Rare Earth Resources Research Articles

Mesoporous SiO2 Nanoparticles: A Unique Platform Enabling Sensitive Detection of Rare Earth Ions with Smartphone Camera

Fast and sensitive detection of dilute rare earth species still represents a challenge for an on-site survey of new resources and evaluation of the economic value. In this work, a robust and low-cost protocol has been developed to analyze the concentration of rare earth ions using a smartphone camera. The success of this protocol relies on mesoporous silica nanoparticles (MSNs) with large-area negatively charged surfaces, on which the rare earth cations (e.g., Eu3+) are efficiently adsorbed through electrostatic attraction to enable a “concentrating effect”. The initial adsorption rate is as fast as 4025 mg (g min)−1, and the adsorption capacity of Eu3+ ions in the MSNs is as high as 4730 mg g−1 (equivalent to ~ 41.2 M) at 70 °C. The concentrated Eu3+ ions in the MSNs can form a complex with a light sensitizer of 1,10-phenanthroline to significantly enhance the characteristic red emission of Eu3+ ions due to an “antenna effect” that relies on the efficient energy transfer from the light sensitizer to the Eu3+ ions. The positive synergy of “concentrating effect” and “antenna effect” in the MSNs enables the analysis of rare earth ions in a wide dynamic range and with a detection limit down to ~ 80 nM even using a smartphone camera. Our results highlight the promise of the protocol in fieldwork for exploring valuable rare earth resources.

Internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) revealed using 3D models of gravity and magnetic data

The Alnö Complex in central Sweden is one of the largest alkaline and carbonatite ring-shaped intrusions in the world. Presented here is the 3D models of ground gravity and aeromagnetic data that confirm some of the previous ideas about the 3D geometry of the complex but also suggest that the complex may continue laterally further to north than previously expected. The data show the complex as (i) a strong positive Bouguer anomaly, around 20 mGal, and (ii) a strong positive magnetic anomaly, exceeding 2000 nT. Magnetic structures are clearly discernible within the complex and surrounding area. Both gravity and magnetic inversion models suggest that dense (>2850 kg/m3) and magnetic (>0.05 SI) rocks extend down to about 3.5–4 km depth. Previous studies have suggested a solidified magma reservoir at this approximate depth. The inversion models further suggest that two apparently separate regions within the complex are likely connected at depth, starting from 800 to 1000 m, implying a common source for the rocks observed in these two regions. Modelling of the aeromagnetic data indicates that a >3 km wide ring-shaped magnetic high situated in the sea north of Alnö Island may be a part of the complex. This could link a smaller satellite intrusion in Söråker on mainland to the larger intrusion on Alnö Island. While the rim of the ring must consist of highly magnetic rocks to support the anomaly, the centre has relatively low magnetisation and is probably made up of low-magnetic wall-rocks or metasomatised wall-rocks down to about 2 km depth. Below this depth the 3D susceptibility model suggests higher magnetic susceptibility values. Worldwide alkaline and carbonatite complexes are the main resources for rare earth elements (REEs), and owing to the size of the Alnö Complex, it can be highly prospective for REEs at depth.

Electrochemical Formation of Dy Alloys in a Molten CaCl2-LiCl System

The molten salt electrochemical process has been studied by Ito and co-workers including the present authors and many other researchers. The authors reported a unique phenomenon during the electrochemical formation of Dy-Ni alloys in molten LiCl-KCl-DyCl3: DyNi2 film with thickness of 60 µm was formed in 2 h at 700 K. The growth rate of DyNi2 was extremely high, compared with the conventional solid phase diffusion at temperatures lower than half of the melting temperature of DyNi2, i.e., 1531 K. In addition, the growth rate was found to be strongly affected by electrochemical parameters such as potential and current density. This phenomenon was termed “electrochemical implantation”, because it was different from the ordinary concepts of electrodeposition followed by solid phase diffusion. The authors also reported that anodic polarization of the formed DyNi2 resulted in the rapid dissolution of Dy to form other Dy-Ni phases. The obtained phase and morphologies were dependent on the applied potential. This phenomenon was named “electrochemical displantation”. The use of rare earth (RE) - iron group alloys has increased significantly in a number of industrial fields over the past few decades. In particular, the demand for Dy-added Nd-Fe-B magnets is rapidly increasing because these magnets are indispensable for high-performance motors in electric vehicles and hybrid electric vehicles. These magnets need to possess sufficient thermal stability for use in such motors in high-temperature environments. The addition of Dy is necessary to improve the thermal stability of Nd-Fe-B magnets. However, there is the concern about a shortage of RE metals because of the uneven distribution of RE resources. Against this background, it is necessary to develop an inexpensive and environmentally friendly recovery/separation process for RE metals, especially the recovery of Dy and Nd from magnet scraps. We proposed a new separation and recovery process for RE metals from scraps using molten salt and an alloy diaphragm. The new process is based on our previously discovered phenomena, i.e., “electrochemical implantation” and “electrochemical displantation”. RE containing scrap is used as the anode. A RE-transition metal (TM) alloy is used as the diaphragm, which functions as a bipolar electrode. During electrolysis, all the RE metals in the anode are dissolved in the molten salt as RE ions. One or several specific RE ions are selectively reduced to form RE-TM alloys on the alloy diaphragm according to their formation potentials and/or alloying rates. Subsequently, the RE atoms chemically diffuse through the alloy diaphragm and are dissolved into the molten salt as RE ions in the cathode room. The permeated RE ions are finally deposited on the Mo or Fe cathode as RE metals. The RE ions remaining in the anode room can be collected by electrolysis using another cathode in the anode room. Almost all impurities remain in the anode room as residue or anode slime. This new process was first applied to chloride melts, and the separation of Dy from Nd and Pr were investigated using Cu, Ni and Zn cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 and LiCl-KCl-DyCl3-NdCl3-PrCl3 systems. The highest mass ratio of Dy/Nd+Pr in Dy-Nd-Pr-Ni alloy sample was found to be 50 at 0.65 V (vs. Li+/Li) for 1 h by ICP-AES. The present study focused on the electrochemical formation of Dy alloys in a molten CaCl2-LiCl system at 873 K. Furthermore, the separation of Dy and Nd was investigated with Fe electrodes.

Compound leaching behavior and regularity of ionic rare earth ore

Ammonium sulfate in situ leaching process is the most widely used extraction technology for ionic rare earth (RE) ores. Although the leaching process is simple, the leaching rate is satisfactory; moreover, the leaching solution has high impurities, serious ammonia pollution, and other problems. The leaching rate and leaching efficiency using a single ammonia-free leaching agent are low, particularly for low-grade complex ores. In this study, a leaching experiment and kinetic analysis of a combined leaching agent for an ionic RE ore with low grade and high impurity content were carried out.The results show that the leaching rate of RE3+ is 97.58%, and the concentration of Al3+ in the leaching solution is 0.016 g/L when a combined leaching agent composed of QZX-02 and ammonium sulfate (mass ratio of 7:3) was used to leach the ionic RE ore. Compared with using ammonium sulfate alone, the leaching rate of RE increased by 8.96%, and the concentration of Al3+ decreased by 0.069 g/L. Both of the leaching process of ammonium sulfate and the combined leaching agent are controlled by internal diffusion kinetics, and the apparent activation energies are 8.59 kJ/mol and 7.34 kJ/mol, respectively. The lower apparent activation energy makes the combined leaching agent possess a higher leaching efficiency. The analysis of Fourier transform infrared (FTIR) spectras and scanning electron microscopy (SEM) images indicate that the combined leaching agent and impurity ions could produce carboxylic acid organic compounds on the surface of clay minerals, with the result that the leaching of impurity ions is suppressed and the leaching efficiency of RE ions is improved. The application of this combined leaching agent can alleviate the ammonia pollution caused by the ammonium sulfate leaching process and effectively improve the utilization rate of RE resources.

Microstructure and magnetic properties of core-shell Nd-La-Fe-B sintered magnets

To balance the utilization of rare earth (RE) resource, abundant La has been incorporated into the Nd-Fe-B sintered magnets via the binary main phase (BMP) approach. Microstructure and magnetic properties of the Nd-La-Fe-B BMP magnets with increasing La substitution from 0 to 45 wt% were investigated. The results show that RE-rich intergranular phase with high oxygen content forms easily in the triple junction region for the La-substituted magnets. Those hcp-RE2O3 precipitates exhibit poor wettability with the matrix phase, leading to the direct exchange coupling of adjacent grains. As a result, the coercivity of Nd-La-Fe-B BMP magnets is dramatically reduced. Fortunately, the remanence can be maintained at a high level, ascribing to the inhomogeneous RE distributions among the grains (core-shell morphology), and the stable tetragonal phase after high-temperature sintering. With 27 wt% La substitution for Nd in the BMP magnet, the remanence decreases from 13.15 to 13.01 kGs by merely 1.06%. This work suggests that if one can optimize the microstructure by constructing magnetically isolated grains, low-cost Nd-La-Fe-B BMP magnets can be promising candidates for mass production.

The hydrothermal alteration of carbonatite in the Fen Complex, Norway: mineralogy, geochemistry, and implications for rare-earth element resource formation

ABSTRACTThe Fen Complex in Norway consists of a ~583 Ma composite carbonatite-ijolite-pyroxenite diatreme intrusion. Locally, high grades (up to 1.6 wt.% total REE) of rare-earth elements (REE) are found in a hydrothermally altered, hematite-rich carbonatite known as rødbergite. The progressive transformation of primary igneous carbonatite to rødbergite was studied here using scanning electron microscopy and inductively coupled plasma-mass spectrometry trace-element analysis of 23 bulk samples taken along a key geological transect. A primary mineral assemblage of calcite, dolomite, apatite, pyrite, magnetite and columbite with accessory quartz, baryte, pyrochlore, fluorite and REE fluorocarbonates was found to have transformed progressively into a secondary assemblage of dolomite, Fe-dolomite, baryte, Ba-bearing phlogopite, hematite with accessory apatite, calcite, monazite-(Ce) and quartz. Textural evidence is presented for REE fluorocarbonates and apatite breaking down in igneous carbonatite, and monazite-(Ce) precipitating in rødbergite. The importance of micro-veins, interpreted as feeder fractures, containing secondary monazite and allanite, is highlighted. Textural evidence for included relics of primary apatite-rich carbonatite are also presented. These acted as a trap for monazite-(Ce) precipitation, a mechanism predicted by physical-chemical experiments. The transformation of carbonatite to rødbergite is accompanied by a 10-fold increase in REE concentrations. The highest light REE (LREE) concentrations are found in transitional vein-rich rødbergite, whereas the highest heavy REE (HREE) and Th concentrations are found within the rødbergites, suggesting partial decoupling of LREE and HREE due to the lower stability of HREE complexes in the aqueous hydrothermal fluid. The hydrothermal fluid involved in the formation of rødbergite was oxidizing and had probably interacted with country-rock gneisses. An ore deposit model for the REE-rich rødbergites is presented here which will better inform exploration strategies in the complex, and has implications for carbonatite-hosted REE resources around the world.

A hierarchical clustering based method to evaluate reuse of rare earth tailings under cloud computing environment

Because of their unique electronic, magnetic and optical features, the rare earth has become an important strategic resource. Moreover, improving the exploitation of rare earth resources is very significant. To our knowledge, for the first time the hierarchical clustering technology under Map Reduce environment is utilized to process the experiment data of the tailings of rare earth ion in this paper. According to analyze of the experiment data, the leaching trend of rare earth ions in tailings under optimum conditions is researched. Finally, the data analysis shows that when the volume of sampling location is 400 ml, it can not only increase the concentration of rare earth ions in the leaching solution to ensure the economy and maneuverability of subsequent rare earth enrichment, but also insure the leaching rate of rare earth in the tailings and improve the utilization ratio of rare earth resources.

Effect of Heat Treatment on Microstructure and Magnetic Properties of Ce-Doped NdFeB Ribbons

The substitution for Nd by abundant element cerium (Ce) is a practical way for the comprehensive utilization of rare earth resources in NdFeB permanent magnets. In this letter, we have prepared the Ce-doped NdFeB ribbons and conventional NdFeB ribbons by melt quenching method and investigated the effects of heat treatment on the crystallization behavior, microstructure, and magnetic properties of the alloy. The results show that: (1) The crystallization behavior and the microstructural changes of the (Nd,Ce)FeB magnets are similar to the conventional NdFeB magnet when heat treatment. In addition, the Ce2Fe14B phase has a significant effect on the properties of the whole magnets. (2)The NdFeB phase and CeFeB phase are relatively close to each other after being precipitated from the amorphous phase. The coupling effect between the two phases is strong enough to weaken the effect of the addition of Ce and making the properties of the NdFeB magnets to not reduce too much after adding Ce.

A Semi-automatic System for Efficient Recovery of Rare Earth Permanent Magnets from Hard Disk Drives

Rare earth permanent magnets (REPMs) are essential components in many electrical and electronic products, including clean energy applications. Currently over 90% of the world's rare earth elements (REEs) are produced in China, leading many other countries to classify REES as critical materials. Recycling is one of the approaches to address the supply risks. Unfortunately, to date, the recycling rate of REPMs has been very low and no industrial scale recovery of REPMs from end of life products exists. As a result, REEs end up either in the landfill or in the smelting slag while other more “common” metals are recycled. One explanation for why REPMs have not been retrieved from used products is that it can be time consuming and expensive if the labor cost is high. This paper reports the development of a semi-automatic system for profitably recovering REPMs from hard disk drives to maximize REEs resource efficiency.

Elevated concentrations of naturally occurring radionuclides in heavy mineral-rich beach sands of Langkawi Island, Malaysia

Study is made of the radioactivity in the beach sands of Langkawi island, a well-known tourist destination. Investigation is made of the relative presence of the naturally occurring radionuclide 40K and the natural-series indicator radionuclides 226Ra and 232Th, the gamma radiation exposure also being estimated. Sample quantities of black and white sand were collected for gamma ray spectrometry, yielding activity concentration in black sands of 226Ra, 232Th and 40K from 451±9 to 2411±65Bqkg−1 (mean of 1478Bqkg−1); 232±4 to 1272±35Bqkg−1 (mean of 718Bqkg−1) and 61±6 to 136±7Bqkg−1 (mean of 103Bqkg−1) respectively. Conversely, in white sands the respective values for 226Ra and 232Th were appreciably lower, at 8.3±0.5 to 13.7±1.4Bqkg−1 (mean of 9.8Bqkg−1) and 4.5±0.7 to 9.4±1.0Bqkg−1 (mean of 5.9Bqkg−1); 40K activities differed insubstantially from that in black sands, at 85±4 to 133±7Bqkg−1 with a mean of 102Bqkg−1. The mean activity concentrations of 226Ra and 232Th in black sands are comparable with that of high background areas elsewhere in the world. The heavy minerals content gives rise to elevated 226Ra and 232Th activity concentrations in all of black sand samples. Evaluation of the various radiological risk parameters points to values which in some cases could be in excess of recommendations providing for safe living and working. Statistical analysis examines correlations between the origins of the radionuclides, also identifying and classifying the radiological parameters. Present results may help to form an interest in rare-earth resources for the electronics industry, power generation and the viability of nuclear fuels cycle resources.

Addressing Criticality in Rare Earth Elements via Permanent Magnets Recycling

Rare earth elements (REEs) are critical for many advanced technologies and are faced with potential supply disruptions. Recycling of permanent magnets (PMs) can be good sources for REEs which can help minimize global dependence on freshly mined REEs, but PMs are rarely recycled. Recycling of PMs has been discussed with respect to improving REEs resource sustainability. Some challenges to be addressed in order to establish industrially deployable technologies for PMs recycling have also been discussed, including profitability, energy efficiency and environmental impacts. Key considerations for promoting circular economy via PMs recycling is proposed with the focus on deciding the target points in the supply chain at which the recycled products will be inserted. Important technical considerations for recycling different forms of waste PMs, including swarfs, slags, shredded and intact hard disk drives magnets, have been presented. The aspects of circular economy considered include reusing magnets, remanufacturing magnets and recovering of REEs from waste PMs.

Rare Earth Elements Resources and Different Recovery Techniques from Egyptian Ores

Rare Earth Elements Resources and Different Recovery Techniques from Egyptian Ores

Exploring blast furnace slag as a secondary resource for extraction of rare earth elements

To explore blast furnace slag as a secondary resource for rare earth elements (REEs), blast furnace slag containing lanthanum (La), cerium (Ce), erbium (Er) and neodymium (Nd) in concentrations of 17, 16, 4 and 44 ppm, respectively, was processed with sulfuric acid while optimizing the parameters of acid concentration, temperature and pulp density. The experiments showed that recovery rates of 92, 36, 35 and 52 percent for La, Ce, Nd and Er, respectively, were achieved at 1 to 5 weight/volume (w/v) percent pulp density using particles smaller than 250 µm and treating with 1 M sulfuric acid for one hour at room temperature. Raising the temperature to 95 °C promoted the dissolutions of Ce and Nd to 89 and 84 percent, respectively, for the same 1 M acid concentration and one-hour duration at 5 w/v percent pulp density. Cyanex 923 was preferred over Cyanex 301 for the purification of REEs from leach liquor. In another route, the leach liquor was subjected to precipitation with 0.5 to 1 M oxalic acid, resulting in a product with 4 to 5 percent concentration of REEs.

Global Potential of Rare Earth Resources and Rare Earth Demand from Clean Technologies

Rare earth elements (REE) are widely used in high technologies, medical devices, and military defense systems, and are especially indispensable in emerging clean energy. Along with the growing market of green energy in the next decades, global demand for REE will increase continuously, which will put great pressure on the current REE supply chain. The global REE production is currently mainly concentrated in China and Australia; they respectively contributed 85% and 10% in 2016. However, there are 178 deposits widely distributed in the world, and reported REE resources as of 2017 totaled 478 megaton (Mt) rare earth oxides (REO); 58% of these deposits contained exceed 0.1 Mt REO; 59 deposits have been technically assessed. These resources could sustain the global REE production at the current pace for more than a hundred years. It is noted that REE demand from clean technologies will reach 51.9 thousand metric tons (kt) REO in 2030, Nd and Dy, respectively, comprising 75% and 9%, while these two elements comprise 15% and 0.52% of the global REE resources, respectively. This indicates that Nd and Dy will strongly influence the development of exploring new REE projects and clean technologies in the next decades.

Magnetic properties and microstructure of melt-spun Ce17Fe78−xB6Hfx (x = 0–1.0) alloys

Ce17Fe78−xB6Hfx (x=0–1.0) alloys were fabricated by a melt-spinning technique in order to study their magnetic properties and microstructure. Magnetic investigations of Ce17Fe78−xB6Hfx (x=0–1.0) alloys show that the room-temperature coercivity increases linearly from 352kA/m at x=0 to 420kA/m at x=1.0. The Curie temperature (Tc) decreases monotonically from 424.5K to 409.1K. The Ce L3-edge X-ray absorption near edge structure (XANES) spectrums reveal that there is more Ce4+ in ribbons under total electron yield (TEY) than fluorescence yield (FY). Hf addition has no effect on the weight of Ce3+ and Ce4+ in CeFeB-based alloys. The grain refinement and microstructure uniformity are essential for improving the magnetic properties of Hf-doped alloys. This paper may shed light on the further development of the Ce-based magnets and offer a feasible way for using the rare earth resources effectively.

Sources of Extraterrestrial Rare Earth Elements: To the Moon and Beyond

The resource budget of Earth is limited. Rare-earth elements (REEs) are used across the world by society on a daily basis yet several of these elements have <2500 years of reserves left, based on current demand, mining operations, and technologies. With an increasing population, exploration of potential extraterrestrial REE resources is inevitable, with the Earth’s Moon being a logical first target. Following lunar differentiation at ~4.50–4.45 Ga, a late-stage (after ~99% solidification) residual liquid enriched in Potassium (K), Rare-earth elements (REE), and Phosphorus (P), (or “KREEP”) formed. Today, the KREEP-rich region underlies the Oceanus Procellarum and Imbrium Basin region on the lunar near-side (the Procellarum KREEP Terrain, PKT) and has been tentatively estimated at preserving 2.2 × 108 km3 of KREEP-rich lithologies. The majority of lunar samples (Apollo, Luna, or meteoritic samples) contain REE-bearing minerals as trace phases, e.g., apatite and/or merrillite, with merrillite potentially contributing up to 3% of the PKT. Other lunar REE-bearing lunar phases include monazite, yittrobetafite (up to 94,500 ppm yttrium), and tranquillityite (up to 4.6 wt % yttrium, up to 0.25 wt % neodymium), however, lunar sample REE abundances are low compared to terrestrial ores. At present, there is no geological, mineralogical, or chemical evidence to support REEs being present on the Moon in concentrations that would permit their classification as ores. However, the PKT region has not yet been mapped at high resolution, and certainly has the potential to yield higher REE concentrations at local scales (<10s of kms). Future lunar exploration and mapping efforts may therefore reveal new REE deposits. Beyond the Moon, Mars and other extraterrestrial materials are host to REEs in apatite, chevkinite-perrierite, merrillite, whitlockite, and xenotime. These phases are relatively minor components of the meteorites studied to date, constituting <0.6% of the total sample. Nonetheless, they dominate a samples REE budget with their abundances typically 1–2 orders of magnitude enriched relative to their host rock. As with the Moon, though phases which host REEs have been identified, no extraterrestrial REE resource, or ore, has been identified yet. At present extraterrestrial materials are therefore not suitable REE-mining targets. However, they are host to other resources that will likely be fundamental to the future of space exploration and support the development of in situ resource utilization, for example: metals (Fe, Al, Mg, PGEs) and water.

On the Extraction of Rare Earth Elements from Geothermal Brines

The availability of rare earth elements from primary resources has come into question in the last two decades. This has sparked various government and industry initiatives to examine potential rare earth element resources apart from virgin ore bodies. Geothermal fluids are potentially significant sources of valuable minerals and metals, while co-recovery with geothermal energy production would be an attractive sustainable system. In this work, we give a brief survey of data collected on rare earth element concentrations in geothermal fluids. A survey of methods and technologies for extracting rare earth elements from geothermal is discussed along with the feasibility of recovering rare earth elements from geothermal brines. Based on the findings of this study, rare earth element extraction from geothermal fluids is technically possible, but neither economically viable nor strategically significant at this time.

Effect of Ga addition on the valence state of Ce and magnetic properties of melt-spun Ce17Fe78-xB6Gax (x = 0-1.0) ribbons

The Ce17Fe78-xB6Gax (x=0-1.0) ribbons were fabricated by a melt-spinning technique in order to study the mechanism of the valence variation of Ce and their magnetic properties as well as improve the thermal stability of Ce-based rare earth permanent magnets. The systematic investigations of the Ce17Fe78-xB6Gax (x=0-1.0) alloys show that the room-temperature coercivity increases significantly from 352 kA/m at x = 0 to 492 kA/m at x = 1.0. The Curie temperature (Tc) increases monotonically from 424.5 K to 433.6 K, and the temperature coefficients of remanence (α) and coercivity (β) of the ribbons are better off from -0.56 %/K, -0.75 %/K for x = 0 to -0.45 %/K, -0.65 %/K for x = 0.75 in the temperature range of 300–400 K, respectively. The Ce L3-edge X-ray absorption near edge structure (XANES) spectrums reveal that there is more Ce4+ in ribbons under total electron yield than fluorescence yield as Ce has a high affinity with oxygen. The weight of Ce3+ increases while the weight of Ce4+ decreases in Ga-added alloys. The refined grain size and a more uniform microstructure are mainly attributed to the improved magnetic properties and thermal stability with Ga doping. This paper may serve as a reference for further developing the so-called gap magnets and the effective utilization of the rare earth resources.

Effect of cerium ions initial distribution on the crystalline structure and catalytic performance of CeY zeolite

CeY samples with different cerium (Ce) ions initial distribution were prepared by diverse preparation processes. The correlative influence of Ce ions distribution on the intracrystalline structure and catalytic mechanism of Y-type zeolite was studied by X-ray diffraction (XRD), Rietveld refinement, X-ray fluorescence spectrometry (XRF), energy-dispersive X-ray spectroscopy (EDS), infrared (IR) spectra, NH3 temperature-programmed desorption (NH3-TPD), N2 physical adsorption-desorption and micro-activity test (MAT). The results indicated that Ce ions were concentrated on the surface (supercage) of CeY zeolite would reduce the number of acid sites and the ratio of Brönsted acid and Lewis acid (B/L). Once Ce ions concentrated in the sodalite cage, it would participate in the coordination with framework oxygen atoms under the condition of steric hindrance. Meanwhile, Ce ions would preferentially promote the B/L value of weak acid by retaining more intracrystalline framework Al atoms in sodalite cage, which was beneficial to the conversion of heavy oil in FCC process. The optimal initial-distribution of Ce ions could not only save the consumption of rare earth resources but also give the best catalytic performance of CeY zeolite catalysts, and these advantages and attributes enabled it to have the potential to be applied in industrial applications.

Rare-earth leaching from Florida phosphate rock in wet-process phosphoric acid production

Phosphorite, or phosphate rock, is the most significant secondary rare-earth resource. It contains high amounts of phosphate-bearing minerals along with low contents of rare earth elements (REEs). In Florida, about 19 Mt of phosphate rock are mined annually and most are used to manufacture fertilizers using a wet process, in which sulfuric acid reacts with phosphates to produce phosphoric acid and phosphogypsum. In the wet process, REEs are also leached out into solution and eventually get lost in the leaching residue and phosphate fertilizer. Recovering REEs from Florida phosphate rock in the wet process will be beneficial to broadening rare-earth availability, improving the quality of phosphoric acid product and protecting the environment. This study focuses on the influences of wet-process operating conditions on REE leaching efficiency. The results indicate that REE leaching efficiency increases with phosphoric acid addition in the initial pulp. At a temperature of 75 °C, a stoichiometric ratio of sulfuric acid (H2 SO4) to calcium oxide (CaO) of 1.05 and a weight ratio of liquid to solid of 3.5, REE leaching efficiency reached a relatively high value of 52.82 percent. The trends of REE leaching efficiency were similar to those for phosphoric acid (P2O5). Extensive tests on the leaching residue showed that during leaching, about 90 percent of the REEs were released from the phosphate rock but only 52.82 percent ended up in the leaching solution. This phenomenon can be attributed to two factors: (1) the effect of phosphate ions (PO 4 3- ) in the solution, which caused REE ions to form REE phosphates and be precipitated into the leaching residue, and (2) the influence of large amounts of anions such as sulfate (SO 4 2- ), dihydrogen phosphate (H2 PO 4 - ) and hydrogen phosphate (HPO 4 2- ) anions as well as the polar molecule H3 PO4, which surrounded the REE cations and formed an ion atmosphere that prevented the PO43- from contacting and combining with REE cations. Interaction of these two opposite effects determined the REE distribution between leaching solution and residue.