Individual Rare Earth Research Articles

Partitioning of lanthanides and Y between immiscible silicate and fluoride melts, fluorite and cryolite and the origin of the lanthanide tetrad effect in igneous rocks

Some F-rich granitic rocks show anomalous, nonchondritic ratios of Y/Ho, extreme negative Eu anomalies, and unusual, discontinuous, segmented chondrite-normalised plots of rare earth elements (REE). The effects of F-rich fluids have been proposed as one of the explanations for the geochemical anomalies in the evolved granitic systems, as the stability of nonsilicate complexes of individual rare earths may affect the fluid-melt element partitioning. The lanthanide tetrad effect, related to different configurations of 4f-electron subshells of the lanthanide elements, is one of the factors affecting such complexing behaviour. We present the first experimental demonstration of the decoupling of Y and Ho, and the tetrad effect in the partitioning of rare earths between immiscible silicate and fluoride melts. Two types of experiments were performed: dry runs at atmospheric pressure in a high-temperature centrifuge at 1100 to 1200°C, and experiments with the addition of H 2O at 700 to 800°C and 100 MPa in rapid-quench cold-seal pressure vessels. Run products were analysed by electron microprobe (major components), solution-based inductively coupled plasma mass spectrometry (ICP-MS) (REE in the centrifuged runs), and laser ablation ICP-MS (REE and Li in the products of rapid-quench runs). All the dry centrifuge runs were performed at super-liquidus, two-phase conditions. In the experiments with water-bearing mixtures, minor amounts of aqueous vapour were present in addition to the melts. We found that lanthanides and Y concentrated strongly in the fluoride liquids, with two-melt partition coefficients reaching values as high as 100–220 in water-bearing compositions. In all the experimental samples, two-melt partition coefficients of lanthanides show subtle periodicity consistent with the tetrad effect, and the partition coefficient of Y is greater than that of Ho. One of the mixtures also produced abundant fluorite (CaF 2) and cryolite (Na 3AlF 6) crystals, which enabled us to study fluorite-melt and cryolite-melt REE partitioning. REE concentrations in fluorite are high and comparable to those in the fluoride melt. However, fluorite-melt partition coefficients appear to depend mostly on ionic radii and show neither significant tetrad anomalies, nor differences in Y and Ho partitioning. In contrast, REE concentrations in cryolite are low (∼5–10 times lower than in the silicate melt), and cryolite-melt REE partitioning shows very strong tetrad and Y-Ho anomalies. Our results imply that Y-Ho and lanthanide tetrad anomalies are likely to be caused mainly by aluminofluoride complexes, and the tetrad REE patterns in natural igneous rocks can result from fractionation of F-rich magmatic fluids.

Investigation of the separation of scandium and rare earth elements from red mud by use of reversed-phase HPLC.

A chromatographic method has been developed for separation and determination of scandium (Sc) and rare earth elements (REEs) in samples from a red mud (RM)-utilization process. Reversed-phase high-performance liquid chromatography (RP-HPLC) with post-column derivatization using 4-(2-pyridylazo)-resorcinol (PAR) and UV-visible detection at 520 nm was tested using different gradient elution profiles and pH values to optimize separation and recovery, primarily for Sc but also for yttrium and the individual lanthanides, from iron present in the samples. The separation was performed in less than 20 min by use of a mobile phase gradient. The concentration of alpha-hydroxyisobutyric acid ( alpha-HIBA), as eluent, was altered from 0.06 to 0.4 mol L(-1) (pH 3.7) and 0.01 mol L(-1) sodium salt n-octane sulfonic acid (OS) was used as modifier. Very low detection limits in the nanogram range and a good resolution for Sc and REEs except for Y/Dy were achieved. Before application of the method to the red mud samples and to the corresponding bauxites, Sc and REEs were leached from red mud with 0.6 mol L(-1) HNO(3) and mostly separated, as a group, from the main elements by ion exchange/selective elution (6 mol L(-1) HNO(3)) in accordance with a pilot-plant process developed in this laboratory. After evaporation of the eluent to dryness the extracted elements were re-dissolved in the mobile phase. By use of this chromatographic method Sc, which is the most expensive of the elements investigated and occurs in economically interesting concentrations in red mud, could be separated not only from co-existing Fe but also from Y/Dy, Yb, Er, Ho, Gd, Eu, Sm, Nd, Pr, Ce and La. All the elements investigated were individually recovered. Their recoveries were found to be nearly quantitative.

Ceramics composites Si 3N 4–SiC (w) containing rare earth concentrate (CRE) as sintering aids

Due to densification difficulties related to ceramics composites fabrication, a considerable research effort is being made to optimize processing methods of these materials, such as selection of adequate sintering aids and advanced powder synthesis technology. The use of rare earth concentrate (CRE) as sintering aid in Si 3N 4–SiC (w) ceramics composites is a new approach, to obtain silicon nitride based ceramics with good mechanical properties. Using CRE as obtained, makes unnecessary to perform the step of individual rare earth separation, with resultant time and cost reduction. In this work, different compositions of silicon nitride based matrix reinforced with silicon carbide whiskers were hot uniaxially pressed, followed by physical (specific mass, X-ray diffraction and scanning electron microscopy analysis) and mechanical (microhardness and fracture toughness) properties evaluation. For comparison, density and mechanical properties of the unreinforced silicon nitride matrix samples were also evaluated. Good density and mechanical properties results confirmed the viability and efficiency of the CRE as sintering aid, to obtain dense and tough Si 3N 4–SiC (w) ceramics composites.

Analytical separations of lanthanides and actinides by capillary electrophoresis.

The separation of lanthanide and actinide elements belongs to one of the most challenging tasks of the separation science, due to a great similarity in their physical and chemical properties. The electrophoretic separation can be accomplished in the presence of suitable complex-forming agents, from which alpha-hydroxyisobutyric acid (HIBA) has been used most often. In the most effective capillary electrophoretic mode--capillary zone electrophoresis (CZE)--a complete separation of lanthanide ions can be accomplished within a few minutes. Various electrophoretic methods can be relatively easily adopted for the determinations of individual lanthanide elements in certain kinds of technical materials, concentrates, precursors, etc., where the high speed and low costs of analysis characteristics of capillary electrophoresis (CE) may be advantageously exploited. Electrophoretic techniques may also be employed for speciation studies, especially for examinations of the behavior of actinides in the environment.

Complete separation of rare earth elements from small volume seawater samples by automated ion chromatography: method development and application to benthic flux

A new Ion Chromatography–Inductively Coupled Plasma Mass Spectrometry (IC–ICP-MS) method is presented for measuring individual rare earth elements (REEs) in small volume (5 ml) seawater samples, with the goal of measuring pore water REEs. The method is shown to be accurate and reproducible for small volumes of a seawater reference standard within the determined precisions. The method has reasonable yield (75%), and, more importantly, is shown to not internally fractionate individual REEs. After describing the method, data from bottom, overlying and interfacial pore waters from four sites (three California margin, one Chile margin) are presented. These data show that there is a REE flux from sediments into bottom water. This flux ranges from 10 −11 to 10 −8 mol cm −2 ky −1 at these sites and is, therefore, on the same order as riverine input to the oceans. Benthic chamber samples support these flux estimates. When pore water and benthic chamber water are normalized to PAAS, the REE patterns can be characterized using three descriptors: the magnitude of the Ce anomaly (always negative), a “MREE bulge” and “HREE enrichment.” However, when normalized to bottom water, LREE>HREE and there is a significant positive Ce anomaly. These features generally support current understanding: that the REEs in the ocean are strongly influenced by organically driven processes. A key proviso is that the fluctuations in the Ce anomaly should be considered to be the net result of changes in dissolved La and Pr, and not mainly a function of Ce oxidation.

Accumulation of rare earth elements in maize plants (Zea mays L.) after application of mixtures of rare earth elements and lanthanum

Rare earth elements are applied in China to improve crop production, and the distribution patterns of individual rare earth elements in native plants have widely been reported. But our knowledge is still limited about the dose-dependent accumulation of individual rare earth elements in agricultural crops after application of rare earth elements. Effects of lanthanum and mixtures of rare earth elements were studied in pot experiments on the accumulation of individual rare earth elements in maize plants. All plant samples were divided into plant tops and roots. On addition of mixtures of rare earth elements and lanthanum to the soil, a significant dose-dependent accumulation of individual rare earth element(s) was found in the roots and in the plant tops. Application of mixtures of rare earth elements at >10 mg kg−1 soil, resulted in a significant increase in contents of light rare earth elements in the roots, and at a dose of 50 mg kg−1 soil, a similar phenomenon was found in the plant tops. When mixtures of rare earth elements were replaced by lanthanum alone, at a dose higher than 10 mg La kg−1 soil, a significant increase in La content occurred in the roots and in the plant tops. The content ratio of La to Ce in maize plants appeared to increase as the application doses of rare earth element(s) increased. At a highest dose (50 mg kg−1soil), the transport of the absorbed La from the roots to the plant tops might be substantially reduced after treatment with lanthanum alone, compared with mixtures of rare earth elements. Increasing the application doses of rare earth element(s) appeared to cause a positive Gd and negative Ce anomaly in the roots and in the plant tops, and the anomaly was more obvious in the plant tops than in the roots. The results indicated that the Gd and Ce anomaly in corns might be considered as important parameters for the safety assessment of agricultural application of rare earth elements.

Two thousand years of atmospheric rare earth element (REE) deposition as revealed by an ombrotrophic peat bog profile, Jura Mountains, Switzerland.

A peat core from a Swiss bog represents 2110 14C years of peat accumulation and provides a continuous record of atmospheric rare earth element (REE) deposition. This is the first study providing a time-series of all REE originating from the atmosphere. Concentrations of the 14 REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were determined using inductively coupled plasma-mass spectrometry (ICP-MS) after dissolution of 200 mg aliquots of age-dated peat samples with 3 ml HNO3 and 0.1 ml HBF4 at 240 degrees C in a microwave autoclave. Strict quality control schemes were applied to ensure the accuracy of the applied analytical methodology. Previous analyses of selected REE by instrumental neutron activation analysis (INAA) in the same set of peat samples revealed that INAA frequently under- or overestimated REE concentrations in a systematic manner. Concentration profiles obtained for all REE were almost identical, except for Ce and Eu. Calculation of enrichment factors (EF) revealed a distinct depletion of heavy REE relative to light REE in peat samples since the beginning of the 19th century which marks the onset of the Industrial Revolution in Europe, suggesting a pronounced influence by anthropogenic activities. Enrichments of REE calculated using Sc as a reference element exceeded unity, relative to the Upper Continental Crust. Overall, EF in all peat samples ranged from 1.96 for Sm to 2.34 for Gd, with considerably lower EF for Ce (1.82) and Eu (1.44), respectively. A significant enrichment of all REE which may have been caused by military activities, was observed in the peat sample dating from World War II (1944); this exceptional sample, however, is not enriched in Ce. The concentration profiles of REE were similar but not identical to those of other lithogenic, conservative reference elements such as Sc, Y, Al, Zr and Ti. While it has been suggested that individual REE concentrations or the sum of REE can be used as a reference parameter to calculate crustal EF in environmental samples the data presented here indicates that anthropogenic emissions of REE cannot simply be ignored.

Distributions of rare earths and heavy metals in field-grown maize after application of rare earth-containing fertilizer

Rare earths are widely applied in Chinese agriculture to improve crop nutrition through the use of fertilizers, yet little is known of their accumulation in field-grown crops. We have studied the distribution of 16 rare earths (Sc, Y and 14 lanthanide elements) in field-grown maize and the concentration of heavy metals in the grains after application of rare earth-containing fertilizer. When maize entered the vigorous vegetation growth stage (e.g. early stem-elongation stage), rare earth-containing fertilizer was applied to the soil with irrigation water. At 10 days after application of the rare earths, significantly dose-dependent accumulative effects of individual rare earth concentrations in the roots and the plant tops of maize were observed, with the exception of Sc and Lu. At the level of 2 kg rare earths ha −1, accumulative concentrations of most light rare earths (e.g. La, Ce, Pr and Nd) and Gd in the plant tops were much larger than those in the control. Concentrations of individual rare earths in a field-grown maize after application of rare earths decreased in the order of root≫leaf>stem>grain. During the maize growth period, selective accumulation of individual rare earths (e.g. La, Ce) in the roots seemed to be in dynamic equilibrium, and the distribution of these elements in the plant tops was variable. At a dosage of less than 10 kg rare earths ha −1, no apparent accumulative concentrations of individual rare earths appeared in the maize grains. Under the experimental conditions, application of rare earth-containing fertilizer did not induce an increase in the concentrations of heavy metals in the grains. We conclude that the present dosage of rare earths (<0.23 kg ha −1 year −1) currently applied in China can hardly affect the safety of maize grains in arable soil, even over a long period.

Burn-up measurements on nuclear reactor fuels using high performance liquid chromatography

Burn-up measurements on thermal as well as fast reactor fuels were carried out using high performance liquid chromatography (HPLC). A column chromatographic technique using di-(2-ethylhexyl) phosphoric acid (HDEHP) coated column was employed for the isolation of lanthanides from uranium, plutonium and other fission products. Ion-pair HPLC was used for the separation of individual lanthanides. The atom percent fissions were calculated from the concentrations of the lanthanide (neodymium in the case of thermal reactor and lanthanum for the fast reactor fuels) and from uranium and plutonium contents of the dissolver solutions. The HPLC method was also used for determining the fractional fissions from uranium and plutonium for the thermal reactor fuel.

Rare earth element content in various waste ashes and the potential risk to Japanese soils

Selected chemical characteristics of rare earth elements (REEs) in 89 waste ash samples, including food scrap ashes (FSA), animal waste ashes (AWA), horticulture waste ashes (HWA), sewage sludge ashes (SSA) and incinerator bottom ashes (IBA), were examined in this study. The results showed that Y, La, Ce, Pr, Nd, Dy, Yb, Ho, Er, Tm, Lu in the waste ash samples were normally distributed, but Sc, Sm, Eu, Gd, Tb were not. Average REE concentrations followed the sequence of Ce>La≒Y>Sc>Nd>Sm>Pr>Gd>Dy>Eu>Tb>Er>Yb>Ho>Lu>Tm. Of the five types of waste ashes, total REE contents (∑REE) ranged from 54 to 130 mg/kg, following the sequence of SSA>HWA>IBA>AWA>FSA; individual REE concentrations were within 0.04–20, 0.1–29, 0.2–33, 0.1–44 and 0.01–41 mg/kg for FSA, AWA, HWA, SSA and IBA, respectively. Crust-normalized REE patterns indicated that SSA was enriched with Sc, Sm, Eu, Gd, Tb and slightly enriched with La, Ce; IBA was enriched with Eu, Tb and slightly with La, Y, Ce; FSA was slightly enriched with Sm, Eu, Tb; REEs were not found to be elevated in HWA and AWA. Comparison of REE content in the waste ashes and in six principal Japanese agricultural soils indicated that application of FSA, AWA and HWA to agricultural land will cause no REE problem, but continuous application of SSA or IBA may cause Sc, Sm or Eu accumulation in some of the soils.

Studies on application of polyacrylate anion-exchangers in sorption and separation of iminodiacetate rare earth element(III) complexes

Polyacrylate anion-exchanger resins are considered economically useful for selective isolation, concentration and recovery of nickel, iron, copper and cobalt cyanide complexes. They also find wide application in food processing, pharmaceutical industry, sugar refining, etc. This kind of polyacrylate anion-exchangers has been applied by us to separate rare earth element complexes with IMDA. Strongly basic gel and macroporous polyacrylate anion-exchangers Amberlite IRA 458 and Amberlite IRA 958 were used. The following pairs of iminodiacetate rare earth element complexes were selected for separation: Sm(III)–Ho(III), La(III)–Nd(III), La(III)–Pr(III) based on the affinity of these elements for strongly basic anion-exchangers. The results obtained indicate the possibility of application of anion-exchangers of this type for separation of individual lanthanide pairs in macro–micro systems. High yield of the obtained preparations is the evidence for the practical application of this method.

Phosphodiester hydrolysis by lanthanide complexes of bis-tris propane.

Potentiometric titrations of the mixtures of lanthanide(III) perchlorates and bis-Tris propane (BTP) reveal formation of dinuclear hydroxo complexes M2(BTP)2(OH)n(6-n), where M = La(III), Pr(III), Nd(III), Eu(III), Gd(III), and Dy(III) and n = 2, 4, 5, or 6, in the pH range 7-9. ESI-MS data confirm the presence of dinuclear species. Kinetics of the hydrolysis of bis(4-nitrophenyl) phosphate (BNPP), mono-4-nitrophenyl phosphate (NPP), and 4-nitrophenyl acetate (NPA) in the lanthanide(III)-BTP systems has been studied at 25 degrees C in the pH range 7-9. The second-order rate constants for the hydrolysis of BNPP by individual lanthanide hydroxo complexes have been estimated by using the multiple regression on observed rate constants obtained at variable pH. For a given metal, the rate constants increase with increasing in the number n of coordinated hydroxide ions. In a series of complexes with a given n, the second-order rate constants decrease in the order La > Pr > Nd > Eu > Gd > Dy. Hydrolysis of NPP follows Michaelis-Menten-type "saturation" kinetics. This difference in kinetic behavior can be attributed to stronger binding of NPP dianion than BNPP monoanion to the lanthanide(III) species. Activities of lanthanide complexes in the hydrolysis of NPA, which is 10(6) times more reactive than BNPP in alkaline or aqueous hydrolysis, are similar to those in BNPP hydrolysis indicating unique capability of lanthanide(III) cations to stabilize the transition state of phosphate diester hydrolysis. Results of this study are analyzed together with literature data for other metal cations in terms of the Brønsted correlation and transition state-catalyst complexation strength.

Effects of lanthanum and mixtures of rare earths on ammonium oxidation and mineralization of nitrogen in soil

SummaryRare earths are applied widely in Chinese agriculture to improve crop nutrition and incidentally in fertilizers, yet little is known of their effect on the biological functioning of the soil. We have studied the effects of lanthanum and of mixtures of rare earths on the potential ammonium oxidation and nitrogen mineralization in soil by incubation experiments in the laboratory. The no‐observed‐effect and median effective concentrations of the rare earths on these two processes are reported, and their corresponding mechanisms are discussed. For mixtures, the no‐observed‐effect concentrations relating to potential ammonium oxidation and N mineralization were at 393 and 373 mg rare earths kg−1 soil, respectively, and their median effective concentrations were at 1576 and 1108 mg kg−1 soil, respectively. When lanthanum was applied alone, the no‐observed‐effect concentrations relating to potential ammonium oxidation and N mineralization were at 432 and 443 mg La kg−1 soil, respectively, and their median effective concentrations were at 18 212 and 1237 mg kg−1 soil, respectively. Therefore, the influence of mixtures of rare earths on potential ammonium oxidation or on N mineralization was slightly stronger in comparison with that of lanthanum. Mineralization of nitrogen is apparently more sensitive to the stress caused by rare earths than ammonium oxidation. We conclude that the influence of individual rare earths in the mixtures on the above two processes can be additive and that the present dosage of mixed rare earths (&lt; 230 g ha−1 year−1 or 0.15 mg kg−1 soil year−1) currently applied in China can hardly affect the potential ammonium oxidation and N mineralization in the soil even over a long period.

Recovery of europium by chemical reduction of a commercial solution of europium and Gadolinium chlorides

A chemical reduction–precipitation process was applied to the separation and recovery of high-grade europium oxide from a europium/gadolinium mixture containing 1.90% Eu 2O 3. The effects on europium recovery of the presence of mercury in the reducing agent, temperature, aging time, the nature of the sulfate carrier, and the method of addition of the precipitation agent were studied in detail. Similar grades (95.0±0.5% Eu 2O 3) were obtained with both Zn amalgam and pure Zn powders. The precipitation with sulfuric acid was more selective as compared to that with ammonium sulfate (95% and 80% Eu 2O 3, respectively, for 95% recovery). The continuous addition of the precipitating agent was the main factor responsible for improving europium grades, which increased from 93% to 97% in the first stage, with less acid requirements (SO 4 2−: Eu molar ratio decreased from 16 to 5.3). After two stages of reduction–precipitation, grades were higher than 99.99% Eu 2O 3 and recovery was 94%. The levels of individual rare earth impurities in the final Eu 2O 3 product were below 0.001%.

Selective transport of lanthanides through supported liquid membranes containing non-selective extractant, di-(2-ethylhexyl)phosphoric acid, as a carrier

Permeation of lanthanides (Ln) between aqueous nitrate solutions of different acidity through supported kerosene membrane containing di-(2-ethylhexyl)phosphoric acid (DEHPA) as a carrier has been studied. Mass transfer of Ln cations has been determined in terms of permeability coefficients ( P) by on-line FIA measurement of metal concentrations in strip solution. Acidity of feed solution ranged from pH 1.2 to 4.2 (ionic strength 0.1 mol l −1 (HNO 3, NaNO 3)) while that of strip solution was kept constant at 0.1 mol l −1 HNO 3. Carrier concentration has been changed in the range from 10 to 10 3 mmol l −1. Both, the P versus feed pH plots measured at low and at high DEHPA concentrations as well as P versus DEHPA concentration plots exhibited maxima. Permeability coefficients were decreasing when advancing in the lanthanide series and significant differences in behaviour of individual lanthanides has been observed. The conditions of separation of light and heavy lanthanides and mutual separation of light lanthanides have been suggested. Based on these and previous results, composition of transported species, presence of maxima on measured curves, and formation of gel-like substance in feed solution and on membrane-feed solution interface are discussed.

Assessment of the bioavailability of rare earth elements in soils by chemical fractionation and multiple regression analysis

The bioavailability of rare earth elements (REEs) in soils was evaluated, based on the combination of chemical fractionation and multiple regression analysis. REEs in soils were partitioned by a sequential extraction procedure into water soluble (F(ws)), exchangeable (F(ec)), bound to carbonates (F(cb)), bound to organic matter (F(om)), bound to Fe–Mn oxides (F(fm)) and residual (F(rd)) fractions. Alfalfa ( Medicago Staiva Linn.) had been grown on the soils in a pot-culture experiment under greenhouse conditions for 35 days. The concentrations of REEs in fractions and plant were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Chemical fractionation showed that (F(ws)) fraction of REEs was less than 0.1% and residual (F(rd)) was the dominant form, more than 60% in soils. Bioaccumulation of REEs was observed in Alfalfa. REE availability to the plant was evaluated by multiple regression analysis. F(ws), F(ec), F(cb) and F(om) fractions were significantly correlated with REE uptake by alfalfa. But the exchangeable Pr(F(ec)) was significantly correlated with Pr concentration in alfalfa. F(ec), F(cb) and F(om) greatly contributed to La and Nd bioavailability; F(ec) and F(om) to Ce, Gd and Dy; F(ec) and F(cb) to Yb; and F(ws), F(ec) and F(om) to total REEs. This meant that the bioavailability of different species of REEs varied with individual REE. The results of this study indicated that the sequential extraction procedure, in conjunction with multiple regression analysis, may be useful for the prediction of plant uptake of REEs from soils.

Eriochrome Black T as a post-column reagent for the ion chromatographic determination of rare earths

The use of Eriochrome Black T in an alkaline, 40% methanol solution was found to be appropriate as post-column reagent for the determination of rare earths by ion chromatography. Detection of individual lanthanides and lanthanum was carried out at 512 nm and 650 nm after separation by dynamic cation exchange chromatography with gradient elution on C 18 column and employing a solution containing α-hydroxyisobutiric acid/sodium octanesulfonate at pH 3.8 as eluent. The effect of the presence of micelles in the post-column reagent was studied. Sensitivities obtained by the addition of the cationic surfactants cetylpyridinium chloride (CPC) and hexadecyltrimethylammonium bromide (CTAB) were lower than those measured without surfactant addition. In some cases, the signal was totally suppressed. No change in sensitivity was observed with non-ionic (Triton X-100) or anionic (sodium dodecylsulphate, SDS) surfactants but a slight improvement in the baseline noise was observed with the SDS. An evaluation of the influence of chemical and operational variables on the post column reaction (PCR) reagent was carried out either by spectrophotometric tests or by chromatographic experiments. A comparison was performed between three PCR reagents: Eriochrome Black T and xylenol orange in the presence of a cationic surfactant and arsenazo III. Calibration response was linear up to an analyte concentration of 5.0 μg ml −1. Absolute detection limits lower than 7 and 17 ng were obtained at the detection wavelengths of 650 nm and 512 nm respectively, for all the natural lanthanides and lanthanum.

The non-destructive determination of REE in fossilized bone using synchrotron radiation induced K-line X-ray microfluorescence analysis

The sensitivity and applicability of the synchrotron radiation induced X-ray microfluorescence (μ-SRXRF) spectrometer at the Hamburg synchrotron laboratory Hasylab for the determination of the distribution of trace concentrations of rare-earth elements (REE) in fossilized bone are discussed and critically compared to those of other trace analytical methods such as instrumental neutron activation analysis (INAA) and LAMP-ICPMS (laser ablation microprobe inductively-coupled plasma mass spectrometry). Measurements were carried out on two bone samples from contrasting terrestrial depositional environments at Olduvai Gorge (Tanzania). Results indicate that the microdistribution of the REE in these biological materials is not homogeneous and that the relative abundance of these elements can provide information on the palaeoenvironment during the fossilization process. The heterogeneous distribution of the REE can be determined in a quantitative and completely non-destructive manner provided the concentrations of individual REE are above 10 μg/g.

Separation and Estimation of Lanthanides as Mixed-Ligand Complexes with Hexafluoroacetylacetone and Tri-n-octylphosphine Oxide Using Solvent Extraction and Gas Chromatography

The application of gas chromatography (GC) to the analysis of lanthanides as mixed ligand complexes with hexafluoroacetylacetone (HFAA) and tri-n-octylphosphine oxide (TOPO) is investigated. Thermogravimetric studies indicate that these complexes are volatile without decomposition at low temperature (100–200°C). The volatility of mixed chelates is found to increase with the decreasing radius of the trivalent lanthanide ion. Trivalent lanthanide ions are found to be quantitatively extractable with HFAA, a neutral donor, and TOPO as a mixed ligand complex in the pH range 2–7. The organic extract can be directly fed into a GC for separation and estimation. The optimum conditions for the estimation of lanthanides using GC are established. Chromatograms of lanthanides at different concentration ratios illustrate the possibility of the estimation of one lanthanide ion when as much as a 10-fold excess of other lanthanide ions is present in a mixture. Calibration curves of each of the individual lanthanides and their mixtures are studied in the concentration range 0.2–25 µg/mL

Studies of sorption and separation processes of rare earth element complexes on the anion-exchanger Wofatit SBW in the CH 3OH–HNO 3 system

For the 90% v/v CH 3OH–10% v/v 7 M HNO 3 system the affinity series of nitrate complexes of rare earth elements(III) for the strongly basic anion-exchanger Wofatit SBW×4% DVB was determined. The effect of ammonium nitrate and polar organic solvent addition on the effectiveness of separation of the ion-exchanging pair Y(III)–Nd(III) on Wofatit SBW×4% DVB as well as that of macrocomponent (yttrium) concentration on the yield of the purification process on Wofatit SBW×6% DVB were investigated. The weight and bed distribution coefficients for individual rare earth elements(III) were determined. It was shown that the neodymium content in the purified yttrium(III) can be decreased from 1% to 10 −3% under controlled conditions.