Precipitation Of Rare Earth Elements Research Articles

Rare-earth element (REE) remobilization and fractionation in bauxite zones from sedimentary kaolin deposits, western Georgia (USA), Upper Coastal Plain

Rare-earth elements (REE) are critical minerals that are indispensable for high-tech products and technologies. Significant efforts have been focused on the exploration and identification of new and domestic reserves of REE. This study reports geochemical and mineralogical occurrences of accumulated REE with significant fractions of ion-adsorption clays (IAC) within bauxite-kaolin ore, hosted within sedimentary strata. This deposit type can be found throughout portions of Georgia and eastern Alabama (USA) in the Southeast Upper Coastal Plain. These deposits were developed by high degrees of chemical weathering of older, kaolinite-rich sedimentary strata. Several major changes in whole rock mineralogy and geochemistry occurred, leading to the development of zones of REE depletion, fractionation, and accumulation. Depletions of REE in the bauxite zone were significant, with whole rock contents of ∼50% ΣREE relative to average upper continental crust (UCC). Fractionated REE were observed by low La/YbN values (La/YbN = 0.2) due to depletion in LREE (<40% UCC) with concomitant HREE retention (∼1.1–1.3 times UCC). Strongly positive Ce/Ce* anomalies (Ce/Ce* = 1.3), very low ion-exchangeable Ce contents (Ce/LREE = 0.1), and low solubility of Ce (0.9–1.2%) under reducing conditions compared to all other LREE (4.5–9.9%) were further observed. These characteristics were strong indications of REE fractionation that occurred during formation of the bauxite zone. Underlying the bauxite zone, accumulations of the remobilized REE were substantial. At the base of the lower kaolin zone, elevated ion-exchangeable REE contents were notable (11–33% for total REE), and more specifically 11–12% for LREE, ∼28% for ΣTb-Lu, and ∼ 33% for Y. The elevated ion-exchangeable contents coincided with whole rock contents that were ∼ 250% ΣREE relative to UCC. These REE accumulations occurred within organic-rich strata at the base of the section. This setting represents a significant difference relative to the REE accumulations in profiles for the granite-regolith deposit type. These findings highlighted the movement of dissolved REE, accumulation as sorbed species, as well as the potential role that organic ligands play during REE precipitation and sorption processes. These results permit consideration for further research into REE occurrences in clay deposits of sedimentary origin, which have been underexplored compared to granite-regolith REE deposits.

Separation of rare earth elements using chelation-assisted electrodialysis

Rare earth elements (REE) find crucial applications in electronics, clean energy, aerospace, automotive, and defense sectors. However, the conventional solvent extraction (SX) technique currently dominates the process of isolating individual REE into pure elements, presenting challenges due to its extensive stage requirements and environmental footprint. To address these limitations, this study explores chelation-assisted electrodialysis (ED) as a promising alternative to SX for efficiently separating light and medium REE from binary and tertiary solutions. By incorporating chelating agents into the ED process, we aim to enhance separation efficiency while mitigating the drawbacks associated with SX. A laboratory-scale ED system with a microflow cell consisting of five pairs of Neosepta® cation and anion exchange membranes in an alternating configuration was utilized. Aminopolycarboxylic acids such as Ethylenediaminetetraacetic acid (EDTA), diaminocyclohexanetetraacetic acid (DCTA), N-(2-hydroxyethyl) ethylenediaminetriacetic acid (HEDTA) and diethylenetriamine-pentaacetic acid (DTPA) were employed as chelating agents to increase the selectivity of REE separation. The effects of operating voltage, operation mode, pH, type of electrolytes, and membrane configuration on the separation process were investigated. ED was conducted at varying concentrations of REE and chelating agents, and the system was optimized for the highest separation factors. It was observed that the separation factors increased by increasing the voltage due to the higher ionic mobility of non-chelated REE at higher voltages. Precipitation of REE in ED compartments was one of the main challenges in the tests. To prevent the precipitation, a modified membrane configuration and an optimized pH window of 3.0–4.5 were applied. At optimized operating conditions, the REE separation factors of up to 42 were achieved, which were up to 20 times greater than those reported for the conventional SX process. The final REE concentrations in the concentrate compartment were comparable with those calculated from the dissociation equilibrium equations and in most cases, less than 10 % error was observed between the experimental results and the calculations.

Recycling of NdFeB magnets: Model supported iron minimization via in-situ hydrolysis during leaching and hematite precipitation in an autoclave

The NdFeB magnets are a significant component of technological applications, which contain a remarkable quantity of rare earth elements (REEs). For this reason, the recycling of NdFeB magnets is essential for the reuse of these elements. This research represents the recycling strategy of NdFeB magnets, which consists of iron minimization through in-situ hydrolysis during oxidative leaching and hematite precipitation in an autoclave. The influence of the experimental parameters in the hydrolysis of Fe3+ in a nitric acid medium on the formation of a mixture of iron oxide hydroxide was examined in detail. Afterward, the effect of the temperature, time and, water addition on the iron and REEs precipitation in the autoclave was investigated by the ANOVA analysis based on the Box-Behnken design. According to the particle swarm optimization algorithm, maximum REEs extraction and minimum iron extraction were achieved in a solution of 1.82 mol/L nitric acid, at a solid/liquid ratio of 11/100, a temperature of 60 °C, and a stirring speed of 415 rpm. The mean leaching efficiencies of REEs and iron are calculated to be 76% and 7%, respectively. The optimal parameters for hematite precipitation in the autoclave were determined to be a process temperature of approximately 137 °C, a processing time of approximately 3 h and 55 min, and a water addition of approximately 20%. The optimum parameters are in harmony with the validation experiments.

Bioleaching of ion-adsorption rare earth ores by biogenic lixiviants derived from agriculture waste via a cell-free cascade enzymatic process

Biogenic organic acids are considered environmentally friendly alternatives to ammonium sulfate for leaching ion-adsorption rare earth ores. Fermentation is popular for their production, but undesired cell metabolites and residual medium components could dampen the leaching performance. High feedstock cost is another major barrier for their applications. To tackle these challenges, a cell-free cascade enzymatic process was developed to produce gluconate from low-cost rice straw. Gluconate production by fermentation and enzymatic catalysis was first compared, and it was found that the enzymatic process gave a 99% yield within 24 h, while it was only 60% for fermentation after 48 h. The gluconate from enzymatic process was superior to that from fermentation in terms of leaching efficiency (100% vs. 18.1%). The precipitation of rare earth elements (REEs) by residual phosphate was identified as the major contributor to the low leaching performance by gluconate produced via fermentation. The gluconate derived from rice straw via the cascade enzymatic process did not show a compromised leaching efficiency, reaching 100% as well. This study sheds lights on how enzymatic process could be adopted to circumvent interferences for REEs recovery by fermentative impurities, and opens a new avenue for potentially economical production of biogenic lixiviants from renewable and cheap feedstocks.

A Simple Process for the Recovery of Rare Earth Elements and Iron from Sulfuric Acid Leaching Solution of NdFeB Magnets by Double Salt Precipitation

ABSTRACT Recovery of rare earth elements (REEs) from spent NdFeB magnets is important to meet the increasing demand for magnets and high-tech applications. In general, pretreatments of spent NdFeB magnets are necessary to recover REEs such as Nd, Pr, and Ce from the magnets. In this work, a simple process was proposed to recover REEs without any pretreatment of NdFeB magnets by using precipitation of REE(III) double salt. The correlations among several variables on the precipitation of REE(III) double salt were investigated by using synthetic solutions such as the molar ratio of Na(I) and sulfuric acid to Nd(III), the concentration of Nd(III) and Fe(III). The REES and iron present in NdFeB magnets were completely dissolved in 2 M H2SO4 solution at room temperature. The dissolved REE(III) ions were then directly separated by precipitation of double salt when Na2SO4 was added at 80°C. After REEs precipitation, the addition of iron powder to the filtrate at room temperature reduced Fe(III) to Fe(II) and removed a small amount of Cu(II) and Co(II) by cementation. Then Fe(II) and Na2SO4 were separated by precipitation of Fe(OH)2 when solution pH was adjusted to 8. The conditions for the precipitation of Nd(III) double salt were thermodynamically verified. Mass balance of continuous experiments indicated that it was possible to recover REEs and iron with high purity by the proposed process in this work.

Recovery of rare earth elements from coal flyash using deep eutectic solvents as leachants and precipitating as oxalate or fluoride

This paper presents results of the study on the applicability of deep eutectic solvents (DES) for the recovery of rare earth elements (REE) from coal flyash (CFA) assaying REE 0.22%. The combination of DES used was choline chloride (ChCl) with lactic acid (LA) and ChCl with para toluene sulphonic acid monohydrate (pTSA). Besides the synthesis and characterisation of the DES systems, detailed study on their flow behaviour as a function of temperature and viscosity was also made. Screening studies indicated better leaching performance when the molar ratio of ChCl:pTSA and ChCl:LA were 1:1 and 1:2 respectively. Influence of various process parameters like temperature, solid to liquid ratio, reaction time and dilution ratio of DES with water on the leaching efficiency of REE and other impurity ions was investigated using the best molar ratio combination identified for the two systems. Performance of the DES systems were compared with that of individual hydrogen bond donors (HBD) namely, LA and pTSA, hydrogen bond acceptor (HBA) viz. ChCl as well as with H2SO4. The dissolved REE from the DES medium were selectively and quantitatively recovered by chemical precipitation. The DES systems gave REE leachability of about 85–95%. The mixture of ChCl:pTSA(1:1) showed higher leach recovery and faster kinetics compared to ChCl:LA(1:2). Both DES systems gave a decisive 5–8% higher leachability than the individual HBDs (LA and pTSA) and HBA (ChCl) which constitute the respective eutectic. Comparison of leaching performance of REE using DES with that of H2SO4 indicated significant enhancement, about 35%, with the former over the inorganic acid. A probable leaching mechanism of REE with the DES used is also proposed. Precipitation of REE from the DES medium was near complete with oxalic acid and NaF reagents.

Separation of rare earth elements from a South American ionic clay lixivium by sequential precipitation

Ionic clays, formed by natural weathering of rare earth element (REE)-containing minerals and surface adsorption of liberated ions, are a critical REE resource. Here, the sequential precipitation of impurities and REEs from the desorption of a South American ionic clay is investigated. Selective sequential precipitation profiles are constructed by stepwise addition of 1.3 M ammonium bicarbonate to the lixivium. During sequential precipitation, ammonium bicarbonate first behaves as a pH adjustor to remove co-extracted impurities as hydroxides, and then behaves as both a carbonate ion source and a pH adjustor to precipitate the REEs as carbonates. Impurity precipitation is completed at pH 6.0 and REE precipitation is completed at pH 6–7.5; however, total carbonate concentration during the impurity precipitation step must be kept low to prevent REE loss. To gain a better understanding of the REE precipitation step, thermodynamic calculations using the Davis model are performed. Dysprosium is studied as a model REE and its speciation diagram as a function of pH and total carbonate and sulfate ion concentrations is constructed. It is found that the primary factors controlling REE precipitation are pH, carbonate, and sulfate concentrations. The knowledge gained in this work provides a deeper understanding of the sequential impurity and REE precipitation processes from the desorption lixivium of a unique ionic clay from South America. The results would help guide future work on REE separation from this distinct ionic clay.

Recovery of rare earth elements from spent NiMH batteries using subcritical water extraction with citric acid

Spent nickel-metal hydride (NiMH) batteries contain high concentrations of rare earth elements (REEs), nickel (Ni), and cobalt (Co). Subcritical water extraction (SWE) process with citric acid as the leaching reagent was applied to spent NiMH batteries. The effects of acid concentration, solid to liquid ratio (S/L), reaction time, and reaction temperature were examined. Leaching efficiency increased with increasing acid concentration, reaction time and temperature, and decreased as S/L increased. Total of 90.85% of lanthanum (La), 88.84% of cerium (Ce), 90.85% of neodymium (Nd), 90.70% of Ni, and 91.62% of Co were leached out using 2.0 N of citric acid, S/L of 10 g/L, at 150 °C in 5 min. Selective precipitation of REEs was induced by the addition of diluted waste phosphoric acid (H3PO4) to the leaching solutions. At [H3PO4]:[REEs] of 10:1, pH 2.0, and 65 °C, 99.3% of La, 98.8% of Ce, and 99.0% of Nd were precipitated, which correspond to overall recovery of 90.2% of La, 87.8% of Ce, and 89.8% of Nd. The results showed that SWE using citric acid followed by selective precipitation with H3PO4 could effectively recover REEs from spent NiMH batteries.

Mineralogical and Geochemical Evidence of Dissolution-Reprecipitation Controlled Hydrothermal Rare Earth Element Mineralization in the Amba Dongar Carbonatite Complex, Gujarat, Western India

Abstract The Amba Dongar carbonatite complex in western India comprises an inner ring of carbonatite breccia surrounded by a sövite ring dike. The various carbonatite units in the body include calcite carbonatite, alvikite, dolomite carbonatite, and ankerite carbonatite. The carbonate phases (calcite and ankerite) occur as phenocrysts, groundmass phases, fresh primary grains, and partially altered grains and/or pseudomorphs when hydrothermally overprinted. Rare earth element (REE) enrichment in the groundmass/altered calcite grains compared to the magmatic ones is ascribed to the presence of micron-sized REE phases. Fluorapatite and pyrochlore constitute important accessory phases that are altered to variable extents. Higher concentrations of Sr, Si, and REEs in fluorapatite are suggestive of a magmatic origin. Fresh pyrochlore preserves its magmatic composition, characterized by low A-site vacancy and high F in the Y-site, which on alteration becomes poorer in Na, Ca, and F and displays an increase in vacancy. The C-O isotope compositions of the carbonates also corroborate the extensive low-temperature hydrothermal alteration of the carbonatites. The REE mineralization is the result of interaction of the carbonatite with a sulfur-bearing, F-rich hydrothermal fluid that exsolved from late-stage carbonatitic magmas. The hydrothermal fluids caused dissolution of the primary carbonates and simultaneous precipitation of REEs and other high field strength element (HFSE)-bearing minerals. Complex spatial associations of the magmatic minerals with the REE fluorocarbonates, [synchysite-(Ce), parisite-(Ce), bastnäsite-(Ce)] and florencite-(Ce) point to the formation of these REE phases as a consequence of postmagmatic hydrothermal dissolution of the REEs from fluorapatite, pyrochlore, and carbonates. Ubiquitous association of fluorite and barite with REE minerals indicates transport of REEs as sulfate complexes in F-rich fluids. Precipitation of REE fluorocarbonates/florencite resulted from fluid-carbonate interaction, concomitant increase in pH, and decrease in temperature. Additionally, REE precipitation was aided and abetted by the removal of sulfur from the fluid by the precipitation of barite, which destabilized the REE sulfate complexes.

Separation and coextraction of REEs and Fe from NdFeB sludge by co-leaching and stepwise precipitation

NdFeB sludge is a waste with high economic value. NdFeB waste recycling has the disadvantage that only rare earths are recycled, but iron (Fe) is not recycled, which results in large amounts of secondary solid waste. In this paper, a process flowchart of the co-extracted rare earth elements (REEs) and Fe by co-leaching and stepwise precipitation from NdFeB sludge was developed. The results show that after the NdFeB sludge was pretreated, co-leaching with hydrochloric acid, rare earth precipitation with oxalic acid, and Fe precipitation with reduction iron powder, 98.28% of the REEs were recovered in the form of RE2(C2O4)3·10H2O, and 94.65% of the Fe was recovered in the form of FeC2O4·2H2O. Due to the low solubility product constants of the rare earth oxalates, when oxalic acid was added to the leachate, the REEs precipitated rapidly, while Fe was still present as FeCl4–, Fe(C2O4)2–, and FeC2O4+ in the precipitated REEs solution. Therefore, the selective separation and precipitation of REEs and Fe was achieved. The process has the advantages of high comprehensive utilization of resources and no secondary solid waste or wastewater pollution.

Low residual dissolved phosphate in spent medium bioleaching enables rapid and enhanced solubilization of rare earth elements from end-of-life NiMH batteries

Successful heterotrophic bioleaching with high metal yields requires an efficient leaching agent production and minimization of secondary reactions such as precipitation of leached metals with growth medium components. In this study, the role of the secondary reactions on bioleaching of spent nickel-metal-hydride batteries was investigated. Substitution of K2HPO4 by yeast extract (YE) reduced precipitation of both base metals and rare earth elements (REEs). REEs were proportionally more affected by precipitation than base metals. Optimizing the ratio of YE to glucose in the growth medium resulted in glucose to gluconic acid conversion yield of 90% by Gluconobacter oxydans. In one-day leaching with YE medium, 28.8% Mn, 52.8% Fe, 22.9% Co, 12.0% Ni, and 19.5% of total REEs were extracted. The leach liquor obtained with the YE medium resulted in leaching of 1.5 and 11.0 times more of total base metals and REEs, respectively, than with phosphate medium. Experimental results were consistent with geochemical modeling results corroborating the benefit of low phosphate concentrations in leaching systems at neutral to moderately acidic pH. In summary, substitution of K2HPO4 with YE in gluconic acid production phase with G. oxydans reduced subsequent base metal and especially REE precipitation during leaching and, thus, enhanced the overall metal extraction.

Parametric study and speciation analysis of rare earth precipitation using oxalic acid in a chloride solution system

Oxalic acid precipitation is a common step in the purification of rare earth elements (REE) from a concentrated pregnant leach solution (PLS). However, the presence of contaminants such as Al, Fe, and Ca in given amounts decreases the REE precipitation efficiency and product purity while also increasing the amount of oxalic acid needed to maximize recovery. As such, a statistically designed test program was performed to identify the optimal conditions necessary for a relatively low REE content PLS containing elevated concentrations of contaminant ions. The performance objective was maximization of REE precipitation efficiency while minimizing the oxalic acid dosage. A central composite design was utilized to quantify performance impacts and identify the ultimate set of parameter values for oxalic acid dosage, Fe(III) contamination concentration, solution pH, and reaction temperature. The resultant model suggested that oxalic acid dosage and reaction pH are the most significant factors for the REE precipitation efficiency, followed by the interaction of oxalic dosage and Fe concentration. Test results indicate that increasing the oxalic acid concentration from 0 g/L to 80 g/L improved the REE precipitation efficiency from approximately 4.2% to 95.0%. Furthermore, raising the solution pH from 0.5 to 2.5 considerably enhanced the precipitation efficiency from 0.0% to 98.9%. A solution temperature elevation decreased REE recovery, which indicated an exothermic reaction between REEs and oxalate anions. Finally, a high level of Fe contamination adversely impacted REE precipitation efficiency. To further the understanding of the REE-oxalate system, a fundamental solution chemistry study was performed using the equilibrium constants of the reactions. The study resulted in the development of oxalate speciation diagrams and provided an analysis of the REE precipitation characteristics at various oxalate anion concentrations and Fe(III) contamination levels using MINTEQ software. The dominant Fe(III) species in the solution system were found to be Fe-(C2O4)33-, Fe-(C2O4)2-, and Fe-(C2O4)+, which consume the majority of the oxalate anions. The simulated model was found to be in agreement with the experimental findings and helped to explain the adverse impact of increased iron concentrations on REE precipitation efficiency.

Development of an innovative process involving the use of ionic liquids for the recovery and purification of rare earths from permanent magnets and NIMH batteries

Background: Nowadays, the industry trends are reflecting an increase in the consumption of products containing rare earth elements (REEs), which leads to the generation of several REE-containing residues such as spent permanent magnets (SPM), permanent magnet swarf (PMS), and nickel metal hydride (NiMH) batteries. Methods: Due to the risk of supply and to decrease the dependency of Europe in obtaining REEs, an innovative process for obtaining REEs in the form of rare earth oxalates (REOx) that can be easily transformed to an xide mixture by calcination is proposed. The proposed method includes leaching of REEs from SPM, PMS, and NiMH batteries using different solvents such as ionic liquids and/or mineral acids; precipitation of REE in the form of REOx and purification of the final products by an ionic liquid extraction (ILE) process for removing the impurities using Cyphos 101 as ionic liquid. Intensive research, based on laboratory tests, is described for each of the parts of the process with the aim of providing optimized results. Results: In this study, &gt;99% recovery of the REE initially present in the leachates after the leaching phase is achieved, with a purity of the REOxafter the precipitation and purification steps higher than 95%. Conclusion: A novel and innovative process for the extraction of REEs from secondary sources has been investigated in this paper, demonstrating strong potential for its implementation. The REEEs recovery rate and the purity obtained together with the low environmental impact of this process compared to conventional ones can contribute to a greener future where the usage of REEs will presumably be even more relevant.

Rare earth element precipitation induced by non-redox transformation of magnetite to hematite: Microtextural and geochemical evidence from the Kamthai carbonatite complex, western India

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 bastnäsite, hydroxyl-parisite, röntgenite, 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 bastnäsite-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, röntgenite, 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.

Iron and sulfur isotopic compositions of carbonatite-related REE deposits in the Mianning–Dechang REE belt, China: Implications for fluid evolution

Carbonatite-related rare earth element (REE) deposits are the most significant source of REEs worldwide. The processes of REE precipitation, enrichment, and mineralization remain controversial. The Cenozoic Mianning–Dechang (MD) REE belt, located in Sichuan Province, southwestern China, comprises one giant (Maoniuping), one large (Dalucao), and two small–medium (Muluozhai and Lizhuang) deposits. These deposits provide a continuous record of fluid evolution, and thus are ideal for investigating the processes of REE mineralization in carbonatite-related REE deposits. Given that sulfate (i.e., barite and celestite) and sulfide (i.e., pyrite and galena) minerals crystallized and precipitated in the pegmatitic to hydrothermal stages, respectively, the REE minerals formed later than the sulfate minerals. However, the formation sequence of the sulfide minerals and bastnäsite is unclear, although both pyrite and bastnäsite formed in the late hydrothermal stage. We used S isotope data for sulfate and sulfide minerals and Fe isotope data for pyrite to investigate the composition and evolution of ore-forming fluids during the magmatic–hydrothermal stages. The sulfate minerals have positive δ34SCDT values (+3.2‰ to +8.3‰), and the sulfide minerals have negative δ34SCDT values (−13.5‰ to − 5.6‰) in the four REE deposits. In the Maoniuping deposit, δ34SCDT values for barite from the pegmatitic stage (+4.7‰ to +5.7‰) are higher than for barite from the hydrothermal stage (+4.1‰ to +4.5‰), which indicate that hydrothermal activity led to relative enrichment in isotopically light S. The δ34SCDT values for barite (+3.2‰ to +5.5‰) are lower than for celestite (+6.2‰ to +7.2‰) from the pegmatitic stage in the Dalucao deposit. The δ34SCDT values for galena (−13.5‰) are also lower than for pyrite (−13.5‰ to −7.2‰) from the hydrothermal stage in the Guangtoushan section. In general, δ34SCDT values change from positive to negative values (+8.3‰ to −16.4‰) as the fluids evolved from the pegmatitic to hydrothermal stages, which can be attributed to a decrease in oxygen fugacity (fO2) and addition of sediment containing isotopically light S. Iron isotopic compositions of pyrite from the hydrothermal stage show significant variations (δ56FeIRMM-014 = −0.03‰ to +0.65‰ for the Maoniuping deposit; −0.14‰ to 0.00‰ for the Dalucao deposit; +0.05‰ to +0.35‰ for the Lizhuang deposit), and are higher than those for the carbonatites (δ56Fe IRMM-014 = −0.47‰ to −0.17‰). These data indicate there are two sources of Fe in the MD REE belt, which are the carbonatite–nordmarkite magma and 56Fe-rich sediment. Paleozoic–Mesozoic volcanic–sedimentary and Mesozoic clastic and carbonate rocks are exposed in the MD REE belt. In general, the S–Fe isotope data, along with geological and petrographic observations, indicate that the REE minerals formed later than the sulfate minerals, and the S–Fe were derived from both carbonatite magma and sediment containing isotopically light S and heavy Fe.

Thermodynamic Analysis of Precipitation Characteristics of Rare Earth Elements with Sulfate in Comparison with Other Common Precipitants

The selective precipitation of rare earth elements (REEs) in acidic media often plays a key role in the effective extraction of these elements from various sources such as ores and recycling streams. In this study, the precipitation characteristics of REEs with sulfate, a frequently used precipitant, were carefully examined, and the results were compared with those of other precipitants, such as phosphate, oxalate, and fluoride/carbonate systems. Emphasis is given on various forms of precipitates, such as anhydrous sulfate, octa-hydrated sulfate, and sodium double salt, in which the sodium double salt was compared with the anionic double salt precipitation of the fluoride-carbonate system. It was found that anions such as Cl−, NO3−, and SO42− play an important role in the precipitation behavior, particularly through complexation with the dissolved REEs. In general, the effectiveness of precipitation follows the order of sodium double salt, a hydrated form of sulfate, and anhydrous sulfate. In this study, it was observed that the synergistic role of a double salt precipitation, either cationic or anionic, is frequently as effective as that of oxalate and phosphate, even in a low pH range.

Effect of various ligands on the selective precipitation of critical and rare earth elements from acid mine drainage

Acid mine drainage (AMD) has been of environmental concern for decades but recently found to be a viable source of critical elements including rare earth elements (REEs). Recovery of these elements while treating AMD for environmental compliance improves the sustainability of the treatment process. The precipitation behavior of the REEs and other cations during the AMD neutralization process depends strongly on the solution chemistry, available ligands, and concentration of elements. Several chemicals were used to study the effect of various ions/ligands (i.e., OH−, SO42−, NH4+, CO32−, and PO43−) on precipitation behavior of REEs and other elements from AMD as a function of pH. It was found that only up to 70% of total REEs can be recovered using NaOH at circumneutral pH. (NH4)OH suppressed the precipitation of REEs up to pH 8. The presence of phosphate and carbonate ions in the solution increased the precipitation yield of REEs at lower pH values. Both Na2HPO4 and Na2CO3 were found to increase the precipitation of REEs at pH below 7, as over 85% of REEs were recovered. Calculated saturation indices and speciation diagrams for selected REEs confirmed the experimental data. Considering the elemental recovery values, environmental effects, as well as chemical consumption and cost, a two-step AMD treatment process using Na2CO3 was formulated. Through the proposed process, 90% of the aluminum was recovered in the first step (at pH 5), while 85% of REEs was recovered in the second step (at pH 7) with a significantly high concentration of 1.6%.

Recovery of technologically critical lanthanides from ion adsorption soils

Rare earth elements (REEs) are in increasing demand due to rapidly rising use in consumer technology, the automotive industry and in renewable energy generation systems, amongst other technology sectors. Ion-adsorption type REE ore deposits are currently being exploited in China’s southern provinces and there is increasing interest in identifying potential reserves globally. Here we investigated the extraction of REEs from an ion-adsorption clay sampled at a surficial deposit in Madagascar. Using a 1 M NH4Cl lixiviant salt solution, chosen based on experimental evidence to maximise REE extraction, minimises undesirable dissolved Al in eluate. Lower Al concentration in solution reduces its interference with NH4+ in oxalate precipitation of REEs in the extraction process. We show that NH4Cl solutions can be used to efficiently extract REE with relatively low lixivient volumes in a through-flow column system. We show that when extraction with a pulse of lixiviant is followed by a rinsing step, there are several identifiable stages during the extraction process, including a marked increase in total lanthanides extracted, which is correlated with the breakthrough of ammonium ions, and where the eluted dissolved Al concentration decreases from its peak concentration.

Rare earth elements deposits in China: Spatio-temporal distribution and ore-forming processes

<p indent=0mm>China dominates the world REE (rare earth elements) resources, 98% of which are from carbonatite-related REE deposits. Extensive studies of this type of REE deposits are available, but it is still poorly understood how carbonatite magmas were generated and how REEs were transported and precipitated in such magmas. On the basis of previous studies, this paper synthesizes the spatio-temporal distribution of this type of REEs deposits in China and their major features, including characteristics of ore-forming fluids, and discusses existing genetic models regarding the origin of causative magma, and mechanics of REE enrichment, transportation and precipitation. In China, carbonatite-related REE deposits occur in the craton margin environments with four major REE metallogenic belts: the Mesoproterozoic Bayan Obo-Langshan belt (e.g., the Bayan Obo deposit), the early Mesozoic eastern Qinling-Dabie belt (e.g., the Miaoya deposit), the late Mesozoic Zibo-Laiwu-Weishan belt (e.g., the Chishan deposit), and the Cenozoic Mianning-Dechang belt (e.g., the Maoniuping deposit). In these belts, REE-hosting carbonatites were emplaced in continental rift zones or along large-scale strike-slip faults at the Precambrian craton margins. The causative magmas were originated from partial melting of enriched lithospheric mantle sources, which may have undergone metasomatism by subducted slab-related fluids/melts, and may have also asthenospheric material involvement. These magmas may have formed through melt immiscibility and fractional crystallization from primary carbonated silicate melt. The melt immiscibility may include unmixing between alkaline silicate and carbonate melts, or multi-phase melt immiscibility of carbonate melt, mafic or ultramafic melt, phosphomagnesite melt, and alkaline silicate melt. The immiscibility and/or crystal fractionation of mafic mineral can lead to the formation of carbonate melts rich in REEs. The newly discovered lithofacies zonation at Bayan Obo, with a biotitite outer zone, implies a magmatic evolution of a silica-rich parent magma. The low REE concentrations and LREE/HREE ratios of biotitite indicate possible LREE enrichment in the evolved carbonatite magma by biotite fractional crystallization. The crystallization of carbonate minerals during the upwelling and emplacement of carbonatite magmas, may further enrich late-stage carbonatite melts and carbonatite fluids in LREE. This process can better explain the REE mineralization dominantly in the late-stage of carbonatite magmatism or post-magmatic fluid stage. The melt, melt-fluid and fluid inclusion results for Bayan Obo, Maoniuping and Chishan indicate SO₄²⁻ and CO₂-rich carbonatite fluids. The microthermometry and SEM/EDS results for primary melt-fluid inclusions hosted in fluorite from Maoniuping indicate that carbonatite fluids were extremely rich in SO₄²⁻, and underwent an unmixing process between sulfate melt and aqueous fluid. Both inclusion and experimental results indicate that the sulfate has a very high solubility in SiO₂-bearing aqueous fluids, inconsistent with the SiO₂-free system. The geochemical thermodynamic results also confirm the SO₄²⁻ -dominated agent for REE transportation. The unmixing process between sulfate melts and aqueous fluids would lead to extensive decrease of SO₄²⁻ in the fluid, and bulk REE precipitation. The rapid evolution of carbonatite fluids prevents long distance migration of carbonatite fluids, resulting in all REE mineralization within, or proximal to the carbonatite bodies. The strong mineralization would occur in the central zone or the shallow level and then would become weaker outwards and downwards of carbonatite bodies.

Extractive Separation of Oxalic and Nitric Acids Using Tributyl Phosphate

The extraction of nitric and oxalic acids by neutral compounds TBP, DBBP, and TBPO have been studied. The optimal conditions of their separation are determined. The simulation of separation process of nitric and oxalic acids from waste solutions after the oxalate precipitation of rare-earth elements using undiluted TBP as extractant is performed by the simple counterflow method and the counterflow method with part of flow being returned into the center of cascade.