Rare Earth Elements And Yttrium Content Research Articles

The mechanism study on the integrated process of NaOH treatment and citric acid leaching for rare earth elements recovery from coal fly ash

Rare earth elements and yttrium (REY) have vital functions in the global economy because of their numerous applications. Coal fly ash (CFA) is considered a potential alternative resource for REY. In this paper, sequential chemical extraction procedure, NaOH treatment, and citric acid leaching were used to study modes of occurrence, enrichment, and recovery of REY in CFA after physical separation. The proportion of REY (84%) bond to aluminosilicate phase in the separated sample is higher than that in the raw CFA. Monazite, apatite, scheelite, and aluminosilicate phase were proved to be REY carriers via SEM-EDS observation. REY in CFA was enrichment by NaOH treatment, and the glassy phase dissolution conformed to shrinking core model. The dissolution was first controlled by a chemical reaction and then inner diffusion, with activation energies of 70.89 and 3.21 kJ/mol and reaction orders of 1.02 and 0.73, respectively. The gel conjunction and zeolite generation limited CFA dissolution, concluded from the chemical reaction verification, SEM observation, and XRD analysis. The REY content after multi-step NaOH treatment increased to 2135 μg/g with an enriched factor of 2.08. Citric acid (0.05 mol/L) leaching was investigated and REY recovery is 55%. A conceptual integrated process of NaOH treatment and citric acid leaching for the CFA utilization was designed. This paper will provide a theoretical fundamental and technological support for REY recovery.

Sources of rare earth elements and yttrium in the early Cambrian phosphorites in Zhijin, southwest China

The early Cambrian Zhijin phosphorite in Guizhou province, China, has high rare earth elements and yttrium (REY) contents of up to 2500 ppm, with heavy REY (HREY) accounting for ∼30 % of the total REY. However, their REY sources are not well-determined. Herein, elemental geochemistry and Sr–Nd isotopes of phosphorites in four sections from the Zhijin phosphorite ore area were investigated, primarily to constrain the contributions of seawater and terrestrial REY sources to the REY enrichment in these phosphorites. Zhijin phosphorites have high Y/Ho (45–63) and seawater signature’s 87Sr/86Sr(i) ratios (0.7085–0.7092), suggesting a partial contribution from seawater-sourced REY. On the other hand, Zhijin phosphorites have εNd(t) values of −8.6 – −6.8, indicative of the great influence from continental weathering. The Y/Ho ratios exhibit negative correlations with their Zr contents and SmN/YbN ratios; meanwhile the 87Sr/86Sr(i) ratios exhibit positive correlations with their Sr contents and REY contents, indicating that terrestrial source contributions played an important role in REY enrichment in Zhijin phosphorites. Furthermore, the provenance of Zhijin shales indicates the terrigenous granite weathering, during which the regolith-hosted REY could be transported to Zhijin shallow seawater, providing abundant REY to Zhijin phosphorites. We proposed that the REY enrichment in Zhijin phosphorites could be associated with high REY seawater induced by granite weathering. This study provides a new perspective on the relationship between granite weathering and marine REY deposition, which may be a common phenomenon in geological history but remains to be fully investigated in future.

Assessment of the Effect of Organic Matter on Rare Earth Elements and Yttrium Using the Zhijin Early Cambrian Phosphorite as an Example

The geochemistry of rare earth elements and yttrium (REY) in phosphorite has been widely studied. However, the effect of organic matter on REY enrichment has not been well determined. We utilized paired inorganic (δ13Ccarb) and organic (δ13Ccarb) carbon isotopes, total organic carbon (TOC), and REY content (∑REY) of the Zhijin Motianchong (MTC) phosphorite and compared them with those of Meishucun (MSC) phosphorite to reveal the effect of organic matter on REY. The δ13Ccarb of the MTC area (≈0‰) is heavier than that of the MSC area (−5.23‰ to −1.13‰), whereas δ13Corg is lighter (−33.85‰ to −26.34‰) in MTC than in MSC (−32.95‰ to −25.50‰). Decoupled δ13Ccarb and δ13Corg in MTC indicate the contribution of chemoautotrophic organisms or methanotrophic bacteria. Compared to the MSC phosphorite, the MTC phosphorite has higher ∑REY and TOC, and these parameters have a positive relationship. MTC phosphorite has REY patterns resembling those of contemporary organic matter. Furthermore, dolomite cement has a higher ∑REY than dolomite in the phosphorus-bearing dolostone. Additionally, pyrites are located on the surface of fluorapatite in the Zhijin phosphorites. It is reasonable to suggest that the REY was released into the pore water owing to the anaerobic oxidation of organic matter at the interface between seawater and sediment, resulting in the REY enrichment of Zhijin phosphorites.

Geochemistry of REY-Enriched Phosphorites in Zhijin Region, Guizhou Province, SW China: Insight into the Origin of REY

The rare earth elements and yttrium (REY)-enriched phosphorites in the Zhijin region, southwest China, have attracted much attention, yet its origin has not been sufficiently addressed. The geology, mineralogy and geochemistry of samples from four sections of the early Cambrian age from the Zhijin region were studied to attain the redox condition and origin of REY. Data from in situ analysis show that REY are mainly contained in francolite, and the two types of francolite (bioclastic and granular) have no distinct difference in REY content (ΣREY). A Ce anomaly indicates an oxic condition in primary seawater. An Eu anomaly and ratios of redox sensitive elements (RSEs) indicate a fluctuating redox condition during phosphorite deposition. Shale-normalized REY patterns of whole rock and francolite show a hat-shaped pattern, indicating the effect of diagenetic processes. The Y/Ho ratio of the selected sections ranges from 38.13 to 61.93, and together with the Y anomaly, LaN/NdN ratio, LaN/SmN ratio, and LaN/YbN ratio, this indicates a seawater origin. This is supported by the Ce/Ce* of the phosphorite that ranges from 0.32 to 0.52 and the Eu/Eu* that ranges from 0.88 to 1.82, which is similar to the characteristics of seawater and deep-sea mud. We also propose a minor contribution of terrigenous debris and influence of diagenesis and hydrothermal processes.

Genetic model for early Cambrian reef limestone-hosted Pb-Zn deposits in the world-class Huayuan orefield, South China: New insights from mineralogy, fluorite geochemistry and sulfides in situ S-Pb isotopes

The Xiangxi-Qiandong metallogenic belt (>300 Mt sulfide ores @∼4.0 wt% Pb + Zn), located at the southeastern margin of the Yangtze Block, is one of the important Pb-Zn producers in China. Although carbonate-hosted Pb-Zn deposits in this district have attracted great attention during past decades, many issues, particularly the ore genesis and geodynamic setting, remain unclear. In this study, we take the Limei and Yutang deposits as typical case studies, using detailed geology, rare earth elements and yttrium (REY) geochemistry of fluorite and sulfides in situ S-Pb isotopes, to propose a new model for early Cambrian reef limestone-hosted Pb-Zn deposits in the district. REY contents (0.47 to 8.67 ppm; mean = 3.99 ppm) in fluorite from Limei and Yutang slightly deplete in LREE and HREE relative to MREE, indicating that the REEs and metals were transported predominantly as chloride complexes in a low-temperature (<200 °C) hydrothermal fluid with high saline. New δ34S values of sulfides (+27.66 to + 35.46‰ in Limei and + 24.80 to + 36.07‰ in Yutang) imply that S2- was originated from evaporite sulfate within ore-hosting strata via thermo-chemical reduction (TSR) as the presence of reducing agents (bioclastic limestone and organic matter). In situ δ34S values show a slightly large range (variation up to 11.27‰) and vary significantly within single grain (up to 4.60‰), which may be inherited from the S composition of H2S in the original fluid. In situ Pb isotopic ratios of sulfides from Limei (206Pb/204Pb = 18.001–18.269, 207Pb/204Pb = 15.645–15.796 and 208Pb/204Pb = 38.243–38.597) and Yutang (206Pb/204Pb = 18.135–18.384, 207Pb/204Pb = 15.714–15.924 and 208Pb/204Pb = 38.347–38.874) positively correlates in Pb-Pb diagrams, indicating the mineralizing metals are mainly derived from Proterozoic basement rocks with an amount of contribution from early Cambrian sedimentary rocks. Mineralogy, fluorite REY geochemistry and sulfides in situ S-Pb isotopes together with previously reported mineralization ages suggest that the mixing of metal-rich fluid from basement rocks and the H2S-rich fluid originated from ore-hosting strata plays an important role in forming the Pb-Zn deposits of Limei and Yutang. This study provides a typical example for better understanding the genesis and geodynamic setting of MVT deposits in the foreland basin, South China.

Mechanism and Influencing Factors of REY Enrichment in Deep-Sea Sediments

Deep-sea sediments with high contents of rare-earth elements and yttrium (REY) are expected to serve as a potential resource for REY, which have recently been proved to be mainly contributed by phosphate component. Studies have shown that the carriers of REY in deep-sea sediments include aluminosilicate, Fe-Mn oxyhydroxides, and phosphate components. The ∑REY of the phosphate component is 1–2 orders of magnitude higher than those of the other two carriers, expressed as ∑REY = 0.001 × [Al2O3] − 0.002 × [MnO] + 0.056 × [P2O5] − 32. The sediment P2O5 content of 1.5% explains 89.1% of the total variance of the sediment ∑REY content. According to global data, P has a stronger positive correlation with ∑REY compared with Mn, Fe, Al, etc.; 45.5% of samples have a P2O5 content of less than 0.25%, and ∑REY of not higher than 400 ppm. The ∑REY of the phosphate component reaches n × 104 ppm, much higher than that of marine phosphorites and lower than that of REY-phosphate minerals, which are called REY-rich phosphates in this study. The results of microscopic observation and separation by grain size indicate that the REY-rich phosphate component is mainly composed of bioapatite. When ∑REY &gt; 2000 ppm, the average CaO/P2O5 ratio of the samples is 1.55, indicating that the phosphate composition is between carbonate fluoroapatite and hydroxyfluorapatite. According to a knowledge map of sediment elements, the phosphate component is mainly composed of P, Ca, Sr, REY, Sc, U, and Th, and its chemical composition is relatively stable. The phosphate component has a negative Ce anomaly and positive Y anomaly, and a REY pattern similar to that of marine phosphorites and seawater. After the early diagenesis process (biogeochemistry, adsorption, desorption, transformation, and migration), the REY enrichment in the phosphate component is completed near the seawater/sediment interface. In the process of REY enrichment, the precipitation and enrichment of P is critical. According to current research progress, the REY enrichment is the result of comprehensive factors, including low sedimentation rate, high ∑REY of the bottom seawater, a non-carbonate depositional environment, oxidation conditions, and certain bottom current conditions.

Rare earth elements and yttrium in Pennsylvanian coals and shales in the eastern part of the Illinois Basin

The objective of this study was to evaluate rare earth elements and yttrium (REY) concentrations in Pennsylvanian coal-bearing strata in the eastern part of the Illinois Basin (Indiana), specifically targeting coals and marine shales associated with the coals. Samples were collected from several coal mines and three boreholes. In total, 105 samples were analyzed using inductively coupled plasma - optical emission spectrometry (ICP-OES), including 69 coals, 31 shales, and 5 paleosols. Concentrations of REY in the coals vary from less than 200 ppm to more than 3000 ppm (on ash basis). Indirect evidence, including REY versus ash relationships, REY distribution patterns, and REY content in raw coal compared to that in washed coal, suggests that the organic association may be an important mode of REY occurrence in these coals. The Lower Block and the Upper Block Coal Members of the Brazil Formation and some coals of the Staunton Formation have the highest REY concentrations among those studied. Concentrations of REY in marine shales range from less than 200 to 800 ppm on ash basis. The majority of shale samples studied vary little from the REY values of the continental crust, but some show enrichments. Our results suggest that, while post-combustion coal ash of the high-REY coals are a potential source of these elements, significant efforts and resources are needed to make the studied shales a viable REY resource.

Rare Earth Elements and Yttrium (REY) in coal mine drainage from the Illinois Basin, USA

The ever-growing demand in the USA and in the modern economy for rare earth elements, defined here as the lanthanide elements plus yttrium (REY), motivates the development of economically feasible and environmentally friendly approaches for domestic REY resources. Non-conventional sources, including coal mine drainage (CMD) hosting elevated concentrations of REY, have been explored as attractive secondary sources for metals recovery. Consequently, in this study we investigate CMD from abandoned coal mines in the Illinois Basin as a potential REY resource.We collected CMD from 35 abandoned coal mine sites in the Illinois Basin and investigated trends in REY enrichment and their association with CMD geochemical characteristics, including pH, the presence of other chemical elements of economic significance (i.e., Zn, Ni, Cr, Cu, V) as well as spatial patterns in relation to Permian magmatic intrusions of the Hicks Dome, a potential source of REY in the Illinois Basin. Additionally, the REY contents in possible source rocks for Illinois CMD were measured including coal from an underground mine and coal preparation plant in southern Illinois, mafic igneous rocks associated with Hicks Dome, and hydrothermal fluorite from Illinois fluorspar district.The REY concentrations in samples of CMD (filtered fraction) and associated coal and non-coal solids were determined by ICP-MS. The total concentration of REY in CMD, ΣREYCMD varied between 1 and 9879 μg/L with an average of 1059 μg/L and critical-ΣREYCMD (Nd, Eu, Tb, Dy, and Y) varied between 0.3 and 7212.5 μg/L with an average of 611 μg/L. Basin-wide, we found no statistical correlation between ΣREYCMD and (1) pH of the CMD, or (2) proximity to the Permian magmatic intrusion at Hicks Dome in southern Illinois. The REYCMD values normalized to North American Shale Composite (NASC) REYCMD/REYNASC exhibit enrichments in middle-REY for all CMD, but also enrichments in light-REY in some CMD. Statistically, we observed that ΣREYCMD displays significant direct correlations with Al, Si, SO4, Zn, Ni, Co, and Cu and no-correlation with Fe, Ca, PO4, Ba, and V.Synthesis of the geochemical data suggests that coal mining sites with the highest ΣREYCMD and critical-ΣREY contents include non-coal bedrock dominated by silicates (high clay content) and coal mine wastes that were impacted by metal-rich hydrothermal solutions, which are predominantly located along the western and northern margins of the Illinois Basin. Particularly, sites with the highest hydrothermal input as approximated by Mississippi Valley-type mineralization (i.e., Zn contents) are prime candidates for REY, as well as other elements of potential economic value such as Al, Ni, Cr, V, and Co. Thus, CMD in the Illinois Basin could become a potential alternative domestic source of extractable REY, especially critical-ΣREY, as well economically valuable metals.

The rare-earth elements distribution in the Bazhenov shales

The rare-earth elements and yttrium (REY) distribution data with depth in the Bazhenov formation are given for the case of the one well in the Nizhnevartovsk arch of the Western Siberia, Russian Federation. According to the correlation analysis, it was found that REY (mainly LREE) is concentrated in apatite more than in clays or plagioclase, while HREE is preferably accumulated in clay minerals. It was estimated that the water extracts from the Bazhenov formation contain REY up to 0.014 ppb, while LREE is contained in 3.6 times more than HREE. An attempt to estimate the REY content in the pore water of the Bazhenov formation was made using water extract composition data.

Study on the modes of occurrence of rare earth elements in coal fly ash by statistics and a sequential chemical extraction procedure

Rare earth elements and yttrium (REY) are strategically important materials in the defense, aerospace, automation and electronic industries, and therefore, REY has been referred as the “vitamin of industries.” The recovery of REY from coal fly ash has been recognized as a promising way to expand REY sources, and characterization of REY in coal fly ash will be critical for its subsequent exploitation and utilization. The work reported here investigates the modes of occurrences of REY in fly ash. Coal fly ash samples were collected from Guizhou Province. The results of the particle size classification showed that the content of total REY as well as that of individual components increased with a decrease in the particle size, and REY showed a moderate degree of enrichment in the smaller particles. The REY content was found to be a strongly and positively correlated with the content of silicon and aluminum through Pearson correlation and regression correlation analysis. A mathematical model between REY and Si/Al was established and this can be used to predict the content of REY with known Si and Al content. A sequential chemical extraction procedure for REY in coal fly ash was designed, and results from these tests showed that the silicate & aluminosilicate form was the dominant mode of occurrence of REY; this form accounted for 80% of the material. Hence the silicate & aluminosilicate form, which contains the most REY, must be the focus of subsequent recovery processes.