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Common collectors for rare earth mineral (REM) flotation, which include carboxylates and hydroxamates, face problems such as being non-selective and sensitive to impurity ions. A type of ionic liquid (IL), tetraethylammonium mono-(2-ethylhexyl)2-ethylhexyl phosphonate ([N2222][EHEHP]), has been investigated previously for rare earth elements (REE) solvent extraction, and was proven to be selective and effective. In this work, [N2222][EHEHP] was evaluated as a collector in bastnasite (a primary REM source for REE production) flotation for the first time. The results were compared with quartz and hematite, two common gangue minerals in REM deposits. Zeta potential measurements and Fourier-transform infrared spectroscopy (FT-IR) were completed to investigate the surface chemical properties involved in the flotation of these minerals using this collector. The findings were compared with microflotation results. FT-IR and zeta potential measurements suggest adsorption of the collector's phosphonate group onto bastnasite and hematite, likely through chemisorption; whereas for quartz, the minimum microflotation recovery is likely due to no adsorption of IL on its surface. Microflotation results show higher collectability of [N2222][EHEHP] for hematite than bastnasite, the latter only shows appreciable recovery at pH 5 with elevated dosage of IL (500 g/t). To achieve better separation, a two-stage flotation scheme was designed and evaluated by bench scale flotation on a synthetic mineral mixture. The concentrates and tails were analyzed by magnetic separation, and it is found that bastnasite recovery over 90% with maximum upgrade ratio 1.7 can be achieved with elevated collector dosage.

The interaction of rare earth bearing (La, Nd, Dy) aqueous solutions with calcite crystals at ambient and hydrothermal conditions (25–220 °C) results in the solvent-mediated surface precipitation a...

Herein, a new clean extraction technology for the decomposition of bastnasite concentrate by utilizing the microwave radiation is proposed, which prevented Ce(III) from being oxidized to its tetravalent form. The process includes microwave radiation roasting to nonoxidatively decompose the bastnasite concentrate, mechanism analysis of Ce(III) not being oxidized to Ce(IV), hydrochloric acid leaching of the nonoxidative roasted ore, and kinetics analysis of the leaching process. The experiments were carried out concentrating on the effect of roasting temperature and holding time on the decomposition rate of the bastnasite concentrate and the oxidation rate of cerium and the effect of acidity, liquid-solid ratio, leaching temperature, and stirring rate on the leaching kinetics of the nonoxidative roasting ore. When the roasting temperature is 1100 °C, the holding time is 20 min, and the m(C)/m(REFCO3) ratio is 0.2, the results show that the leaching efficiency of rare earths can reach 85.45% under the conditions 3 mol/L HCl, 90 °C, 60 min, 9 mL/g liquid-solid ratio, and 300 rpm stirring rate. The X-ray diffraction and scanning electron microscopy analyses of the samples before and after acid leaching show that the rare earth oxides were completely leached and Ce(III) was not oxidized to its tetravalent form. The apparent activation energies of leaching rare earths were calculated as 14.326 kJ/mol, and the HCl leaching process can be described by a new variant of the shrinking-core model, in which both the interfacial transfer and the diffusion through the product layer influenced the reaction rate. Furthermore, a semiempirical rate equation was created to describe the leaching process of the nonoxidative roasted ore.

This study deals with the calcination of a rare earth bearing ore to produce rare earth oxides in a fluidized bed reactor, with the aim of demonstrating the advantage of calcining bigger particles to decompose stable minerals such as monazite by its mineral association within a particle. Rare earth oxides were produced by the decomposition of its bearing minerals, bastnasite and monazite along with the gangues. During the calcination, bastnasite decomposed at relatively low temperature while monazite reacted CaO at high temperature. The formation of cracks, revealed by BET and SEM analysis, allowed the particle’s degassing while the size remained constant, thus describing a crackling core behavior. The association of monazite to calcite for bigger particles (−60 mesh) allowed its decomposition to produce rare earth oxides with a monazite conversion of 50 %. Also, an extraction process comprised of calcination and mild acid leaching enriched the rare earth oxides in the ore by 3.34 and improved leaching efficiency of the gangues compared to smaller size (enrichment ration of 2.35). Using bigger particle sizes in the upstream process of a mining industry, i.e. comminution, can also reduce the energy consumption.

The performance of the Pickering emulsification process to selectively separate rare earth-bearing minerals from the associated gangue and to concentrate them in a novel environmentally friendly approach was enhanced by adjusting the interfacial conditions and the formulation parameters. The present study investigated the effects of interfacial tension, oil polarity and viscosity on the selective separation. Modifying the emulsion formulation and selecting an appropriate oil, oil to water volume ratio, and solid mass fraction can enhance the recovery and grade of rare earth bearing minerals in the product when compared with conventional flotation. Various oils with different viscosities and chemical compositions (silicone oil, oleic acid, paraffin, and kerosene) supplemented with an additive (1% 1-hexanol) to modify the interfacial tension, and a continuous phase other than water (i.e., 90% ethylene glycol) were tested. An oil viscosity of 200 cSt, oil-to-water ratio of 10%v, and a solid particle concentration of 5 wt% provided the best selectivity. Since silicone oil is not economically feasible at industrial scale, paraffin oil, which is less expensive, was tested and provided better selectivity. We employed a Niobec ore containing bastnasite and monazite with total rare earth elements of 3.3 wt%. The recovery of a one-stage emulsification was improved significantly by up to 56% using paraffin oil. It also resulted in a product enrichment ratio of approximately 2.7.

Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnasite [(Ce,La)FCO3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. Here, the adsorption of octyl hydroxamic acid onto bastnasite was measured using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnasite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnasite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnasite than with a common gangue mineral, calcite (CaCO3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength of metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores.

Dissolution in choline-chloride based deep eutectic solvents (DES) of rare earth elements (REE) from high-purity single carbonate salts of Y, La, Ce, Nd and Sm and from their multicomponent mixtures and also bastnasite mineral was assessed with a prospect to gain an understanding on the leaching behavior of bastnasite ores as REE source from DES suspensions. Urea, malonic acid and citric acid were used in different proportions with choline chloride in order to form deep eutectic solvents with desired viscosity and functionality. The results obtained prove promising for use insolvato-metallurgical processes in terms of selective dissolution of the higher-atomic-number (Z) rare earth elements at the expense of the lower-ZREEs and the gangue-originating metal impurities, thus initiating separation among the different REE members from the early hydrometallurgical steps.

Bastnasite is an important mineral resource in the production of rare earth materials and is usually beneficiated by flotation. The flotation of bastnasite is problematic due to the competitive adsorption of hydroxamate collector on bastnasite 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 bastnasite 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 bastnasite was almost unaffected when EDTA was present. The separation index between bastnasite 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 bastnasite 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 bastnasite flotation.

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 (

Common rare earth (RE) minerals, such as bastnasite and monazite, may be formed in deposits associated with carbonate gangue, such as calcite and dolomite. Sodium oleate is a widely used collector for the flotation of both RE and gangue minerals, which might, therefore, be an inefficient process due to the lack of selectivity of this collector. Since these minerals are also sparingly soluble in solution, they could release their constituent ions into the solution, which could affect the floatability of other minerals. In this study, the interactions of sodium oleate with bastnasite and monazite in the presence of dissolved dolomite species have been investigated. Microflotation tests were carried out to explore the effects of these dissolved species on the floatability of the RE minerals. Zeta potential measurements and XPS characterization were carried out to understand how the species affect the collector adsorption. To complement these characterizations, density functional theory (DFT) simulations were conducted to investigate the collector-mineral and collector-adsorbed species (on the mineral surface) interactions. The results show that collector-dolomite interaction energy is greater than that of collector-adsorbed species, but lower than collector-monazite interaction energy, explaining the decrease in the minerals' recovery upon exposure to the dissolved mineral species. It is also shown that oleate ions (Ol–) have the strongest interaction with the minerals compared to other oleate species such as acid soap (HOl2–) and oleate dimer (Ol22−). The behavior (strength and selectivity) of sodium oleate towards RE minerals and dolomite, as compared to other RE mineral collectors (such as aromatic hydroxamate), is attributed mainly to the collector's and the minerals' structure. The long hydrocarbon chain of sodium oleate which imparts hydrophobic characteristic to the minerals, makes it stronger collector than benzohydroxamate. Moreover, sodium oleate (with linear structure), unlike the aromatic hydroxamate, can approach the mineral easier due to lesser steric hindrance effect and higher reactivity of O involved in the interaction, making it less selective. In addition, it can interact easily with dolomite due to the presence of more exposed active sites than RE minerals.

The production of mixed rare earth oxide powder from a thorium containing bastnasite ore by sulfuric acid bake-water leaching followed by precipitation with oxalic acid and thermal decomposition of the oxalates was investigated. The sulfuric acid baking was performed at 250 °C and the optimum baking time was found to be 3 h. Using deionized water as lixiviant, 92.6% La, 86.8% Ce, 86.9% Pr, 82.3% Nd, 95.4% Th and 31% Y were dissolved from the baked ore at 25 °C after 30 min of leaching. The effect of solid-to-liquid ratio on the dissolution of the rare earth elements and thorium shows that when the solid ratio in the water increased from 1:10 to 1:3, the dissolution percentage decreased. The final mixed rare earth oxide powder contained 88.54% REO and 6% ThO2 together with small amounts of other impurities. The SEM mapping results revealed that the produced REO has an irregular crystal shape. Based on the experimental results obtained from the current study, a flowsheet was proposed for the production of mixed rare earth oxide powder from a specific complex bastnasite ore.

Carbonate gangue in historically important post-Variscan polymetallic Pb-Zn-Cu-Ag vein systems in the Upper Harz Mountains has elevated rare earth element contents (ΣREE+Y, 1500 ± 340 ppm; n = 16) in bulk samples. This enrichment is due to the occurrence of abundant micrometer-sized synchysite inclusions in calcite, identified via Raman spectroscopy. Calcite bulk analyses have roof-shaped PAAS-normalized REE patterns with a Eu peak but without Ce or Y anomalies and with a steeply dipping HREE pattern. Microbeam analysis (electron microprobe and LA-ICPMS) identifies these patterns as dominated by synchysite-(Ce–Nd) with strong Eu enrichment in the weight percent range and LREE/HREE fractionation (La/Lu ~ 100, PAAS-normalized). The synchysite component in calcite gangue is detected in polymetallic veins all over the Harz Mountains, which seems to be a diagnostic feature of the region and suggests a large-scale Mesozoic fluid system. However, the Upper (western) Harz systems with no fluorite have more elevated REE content, compared with the Lower (eastern) Harz fluorite-rich systems with less REE content. Carbonate gangue in the Upper Harz systems has homogeneous 87Sr/86Sri around 0.714 and eNdi of ~ − 9, while carbonate gangue in the Lower Harz systems has 87Sr/86Sri around 0.716 and eNdi of − 2 to − 5. Fluorite in the Lower Harz Mountains has strong positive Y anomalies and variable Eu anomalies at generally low REE abundances and no REE-mineral inclusions. Both Sr and Nd isotope compositions in the fluorite are very variable and indicate an open system (87Sr/86Sri, 0.710–0.718; eNdi, − 3 to − 17). The synchysite MREE enrichment in calcite gangue in the Upper Harz Mountains compares favorably with carbonatite-related LREE-dominated bastnasite from China and elsewhere and allows an interesting perspective as a by-product of Pb–Zn mining.

More recent data of Greek bauxites from the Parnassos-Ghiona active mines prove that rare earth elements (REEs) occur mainly in the form of authigenic/diagenetic LREE3+ carbonate and phosphate minerals (bastnasite/parisite group and florencite). Bulk geochemistry of representative samples, from underground mines and open pits, showed an increased content in LREE (ΣLREE—from La to Gd—varying between 106 and 913 ppm; avg. ΣLREE = 321 ppm; n = 17), and lower HREE (ΣHREE—from Tb to Lu including Y—varying between 45 and 179 ppm; avg. ΣHREE = 95; n = 17). The overall REE concentration (ΣREE + Y+Sc) varies from 192 to 1109 ppm (avg. 463 ppm; n = 17). The most abundant REE is Ce (min: 67 ppm; max: 655 ppm; avg. 193 ppm; n = 17), exhibiting in general a positive geochemical anomaly (avg. Ce/Ce* -CeA-: 2.6), identical to the case of marine Fe–Mn-crust and terrestrial desert vanish, implying also that Ce4+ may exist either in REE-oxides and/or epigenetically sorbed in Fe-oxides. On the other hand, Nd content, which is more interesting for the industry, is lower (avg. 41 ppm; n = 17). The concentration of REEs is much higher in Fe-rich (red) bauxite, compared to Fe-depleted (white) bauxite (avg. ΣREE + Y+Sc = 569 ppm and 268 ppm, respectively). The new data presented herein show a rather lower REE potential of Parnassos-Ghiona bauxites, compared to previous literature, but similar values compared to karst-type bauxites of the globe. Although their REE concentration is higher compared to that of various geochemical reference materials (i.e., positive REE geochemical anomalies in comparison with chondrites, UCC, PAAS, NASC, and ES), it is vitally lower compared to REE resources being mined, such as REE–Fe–Nb–Th deposits. A trend similar to REE geochemical trend also stands for most of the trace elements that are present in Greek bauxites—mainly HFSE—except for LILE. Besides, Greek bauxite metallurgical residue’s (red mud) REE content seems to be remarkably increased by almost two times compared to that of the Parnassos-Ghiona bauxite parent material. Scandium is another critical element. In the studied bauxites, it varies from 29 to 73 ppm (avg. 47 ppm; n = 17); it is typical for the Mediterranean and EU bauxites and laterites, but much lower compared to the exploitable Australian laterites. The Fe-rich samples contain higher concentrations of Sc compared to Fe-depleted (avg. 54 and 33 ppm, respectively). This means that common red Greek bauxite is rather more exploitable, with regard to Sc (and the rest REE), but not the white one (which is of high quality in terms of Al). Bulk geochemistry indicates that Sc is correlated to Fe but not to Zr, while microscale observations demonstrated the presence of fine-grained scandian-zircons. This is in line with a very recent study proving that Sc is mainly present in Fe-oxide minerals (mainly hematite and goethite) and zircons. Bulk geochemical Fe–Pb and Fe–As positive correlations are also verified among the associated trace elements. Finally, the investigation of the REE vertical distribution in a characteristic deposit of the B3 horizon (i.e., Pera Lakkos mine case study), showed that the REE concentration is increased in the Fe-rich domain (lying above the footwall limestone), as well as in the coal layer interstratified between the Fe-depleted domain and the hanging wall limestone. However, it is revealed that the Ce/Ce* (CeA) is increased in the coal layer and is raised to the uppermost Fe-depleted domain, but not the lowermost Fe-rich bauxite domain. This might be attributed to the Ce3+ ↔ Ce4+ and the LREE re-mobilization during the supergene/epigenetic processes.

Rare-earth deposits associated with intrusive carbonatite complexes are the world’s most important source of these elements (REE). One of the largest deposits of this type is Maoniuping in the Mianning-Dechang metallogenic belt of eastern Tibet (Sichuan, China). In the currently mined central part of the deposit (Dagudao section), REE mineralization is hosted by a structurally and mineralogically complex Late Oligocene (26.4 ± 1.2 Ma, 40Ar/39Ar age of fluorphlogopite associated with bastnasite) hydrothermal vein system developed in a coeval syenite intrusion. Low-grade stockworks of multiple veinlets and breccias in the lower part of the orebody grade upwards into progressively thicker veins (up to 12 m in width) that are typically zoned and comprise ferromagnesian micas (biotite to fluorphlogopite), sodium clinopyroxenes (aegirine to aegirine-augite), sodium amphiboles (magnesio-arfvedsonite to fluororichterite), K-feldspar, fluorite, barite, calcite, and bastnasite. The latter four minerals are most common in the uppermost 80 m of the Dagudao section and represent the climax of hydrothermal activity. Systematic variations in the fluid inclusion data indicate a continuous hydrothermal evolution from about 230–400 °C (fluid inclusions in feldspar, clinopyroxene, and amphibole) to 140–240 °C (fluid inclusions in bastnasite, fluorite, calcite). Hydrothermal REE transport was probably controlled by F−, (SO4)2−, Cl−, and (CO3)2− as complexing ligands. We propose that at Dagudao, silicate magmas produced orthomagmatic fluids that explored and expanded a fissure system generated by strike-slip faulting. Initially, the fluids had appreciable capacity to transport REE and, consequently, no major mineralization developed. The earliest minerals to precipitate were alkali- and Fe-rich silicates containing low levels of F, which caused progressive enrichment of the fluid in Ca, Mg, F, Cl, REE, (SO4)2−, and (CO3)2−, leading to the crystallization of aegirine-augite, fluororichterite, fluorphlogopite, fluorite, barite, calcite, and bastnasite gradually. Barite, fluorite, calcite, and bastnasite are the most common minerals in typical ores, and bastnasite generally postdates these gangue minerals. Thus, it is very probable that fluid cooling and formation of large amount of fluorite, barite, and calcite triggered bastnasite precipitation in the waning stage of hydrothermal activity.

Apatite is one of the important host minerals of the rare earth elements (REEs). Separation of REEs from apatite has not been studied extensively compared with other main minerals such as monazite, bastnasite and xenotime. Therefore, it is essential to develop an effective method for recovery of REEs from apatite-based ores. This paper presents the results of laboratory studies for the recovery of rare earth elements from an apatite ore sample by using sulphuric acid leaching, solvent extraction, and precipitation processes. Results showed that the most effective dissolutions of light REEs (>85%) and heavy REEs (>89%) from the apatite ore sample were achieved with a dilute sulphuric acid solution (1 M H2SO4) at a temperature of 20 °C in an hour. The heavy REEs present in the pregnant leach solution were almost entirely extracted using 1.2 M di-(2-ethylhexyl) phosphoric acid (D2EHPA) as a cation exchanger, while the most light REEs remained in the raffinate. The heavy REEs loaded into the organic phase were stripped completely by 3 M H2SO4 solution. REEs remained in raffinate and stripped into the aqueous solution were precipitated as RE oxalates by the addition of 0.08 M oxalic acid.

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 bastnasite 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.

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.

The potential of ionic liquid-ionic liquid mineral separation process as a novel ionic liquid-based system to beneficiate rare earth element (REE) bearing minerals was investigated. This multiphase beneficiation system was prepared using two mutually immiscible ionic liquids (IL) as dispersed and continuous phases. A phosphonium/ammonium based ionic liquid as droplet phase and three different ionic liquids as continuous phase were applied to evaluate this approach of beneficiation of REE complex ore. Ionic liquid-ionic liquid mineral separation tests were performed on an actual rare earth complex ore with its main composing minerals consisting of monazite, bastnasite, ankerite, calcite and dolomite. Fourier Transform Infrared (FTIR) spectroscopy, Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) analyses were performed to unveil the nature of interactions between IL droplet phase and each of the minerals composing the ore. Bastnasite and monazite have been found to exhibit stronger chemisorption interactions with phosphonium/ammonium based ionic liquid in comparison with calcite, ankerite and dolomite. Density Functional Theory (DFT) simulations were also conducted to reveal the configuration of ionic liquid moieties on the surface of the minerals through ionic liquid adsorption. It was found that the IL anionic moiety directly interacts with the metal cations on the mineral surfaces through covalent bonds, at the expense of the cationic moiety which is only involved in weaker solvophobic interactions. DFT simulation also indicated that the adsorption geometry of IL is based on cis-conformation where the cationic and anionic moieties adsorb next to each other on the mineral surfaces.

In this study, the ionic liquid betainium bis(trifluoromethylsulfonyl)imide (HBetTf2N), has been applied directly as a leaching agent on a low-grade rare earth element (REE) ore called Rodberg, from the Fen carbonatite complex ore deposit located in Norway. REE in Rodberg are mainly present in the form of fluoro-carbonates of bastnasite group minerals. Factors studied during leaching were water ratio into ionic liquid, leaching temperature, pulp density (%w/v) and retention time. Leaching of Rodberg ore with HbetTf2N resulted to 65–100% recovery of light REE and 40–60% recovery of heavy REE. Additionally > 80–90% of Ca and Mg content dissolves, whereas the HbetTf2N is selective against iron and silicon resulting in a Fe/Si rich residue. The metals dissolved into HbetTf2N after leaching are stripped with an aqueous acidic solution, regenerating the ionic liquid for reuse. Through acid stripping, REE concentration is doubled in the aqueous acidic solution, for further purification. The carboxylic acid functional group attached to the cation side of HbetTf2N is capable of dissolving bastnasite thus enabling the development of new alternative methods for treating low-grade REE primary resources.

Rare earth elements (REEs) are a focus of current research due to their importance in a wide range of industries and technologies. Bayan Obo in China is the largest REE deposit in the world. Although some studies have investigated the banded REE ores in the Bayan Obo deposit, the origin and formation processes of the ores are unclear. In this study, we used X-ray powder diffraction, electron microprobe, laser ablation–inductively coupled plasma–mass spectrometry, and mass spectrometry methods to investigate the mineral assemblages and geochemical characteristics of minerals in banded ores in the Bayan Obo REE deposit. Based on petrographic observations, the early minerals that precipitated were alkali- and Fe-rich silicates, such as aegirine–augite and arfvedsonite, followed by bastnasite, fluorite, barite, calcite, and monazite in the late stage. The REE minerals in the banded REE ores are mainly monazite, bastnasite, and parisite (1–10 vol%) that overprinted gangue minerals, suggesting that REE mineralization occurred during the late hydrothermal stage. The sequence of mineral formation and their evolution caused progressive enrichment in REEs, F, Sr, and Ba. For example, fluorite in the banded REE ores has high concentrations of Sr (252–1910 ppm), Ba (1040–8230 ppm), and light REEs (1001–16,079 ppm), but is depleted in Nb and Ta. The bastnasite is enriched in Sr (885–4046 ppm), Ba (1073–80,809 ppm), and ΣREEs (99,631–158,227 ppm). The fluorite, arfvedsonite, and bastnasite in the banded REE ores have ɛNd(t) values of −3.68–1.78, −5.54, and 0.05, and initial (87Sr/86Sr)i (ISr) ratios of 0.70352–0.70478, 0.70620, and 0.70346, respectively. Based on these data, and the regional geological setting and Pb isotope data, it is proposed that fluorite and bastnasite crystallized from ferrocarbonatite and fine-grained dolomite, and the REE source was a mixture of HIMU mantle and global marine sediments. We also suggest that the carbonatite- or dolomite-hosting ores in Bayan Obo formed by melting of the subcontinental lithospheric mantle, which might have been previously metasomatized by REE- and CO2-rich fluids derived from subducted marine sediments.

Hydrothermal rare earth element (REE) precipitation in carbonatite is generally attributed to increase in pH or decrease in temperature when REE-bearing acidic fluids interact with carbonates. Here, we document microtextures comprising intergrowth of bastnasite, hydroxyl-parisite, rontgenite, synchysite, and pyrochlore, with calcite that pseudomorphically replaces patches of hematite with cellular boxwork-type structure, in calciocarbonatites from the Kamthai alkaline complex in western India. The nature of the REE mineralization grades from proximal bastnasite-dominated to distal hydroxyl-parisite dominated in the boxworks. The microtextural relations and trace element chemistry of hematite, magnetite and calcite, and C-O isotope composition of carbonate are suggestive of extensive low-temperature hydrothermal alteration of the carbonatites. The hematite boxwork structure and the REE mineral-calcite intergrowths often have squarish outlines and are interpreted to have pseudomorphed primary magnetite during fluid-rock interaction. We propose a new mechanism of REE precipitation in magnetite-rich carbonatites involving influx of acidic hydrothermal fluids, which scavenged the REE and other trace elements from magmatic carbonates and apatite. These acidic fluids were responsible for the protonation of magnetite and leaching out of Fe2+, converting them to hematite through a non-redox transformation. The reaction results in 32% volume reduction for every mole of magnetite consumed, generating significant rock porosity, which further aided and abetted fluid-rock reaction and hydrothermal alteration. More importantly, it consumed proton, which increased the fluid pH triggering precipitation of bastnӓsite-group minerals (including bastnӓsite, parasite, rontgenite, synchysite). Close to the magnetite-hematite reaction front, fluor-dominated bastnӓsite-group minerals (mainly bastnӓsite) appear, while away from such fronts, mineralization was enriched in hydroxyl-bastnӓsite group minerals (mainly parisite) as a consequence of decreasing activity of F‐ and/or increasing activity of OH‐ with the progress of magnetite-to-hematite transformation.

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 bastnasite concentrate using supercritical carbon dioxide extraction with nitric acid/tributyl phosphate adducts. Two bastnasite 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 CO2 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 bastnasite 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 bastnasite 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.

The potential of liquid-liquid mineral separation mediated by ionic liquids (ILs) to beneficiate rare earth (RE) bearing minerals was investigated for the first time. Liquid-liquid separation tests were performed on actual RE-bearing ores whereas the role of ionic liquids was exposed using model monazite, bastnasite, calcite and dolomite single minerals. The multiphase beneficiation system consisted of aqueous pulps in which IL/kerosene and IL/ n -hexane non-polar phases were emulsified using three types of phosphonium/ammonium ionic liquids to evaluate their chelation potential. The aqueous pulp pH played a crucial role in terms of mineral recoveries with the highest RE mineral recoveries achieved at pH 4–7. Also, the newly proposed beneficiation method was found to outperform micro-flotation of the same minerals in terms of selectivity. Zeta potential measurements, Fourier transform infrared spectroscopy, and density functional theory simulations were used to interpret the mechanisms governing this new mineral separation route. The ionic liquid anionic moiety was demonstrably found to directly interact through formation of covalent bonds with the metal cation active centers, contrary to the cationic moiety which at most was involved in weaker “non-surface” Coulombic/van de Waals interactions as ion-pair co-ion. Hence with regard to the potential of ionic liquids in minerals beneficiation, liquid-liquid mineral separation could be envisaged as a new alternative for RE mineral separation instead of flotation.

In the present work, a novel α-aminophosphonate extractant (Cextrant 230) was synthesized for the extraction and recovery of cerium and thorium from sulphate medium. The introduction of amine group into the phosphate molecule would enhance the extraction of Ce(IV) and Th(IV). The effects of extractant concentration, H2SO4 concentration and temperature on the metal extraction were investigated in detail. It was found that the extraction of Ce(IV), Th(IV) and REs (La, Gd, Yb) in sulphate medium decreased in the following order: Ce(IV)>Th(IV)>REs(III). A solvent extraction process to extract and recover cerium and thorium from bastnasite leaching was proposed, in which the purities of cerium and thorium products reached 99.9% and 99% with yield of 92% and 98%, respectively.

In this study, the atom substitutions that commonly affect the monazite lattice were considered as potential factors affecting the monazite electrophoretic mobility. The influence of light rare earth elements (LREE) substitutions and the presence of thorium, calcium, and silicate within the monazite crystal lattice was also examined using a natural monazite and synthetic cerium, lanthanum and neodymium monazite materials. Electrophoretic mobility measurements performed after treatment in an electrolyte solution equilibrated with air outline that LREE substitutions and other substitutions observed in the tested natural monazite did not affect the mineral surface properties. Conversely, the electrophoretic mobility of the synthetic monazites was found to be significantly affected by the amount of dissolved carbonate species present in the aqueous media. More precisely, carbonate species were found to decrease the electrophoretic mobility of monazite. Unlike tests performed with a solution equilibrated with air, the electrophoretic mobility of monazite treated in a CO2 depleted electrolyte solution, under controlled atmosphere, were found erratic. This highlights the difficulty in obtaining reliable electrophoretic mobility data when the carbonate content in the supporting electrolyte solutions is not controlled.

We investigated the calcination of a rare earth carbonatite ore from Niobec in Quebec, Canada, containing bastnasite and monazite. The bastnasite 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 bastnasite 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.

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 bastnasite [(Ce,La)CO3F] was explored by using 1-hydroxydodecylidene-1,1-diphosphonic acid (HDDPA) as a collector. The micro-flotation results showed that bastnasite displayed an eminent floatability under pH 7.0–10.0, and HDDPA realized an efficient separation of bastnasite 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 CO32- ions of Ce(Ⅲ) carbonates in/on bastnasite interface, resulting in a high flotation recovery of bastnasite. 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 bastnasite reduced. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) recommended that the surface Ce(III) of bastnasite interacted with the O atoms of HDDPA’s O P(O)O group to generate a four membered ring configuration, which hydrophobized bastnasite particles.

Application of tetrabutylammonium bis(2-ethylhexyl)-phosphate ([N 4444 ][DEHP]), a room temperature ionic liquid (IL), as an aqueous collector for flotation of model monazite and bastnasite minerals was investigated through micro-flotation tests, zeta potential measurements, Fourier Transform Infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The ionic liquid was shown to have superior performance to float both model rare-earth (RE) minerals as compared with calcite, dolomite and quartz minerals as typical gangue minerals. Parallel to this, micro-flotation tests of a rare-earth ore containing bastnasite and monazite minerals were found in line with [N 4444 ][DEHP] stronger collecting power towards RE model minerals even outperforming hydroxamic acid-containing collectors. With regard to the mineral surface chemistry, zeta potential measurements, FTIR characterization and XPS analysis, it was established that [N 4444 ][DEHP] uptake on bastnasite and monazite surfaces was via chemisorption involving specifically the P O and P O groups of the IL anionic moiety. IL anionic and cationic interactions during RE mineral flotation were rationalized in terms of an inner synergistic pathway: IL anionic moiety chemisorbing on bastnasite and monazite surfaces prompting uptake of cationic moiety via electrostatic attraction and/or via hydrophobic chain interactions of the cation alkyl chains with the chemisorbed IL anionic layer. Finally, for calcite as the most responsive among gangue minerals, the characterization techniques divulged the weaker IL-surface interactions. Hence, this investigation opens up new prospects for more selective ionic-liquid collectors to be used in the flotation of RE minerals.

Rare earth metals are essential ingredients for the development of modern industry as well as designing and developing high technology products used in our daily lives. Consequently, the worldwide demand of rare earth metals is rising quickly and predicted to surpass the supply by 40,000 tons annually. However, their availability is declining, mainly due to the export quotas imposed by the Chinese government and actions taken against illegal mining operations. This has laid emphasis to exploit and expand technologies to meet the future necessities of rare earth metals. Bastnasite, monazite, and xenotime are their chief mercantile sources, which are generally beneficiated by flotation, gravity or magnetic separation processes to get concentrates that are processed using pyro/hydrometallurgical routes. To develop feasible and eco-friendly processes, R&D studies are being conducted for the extraction of rare earth metals from leached solutions (chloride, nitrate, sulfate, thiocyanate, etc.) using different cationic, anionic and solvating solvents or ions depending on material and media. Commercial extraction of rare earth metals has been carried out using different extractants viz. D2EHPA, Cyanex 272, PC 88A, Versatic 10, TBP, Aliquat 336, etc. The present paper reviews the methods used for the recovery of rare earth metals from primary as well as secondary resources, with special attention to the hydrometallurgical techniques, consisting of leaching with acids and alkalis followed by solvent extraction, ion exchange or precipitation. The piece of comparative and summarized review will be useful for the researchers to develop processes for rare earth recovery under various conditions.

Summary Separating rare-earth-element-rich minerals from unwanted gangue in mined ores relies on selective binding of collector molecules at the interface to facilitate froth flotation. Salicylhydroxamic acid (SHA) exhibits enhanced selectivity for bastnäsite over calcite in microflotation experiments. Through a multifaceted approach, leveraging density functional theory calculations, and advanced spectroscopic methods, we provide molecular-level mechanistic insight to this selectivity. The hydroxamic acid moiety introduces strong interactions at metal-atom surface sites and hinders subsurface-cation stabilization at vacancy-defect sites, in calcite especially. Resulting from hydrogen-bond-induced interactions, SHA lies flat on the bastnäsite surface and shows a tendency for multilayer formation at high coverages. In this conformation, SHA complexation with bastnäsite metal ions is stabilized, leading to advanced flotation performance. In contrast, SHA lies perpendicular to the calcite surface due to a difference in cationic spacing. We anticipate that these insights will motivate rational design and selection of future collector molecules for enhanced ore beneficiation., Graphical Abstract, Highlights • Salicylhydroxamic acid (SHA) is an effective collector for flotation of bastnäsite • DFT calculations show that the phenol group anchors SHA flat to bastnäsite surface • Spectroscopic results suggest SHA multilayers on bastnäsite at high coverage • This peculiar adsorption explains efficacy of SHA in bastnäsite flotation from ores, Chemical Engineering; Spectroscopy; Physical Inorganic Chemistry; Surface Chemistry

Rare-earth elements play a crucial role in modern technologies and are necessary for a transition to a green economy. Potentially economic deposits of these elements are typically hosted in minerals such as monazite, bastnasite, and eudialyte (a complex Na-Ca-Fe-Zr silicate mineral with Cl), making these prime targets for geological research. Globally, rare-earth mineral deposits commonly show evidence of polyphase development and mineralisation processes, which need to be better understood to improve exploration strategies. The Norra Karr alkaline complex (Sweden) contains a globally significant deposit of rare-earth elements, hosted in the mineral eudialyte. In this study, we focussed on eudialyte crystals in undeformed, cross-cutting pegmatoid veins from Norra Karr. In order to determine their age, we refined an established micromilling method to enable sampling of minerals rich in rare-earth elements for precise analysis of major and trace elements, Nd isotope ratios, and Sm-Nd geochronology down to a scale of

In this work, decanedioic hydroxamic acid (DDHA) was introduced as a novel collector for the flotation separation of bastnӓsite and calcite, and the results were compared with those obtained for the conventional hydroxamic acid collectors benzohydroxamic acid (BHA) and octyl hydroxamic acid (OHA). The microflotation results showed that DDHA had better selectivity than BHA and OHA for the flotation of bastnӓsite from calcite. The flotation of artificially mixed minerals confirmed that the effective separation of bastnӓsite from calcite could be realized in the presence of DDHA. The zeta potentials of mineral surfaces with or without these collectors were measured, and the results indicated that DDHA strongly interacted with the bastnӓsite surface but was not adsorbed on the calcite surface.

As a key source of strategic commodities for advanced technologies, carbonatite-related (carbonatite–nordmarkite complex) rare earth element (REE) deposits are globally important resources. Such deposits have different ore types, scales, ore-formation structures, and evolutionary processes. However, the causes of these variations have not been well studied, which prevents us from understanding the formation of such deposits. The factors that lead to the formation of large carbonatite-related REE deposits have also not been carefully documented. Fortunately, the Cenozoic Mianning–Dechang (MD) REE belt in eastern Tibet contains several medium- and large-scale carbonatite-related REE deposits, including brecciated, weathered, and disseminated ores, providing an ideal opportunity to investigate these factors. Current and this studies show that the deposits in the MD belt have similar formation stages, crystallization sequences, sources, and REE mineralization conditions. Previous studies have shown that the REE mineralization occurred alongside the formation of large-scale overprinted gangue minerals, such as barite, fluorite, and calcite during the lowest-temperature hydrothermal stage ( 4 2−, and CO2 are important for transporting and precipitating REE. Detailed geological mapping suggests that the variation in ore type was caused by local ore-controlling structures, rather than being due to different depths of formation. Bastnasite has similar initial 87Sr/86Sr (0.7059–0.7080), 143Nd/144Nd (0.5123–0.5124), 207Pb/204Pb (15.594–15.648), and 208Pb/204Pb (38.422–71.488) ratios along the whole belt, implying that all the deposits have the same source and the REE were sourced directly from a mixture of crustal and mantle material. The C–O isotopic compositions of the carbonatites (δ18OV-SMOW = 6.4‰ to 10.5‰, δ13CV-PDB = − 3.9‰ to − 8.5‰) and bastnasite (δ18OV-SMOW = 9.5‰–16.3‰, δ13CV-PDB = − 4.7‰ to − 9.3‰) suggest that low-temperature alteration occurred along with REE mineralization. Development of pegmatitic stage and aegirine–augite and arfvedsonite fenitization alteration may promote the formation of large-scale REE deposits. The giant Maoniuping and Dalucao deposits both had pegmatitic stages that involved the formation of coarse-grained barite, fluorite, and calcite with REE contents of up to 6305 ppm, suggesting the pegmatitic stage suggest another REE enrichment event after the magmatic stage, and large-scale REE mineralization. The intense alkali alteration that forms arfvedsonite and aegirine–augite in carbonatite–nordmarkite complexes was only found in the Maoniuping deposit, whereas biotitation was found in the Dalucao and Lizhuang deposits. This suggests that the Maoniuping deposit experienced more intense alteration, which may have led to more effective REE migration from the wallrock into the ore-forming fluids. The mantle source, the evolution of the magma, the presence of a pegmatitic stage, the composition of the fluids, and the high degree of alkaline alteration could have affected the scale of the deposits, in addition to the large volume of carbonatite–nordmarkite complexes and multiple phases of tectonism.

The Morro dos Seis Lagos niobium rare earth element, Ti-bearing lateritic deposit (Amazonas, Brazil) is derived from a primary siderite carbonatite. The complex is the only example of a Nb deposit in which Nb-rich rutile is the main Nb ore mineral. Apart from the laterites, at the current level of exposure the complex consists only of siderite carbonatite; silicate rocks are absent. Three types of siderite carbonatite are recognized: (1) a brecciated and oxidized core siderite carbonatite consisting of up to 95 vol% siderite together with: hematite; pyrochlore; Nb-brookite; Ti-maghemite; and thorobastnasite; (2) a REE- and P-rich variety of the core siderite carbonatite consisting of siderite (up to 95 vol%), hematite, minor pyrochlore, monazite and bastnasite; (3) a border hydrothermal siderite carbonatite with ~70 vol% siderite, barite (~15 vol%), gorceixite (~7 vol%) and minor rhabdophane and pyrochlore. The country rock gneiss in which the carbonatite was emplaced was affected by potassic fenitization, with the formation of phlogopite and orthoclase together with monazite, fluorapatite and bastnasite. The siderite carbonatites exhibit a wide variation of δ13C (−5.39‰ to −1.40‰), accompanied by a significant variation in δ18O (17.13‰ to 31.33‰), especially in the REE-rich core siderite carbonatite, and are explained as due to the presence of both H2O and CO2 in the magma. The core siderite carbonatite is the richest in Fe (48.64–70.85 wt% Fe2O3) and the poorest in Ca (up 0.82 wt% CaO) example of a siderite carbonatite yet recognized The ferrocarbonatite has significant contents of Mn, Ba, Th, Pb and LREE, and a very high Nb (up to 7667 ppm) content due to the presence of Nb-brookite. The substitution 3Ti4+ = Fe2+ + 2Nb5+ recognized in Nb-rich brookite explains enrichment of Nb in the core siderite carbonatite and indicates formation in a reducing environment. The high Nb/Ta ratio (1408–11,459) of the carbonatite is compatible with residual liquids derived by fractional crystallization. The 87Sr/86Sr (0.70411–0.70573) and 144Nd/143Nd (0.512663–0.512715) isotopic data suggest the carbonatite is mantle-derived with essentially no crustal contamination and is younger than the maximum age of 1328 ± 58 Ma (U Pb in zircon). We suggest that the Morro dos Seis Lagos carbonatite complex represents the upper-most parts of a differentiated carbonatite magmatic system, and that the siderite carbonatite is related to late-magmatic-to-carbo-hydrothermal processes.

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. Refereed/Peer-reviewed

By mineral liberation analyzer (MLA) automated quantitative system, the niobium–tantalum ore in this study was classified as refractory mineral of low-grade which was mainly composed of fergusonite, polycrase, ilmenorutile, and bastnasite. Most of niobium and rare earth metals were disseminated in these minerals (particle sizes of 95 % rare earth elements 90 %, and the leaching extent of niobium can reach 84 %.

The Bear Lodge alkaline complex in northeastern Wyoming (USA) is host to potentially economic rare-earth mineralization in carbonatite and carbonatite-related veins and dikes that intrude heterolithic diatreme breccias in the Bull Hill area of the Bear Lodge Mountains. The deposit is zoned and consists of pervasively oxidized material at and near the surface, which passes through a thin transitional zone at a depth of ~ 120–183 m, and grades into unaltered carbonatites at depths greater than ~ 183–190 m. Carbonatites in the unoxidized zone consist of coarse and fine-grained calcite that is Sr-, Mn- and inclusion-rich and are characterized by the presence of primary burbankite, early-stage parisite and synchysite with minor bastnasite that have high (La/Nd)cn and (La/Ce)cn values. The early minerals are replaced with polycrystalline pseudomorphs consisting of secondary rare-earth fluorocarbonates and ancylite with minor monazite. Different secondary parageneses can be distinguished on the basis of the relative abundances and composition of individual minerals. Variations in key element ratios, such as (La/Nd)cn, and chondrite-normalized profiles of the rare-earth minerals and calcite record multiple stages of hydrothermal deposition involving fluids of different chemistry. A single sample of primary calcite shows mantle-like δ18OV-SMOW and δ13CV-PDB values, whereas most other samples are somewhat depleted in 13C (δ13CV-PDB ≈ − 8 to − 10‰) and show a small positive shift in δ18OV-SMOW due to degassing and wall-rock interaction. Isotopic re-equilibration is more pronounced in the transitional and oxidized zones; large shifts in δ18OV-SMOW (to ~ 18‰) reflect the input of meteoric water during pervasive hydrothermal reworking and supergene oxidation. The textural relations, mineral chemistry and C and O stable-isotopic variations record a polygenetic sequence of rare-earth mineralization in the deposit. With the exception of one Pb-poor sample showing an appreciable positive shift in 208Pb/204Pb value (~ 39.2), the Bear Lodge carbonatites are remarkably uniform in their Nd, Sr and Pb isotopic composition: 143Nd/144Ndt = 0.512591–0.512608; eNdt = 0.2–0.6; 87Sr/86Srt = 0.704555–0.704639; eSrt = − 1.5–2.7; 206Pb/204Pbt = 18.071–18.320; 207Pb/204Pbt = 15.543–15.593; and 208Pb/204Pbt = 38.045–39.165. These isotopic characteristics indicate that the source of the carbonatitic magma was in the subcontinental lithospheric mantle, and modified by subduction-related metasomatism. Carbonatites are interpreted to be generated from small degrees of partial melt that may have been produced via interaction of upwelling asthenosphere giving a small depleted MORB component, with an EM1 component likely derived from subducted Farallon crust.

The Foxtrot deposit of Search Minerals contains a range of rare earth element containing minerals including allanite, fergusonite and bastnasite. The Search Minerals Direct Extraction Process for treating these minerals involves coarse crushing of the ore to-6 mesh (3.45 mm), acid treatment at 200 °C in a novel reactor configuration, water leaching, various purification steps to reject iron, aluminum and uranium/thorium (present in small amounts) and finally precipitation of rare earths as a oxalate and calcination to form a mixed rare earth oxide product for refining. The economics of the process are presented.

Nearly the entire worldwide production of europium is recovered, as a minor constituent, from mining bastnasite, monazite ore, or ion absorbing clays. However, this research indicates a process to recycle europium from waste lamp phosphors as a strategy meet the demand for europium. In this process, waste fluorescent lamp powder is retorted, sieved, leached, and precipitated to produce a mixed europium/yttrium rare earth oxide (REO). Europium is separated from yttrium by selectively reducing Eu(III) to Eu(II) using zinc powder and precipitating europium (II) sulfate from solution using sulfuric acid. Screening experiments were conducted observe the effect of pulp density, precipitation time, entrance pH, and stoichiometric ratio sulfate upon the grade and recovery of europium (II) sulfate. The best conditions to maximize grade and recovery of europium (II) sulfate were a 1 h precipitation time, 10× the stoichiometric ratio of sulfate, 100 g/L mixed REO, and the entrance pH equal to 3. The maximum grade of europium sulfate was 95.93%, and the maximum recovery was 73.32%.

Bastnasite is the chief valuable mineral in two of the world’s largest rare earth (RE) mineral deposits and is also found in a number of new RE deposits currently under development. This work used electrophoretic and electroacoustic zeta potential measurements to identify the interaction between bastnasite and several different collectors. The results of these measurements were then compared with microflotation of bastnasite and quartz, a common RE gangue mineral. Zeta potential measurements of bastnasite determined the isoelectric point of bastnasite to occur at approximately pH 6.3 (via electrophoretic measurement) and pH 8.1 (via electroacoustic measurement). Sodium oleate and Flotinor SM15 (a commercial phosphoric acid ester) are both shown to chemically adsorb onto the bastnasite surface. Zeta potential measurements of bastnasite with benzohydroxamic acid indicate significant adsorption, especially from pH 5 to pH 10. The microflotation results show that all three collectors were able to successfully recover bastnasite. SM15 is the least selective collector as it floats both quartz and bastnasite whereas benzohydroxamic acid is able to selectively float bastnasite at pH 9. The recovery of bastnasite using benzohydroxamic acid is also shown to be highly dependent on frother selection. The optimum pH of flotation for all three collectors occurs at pH 9.

The Kangankunde Carbonatite Complex from the Cretaceous Chilwa Alkaline Province in southern Malawi contains ankeritic and siderite carbonatite that are affected by late stage remobilisation by a carbothermal or hydrothermal fluid. The coarse pegmatitic siderite carbonatite that hosts exotic minerals like monazite, synchysite, bastnasite, strontianite and apatite in vugs and cavities constitutes some of the richest rare earth deposits in the world. Besides these minerals, our studies reveal the presence of collinsite and aragonite from the siderite carbonatite. Fine drusy monazites are seen as overgrowths on thin veinlets of siderite within the rare earth mineralised zones. We present unambiguous SEM-based surface textural evidence such as presence of dissolution-corrosion features like etching along cleavage, solution channels, solution pits, sinstered scaly surface, etc. along with rare earth mineralisation that suggests the exotic minerals in the siderite carbonatite did not crystallise from carbonate magma and are a result of sub-solidus processes involving carbonatite-derived fluids. We believe that the monazite-synchysitebastnasite-strontianite-collinsite assemblages were formed by juvenile post magmatic hydrothermal alteration of pre-existing carbonatite by a complex CO2-rich and alkali chloride-carbonate-bearing fluid at ∼250 to 400°C in an open system. This late ‘magmatic’ to ‘hydrothermal’ activity was responsible for considerable changes in rock texture and mineralogy leading to mobility of rare earth elements during fluid-rock interaction. These aspects need to be properly understood and addressed before using trace and rare earth element (REE) geochemistry in interpreting carbonatite genesis.

A solid-stabilized emulsification process was developed to produce a concentrate of the rare earth element (REE)-bearing minerals bastnasite and monazite from an ore that included gangue minerals such as dolomite, calcite, ankerite, silicate, quartz, pyrite, mica, hematite, and barite. The liberated REE-bearing minerals displayed better affinity for oil droplets than the gangue due to differences in surface wettability and eventually adsorbed to the oil-water interface whereas the gangue remained in the water phase. We studied the behavior of the REE-bearing ore in a Pickering emulsification system. We, consequently, determined the ability of Pickering emulsification to separate and concentrate REE-bearing minerals. The enrichment ratio after a single-stage emulsification was 2.9, with a recovery exceeding 50%, and with no need to adjust the pH and/or apply a surface modifier.

Carbonatites are well known as economic resources for rare metals, such as rare earth elements (REE) and Nb. However, the origin and evolutionary processes of carbonatites and related silicate rocks as well as the relevant rare metals enrichment mechanism are highly controversial. In this study, we present detailed petrographic observations and geochemical data on the Miaoya syenite-carbonatite complex, which hosts both Nb and REE resources. The Miaoya syenites consist predominantly of K-feldspar, with minor zircon, nioboaeschynite, pyrochlore, and Fe-Ti oxides, and have positive Nb, Ta, Zr and Hf anomalies on primitive mantle-normalized patterns. There are two types of carbonatites at the Miaoya Complex: calciocarbonatites and ferrocarbonatites. Calciocarbonatites consist mainly of calcite, apatite, and biotite, together with allanite, monazite, bastnasite(-Ce), and parisite-(Ce). Ferrocarbonatites which are the later products of the complex and occur as dykes cutting both calciocarbonatites and syenites, contain ankerite, calcite, apatite, and fluorite, bastnasite-(Ce), and parisite-(Ce). The carbonatites have lower Nb, Ba, U, Th, and Zr, but higher P, Sr and REE concentrations than the associated syenites. However, both rock types have similar zircon U-Th-Pb ages (430–440 Ma), and nearly identical initial 87Sr/86Sr ratios (0.70325 to 0.70413) and eNd(t) values (2.5 to 3.2), implying that they were derived from a common source of carbonated silicate magmas. A genetic model of combined fractionation and immiscibility is proposed for the Miaoya complex. Fractionation of the carbonated silicate magmas lead to Nb enrichment in syenite and the immiscibility of the parental calcium carbonatite melts when the magmas reached a carbonate saturation level, together with partitioning of P, Sr, and REE into the parental carbonatite melts. During further fractionation of the carbonatite melts, REE components were elevated to economic values in the final ferrocarbonatites. This model can be widely applicable to other alkaline-carbonatite complexes and provides a reasonable explanation for extreme enrichment of rare metals in such rocks.

This study is the second part of an ongoing investigation to recover and upgrade rare earth elements (REE) minerals from iron oxide–silicate rich tailings (IST) generated at a South Australian mining operation. Previous work (Part 1) has shown that REE minerals are preconcentrated in a high-intensity magnetic concentrate and non-magnetic tails along with iron oxides and silicate minerals, respectively. As a part of the overall beneficiation and enhanced REE minerals recovery strategy, complementary studies involving downstream froth flotation of the magnetic preconcentrates were conducted and the results presented in this paper. Froth flotation of the preconcentrates was carried out using sodium oleate and hydroxamic acid as collectors in the presence of sodium silicate and starch as depressants. A comparison of rougher flotation of the preconcentrates indicated that hydroxamic acid produced higher total rare earth oxides (TREO) recoveries (91–93%) with enrichment ratio ranging 1.03–1.30, whereas sodium oleate produced relatively higher upgrade (1.50–1.55 ratios) with significantly lower recoveries (12–36%). Scavenger and cleaner flotation tests were conducted on selected concentrates and tails, where further upgrade was achieved at the expense of recovery. Two process flowsheets for recovering REE minerals were then developed. Flowsheet 1 includes magnetic preconcentration followed by flotation using both collectors, whilst Flowsheet 2 includes magnetic preconcentration prior to hydroxamic acid flotation. Typical metallurgical results indicated Flowsheet 1 produced a final concentrate grade of 1.55% at 55% TREO recovery, whilst rejecting 47% Fe and 74% Si, whereas a final concentrate grade of 1.67% at 72% TREO recovery, with 39% Fe and 59% Si removed using Flowsheet 2. The REE minerals, in combination with mainly silicates in the non-magnetic tails, allows better upgrade, with 2.5 times enrichment through hydroxamic acid flotation, compared to 1.93 times enrichment from the REE–iron oxides magnetic preconcentrate. Florencite, which was not recovered and upgraded by magnetic separation, was successfully recovered and upgraded along with bastnasite and monazite by froth flotation. The study has revealed that froth flotation can be used to complement the recovery of REE minerals by magnetic separation, suggesting the IST could be exploited for REE beneficiation. However, it is obvious that minerals liberation and particle size distribution are critical in achieving enhanced REE minerals recovery and upgrade.

We present detailed textural and chemical analyses of the hydrothermal sulfide- and REE-Th-Nb-mineralization observed in the Fen complex (southern Norway), which is the biggest carbonatite-related REE and Th deposit in Europe. The alkaline silicate rocks and carbonatites of the Fen complex underwent two hydrothermal alteration events that caused (i) the formation of sulfides and (ii) (re)-mobilization of REE, Fe and Al. This renders the Fen complex an ideal locality to study the genesis of hydrothermal sulfide and REE mineralization in carbonatites. Our observations record a hydrothermal alteration history of the Fen carbonatite complex, which is relevant to many carbonatite complexes worldwide. The first alteration event (pyrite-stage) caused the crystallization of sulfides (mostly pyrite) in all lithologies and was induced by a sulfide-rich fluid 1 that was probably derived from adjacent mafic alkaline silicate rocks. Veins formed during this hydrothermal event show a typical succession from magnetite via pyrite I + hematite + magnetite to pyrite II. A subsequent alteration event is characterized by the interaction of two evolving fluids, namely (1) a REE-rich fluid 2 that was probably derived from the carbonatites (autometasomatic fluid) and (2) an oxidizing meteoric fluid 3 that mainly introduced Si and was in equilibrium with the basement host rocks. The interaction of these two fluids with the carbonatitic rocks resulted in various characteristic types of calcite-hematite rocks locally called rodberg. During their late-stage silicification by fluid 3, P was mobilized from magmatic apatite and reprecipitated in close-by rodberg veins as small fluorapatite-monazite veins. The interaction of the carbonatite-derived fluid 2 and meteoric fluid 3 also resulted in the formation of distinct zones of LREE-phases, notably REE-F-carbonates (bastnasite, parisite, synchysite), monazite and allanite, and HREE-phases (including samarskite, aeschynite and an unnamed Nb-Fe-REE-Th-oxide. The most pronounced HREE-enrichment occurs in domains of strongest hydrothermal alteration, which was probably caused by preferential precipitation of HREE-rich complexes coupled with later partial leaching of LREE by F-rich fluids during silicification. Thorium-rich minerals were precipitated in close association with HREE-rich minerals implying similar hydrothermal behaviour of Th and HREE.

The influence of NaOH-Ca(OH)2 on magnetizing roasting of iron minerals and on the decomposition reactions of rare earth minerals during coal-based magnetizing roasting is explored in the present work. The effect of alkaline additives was determined by means of SEM-EDS and X-ray diffraction methods in NaOH-Ca(OH)2-coal-tailings mixtures under optimal magnetizing roasting conditions (mass ratio of NaOH, Ca(OH)2, coal and tailings equal to 2.5: 4.5: 2.5: 100, roasting at 650 °C for 2.5 h). Although NaOH results in an adverse impact on magnetizing roasting of hematite, iron in silicate minerals could be released by NaOH-Ca(OH)2 additive as a form of hematite, which is further reduced to ferromagnetic magnetite. Moreover, the reduction ability of gas is improved in presence of coal and water from decomposition reaction of Ca(OH)2. Regarding the decomposition of bastanasite, no evident effect of NaOH-Ca(OH)2 is observed. The roasted products of pristine bastnasite particles are mainly composed of rare earth oxides (REO) with little fluorine, independent on the use of alkaline additives. No high purity REO were determined in the monazite particle by SEM-EDS, which is mainly decomposed into REO and REFeO3.

Raman spectroscopy complimented with infrared spectroscopy has been used to study the rare earth based mineral huanghoite with possible formula given as BaCe(CO3)2F and compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of huanghoite displays three bands are at 1072, 1084 and 1091 cm^-1 attributed to the (CO3)^2- symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of (CO3)^2- symmetric stretching vibration varies with mineral composition. Infrared spectroscopy of huanghoite show bands at 1319, 1382, 1422 and 1470 1091 cm^-1. No Raman bands of huanghoite were observed in these positions. Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554 1091 cm^-1 assigned to the m3 (CO3)^2- antisymmetric stretching mode. The observation of additional Raman bands for the m3 modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands for huanghoite are observed at 687, 704, 718 and 730 1091 cm^-1 and assigned to the (CO3)^2- m2 bending modes. Raman bands are observed for huanghoite at around 627 1091 cm^-1 and are assigned to the (CO3)^2- m4 bending modes. Raman bands are observed for the carbonate m4 in phase bending modes at 722 1091 cm^-1 for bastnasite, 736 and 684 1091 cm^-1 for parisite, 714 1091 cm^-1 for northupite. Raman bands for huanghoite observed at 3259, 3484 and 3589 1091 cm^-1 are attributed to water stretching bands. Multiple bands are observed in the OH stretching region for bastnasite and parisite indicating the presence of water and OH units in their mineral structure. Vibrational spectroscopy enables new information on the structure of huanghoite to be assessed.

In this study, it was observed that the characteristics of pollutants produced during the processes of ore dressing and purification depends on the properties of rare earth and deposits from natural resources. The commercially important rare earth minerals discerned in this study were ion adsorption deposit, carbonate bastnasite and phosphate monazite. The ore dressing process for ion adsorption deposit elution was done by use of ammonium sulfate and calcination, while the process for bastnasite and monazite was smashing/grinding, gravity/magnetic separation and flotation. The process of decomposition/separation is mainly adopted for the purification process of rare-earth oxide by acid/alkali, P507 ()/oxalicacid () and carbonation and calcination. At the ore dressing process, dominant water pollutants were heavy metals, fluoride, sulphate, arsenic, and radioactive compounds, while purification process generally produced harmful gases (HF, , , CO), radioactive tailings and wastewater with heavy metals, fluoride, ammonium, radioactive materials (Th, U), and organic pollutants. Harmful gases were specifically generated from acid/alkali decomposition process while organic pollutants were originated from separation/purification process. To treat wastewater, chemical precipitation could be applied to remove heavy metal, fluoride and radioactive compounds, and stripping and struvite precipitation treated ammonium ions, while oxidation treated organic compounds.

The synergistic effect of mixtures of Cyanex 923 and organophosphorus acids including P204, P507 and Cyanex 272 in extraction of Ce(IV) and Th(IV) from sulfuric acid solutions has been investigated. Under the experimental conditions, the extraction of Ce(IV) presented an significant synergistic effect with the mixed extraction systems of Cyanex 923-P204, Cyanex 923-P507 and Cyanex 923-Cyanex 272. On the contrary, the extraction of Th(IV) showed significant antagonistic effects in the mixed systems. The separation factor for Ce(IV)/Th(IV) reached as 36.8 at a mole fraction of 70% Cyanex 923 in the Cyanex 923-P507 system. It is shown that the mixed extraction systems not only enhance the extraction efficiency of Ce(IV) but also improve the selectivity of Ce(IV) over Th(IV). Furthermore, a fractional extraction process (including 4 stages of extraction, 2 stages of scrubbing and 2 stages of stripping) with the mixed Cyanex 923-P507 to separate Ce(IV) from the bastnasite leach solution has been designed. Cerium solution of Ce-2(SO4)(3) and CeF3 nanoparticle were obtained with 99.8% and 99.9% purity, respectively. (C) 2013 Elsevier B.V. All rights reserved.