; 71 ( B g ), 82 ( A g ), 98 ( B g ), 109 ( A g ), 124 ( A g ), 158 ( A g ), 182 ( A g ), 219 ( A g ), 242 ( A g ), 279 ( A g ), 315 ( B g ), 366 ( A g ), 390 ( B g ), 419 [ B g +( A g ?)], 436 ( A g ), 458 ( A g ), 560 ( A g ) and 575 ( A g ) cm −1. Powder X-ray diffraction patterns revealed a monoclinic pattern for materials sintered at all three temperatures; 1350, 1400 and 1450°C.

Hydrometallurgical process for recovery of metal values from spent nickel-metal hydride secondary batteries

A completely hydrometallurgical process has been developed for the recovery of metal values such as cobalt, nickel and rare earths from spent nickel-metal hydride (Ni-MH) secondary batteries. Effects of hydrochloric acid concentration, temperature, reaction time and solid-to-liquid ratio on leaching of metals contained in the electrode materials of the batteries were studied. The optimal operating conditions were found to be 3 M HCl at a temperature of 95°C and a 3-h leach time, and it was possible to treat up to 5.5 g of scrap in 50 ml of acid solution where the recoveries 100% of cobalt, over 96% of nickel and 99% of rare earths were achieved. A typical chemical composition of the resulting leach liquor was approximately, in grams per liter, 23.4 Ni, 1.7 Co, 3.4 Fe, 0.72 Zn, 0.46 Al, 1.2 Mn, 4.2 La, 0.26 Ce, 0.82 Pr, 2.6 Nd and 0.074 Sm, as well as 50 Cl. The pH of the solution was around 1.2. The rare earth values can be readily recovered from the leach liquor by the use of a solvent extraction circuit with 25% bis(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene, in which a two-stage counter-current extraction at an O:A ratio of 3:1 at an equilibrium pH of 2.0, a single-stage cobalt scrubbing with 0.3 M hydrochloric acid at an O:A ratio of 22:1, and a stripping operation with 2.0 M hydrochloric acid in one contact at an O:A ratio of 5:1 are involved. A mixed rare earth oxide of over 99% purity was obtained by selective precipitation with oxalic acid, and calcination of the precipitate. The total yield of rare earths approached 98%. The cobalt and nickel in the raffinate are effectively separated by selective extraction of cobalt with 25% TOA in kerosene after concentration (up to [Cl −]≈220 g l −1). Nearly complete recovery of cobalt can be achieved by using a three-stage counter-current extraction at an O:A ratio of 2:1, followed by stripping with a dilute hydrochloric acid solution (pH 2.0) in a single stage at an O:A ratio of 4:1. Subsequently the cobalt in the strip liquor and the nickel remained in the raffinate are separately recovered as oxalates by the addition of ammonium oxalate. A pure cobalt product and a nickel oxalate with a purity close to 99.9% were obtained. The total recoveries of cobalt and nickel were found to be approx. 98% and 96%, respectively.

Preparation and characterization of LnPrO 3+ y (Ln=Y and lanthanide)—a series of mixed lanthanide oxides

Citrate gel method has been employed to produce a series of praseodymium based homogeneous mixed rare-earth oxides, LnPrO 3+ y (Ln=Y and lanthanide ion). The ionic size of Ln determines the crystal structure of the mixed oxides. LnPrO 3+ y and CePrO 3+ y crystallise in the fluorite structure, whereas the remaining oxides adopt the C-type structure. The crystal structure and the unit cell parameters of the oxides obtained at 1173 K in static air have been reported. Wet-chemical analysis suggests that the compositions adopting the fluorite structure are non-stoichiometric, whilst the compositions crystallising in the C-type structure are stoichiometric. The surface area has been measured and the adsorption–desorption isotherms obtained for the compositions. The BET surface area of the oxides are in the range 1.5 to 3.5 m 2 g −1 and the isotherms reveal that the oxides are free from porosity.

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.

Structure and oxygen stoichiometry of phases in La–Pr–O system

Citrate gel method has been employed to produce homogeneous mixed rare-earth oxides in La 2− x Pr x O 3+ y (0≤ x≤2) system. The phases obtained at 1473 K in static air have been characterised for the entire range of compositions for their crystal structure. Hexagonal structure is stable for 0≤ x≤0.6 whereas cubic fluorite phase is stable for 1≤ x≤2. The unit cell parameters are reported for the range of single phase compositions. Wet-chemical analysis reveals that the compositions adopting hexagonal structure are stoichiometric ( y=0) whereas the compositions crystallising in the fluorite structure have the y increasing from 0.33 to 0.66 as x is varied from 1 to 2.

Combustion Synthesis, Powder Characteristics and Crystal Structure of Phases in Ce–Pr–O System

The combustion method has been employed to produce homogeneous, single phased mixed rare-earth oxides in Ce1 − xPrxO2−y system for x ranging from 0 to 0.7. A cubic fluorite structure is formed for the compositions 0 ≤ x ≤ 0.7, while for x > 0.7 mixed phases are obtained. The mixed oxides are formed at the furnace temperature of 500 °C in a short duration of 10 min. In view of the importance of these powders in catalysis, crystallite size, surface area and porosity measurements have been carried out. The crystallite size of the powders increases with x while the surface area decreases. As the temperature is increased to 850 °C, the surface area decreases and the effect is much pronounced in cerium rich oxides. The powders on calcination above 900 °C in air results in the demixing of Ce and Pr to give two fluorite phases.

Determination of rare-earth oxide contents in rare-earth oxide mixtures by Auger electron spectrometry

Abstract The content of rare-earth (RE) oxides in RE oxide mixtures (La 2 O 3 , Pr 6 O 11 and Y 2 O 3 ) was determined using Auger electron spectrometry (AES) by utilizing the working curve method. Mixed RE oxide samples were obtained from mixed RE solutions and pressed into an In sheet to avoid charging. AES spectra were recorded in the first derivative mode, and the peak-to-peak heights were used as the peak intensity. La was used as an internal elemental standard. For mixtures containing Pr 6 O 11 and Y 2 O 3 , good working curves were obtained below 30% by weight (wt%). The detection limits of Pr 6 O 11 and Y 2 O 3 were 2.6 and 5.7 wt%, respectively. The experimental determination of the oxide composition agreed approximately with theoretical values.

The recovery of rare earth oxides from a phosphoric acid by-product. Part 2: The preparation of high-purity cerium dioxide and recovery of a heavy rare earth oxide concentrate

The development of a solvent-extraction process for the recovery of high-purity cerium dioxide and a heavy rare earth oxide concentrate from a mixed rare earth oxide is described. Dissolution of the mixed oxide in concentrated nitric acid afforded solutions in which up to 95% of the cerium is present as cerium(IV) which, after dilution with water, can be extracted into a 15 vol% solution of tri-n-butyl phosphate in Shellsol K with high selectivity over the remaining trivalent rare earths. In continuous counter-current trials, four extraction stages were used, followed by four stages of scrubbing with 3 M nitric acid. Stripping of the organic phase was accomplished by reduction of the cerium(IV) with dilute hydrogen peroxide in two stages, giving solutions containing up to 90 g 1 −1 of cerium(III). Addition of oxalic acid to the strip liquors, followed by calcination of the precipitated oxalate, gave cerium dioxide of at least 99.98% purity in about 70% yield. Continuous counter-current extraction of the raffinate from the cerium recovery process in six stages with a 5 vol% solution of di(2-ethylhexyl) phosphoric acid in Shellsol AB at an organic-to-aqueous phase ratio of 3:2, followed by stripping in four stages with 1.3 M nitric acid at an organic-to-aqueous phase ratio of 10:1 gave strip liquors containing up to 8 g −1 of yttrium and 6 g l −1 of dysprosium, together with smaller amounts of heavier rare earths. Recovery to the strip liquors was 98–99% for yttrium and erbium, 50–75% for dysprosium, and 65–75% for holmium. Losses of the principal middle rare earths (samarium, europium and gadolinium) to the strip liquors were only 1–3%. Precipitation and calcination of the oxalate gave a heavy rare earth oxide containing yttrium (41–63% Y 2O 3), dysprosium (17–31% Dy 2O 3), holmium (4% Ho 2O 3) and erbium (4–5% Er 2O 3), together with smaller amounts of other rare earths (total rare earth oxide content 99.4–99.8%).

The recovery of rare earth oxides from a phosphoric acid by-product. Part 1: Leaching of rare earth values and recovery of a mixed rare earth oxide by solvent extraction

The development of a process for the recovery of a mixed rare earth oxide from calcium sulphate sludges obtained in the manufacture of phosphoric acid from a South African apatite ore is described. The leaching of the rare earth values from the sludges by dilute nitric acid is considerably enhanced by the addition of calcium nitrate to the lixiviant, enabling recoveries of up to 85% to be achieved. The rare earth values can be recovered from a leach liquor containing 1.0 M nitric acid and 0.5 M calcium nitrate by the addition of 2.5 M ammonium nitrate and extraction into 33 vol%v dibutyl butylphosphonate in Shellsol 2325. The organic phase can be stripped with water, preferably at temperatures above ambient, to yield a solution of rare earth nitrates from which the mixed oxide can be recovered by the addition of oxalic acid, and calcination of the precipitate. In a continuous counter-current laboratory trial of the process, a total of 140 kg of sludge was processed to produce 265 1 of leach liquor, which was treated in five extraction and five stripping stages to give a strip liquor from which 4 kg of mixed rare earth oxide of 98% purity was recovered. In a pilot-plant evaluation, the organic phase was changed to 40 vol% tributyl phosphate in order to enhance the stripping characteristics (as well as for economy), and the leach liquor was changed to 1.0 M nitric acid plus 3.0 M calcium nitrate, the addition of ammonium nitrate then being unnecessary. Some 3200 kg of mixed rare earth oxalates were prepared and calcined in a rotary kiln to give 1600 kg of mixed oxide of 89–94% purity. In all of the continuous trials the raffinate from the solvent-extraction process was recycled to the leaching stage, without any deleterious effect on the leaching efficiency being apparent.

Electronic properties of Ba2LnIrO6 (Ln = La, Ce, Pr, Eu, Ho, Er, Yb, Lu) perovskites

In the past few years the magnetic and electronic properties of iridium-containing perovskites have attracted considerable interest [1-6], because of the wide fange of variation giving behaviour ranging from semiconducting to metallic, frequently associated with cooperative magnetic properties. Special interest has been focused on the stabilization of unusual oxidation states of some transition-metal cations. In this context, various examples of perovskites in which the Ir s+ cation may be stabilized in an octahedral coordination have been reported [68]. The existence of some stoichiometric phases Ba2LnIrO 6 was initially reported by Thumm et al. [9] and the symmetry of these rare-earth mixed oxides was found to be cubic, whereas the indium analogue was hexagonal. More recently, Lang and Muller [10] have studied a hexagonal phase of a europium-containing perovskite. This letter reports the synthesis, structural characterization from powder X-ray diffraction (XRD) data and study of electronic properties, made from conductivity and Seebeck coefficient measurements, for Ba2LnIrO6 (Ln = La, Ce, Pr, Eu, Ho, Er, Yb, Lu) perovskites.

Simultaneous determination of lanthanum and cerium in mixed rare earths with p-acetylarsenazo by spectrophotometry

A new method has been developed for the simultaneous spectrophotometric determination of small amounts of lanthanum and cerium in the presence of large amounts of rare earth elements. Lanthanum (III) and cerium (III) were determined spectrophotometrically with p-acetylarsenazo as the color reagent in the chloroacetic acid medium at pH 3.1 by measuring the absorbances of the complexes at 670 nm. The remained rare earths were masked with ethylenediaminetetracetic acid and ethylenediaminetetracetic acid—zinc during the analysis. The optimum conditions for the simultaneous determination of lanthanum and cerium have been defined. The individual content of lanthanum (III) and cerium (III) were determined by varying the amounts of EDTA and EDTA-Zn used in the analysis and solving the simultaneous absorbance equations based on the Beer's law. The proposed method has been successfully applied to the determination of lanthanum and cerium in Longnan mixed rare earth oxides and other heavy rare earths without preliminary separation with satisfactory results. The relative errors of all analytical results of the method were not more than 2% with good precision. The procedure does not require separation of lanthanum, cerium and the other rare earth elements.

Cation ordering and the stability of fluorite-related phases in ZrO2-LnO1.5 systems: a phase diagram simulation study using Monte Carlo methods

The authors report Monte Carlo simulation results on cation ordering in a range of fluorite-related phases in various ZrO2-LnO1.5 systems. They restrict their attention to the face-centred cubic array of cations, assuming that the effect of the anion array upon the cation ordering can be simulated via effective cation-cation interactions. The basic interactions of the model include strongly repulsive nearest- (J1) and next-nearest-neighbour (J2) effective pair interactions and a three-spin interaction (J3) term for the nearest neighbours. The ionic size difference between the two cation species is a measure of the strength of the interaction parameter J2 and is a controlling factor for different kinds of ordering arrangement. While pyrochlore-type ordering is found to be stable for large values of J2, the c-type phase is observed for small values of J2. Both phases are found to coexist in the intermediate-parameter range. The authors report complete phase diagrams for two sets of interaction parameters computed within the framework of the 3D Ising model. The simulation results are consistent with electron and X-ray diffraction results on these mixed rare-earth oxide systems.

Defect models for the oxygen potentials of gadolinium-and europium-doped urania

A defect model for the thermochemistry of the mixed rare-earth uranium oxides has been developed. The parameters of the model were determined by fitting the theory to experimental oxygen potential data. The basic defects and associated equilibria found previously for pure urania were used in the mixed oxide defect model. In addition, the model prohibits oxygen interstitial occupancy of six to ten sites neighboring a trivalent dopant ion and assumes vacancy-dopant clusters in an excess of oxygen vacancies. Successful modeling of the oxygen potential as a function of temperature and oxide composition was achieved by assuming gadolinium to be present as isolated ions in the lattice, but europium modeling required complexes consisting of six Eu 3+ and one anion vacancy.

T*-phase superconductivity

The T⋆-phase is a mixed rare earth oxide phase forming at the composition R2CuO4. Its crystal structure is intermediate between the La2CuO4 and Nd2CuO4 structures. Sr-doped samples have Tc onsets as high as 37 K. We discuss the systematics of Tc of T⋆-phases as a function of Sr doping, rare earth mixture and oxygenation. Structural and transport data will also be presented.

Bi2O3-based oxide ion conductors doped with mixed heavy rare-earth oxides

This paper describes the results of preparation and conductivity measurement of Bi2O3-based oxides doped with mixed heavy rare-earth oxides. The range of x values in (Bi2O3)1−x(RE2O3)x for the single fcc phase aas found to be 0.15 to 0.51 Beyond this range the samples were multiphase. The temperature dependence of the conductivity of the samples with fcc structure exhibited an Arrhenius hehavior. The sample of x=0.20 showed the highest conductivity values, which were close or even higher than that ever reported in the literature in the temperature range of 400–800° C.

Preparation of rare earth-silicon-iron alloy by metallothermic reduction

An improved process based on metallothermic reduction was investigated to achieve higher rare earth recovery and a better grade of rare earthsilicon alloy than that produced by the commercial submerged arc method. The process involved reduction of mixed rare earth oxides with a mixed ferro-silicon and aluminium reductant in presence of a CaOMgO or CaOCaF 2 flux which prevented loss of rare earth oxide into the slag phase. The smeltings on 5 kg of alloy per batch scale were carried out in an induction furnace at a temperature of 1500–1550 °C. Rare earth-silicon-iron alloy products containing more than 50% REM, corresponding to over 80% rare earth recovery, were achievable in this procedure.

The influence of superficially applied oxide powders on the high-temperature oxidation behavior of Cr2O3-forming alloys

The effects of superficially applied CeO2, mixed rare earth oxides, Co3O4, and Cr2O3 powders on the isothermal and cyclic oxidation of Ni-Cr alloys and the effects of CeO2 and MgO powders on the isothermal oxidation of Fe-25 wt.% Cr have been studied over the temperature range 940–1150°C in pure oxygen and dry air. The rates of oxidation of both the Ni- and Fe-base alloys were markedly reduced by the application of CeO2 powder. The presence of CeO2 also improved the scale adherence and resulted in marked changes in the oxidation morphology. The presence of Co3O4 or Cr2O3 powders on Ni-Cr alloys or MgO on Fe-Cr also produced changes in the oxidation morphology but did not decrease the rate of oxidation. These results are interpreted in terms of the influence of the oxide powders on the development of scale microstructure and their effectiveness in decreasing grain boundary transport in Cr2O3.

A scheme for the analysis of monazite and monazite concentrates

A scheme using ion-exchange methods is described for the analysis of monazites and monazite concentrates. The sample is opened up with concentrated sulphuric acid, and the resultant solution is applied to a column of Zeocarb 225 resin. After phosphate has been washed out, lead, aluminium, titanium, iron, uranium, calcium and magnesium are eluted with N hydrochloric acid and determined by specific, mainly spectrophotometric, methods. Rare earth elements are eluted with 3 N hydrochloric acid. Cerium is separated from the other rare earths by solvent extraction of its nitrate with methyl iso-butyl ketone; both groups are determined gravimetrically. Thorium is eluted from the ion-exchange resin with 3.6 N sulphuric acid and determined spectrophotometrically with thorin. The sulphuric acid-insoluble minerals are brought into solution by a double fusion method, and the determinations are carried out by a combination of ion-exchange and photometric procedures. Silica, phosphorus pentoxide, tin and chromium are determined by photometric methods, using separate portions of the sample. Lanthanum, yttrium and ytterbium are determined in a 1 M perchloric acid solution of the mixed rare earth oxides (less cerium) using flame photometry. Samarium, praseodymium and neodymium are determined by spectrophotometry.

Yttrium Oxide of High Purity. DTPA-Ion Exchange Process.

The commercial isolation of yttrium compounds from a mixed rare earth oxide source material is possible by an ion exchange chromatographic process using buffered diethylenetrinitrilopentaacetic acid (DTPA) as eluant. DTPA offers particular advantage over other complexing agents specifically for yttrium isolation because of the relative affinities of this chelating agent for yttrium and other rare earths. Further, the moderate water solubility of DTPA acid permits the use of acid from ion exchange resins rather than metal (copper) retaining ion and minimizes precipitation and recovery problems. Rare earth separations are improved with lower crosslinked, finer mesh cation exchange resins and at elevated temperatures.