Distribution Of Rare Earth Elements Research Articles

Late Summer Water Sources in Rivers and Lakes of the Upper Yana River Basin, Northern Eurasia, Inferred from Hydrological Tracer Data

Major ions, stable isotopes, and trace elements, including rare earth elements (REEs), are used as natural tracers in the qualitative assessment of potential water sources in lakes and rivers of the upper Yana River basin, between Verkhoyansk and Chersky Ranges, during the late summer period. Three distinct regions were sampled, and a dominant water source in each region was qualitatively inferred from water chemistry data. The REE distribution pattern was found to be highly regional and controlled by pH and carbonate contents. Mountain headwater stream at the Verkhoyansk Range north slope, the Dulgalakh River, shows an input from a mixture of shallow groundwater and icing meltwater, with a depleted isotopic signature (δ18O below –21‰), d-excess (dex = δ2H − 8·δ18O) above 18, enrichment in Mg and Sr, and depletion in heavy REEs. The Derbeke Depression lakes and streams are fed by rainfall having ultra-low total dissolved solids (TDS) content, below 25 mg/L, and a convex-up REE pattern. In a medium mountainous river at the Chersky Range flank, the Dogdo River, leaching through fissured Jurassic carbonates is a dominant runoff pathway. Riverine water is heavily depleted in light REEs, but enriched in Mo, Rb, Sb, W and U. In the Dulgalakh River water, high positive Sm and Gd anomalies were observed, attributed either to local geology (greenshists), historical mining legacy, or contemporary winter road operations.

Integrative Study Assessing Space and Time Variations with Emphasis on Rare Earth Element (REE) Distribution and Their Potential on Ashes from Commercial (Colombian) Coal

The increasing demand for rare earth elements (REEs), which is associated with their economic importance and the supply risk, has motivated the research for alternative secondary sources of these elements. Coal and coal combustion ash have been pointed out as promising REE raw materials. This research seeks to understand REE fractionation, from feed coals to ashes, considering seasonal variations, and to assess the trends within the ash fractions that can be used for further beneficiation processes. Colombian commercial feed coals, combustion ashes, and their respective fractions were sampled from a Portuguese power plant and were characterized via petrographical, mineralogical, and chemical analyses. The total REE concentrations in the feed coals studied range between 6.97 and 23.15 ppm, while, in the ashes, they vary from 159.9 to 266.6 ppm. Fly ash (FA) from electrostatic precipitator (ESP) presented higher concentrations than the bottom (BA) and economizer (ECO) ashes. Furthermore, REEs and the LREE/HREE ratio increased slightly towards the back rows of the ESP. In the feed coals, the REEs are significantly correlated with ash, and they occur in micrometric phosphate minerals intermixed with clays. In the ashes, the REEs were mostly detected in micrometric particles, with P and Al-Si as the major components. The results from the fractioned samples show that the REEs were enriched in the fine (<25 µm) and nonmagnetic fractions of the ESP FA. A single trial combining sieving and magnetic separation enabled the attainment of a REE recovery of 53%, and a final enrichment factor of 1.25. Coal combustion ashes and their respective size fractions are promising REE raw materials; however, the REE oxide concentrations are below the economical cutoff of 1000 ppm.

Absence of β-carotane as proxies of hydrothermal activity in brackish lacustrine sediments

β -Carotene, the precursor of β -carotane, is commonly rich in brackish sediments and would become unstable theoretically under the exposure to high temperatures, bright light conditions, and acidic or oxdizing environments. However, the specific process and mechanism of the absence of such compounds are still not clear sufficiently. To fill the knowledge gap, in this study we explore the origin of the absence of β -carotane in a 50-m-thick section of the Middle Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, northwest China, based on a combined mineralogical, petrographic, organic and inorganic geochemical study. Biomarker analyses indicate that the β -carotane-free section was deposited in a brackish, reducing, and semi-deep lacustrine environment. Hydrothermal fluid effects during sediment deposition are inferred to have caused the breakdown of β -carotene. The hydrothermal (<100 °C) effects are evidenced by mineralogy and geochemistry, e.g., the hydrothermal-indicative minerals (reedmergnerit, tuff and pyrite), high Fe/Ti and low Al/(Al + Fe) ratios, rare earth elements (REEs) distribution. Associated biomarker variations were found, e.g., low i -alkanes/ n -alkanes, high C 24 Tetracyclic/C 26 Tricyclic terpanes, high (C 19 + C 20 )/(C 21 + C 23 ) tricyclic terpanes, high C 29 /C 30 hopanes, and very low gammacerane/C 30 hopane ratios. Our data suggest that hydrothermal fluids can prevent the preservation of β -carotene, and the absence of β -carotane indicates a period of hydrothermal activity during deposition of the Lucaogou Formation in a 50-meter-thick sequence. • β -Carotanes were found to be absent in a brackish lacustrine sequence. • Hydrothermal fluids have caused the breakdown of β -carotene. • Anomalously low abundance of isomerization alkanes and high C 24 Tet/C 26 TT ratios were also found. • Hydrothermal activity was present in the Permian Lucaogou Formation, Junggar Basin. • Absence of β -carotane can be used as a proxy for hydrothermal activity.

High-entropy (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 ceramic: A promising thermal barrier coating material

• (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 exhibits great high-temperature phase stability up to 1600 °C and excellent chemical compatibility with Al2O3 even at 1300 °C. ○ The grain growth rate of high entropy hafnate is more sluggish than that of Y2Hf2O7. ○ The thermal conductivity of (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 (0.73–0.93 W m −1 K −1 ) is much lower than those of components RE2Hf2O7 and many thermal barrier coating materials. ○ (Y0.2Gd0.2Dy0.2Er0.2Yb0.2)2Hf2O7 can be as next generation thermal barrier coating material. Thermal barrier coating (TBC) materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine. In this study, a novel high entropy hafnate (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 was synthesized by solution combustion method and investigated as a potential TBC layer. The as-synthesized (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 possesses a pure single disordered fluorite phase with a highly homogeneous distribution of rare earth (RE) cations, exhibiting prominent phase stability and excellent chemical compatibility with Al 2 O 3 even at 1300 °C. Moreover, (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 demonstrates a more sluggish grain growth rate than Y 2 Hf 2 O 7 . The thermal conductivity of (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 (0.73-0.93 W m −1 K −1 ) is smaller than those of components RE 2 Hf 2 O 7 and many high entropy TBC materials. Beside, the calculated thermal expansion coefficient (TEC) of (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 (10.68 × 10 −6 /K, 1100 °C) is smaller than that of yttria-stabilized zirconia (YSZ). Based on the results of this work, (Y 0.2 Gd 0.2 Dy 0.2 Er 0.2 Yb 0.2 ) 2 Hf 2 O 7 is suitable for the next generation TBC materials with outstanding properties.

Extraction of a target element from a mixture of rare earth elements in a single-stage process

The generally accepted method for extracting the required element from a mixture of rare earth elements (REE) is to use two cascades, with elements with a higher ordinal number being separated in one cascade, and those with a lower ordinal number in the second cascade (or vice versa). The features of the extraction and separation of rare-earth and associated elements in ores (actinium, yttrium) by extraction with mixtures of cation-exchange and anion-exchange extractants are considered. For the indicated extractants, the dependences of the REE distribution coefficients on the atomic number are opposite. Therefore, a change in the composition of mixtures of these extractants makes it possible to regulate their extraction ability and selectivity of the extraction of elements in a wide range. It is shown that the selection of the composition of the mixtures makes it possible to create conditions under which the required element is extracted worse than the others, and it can be isolated in a single-stage extraction process. In this case, the greater the separation coefficients of neighboring REEs during extraction with each of the extractants, the higher the separation selectivity. For the successful isolation of the required element from a mixture of lanthanides within the framework of one extraction cascade, the separation coefficients between neighboring elements during extraction with individual extractants must be at least 3.0. For some elements (yttrium, actinium), there is a shift in the position of an element in the REE series in terms of distribution co efficients, which consists in the fact that during extraction with one extractant, the distribution coefficient of this element is closer to lanthanum, and with the other extractant, closer to lutetium. It is shown that in this case it becomes possible to separate such an element (for example, yttrium) within one cascade, and the separation coefficients between neighboring elements can be much lower. The separation selectivity increases with the shift of the selected element in the series of lanthanides (according to the distribution coefficients): the greater the shift of the isolated element, the higher the separation factor of the isolated element from the rest of the REEs. Using one extraction cascade instead of two significantly reduces production costs.

Redistribution and chemical speciation of rare earth elements in an ion–adsorption rare earth tailing, Southern China

Mining is an activity that will change the distribution and chemical speciation of rare earth elements (REEs), thus posing a serious threat to the natural environment. However, the distribution and chemical speciation of REEs in ion–adsorption rare earth tailings remain poorly understood. In this study, we investigated the contents and forms of REEs and associated geochemical behavior in rare earth tailings in southeast China. Total rare earth elements (TREEs) contents were lower while the ratios of light REEs (LREEs) to heavy REEs (HREEs) were higher in tailings than in an unmined area. In the unmined area, the distribution characteristics of TREEs and LREEs remained consistent, whereas HREEs differed with increasing depth. However, in the tailing area, the distribution characteristics of TREEs, LREEs and HREEs tended to be consistent, reflecting the outcomes of mining activities on vertical distribution characteristics of REEs. The REEs were dominated by residual and exchangeable forms in the unmined area, while residual and exchangeable REEs accounted for 80% and 20% of the TREEs, respectively, in the three tailings. Additionally, the exchangeable and carbonate–bound REEs increased but Fe/Mn oxide–bound and organic–bound REEs declined in the unmined area, whereas their distribution characteristics were irregular in the tailings. These results suggest that mining activity could curtail REEs contents and redistribute their chemical speciation, further altering geochemical behaviors in the tailings and posing serious risks to adjacent environments.

МОРФОЛОГИЯ И СОСТАВ ИМПАКТНЫХ ПРОДУКТОВ

The object of study is the products of the Zhamanshin crater: tektites – irgisites, subtektites, zhamanshinites. The features of morphology and the compositions of products were determined. In the distribution of rare earth elements of irgisites Eu and Ce anomalies appeared. The crystallized components of jamanshinite consist of phayalite, ferrosilite, magnetite. Large inclusions of zhamanshinite are represented by a solid solution of copper and boron, small ones by galenite with impurities of iron and tungsten. Among the accessor minerals of subtektites, xenotime, iocyte, coesite were found. The proximity of the mineral compositions of subtektites and a number of comets was confirmed.

A review on mineralogical speciation, global occurrence and distribution of rare earths and Yttrium (REY) in coal ash

Rare earths and Yttrium (REY) are a group of critical metals essential for this electronic and digital era. China is the leading producer of REY with more than 90% of global export. Mines of REY are limited and the need for green and efficient energies have augmented the demand of REY and it is putting enormous pressure on global production. REY market is predicted to grow from USD 5.3 billion in 2021 to 9.6 billion by 2026, at a CAGR (Compound Annual Growth Rate) of 12.3%. The need for permanent magnets is propelling the demand of the critical group REY and is expected to rise gradually in the coming years. In the present review, we have summarized the minable REY resources and their applications. The requirement for alternative resource is pivotal to meet our future needs. We have extensively reviewed the studies of REY in coal fly ash (CFA). A comprehensive analysis has been done for the REY resources worldwide for the last several decades in coal ash (CFA and bottom ash) and divulged into the application, speciation and distribution for major coal-consuming countries like China, India, USA, Russia, UK, Poland, etc., individually. We have also made a comparative global study and inferred potential extractable coal ash resources using various parameters such as global average, critical percentage (Cp), outlook coefficient (Cout), etc., for a better understanding of economic exploitation.Research highlightsWe have put up enormous effort to synthesize rare earth elemental data of coal ash from different coal-consuming countries. Following are the major highlights of this review article.We have compiled data on occurrence of Rare Earths and Yttrium (REY) in coal ash from 13 countries such as China, India, USA, UK, Poland, etc.Up-to-date global data of mined REY resources and reserves have been compiled.Broad characterization and classifications of REY have been introduced.Comprehensive analysis of application, speciation and environmental impact of REY in coal ash have also been compiled.Comparative study has been done using parameters such as global average, critical percentage, outlook coefficient, etc. These parameters would help in determining ideal candidates for beneficial extraction of REY.This study would serve as a knowledge resource centre for new research related to REY.

Rare Earth Elements (REEs) Distribution in Topsoil from Ditrău Alkaline Massif Area, Eastern Carpathians, Romania

Rare Earth Elements (REEs) Distribution in Topsoil from Ditrău Alkaline Massif Area, Eastern Carpathians, Romania

First Age and Geochemical Data on Zircon from Riebeckite Granites of the Verkhnee Espe Rare Earth\u2013Rare Metal Deposit, East Kazakhstan

This paper is dedicated to the isotope-geochemical study of zircon from riebeckite granites of the Verkhnee Espe rare earth-rare metal deposit and the specification of its U–Pb age. Zircon from the Verkhnee Espe massif is peculiar in the high content of non-formula elements (up to 43000 ppm REE, up to 22000 Y, and others) and demonstrates a clearly expressed heterogeneous structure. The central and rim zones of the zircon show a “magmatic” rare-earth element (REE) distribution. The intermediate zones are characterized by a flattening of the REE patterns and an anomalous enrichment in REE, Y, Nb, and Ca. This compositional feature of the zircon may be caused by impact of fluid-saturated granite melts enriched in incompatible trace elements. The δ18О values in the zircon are 5.83–7.16‰, which generally corresponds to zircon formed from granitoid melts. The age of zircon from the Verkhnee Espe rare earth–rare metal deposit is 283 ± 3 Ma, which indicates that there is no significant age gap between granite crystallization, on the one hand, and metasomatic processes and ore generation, on the other.

Environmental Settings of Seagrass Meadows Control Rare Earth Element Distribution and Transfer from Soil to Plant Compartments

Environmental Settings of Seagrass Meadows Control Rare Earth Element Distribution and Transfer from Soil to Plant Compartments

РЕДКОЗЕМЕЛЬНЫЕ, БЛАГОРОДНЫЕ И РЕДКИЕ МЕТАЛЛЫ В РУДАХ АЛГАМИНСКОГО РУДОПРОЯВЛЕНИЯ ЦИРКОНИЯ (ХАБАРОВСКИЙ КРАЙ)

Samples of the ore and gravity concentrate from the Algaminskoe zirconium occurrence were studied. Concentrations of rare-earth elements (REE), rare and noble metals were determined. REE content in the ore is 200–300 g/t, with 400 g/t in the gravity concentrate. REE distribution diagrams clearly show Ce depletion and the predominance of intermediate lanthanides and yttrium. The ore and the concentrate contain elevated Hf, W, U, Ta, Au, and Pt, most of which are present in the form of isomorphic admixture in baddeleytte and zircon. Their source is the ancient weathering crust of peralkalic rocks of the Ingili massif. The suggestion has been made that there should be a buried weathering crust enriched in valuable components.

НЕКОТОРЫЕ ОСОБЕННОСТИ РАСПРЕДЕЛЕНИЯ РЕДКОЗЕМЕЛЬНЫХ ЭЛЕМЕНТОВ В ПОВЕРХНОСТНЫХ ОСАДКАХ ЗАЛИВА ТОНКИН (ЮЖНО-КИТАЙСКОЕ МОРЕ)

The peculiarities of the rare-earth elements distribution in the surface bottom sediments in the Gulf of Tonkin (South China Sea) are considered. According to the results of granulometric analysis, the sediments are mainly represented by pelitic silt, silty pelite, and miktites. The REE contents normalized to the chondrite composition show the absence of cerium anomaly, the presence of negative europium anomaly and significant fractionation of light and heavy REE. The values of indicator ratios La /Yb ), Cr/Th, Th/Co, La/Sc, Th/Sc N N indicate the predominance of rocks of intermediate and acidic composition in the erosion areas, due to which sediments were formed. The values of the Ce/La ratio and Strakhov lithochemical modulus (Fe+Mn)/Ti characterize the surface sediments as typical terrigenous without the admixture of endogenous exhalative material. The Eu/Sm ratio values indicate low permeability of the sediments for upward fluid flows, which is consistent with the measured methane concentrations. The analysis of correlations indicates the dominance of the terrigenous source of REE and a significant role of clay minerals and iron hydroxides in the migration and accumulation of REE.

Depositional age, provenance, and palaeoenvironment of the Lower Permian mudstones in the Qiangtang Basin, Tibet: Evidence from geochronology and geochemistry

The geochronology of tuffaceous sandstone and elemental geochemistry of mudstones in the Lower Permian Zhanjin Formation (well QZ‐5) in the Central Qiangtang Basin were studied to determine their depositional age, provenance, tectonic setting, and depositional conditions. Twenty‐six synchronous igneous zircons from tuffaceous sandstone at 596.5 m have a weighted average U–Pb age of 292.5 ± 2.5 Ma, tentatively constraining the sedimentary age of the Zhanjin Formation to the Early Permian. Low SiO2/Al2O3 and Th/Sc ratios indicate a low sedimentary recycling and compositional maturity for the source area of the Zhanjin Formation mudstones. The low Al2O3/TiO2, moderate‐high Fe2O3/Al2O3, high TiO2/Fe2O3, low‐moderate TiO2/Zr, and moderate Co/Th ratios combined with post‐Archean Australian shale‐normalized rare earth element distributions imply that the provenance of the Zhanjin Formation mudstones was mainly from the mixed mafic and felsic sources that is composed of basalt and rhyolite exposed in the Central Qiangtang Basin. The tectonic discrimination plots, low Fe2O3/TiO2, (La/Ce)N, and high Al2O3/(Al2O3 + Fe2O3) ratios reveal that the studied mudstones mostly formed in rift settings, consistent with the geologic evolutionary history of the Early Permian Qiangtang Basin. Trace element ratios (V/Cr and Cu/Zn), enrichment factors (MoEF), and δCe values combined with sedimentary features indicate that almost all the studied mudstones were deposited in an open marine environment along the continental margin, and were associated with oxic and dysoxic water columns.

Origin of metasomatic fluids in the Bayan Obo rare-earth-element deposit

The Bayan Obo REE–Fe–Nb deposit is the largest light rare earth element (REE) deposit in the world, and it has undergone serious hydrothermal reworking processes. However, the origin and nature of metasomatic fluids in this deposit remain controversial. To determine the origin of metasomatic fluids, we conducted a detailed mineralogical and geochemical investigation on the apatite from the ∼ 1.8-km drill core in the Bayan Obo deposit. The textural and geochemical variations of the apatite could trace the hydrothermal metasomatism during REE mineralization. Four types of apatites were identified according to their cathodoluminescence characteristics, including turbid euhedral apatite (Ap-0), rounded pinkish–violet apatite veinlets (Ap-1), yellowish–green apatite aggregates (Ap-2), and apatite with a pinkish–violet core and a yellowish–green rim (Ap-3). According to the in-situ Sr isotopic compositions, these apatites were classified into two groups. Ap-0, Ap-1, and Ap-2 display constant and low 87Sr/86Sr ratios (0.7030–0.7035), whereas Ap-3 displays various Sr isotopic compositions (0.7047–0.7105). The in-situ Th–Pb age of the bastnäsite associated with the Ap-0 ranges from 390 to 425 Ma. The Sr isotopic compositions and geochronological study indicate that metasomatic fluids in the Bayan Obo deposit were obtained from different sources, including the Silurian Bainaimiao arc plutons and sedimentary materials. The four apatite types display various REE distribution patterns, which could account for hydrothermal fluid properties. F-rich and Na-poor fluids metasomatized the precursor Ap-0, releasing REEs from apatites and resulting in low REE contents of Ap-0. Ap-1 and Ap-2 were derived from the same fluid but were characterized by different trace element compositions, which could be attributed to the evolution of hydrothermal fluids with changes in the Na content and F/Cl ratio. The primary Ap-3 was derived from a REE-rich source and was altered by Na-poor and Cl-rich fluids. Metasomatic fluids with different origins and variable chemical compositions result in complex mineral assemblages and geochemical features in the Bayan Obo deposit.

Magmatic origin and petrogenesis characterization of syenite rock from Pakkanadu alkaline complex, Southern Granulite Terrain, India: Implication on emplacement and petrogenetic history

The present study mainly focused on understanding the magmatic origin and petrogenesis characterization based on the Petrography, major, trace and Rare Earth Element (REE) signatures in the alkaline syenite from Pakkanadu alkaline carbonatite complex. The alkaline plutons from South Indian granulite terrain are intruded along with Archaean epidote-hornblende gneisses. The study area was carbonatite complexes of Tamil Nadu and is characterized by a group of rock associations Carbonatite-Syenite-Pyroxenite - Dunite. From Harker various patterns Pakkanadu alkaline complex syenite showed increasing trends of SiO2, Al2O3, Na2O + K2O opposite to decreasing order of CaO, Fe2O3, MgO, TiO2, P2O5 and MnO trend, suggest fractionation of clinopyroxene, hornblende, sphene, apatite and oxide minerals and feldspar that ruled the fractionation. The concentration of trace elements enriched in Large Ion lithophile elements (LILE) (Ba, Sr, and Rb) elements and High Field Strength Elements (HFSEs) indicated that the dyke intrusion by differentiation of magma from a mantle source. Rare earth element (REE) distribution of Light rare earth element (LREE) enriched and High rare earth element (HREE) depleted pattern show strongly fractionated pattern with moderate Eu anomalies. Plots of tectonic discrimination diagrams of Pakkanadu samples fall in the field of syn-COLG field to the VAG syn- COLG field. For the first time, this type of study was carried out in the study region in a detailed manner. The present study significantly exposed the petrography, petrogenesis and magmatic origin process in the Pakkanadu alkaline carbonatite complex.

Distribution and Origin of Major, Trace and Rare Earth Elements in Wild Edible Mushrooms: Urban vs. Forest Areas.

This paper investigates the composition of major, trace, and rare earth elements in 15 different species of wild edible mushrooms and the possible effect of urban pollution on elemental uptake. The collected mushrooms include different species from the green areas of the city, exposed to urban pollution, and from the forests, with limited anthropogenic influence. Through a comprehensive approach that included the analysis of 46 elements, an attempt was made to expand knowledge about element uptake by mushroom fruiting bodies. The results showed a wide variability in the composition of mushrooms, suggesting a number of factors influencing their element uptake capacity. The data obtained do not indicate significant exposure to anthropogenic influences, regardless of sampling location. While major elements’ levels appear to be influenced more by species-specific affinities, this is not true for trace elements, whose levels presumably reflect the geochemical characteristics of the sampling site. However, the risk assessment showed that consumption of excessive amounts of the mushrooms studied, both from urban areas and from forests, may have adverse health effects.

Provenance and Tectonic Setting of Lower Cretaceous Huanhe Formation Sandstones, Northwest Ordos Basin, North-Central China

In adjustment to fulfill the requirements of the investigation regarding the lower Cretaceous sandstone uranium deposit in the Naogaodai area within the northwest of Ordos Basin, twenty-seven sandstone samples obtained from the Lower Cretaceous Huanhe Formation were analyzed for major, trace and rare earth elements (REE). The source of clastic and tectonic background was additionally analyzed. The results show that Huanhe sandstone is feldspar rich sandstone, and also the mineral composition is principally quartz, albite and plagioclase; the ratio of light to heavy rare earth elements (LREE/HREE) is 9.25–10.83, with an average value of 10.00; (La/Yb)CN is 10.20–12.53, with an average value of 11.24, demonstrating that LREE is enriched and fractionated compared with HREE. REE distribution patterns are similar, which additionally reveals that Huanhe sandstone has a homogenous source; the Index of Compositional Variability (ICV) value is 1.17–1.73, with an average value of 1.35, both greater than 1, showing an immature property, which may be first-order cycle deposition. The average value of the Chemical Index of Alteration (CIA) is 50.29, suggesting that the source rock has encountered weak chemical weathering; sandstones are near-source first-cycle provenance, which is not significantly influenced by sedimentary sorting and recycling. The geochemical qualities further indicate that Huanhe sandstone was deposited in a passive margin and experienced moderate weathering.

Re-evaluating monazite as a record of metamorphic reactions

This study presents a re-examination of historical specimens (DG136 and DG167) from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element (REE) distribution between garnet and monazite (and other accessory minerals) during metamorphism. Nine-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed (re)crystallization histories. Trace element data collected from the same ablated volume, interpreted in the context of new phase equilibria modelling that includes monazite, xenotime and apatite, link ages to specific portions of the pressure–temperature (P-T) paths followed by the specimens. These linkages are further informed by garnet Lu-Hf geochronology and xenotime petrochronology. The clockwise P-T paths indicate prograde metamorphism was ongoing by ca. 80 Ma in both specimens. The structurally deeper specimen, DG136, records peak P-T conditions of ~755–770 ℃ and 8.8–10.4 kbar, interpreted to coincide with (re-)crystallization of low Y monazite at ∼75–70 Ma. Near-rim garnet isopleths from DG167 cross in the observed peak assemblage field at ∼680 °C and 9.3 kbar. These conditions are interpreted to correspond with low Y monazite (re-)crystallisation at ∼65 Ma. Both specimens record decompression along their retrograde path coincident with high Y 70–55 Ma and 65–55 Ma monazite populations in DG136 and DG167, respectively. These findings broadly agree with those initially reported ∼20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic reactions. Modern phase equilibria modelling and in situ petrochronological analysis, however, provide additional insight into monazite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite.

Grinding activation effect on the flotation recovery of unburned carbon and leachability of rare earth elements in coal fly ash

Coal fly ash (CFA) as a secondary resource has received a great deal of attention over the past few decades. Research on rare earth elements (REEs) and unburned carbon removal by flotation from CFA is burgeoning, respectively. It will be beneficial if REEs could be rich in the flotation product with the carbon removal. In this study, the optimization of flotation for the unburned carbon removal was investigated and near 100% removal came true with loss on ignition of 56% and the yield of 7.7%. The optimal conditions contain rotation speed of 600 rpm and time of 30 min using the collector of 1200 g/t, the frother of 140 g/t, and the density of 130 g/t for the flotation. The majority of REEs occurred in the tailing after the flotation due to the low yield and REEs contents of the concentrates. The difference of REEs distribution in the tailing and concentrate is more significant in the milled sample. The morphology was also observed to explain the microscale behavior of REEs during the flotation.