Search

The rare-earth elements (REEs, La–Lu, Y) are essential for the development of renewable technologies. Bastnäsite (REECO3F) is a common REE ore mineral that is often subject to hydrothermal alteration at all crustal levels. Mechanisms of hydrothermal bastnäsite alteration therefore govern the evolution of REE deposits, though these mechanisms remain poorly understood. This experimental work investigates the hydrothermal replacement of bastnäsite by rhabdophane (REEPO4∙xH2O, x = 0–1) and monazite (REEPO4) in phosphatic fluids. Two temperature-dependent alteration pathways were identified; both follow the coupled dissolution-reprecipitation (CDR) mechanism. At 90 °C, bastnäsite was replaced by highly-porous metastable rhabdophane which was then replaced by monazite, forming an inner layer of rhabdophane and an outer layer of monazite. At 220 °C, bastnäsite was replaced directly by monazite. Although replacement initiated more quickly at 220 °C, greater overall replacement occurred at 90 °C (~ 61 wt.% after 500 h, compared to ~ 13 wt.% at 220 °C) due to surface passivation by monazite at 220 °C. Geochemical analyses showed REE fractionation during bastnäsite alteration. At 90 °C, rhabdophane was enriched in heavy REEs (Eu–Lu, Y), likely due to the evolving fluid chemistry, while at 220 °C secondary monazite was enriched in Sm and Ho compared to bastnäsite. These results indicate that: 1) the hydrothermal alteration of bastnäsite by rhabdophane and monazite in ore deposits leads to REE immobilisation, with little net loss of REEs to solution; 2) rhabdophane is metastable relative to monazite at 90 °C, and; 3) variable temperatures can cause different mineral textures and REE fractionation trends during hydrothermal alteration and mineral replacement. [ABSTRACT FROM AUTHOR]

In this paper, we evaluated the potentialities of Raman spectroscopy and electron backscattered diffraction (EBSD) in the microscopic characterization of Ca-REE fluorcarbonates (CRFC) belonging to the bastnäsite-synchysite series to provide a "road map" for further investigations with transmission electron microscopy (TEM). EBSD was efective in establishing the sample orientation, setting up the oriented cuts, and ascertaining the effective syntactic relationship among all the detected CRFC phases; however, it failed to distinguish between diferent polysomes. On samples with diferent orientations that were preventively ascertained by EBSD and characterized by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), micro-Raman spectroscopy allows for distinguishing between polysomes based on the diferences in intensity and position of the symmetric stretching vibration (v1) of the carbonate group C O 3 2 − in the region around 1080–1099 cm–1. However, as evidenced by TEM-EDS, what appears as a homogeneous polysome in backscattered electrons (BSE) images may be a disordered intergrowth of compositional faults with a bulk composition being matched with that of a real polysome only by accident. Therefore, we conclude that the Raman signal is sensitive to diferent Ca/(Ca+REE) ratios but not to any ordered distribution of Ca-poor and Ca-rich lamellae within the analyzed volume, making the unambiguous identification of a polysome tricky. Finally, several ordered polysomes were detected at the TEM scale, including a B2S and a long-range polytype with a 32 nm repeat distance along c. The possible implications of the detected microstructure for ore mineral formation are discussed. [ABSTRACT FROM AUTHOR]

Bastnäsite contains considerable amounts of U and Th and has been widely used for U-Th-Pb dating. Hydrothermal alteration of bastnäsite is common in nature but its effects on U-Th-Pb dating are not currently well constrained. Hence the significance of U-Th-Pb ages obtained from altered bastnäsite cannot be evaluated. Here, we present a detailed geochronologic as well as micro- and nano-scale mineralogical study of altered bastnäsite in a Mo-REE deposit, Central China. The original bastnäsite grains were confirmed to have crystalized at 208 Ma but were variably overprinted by a hydrothermal event at 150 Ma. They commonly exhibit typical replacement textures that appear to have formed from a coupled dissolution-reprecipitation process, i.e., a primary unaltered domain surrounded by a porous altered domain. Micro- and nano-scale mineralogical observations strongly suggest that during the coupled dissolution-reprecipitation process, non-radiogenic (common) Pb was incorporated into the altered domains in the form of nanoscale galena inclusions. Such incorporation (even minor) has significantly affected the 206Pb/238U and 207Pb/206Pb ratios due to the low contents of U and its daughter isotopes in bastnäsite, resulting in highly variable, discordant U-Pb dates for the altered domains. In contrast, incorporation of the non-radiogenic Pb has very limited effects (<5%) on the Th-Pb system due to the remarkably high contents of Th and radiogenic 208Pb in bastnäsite. Instead, the scattered 208Pb/232Th ages (208 to 150 Ma) of the altered domains were essentially affected by incomplete replacement, and thus can be used to approximate the lower age limit of the primary hydrothermal activity or the upper age limit of the secondary hydrothermal activity. The results from this study highlight that because of the different orders of magnitude between the U and Th contents in bastnäsite, the mobilization of radiogenic and non-radiogenic Pb during alteration may have significantly different impacts on the U-Pb and Th-Pb systems. Therefore, the two systems should be treated separately during the dating of bastnäsite resulting from secondary hydrothermal events. [ABSTRACT FROM AUTHOR]

Rare earth element (REE) fluorcarbonates are found for the first time in the ore-hosting sequence of the Saf’yanovka Cu–Zn massive sulfide deposit, Middle Urals: bastnäsite, synchysite-(Ce), and synchysite-(Y) in an assemblage with fluorite, calcite, barite, pyrite, and sphalerite. Samples with fluorcarbonates were found at a depth of 262 m in quartz veinlets of an altered zone of pyrite–carbonate–kaolinite–sericite–quartz rocks at the contact with massive pyrite–chalcopyrite and pyrite–sphalerite ores. It is suggested that the REE fluorcarbonates formed from a hydrothermal fluid synchronously with fluorite and calcite. This event can be related to hydrothermal activity at the postcollision stage of the evolution of the Urals fold system. [ABSTRACT FROM AUTHOR]

This study presented the first in a series of investigations currently underway to develop efficacious, cost-effective, and benign processing opportunities to produce rare earth elements (REE)–rich concentrate from an Australian complex low–grade saprolite ore [1.14% total rare earth oxides (TREO) grade], which is primarily exploited for its gold and copper values. This work specifically presented a preliminary flotation investigation carried out on the ore using sodium oleate as a collector. The relative effects of pulp pH, desliming, and depressants were investigated to ascertain any chance of recovering and upgrading REE minerals in saprolite ore using three different processing configurations. Based on the experimental results, flotation processes carried out on raw feed allowed the recovery of the majority of REE minerals (>50%), but the process was unselective, where clay and silicate gangue minerals reported into the flotation concentrate along with the REE minerals. However, desliming before flotation in the presence of depressants (starch and sodium silicate) improved REE minerals flotation selectivity, which produced concentrates assaying 5.87% and 4.22% TREO grades, with corresponding recoveries of 45% and 50% at pulp pH 9 and 10.5, respectively. Mineralogical analysis conducted on selected flotation concentrate indicated that silicate and clay gauge minerals were recovered via the synergistic act of surface activation and entrainment due to their fine to ultrafine nature. A comparison of all the test results revealed a haphazard grade–recovery relationship suggesting that there is an opportunity to further maximize both REE recovery and grade through further flotation studies where other process parameters may be investigated and optimized. The prospect of using magnetic separation has also been suggested. [ABSTRACT FROM AUTHOR]

The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, mining tailings and other unconventional resources to meet cutoff grades and subsequently supply demands. In this work, detailed characterization of tailings from a copper processing plant was carried out to expand the knowledge of their chemical and mineralogical characteristics for REE recovery. The results showed that the REE are mainly mineralized as bastnäsite, monazite, and stetindite, along with uncommon minerals, such as brannerite, stillwellite, and florencite, for which there is limited processing data. In a preliminary effort to recover the REE, the tailings were subjected to gravity, magnetic, and froth flotation separation. Over 90% REE recovery was achieved via froth flotation, whereas magnetic and gravity separation tests recovered up to 86% and 54% REE, respectively. The results from this study suggest that, with systematic optimization studies, REE recovery and upgrade could be enhanced, with significant efforts of minimizing the recovery of key gangue minerals, such as goethite, hematite, and quartz. Overall, the study confirms that the tailings used in this work could be regarded as unconventional REE resources subject to tactical development and optimization of beneficiation methods. [ABSTRACT FROM AUTHOR]

Bauxite deposits are an important source of Al and also host a variety of critical metals, including rare earth elements (REEs). However, the parent rocks of bauxite deposits generally have low REE contents, leading to uncertainty over the REE sources and enrichment mechanisms. In this study, we report high REE (2095 ppm; Ce = 1340 ppm) contents in the Lijiatian bauxite deposit in Luxi County, western Hunan Province, South China. The Lijiatian bauxite deposit is the largest deposit in Hunan Province, with a total Al resources exceeding 7 × 106 tons. The ore-bearing strata in the lower Permian Liangshan Formation (ca. 275 Ma) are comprised a 3–5-m-thick bauxite layer (bauxite ore/clay) and an underlying 4–8-m-thick Fe layer (Fe ore/Fe-rich clay). The high REE contents in the bauxites can be attributed to the widespread presence of bastnäsite. The bastnäsite commonly coexists with authigenic chlorite, which formed at temperatures of 221–285 °C, indicative of a hydrothermal origin. Uranium–Pb dating of the bastnäsite yielded an age of 141.4 ± 7.0 Ma, indicating a hydrothermal overprint occurred during the Early Cretaceous, which resulted in the enrichment of REEs in the bauxites. The high contents of REEs, Ba, and P in the Cambrian Niutitang Formation black shales indicate it was a potential source of these elements for bastnäsite and coexisting barite and apatite. The deep-seated hydrothermal fluids (enriched in HF, CO 2 , and H 2 S) associated with the late Yanshanian extensional tectonic event in South China (155–123 Ma) ascended along fractures. The ascending fluids interacted with the black shales, extracting REEs, Ba, and P. When the fluids reached a certain depth, they mixed with the infiltrating basinal waters to form a mineralising fluid. The fluid then migrated towards the bauxite layers, underwent cooling and depressurisation, and precipitated bastnäsite, barite, apatite, and chlorite. We propose that a hydrothermal event led to the enrichment of REEs in the bauxites in Hunan Province. Considering the scarcity of REEs in the parent rocks of bauxites worldwide, hydrothermal activity likely has a key role in REE enrichment in bauxites. [Display omitted] • The main mineral hosting REE (Ce) in Permian bauxite from southern China is Bastnäsite. • The bastnäsite formed during the Cretaceous period due to hydrothermal fluid activity. • The REEs are source from the basement black shale. [ABSTRACT FROM AUTHOR]

The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, tailings, and other unconventional resources to meet cut-off grades and, subsequently, supply demands. This paper presents an amalgamation of studies conducted on selected complex low-grade iron-oxide-silicate-rich tailings, with the overall aim of developing efficacious methods and associated process mineralogy characterization for enhanced REE minerals recovery and upgrade. To this end, a summary of the overarching key results from froth flotation, magnetic separation, and gravity separation studies of the tailings and their implications are presented in this review. Reconciliation of all the findings reveals lucid links between feed ore properties, mainly mineralogy and particle size distribution, as the key influential factors that affect the beneficiation of real complex low-grade tailings, although distinct differences in physicochemical properties of the valuable and gangue minerals may exist. It is clearly established that the unliberated association between REE and gangue minerals within the ore can lead to either synergistic or antagonistic effects on the quality of concentrates produced. Furthermore, the limitations presented by the poorly liberated minerals are exacerbated by their "fine" nature. With appreciable recoveries obtained using such readily available conventional separation methods, the tailings provide additional REE value to the primary commodities; hence, such material could be considered a potential resource for REE beneficiation. The learnings from the respective beneficiation studies are significantly important as they provide the knowledge base and greater understanding of the mineralogical characteristics and beneficiation response of REE minerals in typical complex, low-grade tailings. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world's market, while its origin is still unclear because of the complicated and diverse REE ore mineralogy and texture. Thescanning electron mircroscopy SEM)-based automated mineralogy allows for the numeric assessment of rocks and ores' compositional and textural properties. Here, we use TIMA (TESCAN Integrated Mineral Analyzer) to quantitatively characterize REE ore mineralogy from the deep drill core within the H8 unit ("dolomite marble") to better understand the deposit. The mineral composition, occurrence, and Ce elemental deportment of the borehole ores at different depths (i.e., 1107 m, 1246 m, 1406 m, 1546 m, and 1682 m) were obtained. The results show that the main types of ores in the investigated samples can be divided into banded REE-Fe ores, banded REE ores, disseminated REE-Fe ores, and veined REE ores. REE and gangue minerals vary significantly in abundance and occurrence. Monazite-(Ce) and bastnäsite-(Ce) are the primary REE host minerals, and both contribute the most to the REE budget. Other REE minerals, such as parisite-(Ce)/synchysite-(Ce), cerite-(Ce), huanghoite-(Ce)/cebaite-(Ce), and aeschynite-(Ce), are significant contributors. The gangue minerals generally include fluorite, barite, magnetite, pyrite, quartz, magnesio-arfvedsonite, and minerals of the biotite and apatite groups, among others. Combined with the newly published mineral-scale chronological and isotopic geochemical analyses, it is reasonable to conclude that the later hydrothermal fluids remobilized and redistributed the original Mesoproterozoic carbonatitic REE minerals and formed a high variable ore mineral assemblage. Furthermore, it is demonstrated that the mineralogical study using TIMA can provide accurate and reliable mineralogy data for the comprehensive interpretation of the complex REE ores, and extend our understanding of the deposit. [ABSTRACT FROM AUTHOR]

The stability relations of cerium and its species in the hydrometallurgical processing of bastnasite were studied using Pourbaix diagrams. Different systems of Ce-(F)-(CO3)-(SO4)-(C2O4)-H2O were constructed using HSC Chemistry software with the necessary thermodynamic data. The Ce-F-H2O system exhibits a large stability region for CeF3 (pH∼ −1.5 – 12). The stability domain of was determined by Ce-CO3-H2 system in the pH of 4.5 – 12. The decomposition behaviours of CeFCO3 were studied by Ce-F-CO3-H2O system which shows the stability domain of CeFCO3 from neutral to basic media. The treatment of CeFCO3 with H2SO4 was investigated by depicting diagrams of Ce-F-CO3-SO4-H2O system. According to this system, CeFCO3 can be decomposed to produce soluble Ce sulphates at around pH 6.2. In contrast, alkaline treatment of CeFCO3 converts it to Ce(OH)3 at pH 11. Finally, the recovery of Ce by oxalate precipitation was studied by Ce-C2O4-H2O system which showed the domain of Ce oxalate decahydrate. [ABSTRACT FROM AUTHOR]

The time and processes of hydrothermal mineralization are long-standing problems in geology. This work addresses these questions with reference to the Maoniuping giant rare earth elements (REE) deposit (southwest China), which has rare earth oxides (REO) reserves of 3.17 million tons with an average grade of 2.95 wt%. Bastnäsite is the dominant economic mineral, occurring as four distinct paragenetic types in the Maoniuping syenite–carbonatite complex: (1) primary euhedral bastnäsite (type-A) in syenite, with isolated melt inclusions; (2) macro-crystalline tabular euhedral bastnäsite (type-B) in pegmatitic dikes, with a diverse variety of fluid inclusions; (3) fine-grained, anhedral veinlet-disseminated bastnäsite (type-C) in syenite; and (4) coarse-grained anhedral bastnäsite (type-D) in carbonatite dikes, occurring as veinlets or interstitial to calcite, fluorite, and barite. From the paragenetic and compositional variations, it is inferred that type-A bastnäsite is of primary magmatic origin, whereas the other three types have characteristics of hydrothermal origins. In situ LA-ICP-MS U-Pb geochronology of the four types of bastnäsite results in lower intercept ages of 28.2 ± 0.5 Ma (n = 95, MSWD = 5.10), 27.8 ± 0.4 Ma (n = 43, MSWD = 0.73), 26.8 ± 0.7 Ma (n = 50, MSWD = 0.83), and 25.8 ± 0.7 Ma (n = 55, MSWD = 1.70), respectively, which are consistent with the weighted average 206Pb/238U and 208Pb/232Th ages by 207Pb-correction method. Compositional variations of clinopyroxene and apatite from the associated syenite, pegmatitic and carbonatitic dikes indicate a genetic relationship of the Maoniuping alkaline complex. The compositions of clinopyroxene range from Ae44–67Di14–18Hd17–41 in pegmatitic dikes, Ae43–66Di6–20Hd21–38 in carbonatitic dikes to Ae68–90Di0–3Hd10–30 in syenite. Apatites in the pegmatitic and carbonatitic dikes have similar compositions with higher F, total REE, and Sr, and lower CaO contents than those in the syenite, which suggests a cogenetic origin for the associated pegmatite and carbonatite. Clinopyroxene and apatite compositions suggest that the pegmatitic melt might differentiate directly from the initial carbonatitic melt rather than the syenitic magma. The bastnäsite U-Pb geochronology and minerals data indicate continuous magmatic-hydrothermal evolution for the REE mineralization in the Maoniuping alkaline complex. [ABSTRACT FROM AUTHOR]

Thermodynamic calculations on the impact of carbonate–bicarbonate fluids cooling from 500 to 100°C on a monazite + calcite association with a simultaneous decrease in pressure from 2000 to 125 bar are performed. It is shown that the REE carbonate–bicarbonate complexes gain importance only at low temperatures. In this case, the total concentration of lanthanides in the fluid turns out to be rather low. This indicates that, in the presence of even insignificant amounts of fluorine and calcium in the hydrothermal system, carbonate–bicarbonate fluids do not lead to the removal of REEs but contribute to their accumulation in the form of precipitating fluorocarbonates. Thus, the role of carbonate-bicarbonate hydrothermal fluids in the transport and deposition of rare earth elements has been assessed for the first time for a wide range of TP-parameters and for the entire series of lanthanides. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monazite and bastnäsite U-Th-Pb dating demonstrate that the Boziguoer deposit formed at ∼ 290–280 Ma. • Post-magmatic hydrothermal processes play a significant role in the mineralization process at Boziguoer deposit. • The alkaline rocks and associated Nb-Ta-Rb-Zr-REE mineralization of the South Tianshan formed in a Tarim mantle plume setting. The Boziguoer alkaline intrusion is located in the South Tianshan Orogenic Belt on the northern margin of the Tarim Craton. The intrusion is entirely mineralized and forms a super-large rare metal (RM) and rare-earth element (REE) deposit dominated by Nb-Ta-Rb, accompanied by Zr-REE. The primary RM minerals include pyrochlore, astrophyllite, and zircon, while the main REE minerals consist of fluocerite, monazite, xenotime, and bastnäsite, which are commonly present as granular aggregates or singularly filling the interstices between gangue minerals. Through a combination of geochronological and geochemical analyses of different types of monazite and bastnäsite in the mineralized alkaline rocks, this study elucidates the role of magmatic-hydrothermal evolution on the Boziguoer RM-REE mineralization and reconstructs the geochronological framework of alkalic magmatic-hydrothermal evolution and mineralization processes, as well as establishing mechanisms responsible for RM-REE enrichment. Petrographic observations and back-scattered electron (BSE) imaging revealed several types of monazite and bastnäsite with different characteristics as follows: (1) type Ia monazite (Mnz-Ia) experienced intense hydrothermal alteration, forming residual cores of monazite mantled by apatite and allanite coronas; (2) type Ib monazite (Mnz-Ib) was partially eroded, forming concentric zoning patterns with a core of monazite, a mantle of apatite, and an outer rim of allanite coronas; (3) type II monazite (Mnz-II) is slightly modified, and commonly associated with fluorite; (4) bastnäsite and fluocerite exhibit a core-rim structure, with the core of fluocerite being brighter than the rim of bastnäsite in BSE images. According to the paragenetic relationships and compositional variations, all two types of monazite are of primary magmatic origin, while bastnäsite is of hydrothermal origin. In addition, principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) results indicate that Mnz-Ia and Mnz-Ib belong to the same group, different from Mnz-II. The latter has higher (Ce/Gd) N and (Th/U) N ratios, indicating relatively low-temperature crystallization of Mnz-II at late stages. In-situ LA-ICP-MS U-Th-Pb dating of monazite and bastnäsite show that Mnz-Ia and Mnz-Ib have ages of ca. 290 Ma, consistent with the zircon age of the intrusion, whereas the Mnz-II and bastnäsite have younger ages of ca. 280 Ma, representing a post-magmatic hydrothermal mineralization event at Boziguoer. These new ages indicate that both magmatic and subsequent hydrothermal processes played critical roles in the RM-REE mineralization in this deposit. The latest findings also support the model that the formation of the alkaline belt where the Boziguoer ore-bearing intrusion was temporally and spatially linked to the Tarim Large Igneous Province that is genetically related to a mantle plume. [ABSTRACT FROM AUTHOR]

Isotopic dating studies have revealed that many carbonatite-related REE ore systems have protracted and complex temporal evolution histories. The mechanisms that cause these complex dating results remain poorly understood. Here, we present an in-situ Sm-Nd and Th-Pb isotopic investigation of monazite and bastnäsite from a geologically-complicated deposit, the world-class Bayan Obo REE deposit of China, with the aim of defining the general mechanisms accounting for the protracted age spread observed in this and many other REE deposits. Monazite and bastnäsite are two principle REE ore minerals in the Bayan Obo deposit. Most of the studied monazite and bastnäsite grains have experienced fluid-aided modification. The modified grains have generally homogeneous Sm and Nd contents and Sm-Nd isotopic compositions, implying low mobility of Sm and Nd during the modification process. Thus, the Sm-Nd chronometer can be used to constrain the primary crystallization timing of the REE minerals at 1293 ± 48 Ma. However, altered REE minerals have apparent 208Pb-232Th ages (1248–261 Ma) that are variably younger than the primary crystallization age. In most samples, Th contents have no correlations with 208Pb-232Th ages, while Pb contents tend to decrease along with the younging trend of 208Pb-232Th ages. NanoSIMS mapping shows that 208Pb and 208Pb/232Th are heterogeneous, and irregularly distributed in the altered grains. Such results are indicative of variable Pb loss during the fluid-aided modification process. Thus, many Th-Pb ages represent partial isotopic resetting and, hence, are geologically meaningless. Completely reset ages cluster at 450–400 Ma or 280–260 Ma, representing two discrete episodes of post-ore hydrothermal activity. Small amounts of monazite and bastnäsite that were newly crystallized during these two overprinting episodes have initial Nd isotopic signatures approaching the time-evolved isotopic compositions of primary ores, which suggests insignificant REE input to the primary ores during these events. This study provides critical evidence to resolve complex dating results and disparate ore genesis models for the giant Bayan Obo deposit. Moreover, our results indicate the resistance of Sm-Nd isotopes, but the susceptibility of Th-(U)-Pb isotopes, to fluid-aided modification. Therefore, younger Th-U-Pb dates in geologically-complicated deposits should be treated with caution as they may represent partial resetting results and/or may not represent events of increased metal tenor. [ABSTRACT FROM AUTHOR]

Bastnäsite is widespread in alkali granite, carbonatite and REE ore deposits. The U-Th-Pb ages of bastnäsite can constrain the mineralization age. Currently, the lack of suitable in situ analysis reference material is the major obstacle of bastnäsite U-Th-Pb geochronology. In this study, the matrix effects of U-Pb and Th-Pb age determination in bastnäsite using glass NIST 610 as the external calibration reference were evaluated with the 193-nm excimer LA-ICP-MS analysis in normal and additional gases laser ablation modes. The obtained U-Th-Pb ages of bastnäsite were approximately 7–11% lower than their reference values in the normal analytical mode (without additional gas). Fortunately, the determined systematic age biases in U-Th-Pb dating were significantly reduced (less than 1–2%) with the addition of water vapor within the ablation chamber. This reduction may be attributed to the observed significant suppression of 206Pb/238U and 208Pb/232Th downhole fractionation in both NIST 610 glass and bastnäsite by introducing a small quantity of water vapor in the ablation chamber. In addition, the obtained 206Pb/238U and 208Pb/232Th ages of bastnäsite K-9, LZ1384, and MAD809 showed great consistency with their corresponding recommended values. The obtained results show that accurate and precise U-Th-Pb ages of bastnäsite can be simultaneously obtained by using glass NIST 610 as the primary calibration standard in 193-nm LA-ICP-MS with the water vapor-assisted method. This simple and effective water vapor-assisted non-matrix-matched laser ablation method helps to promote the geological application of bastnäsite U-Th-Pb geochronology. [ABSTRACT FROM AUTHOR]

The Vuoriyarvi Devonian carbonatite-ijolite-pyroxenite-olivinite complex comprises several carbonatite fields: Neske Vara, Tukhta-Vara, and Petyayan-Vara. The most common carbonatites in the Tukhta-Vara and Neske-Vara fields are calciocarbonatites, which host several P, Fe, Nb, and Ta deposits. This paper focuses on the Petyayan-Vara field, in which the primary magmatic carbonatites are magnesian. The least altered magnesiocarbonatites are composed of dolomite with burbankite and are rich in REE (up to 2.0 wt. %), Sr (up to 1.2 wt. %), and Ba (up to 0.8 wt. %). These carbonatites underwent several stages of metasomatism. Each metasomatic event produced a new rock type with specific mineralization. The introduction of K, Si, Al, Fe, Ti, and Nb by a F-rich fluid (or fluid-saturated melt) resulted in the formation of high-Ti magnesiocarbonatites and silicocarbonatites, composed of dolomite, microcline, Ti-rich phlogopite, and Fe-Ti oxides. Alteration by a phosphate-fluoride fluid caused the crystallization of apatite in the carbonatites. A sulfate-rich Ba-Sr-rare-earth elements (REE) fluid (probably brine-melt) promoted the massive precipitation of ancylite and baryte and, to a lesser extent, strontianite, bastnäsite, and synchysite. Varieties of carbonatite that contain the highest concentrations of REE are ancylite-dominant. The influence of sulfate-rich Ba-Sr-REE fluid on the apatite-bearing rocks resulted in the dissolution and reprecipitation of apatite in situ. The newly formed apatite generation is rich in HREE, Sr, and S. During late-stage transformations, breccias of magnesiocarbonatites with quartz-bastnäsite matrixes were formed. Simultaneously, strontianite, quartz, calcite, monazite, HREE-rich thorite, and Fe-hydroxides were deposited. Breccias with quartz-bastnäsite matrix are poorer in REE (up to 4.5 wt. % total REE) than the ancylite-dominant rocks (up to 11 wt. % total REE). [ABSTRACT FROM AUTHOR]

Bastnäsite is the end member of a large group of carbonate–fluoride minerals with the common formula (REE) CO3F·CaCO3. This group is generally widespread and, despite never occurring in large quantities, represents the major economic light rare earth element (LREE) mineral in deposits related to carbonatite and alkaline intrusions. Since bastnäsite is easily altered and commonly contains inclusions of earlier‐crystallised minerals, in situ analysis is considered the most suitable method to measure its U‐Th‐Pb and Sr‐Nd isotopic compositions. Electron probe microanalysis and laser ablation (multi‐collector) inductively coupled plasma‐mass spectrometry of forty‐six bastnäsite samples from LREE deposits in China, Pakistan, Sweden, Mongolia, USA, Malawi and Madagascar indicate that this mineral typically has high Th and LREE and moderate U and Sr contents. Analysis of an in‐house bastnäsite reference material (K‐9) demonstrated that precise and accurate U‐Th‐Pb ages could be obtained after common Pb correction. Moreover, the Th‐Pb age with its high precision is preferable to the U‐Pb age because most bastnäsites have relatively high Th rather than U contents. These results will have significant implications for understanding the genesis of endogenous ore deposits and formation processes related to metallogenic geochronology research. [ABSTRACT FROM AUTHOR]

Bastnäsite-(Ce), a rare earth element (REE) bearing carbonate (Ce,La,Y,Nd,Pr)CO3F, is one of the most common REE-bearing minerals and has importance from both economic and geologic perspectives due to its large REE concentration. It also provides an example of the structural interplay between carbonate groups and fluorine ions, as well as the complex bonding properties of rare earth elements. We report Raman vibrational and Nd3+ luminescence ( 4 F 3 / 2 → 4 I 9 / 2 , 4 F 3 / 2 → 4 I 11 / 2 , $\left(^{4}{{\text{F}}_{3/2}}{{\to }^{4}}{{\text{I}}_{9/2}}{{,}^{4}}{{\text{F}}_{3/2}}{{\to }^{4}}{{\text{I}}_{11/2}}, \right.$ and 4 F 5 / 2 + 2 H 9 / 2 → 4 I 9 / 2 ) $\left. ^{4}{{\text{F}}_{5/2}}{{+}^{2}}{{\text{H}}_{9/2}}{{\to }^{4}}{{\text{I}}_{9/2}} \right)$ spectra of natural bastnäsite-(Ce) to 50 GPa at 300 K. Two phase transitions are observed under compression. Bastnäsite-I remains the stable phase up to 25 GPa, where it undergoes a subtle phase transition to bastnäsite-II. This is likely produced by a change in symmetry of the carbonate ion. Bastnäsite-II transforms to bastnäsite-III at ~38 GPa, as demonstrated by changes in the luminescence spectra. This second transition is particularly evident within the 4 F 3 / 2 → 4 I 9 / 2 $^{4}{{\text{F}}_{3/2}}{{\to }^{4}}{{\text{I}}_{9/2}}$ luminescent transitions, and it appears that a new rare earth element site is generated at this phase change. This transition is also accompanied by modest changes in both the Raman spectra and two sets of luminescent transitions. Despite these transformations, the carbonate unit remains a stable, threefold-coordinated unit throughout this pressure range, with a possible increase in its distortion. Correspondingly, the rare-earth element site(s) appears to persist in quasi-ninefold coordination as well, implying that the general bonding configuration in bastnäsite is at least metastable over a ~30% compression range. All pressure-induced transitions are reversible, with some hysteresis, reverting to its ambient pressure phase on decompression. [ABSTRACT FROM AUTHOR]

Surface nanobubbles have been identified to play an important role in a range of industries from mineral processing to food science. The formation of surface nanobubbles is of importance for mineral processing in the extraction of complex ores, such as those containing rare earth elements. This is due to the way minerals are extracted utilising froth flotation. In this study, surface nanobubbles were imaged using non-contact atomic force microscopy on a polished cross section containing rare earth minerals. Nanobubbles were found on synchysite under reagent conditions expected to induce hydrophobicity in rare earth minerals, which is required for efficient processing. Synchysite –(Ce) is a rare earth fluorcarbonate mineral containing over 30% rare earth elements. Relatively little research has been conducted on synchysite, with only a few papers on its surface behaviour and flotation. The resulting nanobubbles were analysed and showed an average contact angle of 24° ± 8. These are in line with contact angles found on dolomite and galena by previous studies. [ABSTRACT FROM AUTHOR]

• Iron-oxide-silicate rich tailings was investigated as unconventional REE resource. • Major REE minerals were bastnäsite, monazite, brannerite, and stetindite. • Hematite and quartz were the major gangue minerals. • Magnetic separation was studied as preconcentration method. • Mineralogical and particle characteristics affected selective REE minerals recovery. This work is part of an ongoing investigation being conducted to recover and upgrade rare earth elements (REE) minerals from iron oxide and silicate rich tailings generated at a South Australian mining operation. Detailed mineralogical characterisation via Quantitative Evaluation of Minerals by Scanning electron microscopy (QEMSCAN) of the tailings established the presence of low grade (<1 wt% REE), fine-sized REE minerals. The REE minerals (bastnäsite, monazite, florencite, stillwellite, brannerite, and stetindite) identified were in intimate associations with weakly ferromagnetic/strongly paramagnetic iron oxides (mainly hematite and goethite) and diamagnetic silicate (quartz, illite, and annite) minerals. Chemical analysis showed the tailings comprised 26.2% Fe, 18.6% Si, 3.9% Al, and 1.07% total rare earth oxides (TREO). A rougher–scavenger–cleaner magnetic separation process was deployed to produce two useful streams of REE minerals concentrate and tails using a wet high-intensity magnetic separator (WHIMS). Typical metallurgical results indicated the rejection of 25% of the iron oxides at 0.11 T, whilst producing a magnetic concentrate with TREO recovery of 51% at a grade of 1.25% and non-magnetic tails with TREO recovery of 41% at a grade of 1.08%, both at 1.74 T. Bastnäsite, monazite, florencite, and stillwellite minerals were confirmed to be paramagnetic, whilst stetindite and brannerite were found to be diamagnetic. Whilst the applied magnetic field intensity was the most important factor in the minerals' magnetic separation efficacy, particle size distribution and mineralogical characteristics of ores also had significant effect. The findings exemplify both the challenges and opportunities for the beneficiation of complex, low grade REE-bearing iron oxide silicate rich tailings using WHIMS. They indicate that magnetic separation may be used to achieve modest preconcentration, the success of which is limited by the complex nature of the tailings and its concomitant magnetic properties, and thus warranting the need for further downstream processing (e.g., froth flotation) to produce cleaner, higher grade REE minerals concentrates for subsequent values extraction. [ABSTRACT FROM AUTHOR]

Simplified geological map showing the location of carbonatites, carbonatite-related REE deposits, and bastnäsite-dominated carbonatite-related REE deposits (i.e., where bastnäsite is among the three most abundant REE minerals; Weng et al., 2015; Smith et al., 2016). Map modified after Tang et al. (2013). • Ba, Sr, Ca, Th, U, and Sc commonly replace La and Ce in bastnäsite. • Large-scale bastnäsite crystallization occurred at the later stage of the hydrothermal system. • The process of REE enrichment in the Mianing-Dechang deposits is established. • The barite–calcite–fluorite assemblage can be regarded as a valuable guide in exploration for REE deposits. Bastnäsite is the main ore mineral in many carbonatite-related rare earth element (REE) deposits, which account for ∼51% of rare-earth oxide reserves worldwide. However, the occurrence, geochemistry, and genetic significance of bastnäsite has not been methodically investigated. The Cenozoic Mianning–Dechang (MD) REE belt in Sichuan Province, SW China, contains the Maoniuping, Dalucao, Lizhuang, and Muluozhai deposits as well as numerous smaller REE occurrences. Individual deposits within the belt contain different types of bastnäsite-bearing ore, which provides a unique opportunity to explore in detail the common mechanisms controlling the formation of bastnäsite-rich REE deposits. Here, we present detailed results from field observations and petrographic, geochemical, and fluid inclusion studies of bastnäsite from the main MD deposits. Calcite, fluorite, and barite form stable mineral assemblages that are commonly overprinted by bastnäsite. Homogenization temperatures of fluid inclusions in bastnäsite of ∼150–270 °C (Dalucao and Lizhuang deposits) and 155–210 °C (Maoniuping deposit) are systematically lower than those of fluid inclusions in gangue minerals. Therefore, the petrographic studies and homogenization temperatures both show that large-scale crystallization of bastnäsite took place during the later stage of the hydrothermal system. The bastnäsite, relatively geochemically homogeneous within all of the MD deposits, is enriched in Ba (293–8425 ppm), Th (16.4–2527 ppm), and U (4.19–92.7 ppm), and relatively depleted in high field strength elements such as Nb (0.15–17.4 ppm), Ta (0.06–6.48 ppm), Zr (0.71–31.1 ppm), Hf (0.62–5.65 ppm), and Ti (<60 ppm), the same to carbonatite, and ore veins. In comparison, the samples from the study area show an increase in average REE contents from syenites to carbonatites to ore veins (i.e., bastnäsite-bearing ores) and finally to bastnäsite. Lanthanum and Ce were commonly substituted by Th, U, Sc, Ba, and Sr supplied by more evolved hydrothermal fluids. Combining the present results with existing data, we present a three-stage model for the formation of carbonatite-related REE deposits. First, partial melting of metasomatized sub-continental lithospheric mantle, fluxed by REE- and CO 2 -rich fluids, forms the parental carbonatite–syenite magma. Second, Sr, Ba, and REEs are strongly partitioned into carbonatite melts during liquid immiscibility in the carbonatite–syenite magmatic system. Third, hydrothermal fluids exsolved from the crystalizing syenite and carbonatite magmas form ore veins with early gangue minerals and later bastnäsite overgrowths. Consequently, barite, calcite, and fluorite assemblages are a valuable guide in REE exploration. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The effect of EDTA on the separation of bastnaesite from fluorite by flotation was investigated. • Fluorite can be selectively depressed in bastnaesite flotation by EDTA. • Chemically adsorbed OHA on fluorite can be dissolved into soluble metal-EDTA complexes. • Chemically adsorbed OHA on bastnaesite is still stable after the addition of EDTA. Abstract Bastnäsite is an important mineral resource in the production of rare earth materials and is usually beneficiated by flotation. The flotation of bastnäsite is problematic due to the competitive adsorption of hydroxamate collector on bastnäsite and its associated calcium-bearing gangue minerals such as fluorite. One strategy to solve this problem is to use effective depressants to depress the gangue minerals. However, the current depressants all have some drawbacks. In this study, the effect of ethylenediamine tetraacetic acid (EDTA) as a depressant was tested in the flotation of single mineral of bastnäsite and fluorite and their mixture. The mechanism underpinning the role of EDTA was investigated through theoretical thermodynamic calculation, zeta potential and X-ray photoelectron spectroscopy (XPS) measurements. The results show that fluorite was significantly depressed, while the flotation of bastnäsite was almost unaffected when EDTA was present. The separation index between bastnäsite and fluorite increased from 1.18 to 12.66 with the increase of EDTA concentration from 0 to 7.79 kg/t. It was found that EDTA could dissolve the chemically adsorbed octyl hydroxamic acid (OHA) on fluorite through the formation of soluble Ca-EDTA complexes, whereas the chemically adsorbed OHA on bastnäsite was more stable and could not be transformed into Ce-EDTA spontaneously. Therefore, the flotation of fluorite was selectively depressed by EDTA. The results show that EDTA was a promising depressant for fluorite gangue mineral in bastnäsite flotation. [ABSTRACT FROM AUTHOR]

Dissolution of rare earth elements from bastnasite ore was studied using different leaching agents such as sulfuric acid, hydrochloric acid, acetic acid, citric acid and sodium hydroxide at 70°C, with 1mol/L, solid/liquid ratio of 0.05 between 30 and 180 min. The one-step direct leaching strategy was applied under atmospheric pressure aiming at selective leaching of rare earth elements from a matrix of iron oxides in which the rare earth elements - carbonates & flourides - are embedded. [ABSTRACT FROM AUTHOR]

Abstract A number of gravity separation techniques for rare earth elements (REE) minerals have been investigated and reported in the literature. These include the use of dense/heavy media, Falcon concentrators, Knelson concentrators, spiral concentrators, laboratory scale jigs, and shaking tables. Most of these methods have provided considerable REE minerals recovery and upgrade; but remain at the laboratory testing stage. There are vast quantities of iron-oxide-silicate rich tailings (IST) containing low grade REE in Australia. This work is part of research and development studies currently underway at the University of South Australia to develop economically viable methods to exploit selected IST for their REE contents. In this investigation, the feasibility of exploiting the differences in specific gravity to concentrate REE minerals from a typical IST sample was studied using two gravity separation units, a Knelson concentrator (KC) and Wilfley shaking table. The feed sample and gravity separation products were characterised using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) to study and compare the performance of the KC and shaking table as gravity preconcentration methods. The results indicated that the performance of both the KC and shaking table are significantly dependent on the mineralogical and particle size characteristics of the feed, however, the tabling was found to be the preferred choice over the KC, due to its greater selectivity. Tabling of >38 μm feed samples produced the desired split between the iron oxides and silicate minerals. The results suggest that desliming of the feed to remove fine/ultrafine particles (<38 μm) prior to tabling is key to attaining the desired results with the shaking table. Overall, tabling produced appreciable REE minerals upgrade, with iron oxides occupying the bulk of the concentrates. The test results confirm the complex mineralogy of the IST, which compromised REE minerals upgrade. A modified concentration criterion expression which considers the liberation characteristics of minerals is proposed, which provides a better idea on the feasibility of gravity separation. Graphical abstract Enrichment ratio of major mineral phases after KC and tabling separation of unclassified IST. Unlabelled Image Highlights • KC and shaking table were tested as gravity separation methods. • Particle and mineralogical characteristics affect gravity separation efficiency. • A modified concentration criterion expression is proposed. • Bastnäsite and monazite were upgraded using both KC and tabling. [ABSTRACT FROM AUTHOR]

Highlights • REE fluorcarbonates most widespread minerals in REE ore deposits. • Magnetic properties of parisite, röntgenite, synchysite determined for first time. • Magnetic behaviour varies from paramagnetic to diamagnetic according to REE:Ca ratio. Abstract Rare earth elements (REE) are considered as critical metals for electronics and green technology. The REE fluorcarbonates are one of the main REE ore minerals, common in many different types of REE deposit and yet some of their fundamental properties have still not been determined. This study measured the magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) and determined their elemental compositions using electron probe microanalysis (EPMA). The results provide the first measurements of the magnetic behaviour and susceptibility of REE fluorcarbonates other than bastnäsite-(Ce). The magnetic susceptibility of REE fluorcarbonates varies systematically from one mineral to another and is highly dependent on the mineral chemistry. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) is difficult to measure, generate good signal and acquire accurate readings because it practically always occurs as <5 mg crystals. Its magnetic susceptibility in samples from a REE ore deposit was experimentally determined by magnetic separation and checked by an associated study using a SQUID magnetometer, synchysite-(Ce) behaved as a diamagnetic mineral. This can be explained by the increase of Ca content and decrease of REE content, in addition to the variations in the layered structure common to the REE fluorcarbonate series minerals. Given the wide range of magnetic susceptibility of REE fluorcarbonates, it is important that the mineralogy is determined carefully before setting up a mineral processing flow sheet. [ABSTRACT FROM AUTHOR]

Graphical abstract Metallurgical balance of TREO distribution in flowsheets for flotation of REO using (a) sodium oleate and (b) hydroxamic acid in the presence of sodium silicate and starch. Highlights • Flotation was tested as separation method for rare earth oxides (REO). • Sodium oleate and hydroxamic acid were used as collectors. • Sodium silicate and starch were used as depressants. • Particle and mineralogical characteristics affect REO upgrade. Abstract To investigate the recovery of rare earth elements (REE) as a by-product from iron-oxide silicate rich tailings generated from the extraction of other primary commodities, bench scale flotation tests, in rougher-scavenger-cleaner configuration were studied. Preliminary mineralogical characterisation identified bastnäsite, monazite, stetindite, brannerite, florencite, and stillwellite as the REE minerals, with hematite and quartz being the major gangue minerals in the tailings material. The flotation response of the rare earth oxides (REO) and major gangue phases was investigated using sodium oleate and hydroxamic acid as collectors; and sodium silicate and starch as depressants. Generally, sodium oleate displayed relatively better selectivity for REO than hydroxamic acid in the presence of the depressants. The rougher-scavenger-cleaner flotation configuration using sodium oleate and the depressants produced a final concentrate recovering 63% REO at a grade of 2.25%. This investigation shows that both collectors may be used for REO recovery but the use of depressants is key, in tandem with cleaning of the rougher and scavenger concentrates. The pulp pH also had a strong impact on the flotation recovery of REO, with the selectivity deteriorating with increasing collector dosage. Furthermore, the high proportion of gangue minerals reporting to the concentrates, even with the use of depressants, affected the quality of concentrates grade. This study has shown that particle size distribution and mineralogical characteristics of feed significantly affect the upgrade and recovery of REO. [ABSTRACT FROM AUTHOR]

Dissolution of rare earth elements from bastnasite ores was studied using sulfuric acid at the atmospheric pressure. The one step strategy with sulfuric acid was studied further and the results showed that filtering difficulties do not happen for the chosen parameter combinations. Furthermore, the best parameter combinations were those with low temperatures and low acid concentrations. All in all, direct leaching is a simple process that uses the cheapest acid on the market and offers good leaching recoveries. Attention should be given to the formation of gel, especially when taking the process to the large scale, and the subsequent elimination of Ca from the leachate. [ABSTRACT FROM AUTHOR]

Carboxylates, hydroxamates and organic phosphoric acids are typical collectors used for rare earth mineral flotation. Carboxylates are not selective, while hydroxamates, though selective, require high concentrations to recover a significant amount of rare earth minerals. Other collectors such as organic phosphoric acids, which showed promising rare earth minerals collecting potential, have recently been explored. However, the mechanism of organic phosphoric acid adsorption on the surface of rare earth minerals has not been very well investigated. In this study, zeta potential measurements were conducted to study the surface property of dolomite, monazite and bastnäsite in the presence of benzohydroxamate (hydroxamate), sodium oleate (carboxylate) and Flotinor 1682 (phosphoric acid ester). These measurements, complemented with ATR-FTIR spectroscopy, evaluated the adsorption of the collectors at the surface of the minerals. The adsorption of the collectors was found to be highly influenced by the mineral cations present at the mineral/solution interface and in the solution. Possible adsorption mechanisms are proposed and discussed; some of which agree with those presented in the literature, while others provided different perspective. Although benzohydroxamate was the most selective, potential flotation processes to recover rare earth minerals using sodium oleate and Flotinor 1682 were also suggested. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE) are critical to a wide range of technologies ranging from mobile phones to wind turbines. Processing and extraction of REE minerals from ore bodies is, however, both challenging and relatively poorly understood, as the majority of deposits contain only limited enrichment of REEs. An improved understanding of the surface properties of the minerals is important in informing and optimising their processing, in particular for separation by froth flotation. The measurement of zeta potential can be used to extract information regarding the electrical double layer, and hence surface properties of these minerals. There are over 34 REE fluorcarbonate minerals currently identified, however bastnäsite, synchysite and parisite are of most economic importance. Bastnäsite–(Ce), the most common REE fluorcarbonate, supplies over 50% of the world's REE. Previous studies of bastnäsite have showed a wide range of surface behaviour, with the iso-electric point (IEP), being measured between pH values of 4.6 and 9.3. In contrast, no values of IEP have been reported for parisite or synchysite. In this work, we review previous studies of the zeta potentials of bastnäsite to investigate the effects of different methodologies and sample preparation. In addition, measurements of zeta potentials of parisite under water, collector and supernatant conditions were conducted, the first to be reported. These results showed an iso-electric point for parisite of 5.6 under water, with a shift to a more negative zeta potential with both collector (hydroxamic and fatty acids) and supernatant conditions. The IEP with collectors and supernatant was <3.5. As zeta potential measurements in the presence of reagents and supernatants are the most rigorous way of determining the efficiency of a flotation reagent, the agreement between parisite zeta potentials obtained here and previous work on bastnäsite suggests that parisite may be processed using similar reagent schemes to bastnäsite. This is important for future processing of REE deposits, comprising of more complex REE mineralogy. [ABSTRACT FROM AUTHOR]

Flotation is the most commonly used beneficiation method for rare earth (RE) ores. Due to the dissolution characteristics of the RE minerals and the gangue minerals, they may behave similarly in a flotation system. Previous work has shown that dissolved mineral species from gangue could precipitate/adsorb at the mineral surface affecting the minerals’ flotation behavior. In this work, the effect of dolomite supernatant on the surface of bastnäsite, monazite and dolomite are presented. Zeta potential measurements, complemented with flotation tests, were conducted with and without the presence of the supernatant using benzohydroxamate as the collector. XPS results confirmed the surface speciation, and DFT simulations detail the possible mineral - collector, mineral - precipitated species and precipitated species - collector interactions. The results show that carbonate precipitates and Ca 2+ from the supernatant could adsorb onto the mineral surface through covalent bonding, both affecting the zeta potential and reducing collector adsorption. Another important finding of this study is the potential loss of the collector in the solution due to complexation with ions from the supernatant. These findings confirm that an effective rare earth mineral separation through flotation does not rely solely on the strength of collector-mineral interaction, but rather is highly dependent on the chemistry of the flotation solution. Taking advantage of, or controlling, the surface reactions should be the main target to developing a more efficient and cost-effective flotation process. Different measures have been proposed to reverse/reduce the detrimental effects of the dolomite supernatant to RE mineral flotation. [ABSTRACT FROM AUTHOR]

Olympic Dam is a world-class breccia-hosted iron-oxide copper-gold-uranium ore deposit located in the Gawler Craton, South Australia. It contains elevated concentrations of rare earth elements (REE) which occur as the REE minerals bastnäsite, synchysite, florencite, monazite, and xenotime. This is the first study to focus on the mineralogy and composition of the most abundant REE mineral at Olympic Dam, bastnäsite, and subordinate synchysite. The sample suite extends across the deposit and represents different sulfide mineralization styles (chalcopyrite-bornite and bornite-chalcocite) and breccias of various types, ranging from those dominated by clasts of granite, dykes, and hematite. The REE-fluorocarbonates (bastnäsite and synchysite) typically occur as fine-grained (<50 µm) disseminations in Cu-Fe-sulfides and gangue minerals, and also within breccia matrix. They are also locally concentrated within macroscopic REE-mineral-rich pockets at various locations across the deposit. Such coarse-grained samples formed the primary target of this study. Three general textural groups of bastnäsite are recognized: matrix (further divided into disseminated, fine-grained, and stubby types), irregular (sulfide-associated), and clast replacement. Textures are largely driven by the specific location and prevailing mineral assemblage, with morphology and grain size often controlled by the associated minerals (hematite, sulfides). Major element concentration data reveal limited compositional variation among the REE-fluorocarbonates; all are Ce-dominant. Subtle compositional differences among REE-fluorocarbonates define a spectrum from relatively La-enriched to (Ce + Nd)-enriched phases. Granite-derived hydrothermal fluids were the likely source of F in the REE-fluorocarbonates, as well as some of the CO2, which may also have been contributed by associated mafic-ultramafic magmatism. However, transport of REE by Cl-ligands is the most likely scenario. Stubby bastnäsite and synchysite may have formed earlier, coincident with hydrothermal alteration of granite releasing Ca from feldspars. Other categories of bastnäsite, notably those co-existing with sulfides, and reaching the top of the IOCG mineralization at Olympic Dam (chalcocite + bornite zone) are relatively younger. Such an interpretation is concordant with subtle changes in the REE patterns for the different categories. The common association of bastnäsite and fluorite throughout the deposit is typical of the hematite breccias and can be deposited from neutral, slightly acidic fluids (sericite stability) at T * 300 °C. [ABSTRACT FROM AUTHOR]

Rare earth elements are a critical component in many clean energy technologies. Extraction of individual rare earth elements from natural ores or recycled material is challenging due to the very similar chemical properties across the lanthanide series. Supercritical carbon dioxide has emerged in recent years as a possible extraction medium for rare earth elements, due to its tunability and selectivity as a solvent. In this study, rare earth elements were recovered from bastnäsite concentrate using supercritical carbon dioxide extraction with nitric acid/tributyl phosphate adducts. Two bastnäsite pretreatment methods were used to render the rare earth elements amenable to recovery: 1) dry roasting of the source material at 730 °C for 3 h, and 2) decomposition with 50% sodium hydroxide solution at 150 °C for 4 h. These pretreated powder samples were extracted in supercritical carbon dioxide at 34 MPa and 65 °C, with kinetic samples obtained at 15–30 min intervals. A range of tributyl phosphate/nitric acid adduct compositions (from 2 mol/L H + to 6 mol/L H + ) were used in order to determine the effect of adduct composition on recovery rate. The results showed the fastest extraction with an adduct containing approximately 4 mol/L H + . Adducts with higher acidity showed reduced extraction of cerium, praseodymium, and neodymium. This could be due to the formation of aqueous droplets which dissolve rare earth elements and create an equilibrium limitation, or due to competition between the rare earth nitrates and nitric acid for coordination with tributyl phosphate. Extraction with various adduct concentrations in supercritical CO 2 showed the expected increase in reaction rate with increased adduct concentration. For the 4 mol/L H + adduct at 5.0 mol% adduct concentration, roasted bastnäsite recoveries were 72% for La, 96% for Ce, 88% for Pr, and 90% for Nd after 120 min. For 4 mol/L H + adduct at 5.1 mol% adduct concentration, NaOH digested bastnäsite recoveries were 93% for La, 100% for Ce, 99% for Pr, and 101% for Nd after 90 min. Though further research is needed, these results are a key step in demonstrating applicability of supercritical extraction to rare earth element ores. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two karst bauxites in Sierra de Bahoruco have high REE and a contrasting mineralogy. • REE contents range from 0.07 to 1.40 wt%, and Y from 0.01 to 1.48 wt%. • LREE are hosted in monazite-(Ce), found in both deposits. • El Turco is dominated by secondary Y-phosphates. • The main REE mineral in Aceitillar is hydroxylbastnäsite-(Gd). Karst bauxites have recently received renewed attention for their potential as non-conventional REE sources. Karst bauxites from the Pedernales Peninsula in the Dominican Republic stand among the world's richest in REE. Bauxite ore from two deposits from this bauxite district, Aceitillar and El Turco, have been selected for this study due to their outstanding REE contents and contrasting mineralogy. REE (La to Lu) contents in Aceitillar, range from 0.07 to 0.16 wt%, and Y from 0.01 to 0.13 wt%, whereas El Turco contains between 0.28 and 1.40 wt% REE, and 0.33 to 1.48 wt% Y. The characterisation of REE mineralisation was performed through powder and monocrystal XRD, SEM-EDS, and EMP analyses. REE phosphates and carbonates reveal textural features that suggest significant REE mobilisation and re-deposition within the bauxite profile. The identified REE minerals can be classified into: i) primary monazite(-Ce) and minor monazite(-La); ii) secondary Y- and Nd-dominant phosphates; and iii) secondary Gd- and Nd-carbonates of the (hydroxyl)bastnäsite group. While monazites are ubiquitous in the two studied deposits, secondary phosphates are predominant in El Turco while secondary carbonates are exclusive of Aceitillar. This contrasting mineralogy is explained by the total concentration of carbonate and/or phosphate in the karst bauxite groundwater solutions. REE phosphates are the most stable phases at [CO 3 2−] total /[PO 4 3−] total ≤ 2; whereas REE carbonates are stable at near neutral pH when the total aqueous carbonate concentration is two orders of magnitude higher than that of phosphate. Results of this investigation contribute to a better understanding of the formation REE minerals in the supergene environment and can be applied in REE separation methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • CL colors and peaks of minerals in ores containing bastnäsite were investigated. • Bastnäsite can be identified from color and luminescence intensity in CL images. • Rough content of the bastnäsite in the ores can be estimated from the CL images. • CL imaging can aid the effective exploration of mines with REE reserves. A rapid determination of the rough content of the major rare earth element (REE)-bearing minerals (bastnäsite, monazite, and xenotime) can lead to a drastic reduction of the time required to analyze mineral ores for the extraction of REE metals, thus enabling the efficient exploration of mines with REE reserves. This study presents a method of using cathodoluminescence (CL) imaging to identify bastnäsite in mineral ores and determine the rough bastnäsite content rapidly. By investigating the luminescence colors in CL images and the peaks in CL spectra emitted by minerals in ores that include bastnäsite, the author found that bastnäsite can be identified by detecting dark red or red–orange luminescence in CL images of the ores in the wavelength range 420–680 nm or by detecting areas that emitted no luminescence in the 420–680 nm CL images but that do emit pale red luminescence in CL images in the broader wavelength range 350–1000 nm. The bastnäsite content in the ores can be estimated roughly from the fractional areas identified as bastnäsite in the CL images. The CL images can be obtained within 30 s. Therefore, CL imaging can prescreen mineral ores for subsequent more precise quantitative analyses (e.g., using inductively coupled plasma mass spectrometry or electron-probe microanalysis) by identifying mineral ores having a probable high bastnäsite content. This approach can drastically reduce the time required to explore mines with potential REE reserves. [ABSTRACT FROM AUTHOR]

[Display omitted] • CL colors and peaks of minerals in ores containing bastnäsite were investigated. • Bastnäsite can be identified from color and luminescence intensity in CL images. • Rough content of the bastnäsite in the ores can be estimated from the CL images. • CL imaging can aid the effective exploration of mines with REE reserves. A rapid determination of the rough content of the major rare earth element (REE)-bearing minerals (bastnäsite, monazite, and xenotime) can lead to a drastic reduction of the time required to analyze mineral ores for the extraction of REE metals, thus enabling the efficient exploration of mines with REE reserves. This study presents a method of using cathodoluminescence (CL) imaging to identify bastnäsite in mineral ores and determine the rough bastnäsite content rapidly. By investigating the luminescence colors in CL images and the peaks in CL spectra emitted by minerals in ores that include bastnäsite, the author found that bastnäsite can be identified by detecting dark red or red–orange luminescence in CL images of the ores in the wavelength range 420–680 nm or by detecting areas that emitted no luminescence in the 420–680 nm CL images but that do emit pale red luminescence in CL images in the broader wavelength range 350–1000 nm. The bastnäsite content in the ores can be estimated roughly from the fractional areas identified as bastnäsite in the CL images. The CL images can be obtained within 30 s. Therefore, CL imaging can prescreen mineral ores for subsequent more precise quantitative analyses (e.g., using inductively coupled plasma mass spectrometry or electron-probe microanalysis) by identifying mineral ores having a probable high bastnäsite content. This approach can drastically reduce the time required to explore mines with potential REE reserves. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Huanglongpu deposit developed two stages of REE mineralization (219.4 Ma and 145.9–142.6 Ma). • The early REE mineralization is intimately related to the carbonatite Mo mineralization, which was created in the late Triassic post-collision extensional environment. • The late REE mineralization may be generated by REE remobilization and recrystallization resulting from the Yanshanian magmtism. • The REE mineralization that occurred at 145.9–142.6 Ma was first reported in the Qinling Region. The Huanglongpu deposit is one of the most representative igneous carbonatite-type molybdenum-rare earth element (Mo-REE) deposits in the eastern Qinling metallogenic region. The molybdenum resources exceed 180 kt, whilst the total rare earth resources are about 37.8 kt. However, the age of REE mineralization, sources of ore-forming minerals, and tectonic setting are not well characterized. Therefore, this study carried out detailed mineralogical, geochronological, and geochemical analyses to provide new insights. Monazite, bastnäsite, parisite, and xenotime were found to be the dominant REE-bearing minerals in the Huanglongpu deposit. LA-ICP-MS U-Pb dating of the REE minerals revealed a two-stage REE mineralization: monazite formed at 219.4 Ma, whereas bastnäsite and xenotime formed at 145.9 Ma and 142.6 Ma, respectively. The carbonatites, as the main ore host, were characterized by a strong enrichment of light rare earth element (LREE) and moderately high heavy rare earth element (HREE) contents. Monazite showed different Nd isotopic compositions, with lower ε Nd (t) values ranging between −7.12 and −4.18, while the ε Nd (t) values of bastnäsite and xenotime ranged from −9.57 to −6.49 and from −11.13 to −6.28, respectively. These contrasting geochemical and isotopic signatures suggest that the Huanglongpu REE mineralization occurred over multiple magmatic-hydrothermal events and that the ore-forming material was unlikely to have stemmed from a single enriched mantle (EMI) source. The early REE mineralization stage (219.4 Ma) was closely associated with carbonatite-related Mo mineralization, both of which were products of magmatic mineralization during the crystallization of the host carbonatite emplaced in an extensional environment after the Late Triassic collision. The ore-related magmas may have originated from a hybrid source composed of EMI and partial melting of the lower crust. In contrast, due to the extensive Yanshanian magmatism which could provide massive heat, the later REE mineralization stage (145.9–142.6 Ma) in the Huanglongpu deposit was likely driven by the reactivation and recrystallization of early-formed REE minerals within the host carbonatites, hence representing a hydrothermal redistribution of the primary magmatic ore. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) simulations and experiments were performed to clarify the interaction mechanisms between hydroxamic acid collectors and cerium hydroxides during the flotation of bastnäsite and monazite minerals. These minerals showed considerable floatability at moderately alkaline pH which was related to the adsorption of hydroxamic acids on their surfaces as confirmed by vibrational spectroscopic and zeta potential measurements. DFT simulations showed that at moderately alkaline pH, the interactions between solvated Ce(OH) 2+ and Ce(OH) 2 + and heptyl-hydroxamic acid (HHA) anions resulted in the formation of, respectively, [Ce(OH)(HHA) x (H 2 O) y ] 2−x (x[y = ] = 1[6],2[3],3[1]) and [Ce(OH) 2 (HHA) x (H 2 O) y ] 1−x (x[y = ] = 1[5],2[1],3[0]) complexes. The collector anions were found to interact directly through formation of two covalent bonds between their two polar-head oxygen atoms and cerium in the hydroxide complexes. However, formation of such new bonds resulted in breakage of a few covalent/electrostatic bonds between cerium and water molecules initially present in the first hydration shell of the rare-earth metal cation. Building up in the electric double layer of the semi-soluble minerals, these complexes, and by extension, those from other rare-earth elements belonging to monazite and bastnäsite, are speculated to play a role in the interactions between rare-earth minerals and hydroxamic acid collectors. [ABSTRACT FROM AUTHOR]

The mobility of rare earth elements (REEs) in natural aqueous solutions is of increasing interest due to their application in numerous high-tech and renewable energy technologies (e.g., wind turbines and electric vehicles), as well as their role as tracers in the Earth Sciences. Basic thermodynamic data for water–rock interactions are, however, sparse and partially inconsistent, even for carbonate minerals of the bastnasite group (REE(CO 3 )(OH,F)), which currently represent the most exploited REE ore. Towards the improved quantification of the REE in natural and industrial systems, pure hexagonal hydroxylbastnasite and orthorhombic kozoite (REE(CO 3 )(OH)) were synthesized at hydrothermal conditions and subsequently used as starting material for aqueous dissolution and precipitation experiments. All closed system experiments were performed in air equilibrated aqueous fluids. Reaction progress was followed by measuring pH and REE concentrations at regular intervals. Experiments at 25 °C in the presence of selected concentrations of HCl and NaOH were run for up to 33 days until steady-state pH and REE concentrations were attained. Results indicate that the solubility products ( K SP ) of the reaction REE(CO 3 )(OH) = REE 3 + + CO 3 2 − + OH − are log( K SP ) = − 23.8 ± 0.1, − 24.1 ± 0.3, and − 22.3 ± 0.2 for Nd-, La-hydroxylbastnasite, and Nd-kozoite, respectively at 25 °C. [ABSTRACT FROM AUTHOR]

An understanding of the mineralogy and petrogenesis of rare earth element deposits has significant implications for their economic viability. Lanthanide-bearing compounds are known to produce sharp absorption features in the visible to short-wave infrared region (VIS-SWIR), however, a significant knowledge gap exists between the fields of hyperspectral reflectance spectroscopy and rare earth element mineralogy. Reflectance spectra were collected from four bastnäsite samples, two parisite samples, and one synchysite sample from the visible into the short-wave infrared. These REE fluorocarbonate mineral samples were characterized via scanning electron microscopy and electron probe microanalysis. Sharp absorptions of REE-bearing minerals are mostly the result of 4f-4f intraconfigurational electron transitions and for the light REE-enriched fluorocarbonates, the bulk of the features can be ascribed to Nd3+, Pr3+, Sm3+, and Eu3+. The lanthanide-related spectral responses of the REE fluorocarbonates are consistent across the group, supporting the notion that the REE cation site is very similar in each of these minerals. Carbonate-related spectral responses differed between these minerals, supporting the notion that the crystallographic sites for the carbonate radical differ between bastnäsite, synchysite, and parisite. Exploitable spectral differences include a distinct absorption band at 2243 nm that separates bastnäsite from synchysite and parisite. Similarly, for bastnäsite a dominantly Pr3+-related absorption band located is at 1968 nm, while in synchysite and parisite it occurs at 1961 nm. [ABSTRACT FROM AUTHOR]

Abstract: Bastnasite ore obtained from Indian Rare Earth (IRE) was investigated for its possible use as a phosphor material. The material was characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), photoacoustic spectroscopy (PAS), photoluminescence (PL) and electron paramagnetic resonance spectroscopy (EPR) techniques. XRD studies revealed the semi processed ore to be consisting of single phase CeO2 with no other impurities. EDXRF studies revealed the presence of ‘Th’ and traces of ‘Sm’ along with ‘Ce’ in the sample. PAS studies revealed the presence of strong charge transfer from oxygen to cerium in the system. PL studies confirmed the presence of at least four trivalent rare earths, viz. Sm, Eu, Dy and Tb in the system in trace quantities. The emission spectrum and decay time data were evaluated. It was observed that the rare earth ions are situated at distorted sites in the system surrounded by defect centers. EPR studies confirmed the presence of Ce3+in the system along with electron trapped in oxygen ion vacancies. CIE indices for the ore sample were evaluated and it was seen that the overall emission from the system was in the ‘magenta’ region of the visible spectrum. The emission intensities were also compared with that of commercial samples. [Copyright &y& Elsevier]

The western margin of the Karelia Province of the Fennoscandian Shield consists of Archean crust covered by remnants of Paleoproterozoic (c. 2.5–1.9Ga) metasedimentary rocks. The study area in the eastern part of the margin shows 2.3–2.1Ga cratonic sedimentation followed by 2.1–2.05Ga rift sedimentation and c. 1.91–1.92Ga foredeep to foreland sedimentation related to continent–arc/continent collision. Extreme LREE mobility (loss up >95% of La) is recorded by many samples from these units. Monazite, bastnäsite and, in some cases, allanite have been the prealteration LREE host phases in the LREE depleted samples. Monazite was altered to Th-silicates with variable loss of the LREE, the remaining part of which was incorporated in Th-poor monazite. The depositional age of the sedimentary units was studied by dating (LA-MC-ICPMS) detrital zircon grains, and the age of LREE mobility by dating monazite and xenotime and by whole-rock Sm–Nd modeling. The maximum deposition age of the foredeep to foreland basin is 1.91–1.92Ga based on detrital zircon data and the minimum age of the main foliation in the study area is 1.87–1.86Ga based on the younger age limit of late-to post-tectonic xenotime and the ages of few probable metamorphic zircons. Coeval bastnäsite, with xenotime in a LREE enriched sample, suggests that this was also one important stage of LREE mobility. Monazite crystallizations have occurred 1.76–1.78Ga ago while the Rb–Sr whole rock data suggest that the closure of this isotope system took place 1732±21Ma ago. The Sm–Nd modeling gives ages at 0.4–1.0Ga for LREE depletion. The Sm–Nd age of 412±27Ma can be considered as the age of the latest major LREE depletion event. We propose that alkali-bearing oxidizing fluids started to form in the cratonic sequences due to diagenetic reactions maybe as early as 2.3–2.1Ga. Alkalinity of fluids was later increased by interaction with alkaline 2.05Ga source materials before and during the c. 1.91–1.92Ga foredeep to foreland basin stage. Basin inversion and metamorphic crystallization occurred at 1.91–1.87Ga. Episodes of fluid migration at 1.78–1.73Ga and afterwards were focused along fracture zones and in microfracture networks. The 0.4Ga stage is the most prominent of the <1.7Ga events and is best explained by assuming shield-scale foreland basin related to the Caledonian orogenic front, causing heat redistribution and also fluid circulation in the underlying crystalline basement. The 2.1Ga formed marginal fault has been a very important shield-scale tectonic element and a pathway for fluid circulation for almost 2billion years. [ABSTRACT FROM AUTHOR]

Abstract: Rare earth elements (REEs) comprise the fifteen elements of the lanthanide series as well as yttrium, and may be found in over 250 different minerals. These elements are required for many different applications such as high-strength permanent magnets, catalysts for petroleum refining, metal and glass additives and phosphors used in electronic displays. The only REE bearing minerals that have been extracted on a commercial scale are bastnäsite, monazite, and xenotime. These minerals may be beneficiated using gravity, magnetic, electrostatic and flotation separation techniques. Increased demand for the different products manufactured from REE has resulted in a constriction of supply from China, which currently produces 97% of the world’s rare earths, via export quotas. Many new rare earth deposits are currently being developed to help meet the demand void created by the Chinese export quotas, however most of these developing deposits include rare earth minerals for which there is limited processing knowledge. This paper examines the separation techniques that are currently employed for rare earth mineral beneficiation and identifies areas in need of further research. [Copyright &y& Elsevier]

Abstract: 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, Al3+ 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 15min. The effect of the initial Al3+ concentration at a certain total Al3+ 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. [Copyright &y& Elsevier]

Abstract: 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 bastnäsite (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. [Copyright &y& Elsevier]

Abstract: 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 °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, Al and other impurities. [Copyright &y& Elsevier]

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky complex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components. [ABSTRACT FROM AUTHOR]

Highlights: [•] PDHA is a new flocculant for recovering ultra-fine rare-earth minerals. [•] PDHA is promising to be used to process finely disseminated rare earth ore. [•] Flocculation effect of PDHA on ultra-fine bastnasite grains is apparent. [•] It is of great significance for saving rare earth resources. [ABSTRACT FROM AUTHOR]

We investigated the calcination of a rare earth carbonatite ore from Niobec in Quebec, Canada, containing bastnäsite and monazite. The bastnäsite decomposed at a relatively low temperature of approximately 400 °C while the monazite decomposed through solid-state reactions with associated minerals at temperatures exceeding 700 °C. A global kinetic model was developed that represented the calcination kinetics of the whole ore based on the individual calcination kinetics of the minerals nested in the ore. The decomposition of bastnäsite and the interaction of monazite with calcium oxide in the ore was used to estimate rare earth oxide production during calcination. Initially, the model was developed for small particles and was thus adapted to larger particle sizes by including a coefficient based on physical particle size cut parameters such as surface area, density, and particle diameter. Unlabelled Image • A comprehensive kinetic study was developed for the calcination of rare earth bearing ore. • Bastnäsite and monazite were the main REE-bearing minerals. • Decomposition study was performed by TGA analysis. • Kinetic models were developed for the calcination of each mineral in the ore. • Monazite only decomposed through solid-state reactions with associated minerals (>700 °C). [ABSTRACT FROM AUTHOR]

The recommended hydrophobization mechanism of 1-hydroxydodecylidene-1,1-diphosphonic acid (HDDPA) towards bastnäsite [(Ce,La)CO 3 F]as well as the flotation separation and recovery of bastnäsite from its mixture with calcite. • 1-Hydroxydodecylidene-1,1-diphosphonic acid was used in bastnäsite flotation. • HDDPA achieved an efficient separation of bastnäsite from calcite at pH ∼8.0. • HDDPA3− was glad to replace the CO 3 2- of Ce(III) carbonates on bastnäsite. • The surface Ce(III) of bastnäsite bonded with the O atoms of HDDPA's O P(O)O. To separate and enrich rare-earth elements (REE) minerals from their ores through flotation process has become an attracting topic for REE's strategic position. In the present investigation, the floatability of bastnäsite [(Ce,La)CO 3 F] was explored by using 1-hydroxydodecylidene-1,1-diphosphonic acid (HDDPA) as a collector. The micro-flotation results showed that bastnäsite displayed an eminent floatability under pH 7.0–10.0, and HDDPA realized an efficient separation of bastnäsite from calcite at pH around 8.0. Zeta potential and solution chemistry inferred that at pH 7.5–9.3, HDDPA3− anions were glad to replace the CO 3 2- ions of Ce(Ⅲ) carbonates in/on bastnäsite interface, resulting in a high flotation recovery of bastnäsite. With increasing OH- concentration, the competition ability of OH- against HDDPA anion intensified, gradually the surface Ce(III) hydroxide species increased, and the floatability of bastnäsite reduced. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) recommended that the surface Ce(III) of bastnäsite interacted with the O atoms of HDDPA's O P(O)O group to generate a four membered ring configuration, which hydrophobized bastnäsite particles. [ABSTRACT FROM AUTHOR]