Precipitation Of Rare Earth Elements Research Articles

Chemical distribution of hazardous natural radionuclides during monazite mineral processing

It is very important to calculate the radioactivity concentration for low-grade monazite ore (50%) and different other materials produced as results of chemical processing stages to avoid the risk to workers. Chemical processing of low-grade monazite pass through different stages, washing by hydrochloric acid and digested with sulfuric acid and influence of pH on the precipitation of rare earth elements has been studied. The radioactivity concentrations of 238U(226Ra) and 232Th as well as 40K were calculated in crude low-grade ore and found to be 54,435 ± 3138, 442,105 ± 29,200 and 5841 ± 345 Bq/kg, respectively. These values are greatly higher than the exempt levels 25 Bq/kg. After chemical digestion of the ore, the results demonstrated that un-reacted material contains significant radioactivity reached to approximately 8, 13 and 23% for 238U, 232Th and 40K, respectively. The results show that 60% of 232Th are located in the digested white slurry with small portions of 238U and 40K. Most of 238U radioactivity is extracted in the green phosphoric acid which produced from conversion of P2O5 by H2SO4 into phosphoric acid. The average values of the Raeq for monazite ore, un-reacted black precipitate, white precipitate, brown precipitate and crystalline material samples were calculated and found to be 687,095 ± 44,921, 85,068 ± 5339, 388,381 ± 22,088, 313,046 ± 17,923 and 4531 ± 338 Bq/kg, respectively. The calculated values of Raeq are higher than the average world value (it must be less than 370 Bq/kg). Finally the external hazardous, internal hazardous and Iγr must be less than unity. This means that specific radiation protection program must be applied and implemented during monazite processing.

PRODUCTION OF RARE EARTH ELEMENTS FROM MALAYSIAN MONAZITE BY SELECTIVE PRECIPITATION

Rare earth elements (REEs) are very valuable and have high demands for advanced technology nowadays. REEs can be classified to light rare earth elements (LREEs) and heavy rare earth elements (HREEs). Malaysian rare earth ore especially monazite, is rich with LREEs compared to HREEs. Therefore a study was carried out to extract the REE from Malaysian monazite. The objectives of this study are to determine the content of REEs in Malaysian monazite leach solution, as well as to produce high grade of REEs. Concentrated sulphuric acid was used in digestion process and the filtrate containing the REEs was determined using Inductively Coupled PlasmaMass Spectrometry (ICP-MS). Ammonia solution was used for REEs precipitation from monazite leach solution. The result indicated that REEs was successfully separated from monazite leach solution through selective precipitation using ammonia at pH 2.34 and the percentage of REEs that successfully separated was 70.03 – 81.85%. The percentage of REEs which successfully separated from final solution was 96.05 – 99.10%. Therefore, to have high purification of individual REEs, solvent extraction process should be carried out.

Mineralogical and geochemical studies of brecciated ores in the Dalucao REE deposit, Sichuan Province, southwestern China

The Dalucao deposit, located in western Sichuan Province, southwestern China, in the western part of the Yangtze Craton, is one of the largest and most extensive rare earth element (REE) deposits in the Himalayan Mianning–Dechang REE belt. Moreover, the Dalucao deposit is the only deposit identified in the southern part of the belt. The Dalucao deposit contains the No. 1, 2, and 3 orebodies; the No. 1 and 3 orebodies are both hosted in two breccia pipes, located in syenite–carbonatite host rocks. Both pipes have elliptical cross-sections at the surface, with long-axis diameters of 200–400m and short-axis diameters of 180–200m; the pipes extend downwards for >450m. No. 1 and No. 3 have total thickness varying between 55 and 175m and 14 to 58m respectively. The REE mineralization is associated with four brecciation events, which are recorded in each of the pipes. The ore grades in the No. 1 and 3 orebodies are similar, and consist of 1.0%–4.5% rare earth oxides (REOs). The No. 1 orebody is characterized by a Type I mineral assemblage (fluorite+barite+celestite+bastnäsite), whereas the No. 3 orebody is characterized by a Type II assemblage (fluorite+celestite+pyrite+muscovite+bastnäsite+strontianite). Argon (40Ar/39Ar) dating of hydrothermal muscovite intergrown with REE minerals in typical ores from the No. 1 and 3 orebodies yielded similar ages of 12.69±0.13 and 12.23±0.21Ma, respectively, which suggest that both mineral assemblages formed coevally, rather than in paragenetic stages. Both ages are also similar to the timing of intrusion of the syenite–carbonatite complex (12.13±0.19Ma). The ore-mineral assemblages occur in breccias, veinlets, and in narrow veins. The ore veinlets, which usually show a transition to mineralized breccia or brecciated ores, are commonly enveloped by narrow veins and stringer zones with comparable mineral assemblages. The brecciated ores form 95% of the volume of the deposit, whereas brecciated ores are only a minor constituent of other deposits in the Mianning–Dechang REE belt. The carbonatite in the syenite–carbonatite complexes contains high concentrations of S (0.07–2.32wt.%), Sr (16,500–20,700ppm), Ba (3600–8400ppm), and light REEs (LREE) (2848–10,768ppm), but is depleted in high-field-strength elements (HFSE) (Nb, Ta, P, Zr, Hf, and Ti). The syenite is moderately enriched in large-ion lithophile elements (LILE), Sr (155–277ppm), and Ba (440–755ppm). The mineralized, altered, and fresh syenites and carbonatites exhibit similar trace element compositions and REE patterns. Brecciation events, and the Dalucao Fault and its secondary faults around the deposit, contributed to the REE mineralization by facilitating the circulation of ore-forming fluids and providing space for REE precipitation. Some hydrothermal veins composed of coarse-grained fluorite and quartz are distributed in the syenite–carbonatite complex. The oxygen isotope compositions of ore-forming fluids in equilibrium with quartz at 215°C are −4.95‰ to −7.45‰, and the hydrogen isotope compositions of fluid inclusions in coarse-grained quartz are −88.4‰ to −105.1‰. The syenite–carbonatite complex and carbonatite are main contributors to the mineralization in the geological occurrence. Thus, the main components of the ore-forming fluids were magmatic water, meteoric water, and CO2 derived from the decarbonation of carbonatite. According to the petrographic studies, bastnäsite mineralization developed during later stages of hydrothermal evolution and overprinted the formation of the brecciated fluorite–quartz hydrothermal veins. As low-temperature isotope exchange between carbonates of the carbonatite and water-rich magmatic fluids will lead to positive shifts in δ18O values of the carbonates, C–O isotopic compositions from the bulk primary carbonatite to hydrothermal calcite and bastnäsite changed (δ18OV-SMOW from 8.0‰ to 11.6‰, and δ13C V-PDB from −6.1 to −8.7‰). According to the chemical composition of syenite and carbonatite, REE chloride species are the primary complexes for the transport of the REEs in the hydrothermal fluids, and the presence of bastnäsite and parisite means the REE were precipitated as fluorocarbonates. High contents of Sr, Ba and S in the syenite–carbonatite complex led to the deposition of large amount of barite and celestite.

Recovery of rare earth elements from wet process extraction phosphoric acid

It is shown that an increase in the recovery of rare earth elements in fluorophosphate concentrates, which are obtained by treating the wet process phosphoric acid by ammonium fluoride, is achieved by prior partial neutralization of H3PO4 by ammonia. Therewith the consumption of ammonium fluoride is reduced that provides almost complete precipitation of rare earth elements.

A study of differentiation pattern and rare earth elements migration in geochemical and hydrogeochemical environments of Airekan and Cheshmeh Shotori areas (Central Iran)

The Airekan and Cheshmeh Shotori areas are located about 60 km northeast of Khour, in Isfahan province from Central Iran. Research on characteristics and rare earth elements (REE) pattern in hydrogeochemical environments of these areas suggests the same origin for the elements dissolved in groundwater in these areas. Investigation of migration pattern of REE in hydrogeochemical environments shows that the migration and transportation of REE has occurred through chloride complexes. REEs, leached by water/rock interaction from the Airekan granite, are transported by groundwater and then precipitated in the Cheshmeh Shotori area. Study of the Cheshmeh Shotori sediments shows the presence of a sequence of red oxidized and dark layers. Geochemical characteristics of these sediments reveal that their REE characteristics are mainly inherited from the Airekan granite. Changes in the REE pattern of these sediments with depth show that changes in oxidation and reduction process have not played a significant role in controlling their behavior. It is crucial to note that adsorption of REEs dissolved in water by hydrosilicate increases these elements in depth. The REE behavior shows water/rock interaction between the granitic rocks and groundwater as the main factor of solution, migration and precipitation of REEs in the Cheshmeh Shotori area.

Extraction of some strategic elements from thorium–uranium concentrate using bioproducts of Aspergillus ficuum and Pseudomonas aeruginosa

The activity of the bioproducts from Aspergillus ficuum and Pseudomonas aeruginosa for extraction of thorium (Th4+), uranium (UO22+) and rare earth elements (REEs) from thorium–uranium concentrate was studied. P. aeruginosa produce element-specific ligand (siderophore) that is able to change pH and enhance chelation of Th4+ and UO22+. The produced siderophore at pH 5.3 has the ability to bioleach and is complexed with 68.00% of uranium and 65.00% of thorium. Also, A. ficuum produced different kinds of organic acids which leached 30.00% of uranium and 29.12% of thorium in addition to 20.00% of lanthanum, 33.00% of cerium and 2.51% of yttrium as rare earth elements at pH 3.0. Oxalic acid was efficient for Th4+, UO22+and REEs precipitation. The binocular stereo-microscope (BSM), environmental scanning electron microscope (ESEM) and X-ray diffraction (XRD) analyses confirmed the percentages of extracted metals. Exogenous polysaccharides (EPSs) seem to play an important role in bioleaching and removal of these elements. It was found that EPSs produced by A. ficuum adsorbed Th4+, UO22+ and REEs while that produced by P. aeruginosa adsorbed REEs only.

Removal of ammonia nitrogen from washing wastewater resulting from the process of rare-earth elements precipitation by the formation of struvite

This paper presents a study of the removal of ammonia nitrogen (NH3-N) from washing wastewater resulting from the process of rare-earth elements precipitation using struvite precipitation. Experiments were conducted in batches to examine the effect of an excess of magnesium and phosphate on the removal of NH3-N, and to investigate the feasibility of the reuse of the produced struvite for NH3-N removal. Experimental results showed that any separate excess of magnesium and phosphate did not provide significant increase in NH3-N removal. However, a simultaneous excess of magnesium and phosphate can provide an obvious increase in NH3-N removal, with the remaining NH3-N as a minimum of 8.7 mg/L at the Mg:N:P molar ratio of 1.2:1:1.2. A stable NH3-N concentation of effluents (around 15 mg/L) was maintained through recycling struvite for six cycles. (In each cycle, fresh magnesium and phosphate was supplemented for keeping a steady Mg:N:P molar ratio (1.2:1:1.2) and the decomposition residue of struvite was diss...

Accumulation and fractionation of rare earth elements (REEs) in wheat: controlled by phosphate precipitation, cell wall absorption and solution complexation

Previous studies on rare earth element (REE) bioaccumulation have focused on their accumulation rate and fractionation, but the processes involved remain unclear. In this study, the accumulation and fractionation of REEs in wheat (Triticum aestivum L.) were investigated using solution culture with exogenous mixed REEs. A decrease in REE contents was observed from the roots to the tops of wheat. Significant fractionations of REEs were found in wheat organs as compared to the exogenous mixed REEs. Middle REE (MREE, the elements from Sm to Gd) enrichment and an M-type tetrad effect (an effect that can cause a split of REE patterns into four consecutive convex segments) were observed in the roots, which were probably caused by phosphate precipitation of REEs in/on the roots and absorption of REEs to root cell walls. Light REE (LREE, the elements from La to Eu) and heavy REE (HREE, the elements from Gd to Lu) enrichments were observed in the stems and leaves, respectively, accompanied by conspicuous W-type tetrad effects (an opposite effect to the M-type tetrad effect) in the REE patterns. HREE enrichment decreased from the older to the younger leaves and increased upwards within a single leaf. It is suggested that the solution complexation that occurred in the xylem vessels plays an important role in REE fractionations in the above-ground parts of wheat.

Rapid development of negative Ce anomalies in surface waters and contrasting REE patterns in groundwaters associated with Zn–Pb massive sulphide deposits

Ground and surface waters collected from two undisturbed Zn–Pb massive sulphide deposits (the Halfmile Lake and Restigouche deposits) and active mines in the Bathurst Mining Camp (BMC), NB, Canada were analysed for the rare earth elements (REE). REE contents are highly variable in waters of the BMC, with higher contents typical of waters with higher Fe and lower pH. There are significant differences between ground- and surface waters and between groundwaters from different deposits. The REE contents of surface waters are broadly similar within and between deposit areas, although there are spatial variations reflecting differences in pH and redox conditions. Surface waters are characterised by strong negative Ce anomalies ([Ce/Ce*] NASC as low as 0.08), produced by oxidation of Ce 3+ to Ce 4+ and preferential removal of Ce 4+ from solution upon leaving the shallow groundwater environment. Groundwaters and seeps typically lack significant Ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that Ce oxidation is a rapid process in the surface waters. Deeper groundwaters at the Halfmile Lake deposit are characterised by REE patterns that are similar to the host lithologies, whereas most groundwaters at the Restigouche deposit have LREE-depleted patterns compared to NASC. Halfmile Lake deposit groundwaters have generally lower pH values, whereas Restigouche deposit groundwaters show greater heavy REE-complexation by carbonate ions. Shallow waters at the Halfmile Lake and Stratmat Main Zone deposits have unusual patterns which reflect either the adsorption of light REE onto colloids and fracture-zone minerals and/or precipitation of REE–phosphate minerals. Middle REE-enrichment is typical for ground- and surface waters and is highest for neutral pH waters. The labile portion of stream sediments are generally more middle REE-enriched than total sediment and surface waters indicating that the REE are removed from solution by adsorption to Fe- and Mn-oxyhydroxides in the order middle REE≥light REE>heavy REE.

Multielement Preconcentration of Rare Earth Elements for Their Determination at ppm-Levels in Geological Samples

AbstractA preconcentration procedure is reported for rare earth elements suitable for concentration levels generally found in rocks. This method is of geochemical interest because the abundance of rare earth elements gives important clues to the origin of rock formations.The procedure is based on an anion-exchange separation step followed by a precipitation of rare-earth elements chelates onto a membrane filter. For the investigation of recovery a combined radionuclide tracer and X-ray sensitivity method was used. Detection limits in the sub-μg/g-range are reported.

Experimental studies of the form of transport and the precipitation conditions for REE in sea water

In this paper, some experimental studies on the modes of occurrence and the conditions of transport and precipitation of rare-earth elements (REE) in sea water have been made. The results show that the ions of REE and carbonate radicles can be combined into quite stable and soluble complexes in the medium of weak alkalinity. REE precipitation may result from the dissociation of REE complexes during the evolution of solutions from weakly alkaline to neutral or slightly acidic and in the presence of precipitants for REE, such as P, Ba, Ca, and Mg. That is why REE can be concentrated in carbonate formations. Experimental results also show that REE will be precipitated in the form of phosphate or F-carbonate in the presence of [PO4]3− and F− in the solution. Our experimental results are consistent with the geological characteristics of some REE deposits.

Rare earths in barites: distribution and effects on aqueous partitioning

A large variety of barites collected from marine and continental environments was analyzed by neutron activation for the rare-earth elements (REE) La, Ce, Sm, Eu and Dy. Relative to chondrites, all barites show a decrease of the lighter REE from La toward Eu. The abundance and distribution of rare earths in barites show a distinction of barite types. Deep-sea barites have large REE concentrations as do other authigenic deep-sea minerals and display the chondrite normalized Eu minimum, but not the negative Ce anomaly, of sea water. Other barites, mostly on land, some hydrothermal, and others of shallow marine origin, display lower total Ree concentrations. Chondrite normalized positive Eu anomalies are displayed by those varieties of reducing sedimentary and metamorphic origin. Distribution of REE in barite can be attributed both to crystallographic constraints of substitution, and to solution complexing of REE in the precipitating medium. Plots of rare earth partitioning versus effective ion size suggest that the decreasing enrichment toward Eu for all barite types is caused by crystallographic constraints due to contraction of the substituting REE ion sizes relative to the size of the host Ba ion. Solution effects on REE substitution in barite can be evaluated by writing solid solution distribution equations based on mass action of REE and Ba sulfates and the lanthanide (Ln) solution species Ln (CO 3) −5 4), LnSO + 4, LnCl +2 and LnF +2. Under normal sea water conditions, solution complexing plays a minor role. However, increased alkalinities of reducing sediments and increased brine chlorinities could cause significant complexing and deplete REE heavier than Eu. Besides Dy in barites, this could be true for aqueous precipitation of REE in general.