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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) much greater than 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 H2SO4 with an aliquot of H2O2.Roasted bastnasite made in Baotou (China) by Na2CO3 and leached by HNO3, 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 CeO2 products with high purity of 99.9-99.99%, with a yield of >85%, in which ThO2/CeO2 < 10(-4).

Extraction of rare earth elements from bastnasite (REFCO 3 ) and monazite (REPO 4 ) after fluorine fixation was studied. Chlorination kinetics of fluorine-fixed flotation bulk concentrate with ammonium chloride was found to follow the regional reaction model. The chlorination was found to involve two series steps with nuclear growth occurred in normal to surface direction. Internal diffusion was identified to be the rate limiting step of the chlorination process and an apparent activation energy of 36.8 kJ mol was determined.

The Kizilcaoren fluorite–barite–Rare Earth Element (REE) deposit occurs as epithermal veins and breccia fillings in altered Triassic metasandstones and Oligocene–Miocene pyroclastics adjacent to alkaline porphyritic trachyte and phonolite. This deposit is the only commercial source of REE and thorium in Turkey. Most of the fluorite–barite–REE mineralisation at Kizilcaoren has been formed by hydrothermal solutions, which are thought to be genetically associated with alkaline volcanism. The occurrence of the ore minerals in vuggy cavities and veins of massive and vuggy silica indicate that the ore stage postdates hydrothermal alteration. The deposit contains evidence of at least three periods of hypogene mineralisation separated by two periods of faulting. The mineral assemblage includes fluorite, barite, quartz, calcite, bastnasite, phlogopite, pyrolusite and hematite as well as minor amounts of plagioclase feldspar, pyrite, psilomelane, braunite, monazite, fluocerite, brockite, goethite, and rutile. Fluid inclusion microthermometry indicates that the barite formed from low salinity (0.4–9.2 equiv. wt% NaCl) fluids at low temperatures, between 105 and 230 °C, but fluorite formed from slightly higher salinity (

The main industrial minerals used up to now for rare earth production are bastnasite, monazite, xenotime and rare earth adsorption clays. Bastnasite, monazite and xenotime are all processed by caustic soda leaching or sulfuric acid roasting. For the time being, rare earth adsorption clays have been processed only in China with a quite different technology. Ammonium sulfate solution is sprayed onto the ore – thereby directly producing rare earth ions (RE 3+ ) in aqueous solution. But, most of the current projects dedicated to rare earths raw materials production outside of China are based on different minerals (Eudyalite, Fergusonite, Apatite…). None of these minerals has been treated industrially and all need technology development and lead to complex processes.

¶Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastnasite in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr2O3 vs. Fe2O3 and Cr2O3 vs. Fe2O3/TiO2 diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia.

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.

The composition of REE minerals from the Bayan Obo Fe-REE-Nb deposit, China, varies widely with paragenesis. The properties of fluid inclusions also vary with paragenesis, indicating changing fluid conditions during the deposits formation. In early disseminated monazite and in the main stage banded ores, the chondrite normalised La/Nd ratio varies from similar to 3 to 7, whilst vein-hosted bastnasite and monazite show ratios in the range similar to 4.8 to 5.8. The La-rich portion of this trend (La/Nd > 4) is inferred to correlate with high X(CO2) in the hydrothermal fluid. Minerals with lower La/Nd ratios are inferred to have formed from dominantly aqueous solutions. This correlation is interpreted as arising from the greater retention of neutral species in low dielectric constant, CO2-rich fluids, relative to the dominantly aqueous fluids. At high T, high ligand number complexes of La are predicted to be more strongly associated than for the other REE, leading to the observed fractionation. The La/Nd ratio of later stage REE-fluorocarbonate minerals ranges from similar to 0.6 to 2. This mineralisation took place at lower T (minimum estimates of 250-150 degrees C from fluid inclusions) from dominantly aqueous fluids. Under these conditions the association constants of REE complexes typically increase with atomic number, leading to greater M- to HREE solubilities in hydrothermal fluids. Late stage alteration of all the earlier paragenetic stages by Ba-bearing fluids lead to the release of La into solution. This process was probably controlled by the relative solubilities of end-member REE minerals as well as speciation in the hydrothermal fluid. The fractionation processes inferred from Bayan Obo are relevant to many other REE-rich hydrothermal systems. In particular La-Nd fractionations are common in REE mineralised carbonatites and could be fully accounted for by the models presented here. Copyright (C) 2000 Elsevier Science Ltd.

The crystal structure of parisite–(Ce) was solved and refined to R = 0.044, Rw = 0.037 using three–dimensional X–ray diffraction data (XRD). In contrast to the putative hexagonal cell, weak XRD maxima on precession films demonstrate that the parisite–(Ce) is monoclinic with a space group C 2/ c or Cc . The unit cell was refined as a = 12.305(2), b = 7.1053(5), c = 28.250(5) A, and β = 98.257(14)°. The structure refinement confirmed the space group Cc . Like bastnasite and synchysite, parisite possesses a (001) layer structure, with layers of (Ca) and (CeF) separated by layers of carbonate groups. The [001] layer stacking sequence is ... (Ca), (CO 3 ), (CeF), (CO 3 ), (CeF), (CO 3 ), (Ca), (CO 3 ), (CeF), (CO 3 ), (CeF), (CO 3 ).... The parisite-(Ce) structure can be considered as two portions of the bastnasite structure connected by a (Ca) layer. The insertion of a (Ca) layer would create long [001]* structure voids in the F columns if the bastnasite portions stacked hexagonally; therefore, the two bastnasite portions are offset along [110] by a /6(sin60°) (or [1 − 00] in hexagonal cells, by a /3) such that the oxygen atoms of the vertical edges of the carbonate groups occupy the voids. Polytypism results because a bastnasite portion can shift equally in two possible directions, ±120° from the previous offset vector. The parisite-(Ce) structure elucidated herein is the simplest and most common polytype possible, 2M. The polytype 6R, which was previously believed to be the most common, has not been found during our extensive study.

Textural relationships occurring in a range of settings from the Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China, indicate reaction between monazite [(REE)PO4], bastnasite [(REE)(CO3)F] and apatite. Within dolomite marble-hosted ores monazite grains occur surrounded by zones of intergrown bastnasite and apatite. In fluoritised dolomite marble-hosted amphibole-calcite veins, co-existing apatite and bastnasite are separated by zones of monazite plus calcite, whilst in aegirine-apatite veins hosted by banded aegirine-fluorite-magnetite-bastnasite rocks, they are separated by zones of monazite and fluorite. Modal proportions for minerals in the reaction zones have been used to derive reaction stoichiometries, and suggest the following reactions: Consideration of these reactions, along with published experimental data and other reported mineral assemblages, suggests that the factors controlling the relative stabilities of monazite and bastnasite are the pH, and the activities of HF °, CO3 2−, Ca2+ and PO4 3−. Textures indicating reaction between REE phosphates and fluorocarbonates have been reported from a number of other settings and are consistent with the controls on reaction inferred from this study. The range of assemblages seen at Bayan Obo is a result of the variation between relatively unbuffered fluid compositions, and those buffered by the fluoritisation of the carbonate host rock. Mass-balance calculations suggest some mobilisation of the REE into the fluid phase during reaction, although this did not significantly alter the REE distribution in monazite and bastnasite. The mineral compositions also reveal variation in the REE distribution with different paragenetic settings indicating variation in the composition of the metasomatic fluids. These changes may be related to changes in the fluid source region, or to variations in the fluid chemistry, particularly X CO2, leading to different REE solubilities at different periods in the development of the deposit.

Rare earth element (REE) concentrations were analysed by atom Balashov & Pozharitskaya, 1968; Eby, 1975; von Maravic emission spectrometry (ICP-AES) in whole-rock samples and min& Morteani, 1980; Moller et al., 1980; Viladkar & Paeral separates of plutonic carbonatites from different localities. waskar, 1989) have established that both whole rocks Calcite, dolomite, apatite, and unaltered pyrochlore show parallel and most primary minerals (calcite, dolomite, apatite, to subparallel REE distribution patterns at different enrichment pyrochlore, perovskite and Ca-bearing silicates) are levels. The REE distribution in the whole rocks is controlled by strongly enriched in REE, with enrichment factors inthat of the carbonates because of their high modal amounts and by creasing steadily from Lu to La. The REEs reside mainly that of apatite because of its high REE abundances. REE-rich in the Ca-bearing phases, i.e. carbonates, apatites, Ca, accessory phases such as pyrochlore will influence the whole-rock Nb-oxides and Ca-silicates, where they substitute with pattern only when present in sufficient amounts. On the basis of Sr for Ca. Specific REE minerals such as ancylite, variations in REE distributions and mineral chemistry, several bastnasite, britholite, monazite, parisite, etc. are either rare and volumetrically insignificant accessory phases groups of sovites can be distinguished among the samples studied (with the possible exception of bastnasite in the Mountain here. The highest REE concentrations and the strongest light REE Pass carbonatite; Jones & Wyllie, 1983) or, more com(LREE) enrichment is found in sovites from Oka, Kaiserstuhl, and monly, products of the breakdown of REEand Sr-rich Alno that contain Mg-poor calcites, Si-rich apatites and Ca-bearing primary carbonate and apatite during post-magmatic silicates. These sovites are associated with melilititic or nephelinitic processes (e.g. Andersen, 1984; Lottermoser, 1988, 1990). rocks. Less pronounced LREE enrichment is found in sovites, This study focuses on REE concentrations in wholedolomitic carbonatites and phoscorites from Sokli, Siilinjarvi, Phalrock samples and mineral separates of carbonates, apatite aborwa, Jacupiranga and Fen, which contain Mg-rich calcites and accessory phases of plutonic carbonatites. The sample and/or dolomite, Si-poor apatite and Mg,Fe-silicates (olivine, suite consists mainly of sovites with a few associated phlogopite). These carbonatites are associated with potassium-rich dolomitic carbonatites and silicate rocks from localities peralkaline ultramafic rocks and lamprophyres. world wide. Its aim is to compare REE levels in the most common type of carbonatite and to evaluate the ways in which the REEs are enriched in carbonatites, which have

Within the Nkombwa Hill carbonatite complex, bastnasite-(Ce), (Ce,La)CO3F, has been identified as an abundant mineral in xenoliths hosted by late-stage ferrocarbonatite sills and dykes. Bastnasite-(Ce) occurs as fibrous yellow crystals, about 1 µm in size, replacing monazite and in association with baryte, in a matrix of dolomite. In common with bastnasite-(Ce) from other locations, the bastnasite-(Ce) of Nkombwa Hill contains up to 70% RE2O3, almost entirely as light rare-earth oxides. However, Nkombwa Hill bastnasite-(Ce) is relatively deficient in La and enriched in Pr and Nd.

Reaction of N-phenyl-pivalohydroxamic acid with Ce(III) precursors leads to a homoleptic hydroxamate complex: Ce(IV)[(t)BuC(O)N(O)Ph]4. Electrochemical experiments indicate a significant stabilization of the Ce(IV) cation at Ep,c = -1.20 V versus SCE in the hydroxamate ligand framework. The spontaneous oxidation of Ce(III) in a hydroxamate ligand field is discussed in the context of beneficiation of the light rare earths from the fluorocarbonate mineral bastnäsite.

This paper considers the market trends of the rare earths and how they are strongly influenced by the by-product/co-product nature of their mining and processing. The two main economic minerals for the rare earths are bastnasite and monazite. Monazite is primarily a by-product of mining ilmenite and rutile and is affected by changes in these markets as well as the presence of thorium. Bastnasite is a byproduct of mining iron ore in China and a stand-alone product in the USA. The paper will use conceptional relationships and empirical data to delineate the various by-products/co-products relationships and how they determine observed market behavior.

A dry process for the separation of rare earths has been investigated using a chemical vapor transport reaction mediated by metal halide vapor complexes KRCl 4 (g) and RA n Cl 3+3 n (g) (R = rare earths), in which KCl and AlCl 3 act as complex formers, i.e. transporting agents. Rare earth concentrates of monazite and xenotime were used as raw materials as well as the crude oxides originating from monazite, bastnasite and ionic ores. The concentrates and crude oxides were chlorinated by Cl 2 gas at 1000°C. The resulting RCl 3 reacts with the complex formers KCl and AlCl 3 and was extracted as the vapor complexes, which selectively decompose along a well-controlled temperature gradient to give the RCl 3 . Heavier rare earth chlorides including YCl 3 were generally more readily transported and concentrated in the deposit at temperatures around 600–700°C, and lighter ones in higher temperature fractions at 800–900°C. Chlorides of other elements such as Th, U and P in the raw materials were generally concentrated in lower temperature fractions. Yields of individual rare earths after reaction for 82 h increased with increasing atomic number or decreasing ionic radius of the rare earth ion: 20%–30% for La; 50%–60% for Ce; 60%–70% for Pr and Nd; >80% for Gd-Lu and Y.

The bastnasite of Baotou (China) was roasted in concentrated sulfuric acid at 250-300 degreesC and the calcined products were leached by water. Almost all rare earths (RE) were moved into solutions in trivalent along with some radioactive impurity thorium(IV) (Th(IV))which accounts for 0.4% of RE and other impurities such as Fe(III), Ca, F, P, etc. Through fractional extraction (seven stages for extraction and nine for scrubbing), the mass ratio of Th(IV) and RE (ThO2/REO) in solution has decreased to 5 x 10(-6). The purity of ThO2 product recovered from organic phase is above 99%. The iron(III) in solutions can be removed in the form of precipitation by adding some magnesia into the solutions. Then RE can be concentrated by solvent extraction with 2-ethylhexyl phosphinic acid 2-ethylhexylester (P-507). The results of fractional extraction show that the concentration of total RE in aqueous solutions stripped by hydrochloric acid is over 200 g REO/I with the yield of RE above 99%. Individual RE can be attained by solvent extraction with P507 in the following process.

The mineral weloganite Na2Sr3Zr(CO3)6·3H2O has been studied by using vibrational spectroscopy and a comparison is made with the spectra of weloganite with other carbonate minerals. Weloganite is member of the mckelveyite group that includes donnayite-(Y) and mckelveyite-(Y). The Raman spectrum of weloganite is characterized by an intense band at 1082 cm−1 with shoulder bands at 1061 and 1073 cm−1, attributed to the CO 3 2 - symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of CO 3 2 - symmetric stretching vibration varies with mineral composition. The Raman bands at 1350, 1371, 1385, 1417, 1526, 1546, and 1563 cm−1 are assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for weloganite is significant in that it shows distortion of the carbonate anion in the mineral structure. The Raman band observed at 870 cm−1 is assigned to the (CO3)2− ν2 bending mode. Raman bands observed for weloganite at 679, 682, 696, 728, 736, 749, and 762 cm−1 are assigned to the (CO3)2− ν4 bending modes. A comparison of the vibrational spectra is made with that of the rare earth carbonates decrespignyite, bastnasite, hydroxybastnasite, parisite, and northupite.

The Proterozoic (ca. 2.1 Ga) Blatchford Lake suite hosts significant concentrations of rare metals at the core of a peralkaline granite–syenite pluton. After emplacement of the Grace Lake Granite and the Thor Lake Syenite within it, bodies of nepheline syenite, ijolite, and urtite were intruded beneath the present-day Lake zone. This is the largest of five zones of mineralization and lies close to the apex of the Thor Lake Syenite, a region which was then subjected to albitization, microclinization, and, finally, rare-metal mineralization. The underlying silica-undersaturated rocks contain clots of rare-metal-bearing minerals, including cerianite-(Ce), britholite-(Ce), thorite, and calcium catapleiite, interstitial to nepheline and aegirine. The Lake zone itself contains major quantities of Zr (in zircon), Nb (in ferrocolumbite, pyrochlore group minerals, aeschynite group minerals, and fergusonite-(Y)), and Ce (in allanite-(Ce), monazite-(Ce), and bastnäsite group minerals). Lesser amounts of Ta, Y, heavy rare earth elements, U, Th, and Ga are also present, mainly as minor components of rare-metal-bearing minerals. Electron microprobe analyses of the major rare-metal-bearing minerals are presented.

The Riviera W–Mo deposit is hosted by I- and A-type granitoids of the Neoproterozoic to Palaeozoic Cape Granite Suite that intruded the meta-volcano-sedimentary Malmesbury Group of the Saldania Belt. Scheelite-powellite and molybdenite are the principal ore minerals and are associated with greisen-, reduced endoskarn- and vein-type pervasive alteration of the granitoids. Exoskarn ore makes an insignificant contribution to the total resources. The mineralised body is dome-shaped and located in the roof or cupola of the granitoid pluton. The deposit has an outlined resource of 46 million tons at a grade of 0.216% tungsten (WO3) and 0.02% molybdenum (Mo) with a high grade zone of 7 million tons of 0.30% WO3 and 0.02% Mo. Significant concentrations of Ce–La-enriched allanite, a light rare earth-enriched mineral of the epidote group, were recently discovered in the high tungsten grade, endoskarn part of the Riviera pluton. A resource of some 20 million tons at a tentative average grade of 0.35% ΣREE and has been indicated for this zone. Considering the high demand for rare earth elements this could constitute an economically important by-product and contribute towards the viability of a presently marginal W–Mo deposit. The textural and late stage alteration features of allanite are however complex and could inhibit its recovery and the production of a high grade allanite concentrate. Poikilitic intergrowths of apatite, zircon, monazite, kalkowskite and beckelite, variable chemistry indicated by zoning, metamictization as well as alteration of allanite to parasite and bastnasite will result in poor recovery and present a formidable geometallurgical challenge. Although allanite is not the rare earth mineral of choice by the international metals market the anticipated increased demand for light rare earth elements could change this situation in the future.

Ceramic bodies of mullite composition were prepared from a mixture of calcined alumina and raw kaolin with the addition of bastnasite (rare-earth oxide concentrate) at up to 3% wt and fired at 1400–1650°C. The bastnasite addition effectively enhances mullite formation but the effect diminishes rapidly with increasing temperature. The Al 2 O 3 -rich composition is characteristic of the mullite. The ceramic green compacts with the bastnasite addition can only approx. reach 96% theoretical density at best when heated at 1550–1650°C. The pores in the fired bodies with the bastnasite addition are smaller and uniformly distributed; localized, larger pores are found in the fired bodies without the addition. The slag resistance of the refractories increases slightly with an increasing amount of bastnasite added to the bonding matrix. Bastnasite is not an effective additive for enhancing the slag resistance of steel-plant refractories. The peak temperature in DTA and the valley temperature in the dilatometric analysis, are indicative of mullite formation: the former was found to be 1412°C without bastnasite addition and 1368°C with 3% wt bastnasite addition while the latter was found to be 1420°C without bastnasite addition and 1350°C with 3% wt bastnasite addition.

This paper investigates the development of a new environment friendly approach for treatment of bastnasite. A new process was developed to recover fluorine from bastnasite as synthetic cryolite by-product. The conditions affecting the fluorine removal and recovery in the process, including contact time, acidity, Al 3+ concentration, Al/F molar ratio and different kinds of aluminum salts being used, were investigated. The results indicate that high acidity and large Al/F molar ratio were beneficial to fluoride removal, and that the reaction reached equilibrium after 15 min. The effect of the initial Al 3+ concentration at a certain total Al 3+ amount was slight. Aluminum nitrate was more efficient than aluminum sulfate for the removal of fluoride. Optimum operation parameters for synthesizing cryolite have been obtained and proposed for industrial applications.

Translucent, dark-coloured titanites from a wide variety of geological environments are commonly partly replaced by very fine-grained aggregates of REE-rich minerals (including allanite, monazite, and bastnasite), rutile, quartz, calcite, apatite, and chlorite along grain fractures and boundaries. The aggregates of REE-rich minerals are bordered by an irregular zone of altered titanite, which, by secondary ion mass spectrometry (SIMS), is considerably lower in REEs, U, and Th than the adjacent unaltered matrix. Light REEs and Th are differentially depleted in the altered zone and correspondingly enriched in secondary minerals. Additionally, HREEs and U have been lost to the external system, the loss of HREEs being in proportion to the increase in atomic number. Natural radiation damage was not an important factor in promoting the late alteration of titanite. Titanite which has been subjected to late hydrothermal activity would not remain a closed system in respect to either U or Th decay series and therefore cannot be used for U/Pb and Th/Pb geochronology. The observed leaching and partial dissolution of titanite under hydrothermal conditions are generally consistent with laboratory experimentation, indicating that proper isolation from any communication with hydrothermal fluids is essential in the application of titanite-based ceramics for the immobilization of radioactive waste.

A dry process for the separation of rare earths has been investigated using a chemical vapor transport reaction mediated by metal halide vapor complexes KRCl 4 (g) and RA n Cl 3+3 n (g) (R = rare earths), in which KCl and AlCl 3 act as complex formers, i.e. transporting agents. Rare earth concentrates of monazite and xenotime were used as raw materials as well as the crude oxides originating from monazite, bastnasite and ionic ores. The concentrates and crude oxides were chlorinated by Cl 2 gas at 1000°C. The resulting RCl 3 reacts with the complex formers KCl and AlCl 3 and was extracted as the vapor complexes, which selectively decompose along a well-controlled temperature gradient to give the RCl 3 . Heavier rare earth chlorides including YCl 3 were generally more readily transported and concentrated in the deposit at temperatures around 600–700°C, and lighter ones in higher temperature fractions at 800–900°C. Chlorides of other elements such as Th, U and P in the raw materials were generally concentrated in lower temperature fractions. Yields of individual rare earths after reaction for 82 h increased with increasing atomic number or decreasing ionic radius of the rare earth ion: 20%–30% for La; 50%–60% for Ce; 60%–70% for Pr and Nd; >80% for Gd-Lu and Y.

An investigation of accessory minerals in plutonic rocks from central Madagascar reveals local very low-grade alteration of the primary REE and Th-bearing phases monazite ((LREE,Th)PO4), allanite (CaREEFe2+Al2(SiO7)(SiO4)O(OH)) and thorite (ThSiO4). All examples are found in relatively fresh looking samples, in which alteration occurs on the micron to submicron scale. The alteration occurs associated with micro-fissures and predominantly affects the accessory minerals. One type of alteration is replacement of thorite and monazite by thorogummite, (Th,U)[(SiO4)(OH)4], and rhabdophane, REEPO4·H2O. Some of these secondary phases grow topotactically on the original magmatic crystals. During development of rhabdophane, Pb and Th can be transferred from the monazite precursor to rhabdophane resulting in similar apparent ages for both phases. A second type of alteration, has been investigated in two granites where bastnasite (REECO3F) forms at the expense of allanite, which requires a fluid containing H2O, CO2 and F. In either type of alteration, mass transport of Pb is deduced from galena development in the vicinity of the altered mineral. In other examples, mass transport of REE is assumed based on REE-fractionation in secondary phases. Th-rich minerals (Th-rich monazite, thorite) are more affected by alteration than Th-poor phases. This may be due to chemical disequilibrium at low-temperatures or partial metamictization before alteration. Overlooking such alterations can lead to pitfalls during dating.

WOS: 000257829300007, A mixture of rare earth double sulfates was produced from a Turkish bastnasite-containing pre-concentrate (low grade concentrate) by sulfuric acid baking, subsequent water leaching and precipitation with sodium sulfate. The results of acid baking and leaching indicated that recoveries of rare earth elements up to 90% were readily obtained and the recovery of hydrofluoric acid as a by-product was also possible. Reasonable decontamination of the rare earth double sulfate salt from impurities such as Th, Fe, Al and Mg was possible by rapid precipitation at 50 degrees C using 1.25 times the stoichiometric amount of Na2SO4. The total rare earth double sulfate content (TREDS) was > 90% and analysed 17.3% La, 15.6% Ce, 3.2% Nd, 1.1% Pr, 0.3% Sm, 0.03% Eu, 0.01% Yb and 0.02% Y together with about 0.7% Ca, Fe, All and other impurities. (c) 2007 Elsevier B.V. All rights reserved.

The Strange Lake Zr, Y, REE, Nb, and Be deposit is hosted by a small, high-level, Late-Proterozoic peralkaline granite stock that intruded into high-grade metamorphic gneisses on the Quebec-Labrador border. The stock is extensively altered. Early alteration is manifested by the replacement of arfvedsonite with aegirine. Later alteration involved Ca-Na exchange. Zr, Ti, Y, REEs, Nb, and Be are concentrated in Ca-bearing minerals that, together with quartz, commonly pseudomorph Na-bearing minerals. Fluid inclusions in pseudomorphs comprise several distinct types: high-salinity (13 to 24 wt% NaCl eq.), Ca-rich aqueous inclusions that homogenize to liquid between 135 and 195°C; mixed aqueousmethane inclusions; methane inclusions; and solid-bearing inclusions. Aqueous-methane inclusions represent heterogeneous entrapment of immiscible high-salinity aqueous liquid and methane. Bastnasite (tentatively identified by SEM analysis) occurs as a daughter mineral. Other daughter or trapped minerals include a Y, HREE-bearing mineral, possibly gagarinite, and hematite, galena, sphalerite, fluorite, pyrochlore, kutnahorite (?), and griceite (?). The first three inclusion types also occur in quartz in pegmatites and veins together with lower-temperature, lower-salinity, Na-dominated aqueous inclusions. The entrapment temperature inferred for the aqueous inclusions from microthermometry and the Na-K-Ca geothermometer range from 155 to 195°C for the higher-salinity inclusions and 100 to 165°C for the low-salinity inclusions. A model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground/formational water-dominated hydrothermal system in adjacent gabbroic, calc-silicate, and graphitic gneisses. Reaction of the high-salinity, Ca-rich liquid with the graphitic gneisses led to the production of an immiscible methane gas. Subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200°C. Some time after the onset of Ca metasomatism the high-salinity liquid mixed with a Ca-poor, low-salinity, low-temperature liquid that had leached F and rare metals from the granite. Yttrium and REE mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the Ca-rich and Ca-poor aqueous liquids.

Several aluminosilicate compositions were tested for molten 7075 aluminum alloy attack with and without the addition of 10% Na2CO3. The extent of corrosion was proportional to the silica content of the refractory and especially of the matrix phase. The addition of rare earths up to 15% by weight to the aluminosilicates virtually eiiminated corrosion. Bastnasite, a rare-earth concentrate, was found to be a more effective additive at low concentrations than either CeO2 or La2O3 alone in rendering the aluminosilicates corrosion resistant.

Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al2O3 and residual ‘immobile’ elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO2 and Fe2O3. Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnasite group. Conservative indices, including TiO2/Al2O3 and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous.

Ore-forming solutions and the origin of mineralizing material in the Dalucao rare earth deposit were studied by means of H, O, C, and Si isotope analyses. The δ13C of the bastnasite range narrowly from −8.1‰ to−8.0‰, while the δD values range from −89‰ to −79‰. The quartz δ30Si of the orebody is −0.3‰, and the δD and δ180 of the quartz-fluid inclusion range from −87‰ to +6.0‰, respectively. The δD and δ180 values of the fluorite-fluid inclusion in the ore body are −99‰ to −11.6‰, respectively. The study shows that the compositions of hydrogen and oxygen isotopes in oreforming fluid of Dalucao rare earth deposit lie in the region between magmatic water and meteoric water. Therefore the ore-forming fluid was mixed from magmatic and meteoric water. The carbon isotopic features suggest that carbon of the bastnasite was from the mantle, carbon of fluorite-fluid inclusions in the ore body was from a mixture carbon source, and carbon of quartz-fluid inclusions was from the mantle.

Cerium is the most abundant member of the lanthanide series, those elements having 4f electrons. It is found in nature in the presence of other lanthanides and this mix is often used commercially as a cerium source without separation. Mischmetal, a metallic mix of cerium and other of the lighter lanthanides, is used in the steel industry, in lighter flints, and as getters. Lanthanide concentrate, an oxide mix that includes cerium oxide, is used in some fluid cracking catalysts. Cerium is unique within the lanthanide series because it has two stable oxidation states. Many of the uses of cerium and cerium compounds center around the redox chemistry of the Ce(IV)/Ce(III) couple. Cerium oxide acts as a stabilizer improving oxidation resistance for alloy systems, polymers, and automotive catalytic converter catalysts. Cerium compounds are present in optical coatings, in phosphors for cathode ray tubes, and in paints. Keywords: cerium; bastnasite; monazite; cerium (IV); cerium (III); metal; lanthanides; metallurgy; automobile emissions; catalysts cerium compounds; glass polishing phosphors

ÖZET Eskişehir-Sivrihisar-Kızılcaören köyünde fluorit, barit ve bastııasit içeren kompleks bir cevher yatağı bulunmaktadır. Bu cevher yatağından fluorit, barit ve nadir toprak elementlerinin kazanılması olanaklarının araştırılması amacıyla hazırlanan kompozh numuneler Özerinde zenginleştirme çalışmaları yapılmıştır. Kimyasal bileşimi %4&37 CaF^ %2&92 BaSO^ Ç&3.1 La, %3.0 Ce, %0.4 Nd olan kompozh numuneler fluorit, barit ve nadir toprak elementleri yanında mika, kil, kalsit, kuvars, pirit, limonit, piroluzit ve psüomelan mineralleri de içermektedir.;. Yapılan deneylerde; boyut küçültme, aşındırma ve flotasyon i§lemleri sonucunda %75-85 verimle %90-93 tenörlû barit konsantresi ve %60-70 verimle de %90~93 tenörlü fluorit konsantresi kazanımının mümkün olduğu anlaşılmıştır. Flotasyon işlemleri sırasında nadir toprak elementlerinin batan kısımda toplanması yoluna gidilmiş ve sonuçta, orijinal cevhere göre %75-85 verimle, nadir toprak elementleri tenörlerinde yaklaşık 3 katlık bir artış sağlanmıştır. Fluorit ve baritin flotasyon yoluyla kazanımı sonucunda elde edilen bastnasit ön konsantresi HQ ve HNO3 ile liç işlemine tabi tutularak çözeltiye alma parametreleri optimize edilmiştir. En iyi sonuç 70°C sıcaklık, 3 saat liç sûresi, 1/6 katı-sfVı oram ve 8.0 molar HNO3 ile elde edilmiş ve liç işlemi sonucunda nadir toprak elementlerinin hemen tümünün çözeltiye alınabileceği anlaşılmıştır. SUMMARY A complex ore deposit containing fluorite, barite and bastnasite is located at Kızılcaören Village, Sivrihisar, Eskişehir. The possibilities of recovering fluorite, barite and rare earth elements from composite samples through mineral processing studies were investigated. Chemical composition of the composite sample is 48.37% CaF2, 28.92% BaSC>4, 3.1% La, 3.0% Ce, 0.4% Nd. The composite sample is composed mostly of fluorite, barite and rare earth elements, and less of mica, clay, calcite, quartz, pyrite, limonite, pyrolusite, psilomelane. As a result of comminution, scrubbing and flotation processes, a barite concentrate of 90-93% BaSC>4 with 75-85% recovery and a fluorite concentrate of 90-93% CaF2 with 60-70% recovery were obtained. After separation of barite and fluorite by flotation it was observed that the remaining residue was enriched in terms of rare-earth elements. The rare-earth elements in this product, obtained with 75-85 % recovery, was determined to be three times as great as the original sample. Preconcentrate of bastnasite obtained by reverse flotation were leached using HC1 and HNO3, and the dissolution parameters were optimized. The best results were obtained at 70 °C, 3 hours of leaching time, 1/6 solid-liquid ratio and 8.0 moles/1 HNO3 concentration. Under these conditions, complete dissolution of rare-earth elements was achieved. 130

Several aluminosilicate compositions were tested for molten 7075 aluminum alloy attack with and without the addition of 10% Na2CO3. The extent of corrosion was proportional to the silica content of the refractory and especially of the matrix phase. The addition of rare earths up to 15% by weight to the aluminosilicates virtually eiiminated corrosion. Bastnasite, a rare-earth concentrate, was found to be a more effective additive at low concentrations than either CeO2 or La2O3 alone in rendering the aluminosilicates corrosion resistant.

An X-ray fluorescence (XRFS) and inductively coupled plasma atomic emission spectrometry (ICPAES) were applied to the determination of rare-earth elements in Bastnasite. Sample solutions were obtained by acid decomposition and sodium peroxide fusion. The XRFS of the glass bead sample was measured by selecting lines LaL_, CeL_, PrL_, NdL_ and SmL_. The analytical lines of minimum interference for ICPAES were selected as, La : 379.478nm, Ce : 413.765nm, Pr : 422.293nm, Nd : 406.109,Sm : 446.734 and 443.432nm. Samarium was determined after the correction of spectral interferences from coexisting cerium by matching the contents of cerium of the standard and the sample. The emission intensities were corrected by matching the acid concentrations of the standard and the sample. The analytical results of La, Ce, Pr, Nd and Sm obtained by XRFS agreed well with those obtained by ICPAES. The measured value of cerium with sodium peroxide fusion was slightly larger than that with hydrochloric acid -hydrogen peroxide decomposition.

Mixed rare earth oxides derived from bastnasite and monazite ores were purified with respect to non-rare-earth metallic impurities. The purified oxide was first converted to the fluoride which was then reduced by calcium to the metal (misch metal). The various misch metals were analyzed for impurities and for the percentage of each rare earth element present. The molecular weight of the misch metal was determined both directly and by calculation from the chemical composition. The melting point, transition temperature and lattice parameters were determined for each batch of metal and compared with values calculated from the respective properties of the pure metals and the percentage of each metal present. The hardness is about the same as those found for the high purity individual metals, while the values of the resistance ratio R 300k R 4.2k were one or two orders of magnitude smaller than those reported for the individual pure metals.

A simple operational method for separating cerium from other lanthanides in natural mixtures of cerium dioxide with lanthanide(III) hydroxides, obtained from Vietnamese parisite and Mongolian bastnasite, has been developed. The method is based on drying crude Ln(OH)3×H2O material in air at about 200°C within 6h, followed by leaching Ln(III) with concentrated nitric acid added carefully with stirring to the dried material/water 1∶1.5 slurry. Under optimum conditions cerium (and Th, if present) virtually does not pass into solution while the yield of leaching and the sum of REE oxides (REO) concentration in the after-leach solution reach the maximum values of 97% (mass) and 0.18 kg·dm−3, respectively. Besides an expected decrease of the leaching yield, roasting the starting material at 600°C results in over 7% Ce content in the Ln leached.

The lens-shaped Miaoya carbonatite complex, located west of the Wudang massif, Hubei Province, consists of several types of carbonatites associated with syenites. According to their composition, the carbonatites can be classified into four types, i. e., sovite, alvikite, carbon-bearing alvikite and ankeritic carbonatite. Their average composition is in agreement with the abundance values for carbonatites compiled by Gold (1966). There are three stages recognizable: the earliest sovite and alvikite followed by carbon-bearing alvikite, with ankeritic carbonatite being the latest. Some rules dominating the distribution of major and rare elements are observed with respect to the evolution of these carbonatites, for example, Nb is essentially enriched in sovite. Except for niobite and ilmenorutile, there are also pyrochlore, nioboeschynite and fersmite. RE are concentrated mainly in ankeritic carbonatite, within which bastnasite, parisite and monazite are found. In general, Ca, Nb, and Sr decrease, while Fe, Mg, Mn, and RE increase from earlier to later stages. It is suggested that the carbonatites are genetically connected with syenitic magma.

Two bastnasites - rare-earth fluocarbonate ores - from Mountain Pass, California, each weighing 40 kg, were ground to -200 mesh (75 μm), homogenized, sub-sampled into 432 containers and issued to interested laboratories for analysis in 1979. The methods used for the determination of rare-earth oxides, are discussed and the analytical results have been evaluated statistically. Rare-earth analysis remains a difficult field and, in the two samples, only nine elements have been assigned recommended concentrations. Appendices list the participating laboratories, the main determinations and information on the determination of other elements and oxides.

The spectrofluorimetric determination of terbium(III) as its ternary complex with EDTA and Tiron was studied further with regard to composition of the complex and the procedure was optimized by a simplex method. The results suggest a 1:1 molar ratio of terbium to Tiron for the ternary complex. The optimization study indicated that the three chosen variables (pH, and EDTA and Tiron concentration) are not interactive. The method was converted for use in a segmented-flow system with basic Technicon units and a spectrophotofluorimeter as detector. This procedure is satisfactory for the determination of terbium(III) in the range 0.03–0.24 μg ml −1 at a sampling rate of 30 h −1 . Results were satisfactory for the determination of terbium in lanthanide oxides, mixed oxides, the mineral bastnasite and a green phosphor (Gd 0.96 Ce 0.02 Tb 0.02 F 3 ).

Five rare earth-bearing minerals found in rocks of the Chilwa Alkaline Province, Malawi, are described. Zirconolite, occurring in nepheline syenite, is unusual in being optically zoned, and microprobe analyses indicate a correlation of this zoning with variations in Si, Ca, Sr, Th, U, Fe, Nb and probably water; it is argued that this zoning is a hydration effect. A second compositional zoning pattern, neither detectable optically nor affected by the hydration, is indicated by variations in Th, Ce and Y such that, although total REE abundances are similar throughout, there appears to have been REE fractionation during zirconolite growth from relatively heavy-REE and Th-enrichment in crystal cores to light-REE enrichment in crystal rims.Chevkinite is an abundant mineral in the large granite quartz syenite complexes of Zomba and Mulanje, and analyses are given of chevkinites from these localities. There is little variation in composition within each complex, and only slight differences between them; they are all typically light-REE-enriched. The Mulanje material was shown by X-ray diffraction to be chevkinite and not the dimorph perrierite, but chemical arguments are used in considering the Zomba material to be the same species. Other rare earth minerals identified are monazite, fluocerite and bastnäsite. These are briefly described and microprobe analyses presented.

A method is described for a rapid, sensitive, accurate and precise determination of 12 lanthanides and yttrium by a.a.s. In most analyses the standard addition technique was used to eliminate chemical, ionization and matrix interferences. For samples of similar origin, a procedure with a comparison standard was developed; this proved to be very suitable for routine analyses. The lanthanides and yttrium were determined in bastnasite, monazite and gadolinite. The analyses were performed on solutions containing a maximum sample concentration of 30 g l-1 in 80% of methanol and buffered with alkali ions. The accuracy of the method was checked by independent procedures such as gravimetry, pulse polarography and flame emission spectrophotometry.

The commercial production of rare earth metals by fused salt electrolytic methods is described. These methods are used to make mischmetal, cerium, lanthanum, and didymium (Nd + Pr). The feed materials consist essentially of anhydrous chlorides of the metal to be produced, augmented by additions of nonrare earth salts to yield an electrolyte with satisfactory properties for reduction. The rare earths are derived either from monazite or from bastnasite ores. The anhydrous chlorides are manufactured from the hydrated chlorides by methods which minimize oxidation or hydrolysis. Alternatively, anhydrous chlorides may be used which result from the direct chlorination of rare earth ores by the Gold-schmidt process. These are particularly suitable for electrolysis due to their very low oxychloride content. Fluorides and oxides of the rare earths are produced by wet chemical methods to provide the relatively small quantities of these compounds now used for commercial fused salt electrolysis. Reduction cells in use today are constructed mainly from a) ceramics, b) graphite, or c) iron. The advantages and disadvantages of these types of cells are described together with the typical products which result from their use. Primary attention is given to production of mischmetal (mixed rare earth metal), which is the rare earth metal produced on the largest scale today. Brief reference is made also to production of cerium, lanthanum, and didymium (Nd + Pr) metal. Finally, a resume of the current uses of these metals is presented with reference to recent trends in the industrial applications of the rare earth metals.

SummaryVaterite, the third unstable polymorph of CaCO3, is recognized by optical and X-ray powder techniques as a major constituent in a carbonated calcium silicate hydrogel complex formed from larnite at Ballycraigy, Lame, Northern Ireland. Re-indexed X-ray powder data obtained on synthetic vaterite are provided indicating a hexagonal unit cell with dimensions a = 7·135 Å. and c = 8·524 Å., Z = 6CaCO3. The re-indexing is endorsed by the results of electron diffraction study of synthetic vaterite. Vaterite is shown to correspond to the hypothetical CaCO3 member of the bastnäsite-synchisite mineral series on the basis of extrapolated cell dimensions and optical properties. A structural scheme for vaterite is proposed in which Ca layers replace the CeF layers in bastnäsite, and near-vertical CO3 groups are present. The stability relations of natural vaterite are discussed and comment made on the recent observation of vaterite, in a like environment, in carbonated cements and mortars.

A process for direct chlorination of rare earth ores without the necessary preparation of carbides or other intermediate compounds is described. Complete chlorination of all non-volatile components of the ores is obtained in a special, electrically heated furnace at temperatures between 1000 and 1200°C. The construction of the furnace permits quick replacement of some important components while the furnace is still hot. This reduces the unavoidable corrosion problem. The flowsheet of the process is presented. The process permits a high productive capacity with a small space, low investment, and low labor input. It is possible to process the most varied ores, such as Bastnasite, Monazite, Allanite, Cerite, Xenotime, Euxenite, Fergusonite, Gadolinite, etc., in the same installation. Reference is made to the treatment of off-gases. Fused anhydrous rare earth chlorides, without contaminants, are obtained as the final product, which is very suitable for the production of rare earth metals. This process can also be used to convert pure rare earth oxides to anhydrous chlorides.

A method of Baotou mixed rare earth concentrate leaching was investigated. According to the principle of complex leaching, the quadratic orthogonal regression experiment was used to investigate effect of six factors. An optimal condition of low energy and environment friendly was determined as follows: HCl acidity is 4 mol·L−1, AlCl3 concentration is 2 mol·L−1, reaction temperature is 85 °C, reaction time is 90 min, liquid to solid ratio is 35 ml·g−1, and stirring speed is 100 r·min−1. According to this condition, the leaching ratio of mixed rare earth concentrate is 76.5 %. The analyses of X-ray diffraction shows that bastnasite disappears, and the main peaks of filter residue is monazite and cheralite after leaching of HCl–AlCl3 solution. The result indicates that REFCO3 of the mixed rare earth concentrate can be dissolved, but REPO4 remains in the leaching residue. This method provides a way to separate and extract rare earth.