Enhanced electrical resistivity before N\'eel order in the metals, RCuAs2_2 (R= Sm, Gd, Tb and Dy

We report an unusual temperature (T) dependent electrical resistivity($\rho$) behavior in a class of ternary intermetallic compounds of the type RCuAs$_2$ (R= Rare-earths). For some rare-earths (Sm, Gd, Tb and Dy) with negligible 4f-hybridization, there is a pronounced minimum in $\rho$(T) far above respective N\'eel temperatures (T$_N$). However, for the rare-earths which are more prone to exhibit such a $\rho$(T) minimum due to 4f-covalent mixing and the Kondo effect, this minimum is depressed. These findings, difficult to explain within the hither-to-known concepts, present an interesting scenario in magnetism.Comment: Physical Review Letters (accepted for publication

Examining Perspectives On China\u27s Near-Monopoly Of Rare Earths

China’s behavior as a near-monopolist of rare earths has come under increasing scrutiny in recent years. This thesis first examines the underlying causes behind China’s rise to the status of rare-earths near-monopolist, including government support; lax environmental controls; unregulated production; and relatively low costs compared to the rest of the world. Second, the thesis also examines the preeminent international and domestic factors influencing China’s behavior as a near-monopolist of rare earths. International factors include international demand; international trade pressure; international price-setting authority issues; and geopolitical factors. I next identify domestic factors that exert influence over China’s rare earths-related behavior: environmental protection; rare earth resource protection; rare earths industry regulation; and protecting and aiding China’s domestic rare earths industry. The study concludes with a synthesis of the factors influencing China’s rare-earths-related behavior in the overall context of support and direction by China’s Central Government

ANION EXCHANGE SEPARATION OF TRIVALENT ACTINIDES AND LANTHANIDES

A process for separating americium and curium from rare earths by anion exchange based on selective chloride complexing was developed and tested on a laboratory scale. The separation is accomplished by sorption of americium, curium, and rare earths on Dowex 1-10X resin from a solution of 8 M LiNO/dub 3/ followed by selective elution of rare earths with 10 M LiCl and americium-curium elution with 1 M LiCl. In a laboratory demonstration of this process, greater than 99.5% of americium tracer containing no detectable amounts of rare earths was recovered. (auth

Rare Earth Production and Characterization Studies

The rare earths include elements Sc, Y, and La through Lu are important in many modern technologies. With the exception of Sc and Ce the rare earths are all have similar chemical behaviors with the preferred oxidation state in aqueous solution being +3. Currently, industrial purification of the rare earths is completed by counter current solvent extraction (CCSX). In most CCSX separations, Y extracts with Ho making their separation difficult. However, in a few systems Y exhibits an itinerant behavior. Carboxylic acids of varying sizes and substitutions were investigated in a study of Y itinerant behavior. It was found when carboxylic acids have only one branch that was an alkyl group Y extracted with the early rare earths. As branches are added to the carboxylic acid Y extracted with the heavier rare earths. This series of studies also investigated the rare earths with mechanochemical reactions. Lutetium oxyorthosilicate (LSO) was synthesized by mechanochemical methods using a planetary ball mill which is usually completed at high temperatures. It may be possible to reduce the rare earths using mechanochemical methods at room temperature with no solvents. Mechanochemistry may offer a new method of synthesizing rare earth compounds. The final study involved lowering the operational costs of the production of LSO. Iridium is used as the crucible for melting LSO. It is a platinum group metal with a high value. However, during the synthesis of LSO iridium is lost to the insulating material by a vapor deposition process. A method to recover this lost iridium was developed using a gravity concentration method

Recovery of mixed rare earth oxide and fine powder of metallic iron from spent NdFeB magnet of wind turbines

NdFeB magnet is used in various application such as generators, electric vehicles, hard disc, rare earth roll magnetic separator etc. due to its excellent magnetic properties. Currently, ~26% of rare earths produced worldwide are used for the production of NdFeB magnet, but less than 1% of the rare earths are recycled after completing their life cycle. Due to continuous increase in demand of rare earths and scarcity of their primary resources, end-of-life NdFeB magnet emanated as potential source of rare earths. Therefore, now-a-days research is primarily focused on the utilization of waste NdFeB magnets for recycling and recovery of valuables metals in the usable form. Investigation has been carried out to separate rare earth oxide and metallic Fe directly by magnetic separation after selective oxidation of rare earths in NdFeB magnet. But the magnetic separation is ineffective due to partial oxidation of iron. In the present study, the rare earths are recovered selectively during leaching from the roasted NdFeB magnet powder and the leach residue of iron oxide is utilized to produce fine powder of metallic iron. Mixed oxide of rare earths of 99% purity is obtained from the rare earth rich leach liquor. The reduction of the leach residues has been studied using waste graphite of spent electrodes of arc furnace as reductant, in horizontal tubular furnace at different temperature and for various time period. It is found that 93% of iron oxide reduces to fine powder of metallic iron. The fine powder obtained after reduction, has been characterized by XRD which confirm the conversion of iron oxide to metallic iron phase. Thus, the present investigation highlights the recovery of mixed rare earth oxide and fine powder of metallic iron obtained as valuables from waste NdFeB magnet, which can be utilized directly as raw material for the production of fresh magnet

Rare Earth Elements in Agriculture with Emphasis on Animal Husbandry

Calculations performed in consideration of a continuously increasing world population have revealed that animal production needs to be enhanced worldwide by at least 2 % each year so as to provide sufficient feed. Yet, effective growth promoting agents, in terms of in-feed antibiotics, have been completely banned throughout Europe due to the possible development and spread of multiresistance in bacteria. New efficient, safe and inexpensive feed additives are therefore needed in order to maintain or even further improve performance levels in animal husbandry. Based upon this information, rare earth elements have been considered as promising natural feed additive. Thus, this study was designed to bring together the current research on rare earths in order to analyze the data obtained and to facilitate the discussion of its relevance to agricultural utilization. The term rare earth elements comprises the elements scandium (21), yttrium (39), lanthanum (57) and the 14 chemical elements following lanthanum (58 -71) called lanthanoids. Favoring the tripositive oxidation state, rare earths present a high affinity for ionic bonding, thus a large number of both organic and inorganic rare earth salts may be formed. Nevertheless, rare earths may also form complexes especially with chelating oxygen ligands. In nature, rare earths occur in multiple minerals, such as bastnaesite and monazite which are mainly used for industrial production. Today, rare earths are part of several daily used devices such as lighters, television sets and computers. Additionally they are found in medical technology, nuclear engineering, automobile industry, military devices and even in spacecraft. Furthermore, rare earth-containing drugs are used for the treatment of hyperphosphatemia in chronic renal failure patients and for burn treatment. Based upon their paramagnetic properties, rare earths, especially gadolinium, have also been arranged as contrast agents in magnetic resonance imaging and computer tomography. In the future, among other uses, rare earths might be involved in cancer therapy, treatment and prevention of osteoporosis and atherosclerosis as well as organ transplantation. In China, rare earths have been successfully used at low concentrations as feed additives and fertilizers for decades. Yet, careful interpretation of Chinese data is recommended due to the fact that Chinese papers are often only available in native language and furthermore not up to standard with Western scientific research reports, hence lacking statistical treatment of data and details of experimental methods. However, in China, both yield increases and quality improvements were achieved in multiple plant species including cereals, fruits and vegetables after rare earth application. Recommended application rates vary with the crop species, the application technique (soil, foliar or seed dressing) as well as the timing. As feed additives, rare earths were shown to improve body weight gain and feed conversion in nearly all categories of farming animals (chickens, pigs, ducks, cattle). Additionally, improvements in milk production in dairy cows, in egg production in laying hens and in output and survival rate of fish and egg hatching of shrimps were noticed. Feed additives used thereby predominantly contain light rare earths (La, Ce, Pr, Nd) but even though both organic (nitrates, chlorides etc.) and inorganic (ascorbates, citrates etc.) rare earth feed additives are commercially available, organic ones are claimed to provide better results. Based on the effects reported in Chinese studies, experiments were initiated under Western conditions in order to investigate the action of rare earths on both plant and animal growth. Several Western feeding trials conducted on animals have been able to demonstrate significant performance enhancing effects after dietary rare earth application, while results obtained from experiments on the effects of rare earths on plant growth have been controversial. In pigs, improvements in body weight gain of up to 19 % and in feed conversion rate of 10 % were observed after their diets were supplemented with low-dosed rare earth chlorides. Even better effects were however noticed after rare earth citrates were added to the feed of pigs. Furthermore, under field conditions, rare earths were shown to increase body weight gain by up to 10 % and improve feed conversion by up to 9 % in pigs. Following these results, rare earth containing feed additives in terms of Lancer® have entered the market in Switzerland, where a temporary permission has been granted for their use in pig production. In addition, in broilers, rare earths were also shown to increase final weights by 7 % and improve feed conversion by up to 3 %. Very recent studies also confirmed performance enhancing effects in broilers with increased body weight gain and feed intake of up to 6.6 % and 6.9 %, respectively. In rats, which were used as a small animal model, improvements in body weight gain and feed conversion of 4 -7 % and 3 -11 %, respectively, followed the application of rare earths. Thus, clear performance enhancing effects were achieved in Western studies on rats, pigs and poultry due to dietary rare earth supplementation. However, there are also studies in which positive effects of rare earths on animal performance were not as obvious or not observed at all. A comparison between the results of these feeding experiments as to the mixture of rare earths, the concentration as well as the compound applied showed that these parameters are involved in the magnitude of performance enhancing effects of rare earths. At present, no definitive statement on optimum composition can be made. However, a dose-dependency was observed in several trials and better effects have been achieved when the mixture of rare earths was applied instead of single lanthanum. Additionally, it seems that organic rare earth compounds have a higher impact on animal performance than inorganic ones. This is probable ascribable to different chemical characteristics, which lead to variations in both absorption and bioavailability. Generally, absorption of orally applied rare earths is very low, with more than 95 % being recovered in the feces of animals. According to minute gastrointestinal absorption of rare earths, oral toxicity is very low and comparable to usual table salt. LD50 values determined in various animal experiments rang from 830 mg/kg to 10 g/kg body weight. None of the feeding trials performed reported any effects on the state of health of the animals, which coincides with low oral toxicity and additionally supports the safe application of rare earth feed additives to animals. In addition, no effects on either meat or carcass quality were observed. Likewise, rare earth concentrations determined in organ samples were very low and similar or even lower than in control animals. This is attributed to the ubiquitous occurrence of rare earths, thus also in plants and soils. As a result they also appear in commercial diets and subsequently in animal and human tissue. It has also been shown that rare earth contents in usual vegetable foodstuff are still higher than those in meat obtained from animals additionally fed with rare earths. Therefore, the application of rare earths as feed additive is also considered to be safe for humans. Furthermore, as to current knowledge, no damage is to be expected on the environment as a consequence of rare earth application to agriculture. In fact, as rare earths can improve feed conversion, they may support the efficient use of natural resources, while additionally reducing environmental loads in terms of animal excrements. Hence, with respect to animal, human and environmental safety, rare earths meet legal recommendations of the European Union for their registration as feed additive. Although the mechanism underlying performance enhancing effects of rare earths is not completely understood, several proposals have been made. According to current research, rare earths might exert their action locally within the gastrointestinal tract, including effects on the bacterial micro-flora as well as on nutrient uptake, digestibility and utilization. Likewise, anti-inflammatory and anti-oxidative effects may also contribute to positive effects. Additionally, actions on the intermediate metabolism in terms of effects on cellular functions, growth-and digestibility-related hormones and enzymes or the immune system have also been considered. It might also be possible that rare earths are not yet identified essential elements. Based on the information gained in this study, it has been concluded that rare earths are of high interest as possibly new, safe, inexpensive feed additive in Europe, especially in pig and poultry production

Leaching of rare earths from fine-grained zirconosilicate ore

© 2016 The Chinese Society of Rare Earths. Leaching of rare earths Y, La and Ce by sulphuric acid from fine-grained zirconosilicate ore was investigated using Taguchi method of experimental design. An orthogonal array of L8, 27 which denotes 7 factors at 2 levels was chosen to consider the various factors relevant to the leaching process: baking time, baking temperature, acid dosage, leaching time, leaching temperature, grind size and dilution. Statistical analysis showed that sulphation baking was a significant step for the leaching of rare earths from the whole-of-ore and optimized leaching of rare earths involved the following condition: baking for 3 h at 320 °C at 3.2 g acid/g ore acid dosage followed by water leaching at 20 °C for 1 h and dilution of 20 mL water/g ore using 300 um grind size. The effect of each leaching factor was also discussed

Evaluation Of Rare Earth Element Extraction From North Dakota Coal-Related Feed Stocks

The rare earth elements consist of the lanthanide series of elements with atomic numbers from 57-71 and also include yttrium and scandium. Due to their unique properties, rare earth elements are crucial materials in an incredible array of consumer goods, energy system components and military defense applications. However, the global production and entire value chain for rare earth elements is dominated by China, with the U.S. currently 100% import reliant for these critical materials. Traditional mineral ores including previously mined deposits in the U.S., however, have several challenges. Chief among these is that the content of the most critical and valuable of the rare earths are deficient, making mining uneconomical. Further, the supply of these most critical rare earths is nearly 100% produced in China from a single resource that is only projected to last another 10 to 20 years. The U.S. currently considers the rare earths market an issue of national security. It is imperative that alternative domestic sources of rare earths be identified and methods developed to produce them. Recently, coal and coal byproducts have been identified as one of these promising alternative resources. This dissertation details a study on evaluation of the technical and economic feasibility of rare earth element recovery from North Dakota lignite coal and lignite-related feedstocks. There were four major goals of this study: i) identify lignite or lignite-related feedstocks with total rare earth element content above 300 parts per million, a threshold dictated by the agency who funded this research as the minimum for economic viability, ii) determine the geochemistry of the feedstocks and understand the forms and modes of occurrence of the rare earth elements, information necessary to inform the development of extraction and concentration methods, iii) identify processing methods to concentrate the rare earth elements from the feedstocks to a target of two weight percent, a value that would be sufficient to leverage existing separation and refining methods developed for the traditional mineral ore industry, and iv) develop a process that is economically viable and environmentally benign. To achieve these overall goals, and to prove or disprove the research hypotheses, the research scope was broken down into three main efforts: i) sampling and characterization of potential feedstocks, ii) laboratory-scale development and testing of rare earth element extraction and concentration methods, and iii) process design and technical and economic feasibility evaluation. In total, 174 unique samples were collected, and several locations were identified that exceeded the 300 ppm total rare earth elements target. The results showed that on a whole sample basis, the rare earths are most concentrated in the clay-rich sediments associated with the coal seams, but on an ash basis in certain locations within certain coal seams the content is significantly higher, an unexpected finding given prior research. At Falkirk Mine near Underwood, North Dakota three coal seams were found to have elevated levels of rare earths, ranging from about 300 to 600 ppm on an ash basis. Additionally, exceptionally high rare earths content was found in samples collected from an outcropping of the Harmon-Hansen coal zone in southwestern North Dakota that contained 2300 ppm on an ash basis. The results dictated that extraction and concentration methods be developed for these rare earth element-rich coals, instead of the mineral-rich sediments. This effort also found that that at a commercial-scale, due to non-uniformity of the rare earths content stratigraphically in the coal seams, selective mining practices will be needed to target specific locations within the seams. The bulk mining and blending practices as Falkirk Mine result in a relatively low total rare earths content in the feed coal entering the Coal Creek Power Station adjacent to the mine. Characterization of the coal samples identified that the predominant modes of rare earths occurrence in the lignite coals are associations with the organic matter, primarily as coordination complexes and a lesser amount as ion-exchangeable cations on oxygen functional groups. Overall it appears that about 80-95% of rare earths content in North Dakota lignite is organically associated, and not present in mineral forms, which due to the weak organic bonding, presented a unique opportunity for extraction. The process developed for extraction of rare earths was applied to the raw lignite coals instead of fly ash or other byproducts being investigated extensively in the literature. Rather, the process uses a dilute acid leaching process to strip the organically associated rare earths from the lignite with very high efficiency of about 70-90% at equilibrium contact times. Although the extraction kinetics are quite fast given commercial leaching operations, there is some tradeoff between extraction efficiency and contact time. However, at shorter contact time there is improved rare earths selectivity that results in a more concentrated product due to limiting extraction of unwanted impurities. There is also a significant difference in the extraction kinetics for the more valuable heavier molecular weight rare earths, which are much faster than the light rare earths. The testing showed that in a one-step process consisting of leaching for two hours with 0.5M sulfuric acid at 40°C, a rare earth concentrate of about 1.4 weight percent rare earths could be achieved with about 70% total rare earths extraction, while also producing a residual coal byproduct that has superior qualities to the feed coal, such as reduced ash content. This represents a concentration factor of 24 over the feed coal. The target of two weight percent rare earths could be achieved by a number of secondary processing methods, such as pH modification or forced air oxidation to selectively precipitate impurities from the rare earths-containing solution. The process developed in this study is simple, highly effective, low cost and novel, with several differentiating benefits compared to methods being developed in the literature. These are made possible by the unique properties of North Dakota lignite coals and the weakly-bonded organic association of the rare earth elements. Key differentiators include the use of the raw coal as the feedstock, the ability to use a mild leaching process, and not needing extensive physical beneficiation processes prior to rare earths extraction. The process is environmentally benign and was demonstrated to be economically viable at the current market conditions. Due to the use of the raw coal as the feedstock, the process can be advantageously integrated with any number of coal utilization processes to augment economics, lower costs and maximize efficiency and synergies. This study evaluated a configuration of rare earths extraction combined with activated carbon production co-located at a combined heat and power facility, and was shown to have highly attractive economics even at small scales representing a first-of-a-kind demonstration system

Separation of the rare earths by anion-exchange in the presence of lactic acid

Investigation of adsorption of rare earths and a few other elements to an anion-exchange resin from mixed solvents containing lactic acid shows that the lanthanides are absorbed more strongly than from the alpha-hydroxyisobutryric acid system, but with less separation between adjacent members of the series

Quantitative separation of small amounts of rare earths from thorium, uranium, and zirconium by ion exchange

A successful method has been developed for the determination of certain rare earths in thorium in the fractional ppm range. The procedure is based on the ion-exchange chromatographic separation of the rare earths plus added yttrium carrier from the thorium, followed by emission spectrometric determination of the rare-earth impurities in the yttrium carrier. A simultaneous separation from the rare earths of the common element impurities present in the thorium has been accomplished. A high degree of compensation for procedural errors is achieved by the use of a pure rare earth as both the carrier in the separation and purification procedure and the matrix material in the spectrographic determination