• Resources Recycling
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• v.28 no.6
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• pp.26-35
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• 2019

This study aims to introduce and economical review on the possibilities of rare earth elements(REEs) recovery from coal ashes and the analysis of economical evaluation factors based on the data for securing domestic rare earth elements. The cut-off grade of REEs on recovering from coal ash was confirmed to be 1,000 ppm on total rare earth oxides(TREO) basis, and while the economic value of coal ash changed with contents and specific elements of rare earth elements. This shall be resulted in the price differences of rare earth elements required by the current industry, and it probably varies depending on the future demand of rare earth components. For developing of commercial recovery technology on REEs in coal ashes, many researches have been carried out by various analyzing methods, such as evaluation of holding value of REEs in ashes, assessment between supply and demand of industry, comparison of investment and its profitability for the REEs's production from coal ashes, and so on. Although these methods have been suggested, its recovery system with economical feasibility could not been confirmed up to present. In this reason, the process design of recovering REEs from coal ash shall be researched continuously to solve the problems of the global rare earth market. And also these researches shall be conducted actively in Korea for the purpose of securing the REEs resources and their recovering technologies.

• Journal of Bio-Environment Control
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• v.21 no.4
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• pp.452-458
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• 2012

Rare earth elements fertilizer and Ca were sprayed on eight-year-old 'Fuji'/M.9 apple trees during two consecutive seasons, and fruit quality was quantified at harvest and 5-month long storing in a commercial cooling house at $4^{\circ}C$ and 80~85% RH. In the first season, single-sprayed of rare earth elements fertilizer showed appreciable accumulations of its elements (La, Pr, Gd, and Nd) in the fruit. In the following season, application of higher doses accumulated higher amount, indicating that the accumulation of rare earth elements was dose-dependent. However, rare earth elements did not affect the accumulations of Ca, Mg, and K in 'Fuji' apple fruit showed that there was no interaction between rare earth elements and these macronutrients. Double-spray of 0.2% rare earth elements increased fruit redness at harvest and had exhibited better color. Although at harvest it did not show significant effects on fruit weight, pulp firmness and titratable acidity (TA), but had pronounced effects on inhibiting fruit softness and retarded decrease of TA during storing. Furthermore, it reduced respiration rate and inhibited ethylene production during storing indicated that rare earth elements may be an alternative for prolonging the shelf life of 'Fuji'/M.9 apple fruit.

• Resources Recycling
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• v.29 no.6
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• pp.3-14
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• 2020

This study aims to introduce and review on the recovery technologies of rare earth elements(REEs) from coal ash. Many researchers have been carried out by various beneficiation processes, such as particle size separation, magnetic separation, specific gravity, and flotation to recover rare earth elements from coal ash generated from Pulverized Coal(PC) boiler. Through the beneficiation process, it was confirmed that concentration of rare earth elements was much lower than the 4,700 ppm, and that additional enrichment treatment through wet process was needed for the products recovered after the beneficiation process. It was confirmed that the rare earth elements contained in coal ash were applied to the leaching process after pretreatment such as alkali-fusion to improve leaching efficiency. Although beneficiation and leaching methods have been studied, its optimum recovery technologies for rare earth elements not been confirmed up to now, research on the recovery of rare earth contained in coal ash is reported to continue. In case of Korea, the technology for the recovery of rare earth elements from coal ash and coal by-product could not been confirmed up to present. In these reasons, it is urgent to develop technologies such as beneficiation and leaching process continuously.

• Journal of the Korean Chemical Society
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• v.28 no.1
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• pp.47-53
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• 1984

The separation of the rare earth elements with diethylene triamine N, N, N', N', N"-pentaacetic acid (DTPA) as eluent was carried out at different pH and concentrations by using anion exchange resin column. The rare earth elements were absorbed on the upper of the resin column and the best condition of the separation behavior was 0.025M of DTPA at pH 8.35. The elution order of the rare earths was in the order of the atomic number of the rare earth elements except samarium. The resolution of adjacent rare earth elements that have been separated with 0.025M-DTPA as eluent, was from 3.03 to 1.25 at pH 8.35. Resolution of Ce-Pr was maximum value in 3.03 and Eu-Gd was minimum in 1.25 at condition mentioned above, respectively. The resolution of rare earth elements separated with 0.025M DTPA eluent was very good at pH range of 8.0~8.6.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.85-90
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• 2018

For the recovering rare earths in the spent nickel-metal hydride batteries, 10 M NaOH is added to the solution leached with sulfuric acid. The rare earth powders were precipitated at rate of 98 % at the condition of pH 2.0 or less. The recovered rare earth complex precipitate increased the leaching rate to nitric acid by heat treatment at $800^{\circ}C$ for 4 hours. Subsequently secondary precipitation was performed by adding oxalic acid to the solution in which the rare earth complex precipitate was dissolved. The re-precipitated rare earth powders were converted into oxide form through heat treatment at $800^{\circ}C$ for 4 hours with purity of 99.5 %.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.257-261
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• 2001

The separation of rare earths minerals is very difficult because of their similar chemical properties. The rare earth minerals are used as the mixed rare earth minerals or the misch metal without separation to each element. However, the high purity rare earths are recently produced commercially to each element so they there are used as the materials for high tech. Based on the characterization results for the raw minerals, we have developed a combined process containing gravity seperation, magnetic seperation and flotation. The result obtained from this study is monazite concentration of TREO grade 69.11% and Recovery 56.02%.

• Journal of the Korean Vacuum Society
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• v.5 no.4
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• pp.315-326
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• 1996

The electronic structures of 3d and 4d core-levels of rare-earth atoms in the insulating rare-earth (Sm, Eu, Gd, and Tb) compounds were studied with x-ray photoelectron spectroscopy(XPS). It is shown that the intrinsic satellite structure due to the hybridization disappears for chemically stable-earth trivalent heavy rare-earth insulating compounds as the hybridization between f electrons of rare-earth atoms and p electrons of anion atoms decreases due to the lanthanide contraction. Eu atoms at the surface of the stable insulating trivalent Eu compounds are found to be divalent. The satellite peak of Eu 3d core-level spectra at about 10eV higher binding energy side relative the main peak comes from the multiplet structures of $\underline{3d}4f^6$ configuration. The satellite structure appearing at about 15 eV higher binding energy side relative to the main peak in all insulating rare-earth compounds is due to an energy loss process of creating a plasmon.

• Journal of Powder Materials
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• v.22 no.1
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• pp.27-31
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• 2015

Flat panel display devices are mainly used as information display devices in the 21st century. The worldwide waste flat panel displays are expected at 2-3 million units but most of them are land-filled for want of a proper recycling technology More specifically, rare earth metals of La and Eu are used as fluorescent materials of Cold Cathode Flourscent Lamp(CCFL)s in the waste flat panel displays and they are critically vulnerable and irreplaceable strategic mineral resources. At present, most of the waste CCFLs are disposed of by land-filling and incineration and proper recovery of 80-plus tons per annum of the rare earth fluorescent materials will significantly contribute to steady supply of them. A dearth of Korean domestic research results on recovery and recycling of rare earth elements in the CCFLs prompts to initiate this status report on overseas research trends and noteworthy research results in related fields.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.379-384
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• 2017

An electrochemical reduction of a mixture of NiO and rare earth oxides has been conducted to increase the reduction degree of rare earth oxides. Cyclic voltammetry (CV) measurement was carried out to determine the electrochemical reduction behavior of the mixed oxide in molten LiCl medium. Constant voltage electrolysis was performed with various supplied charges to understand the mechanism of electrochemical reduction of the mixed oxide as a working electrode. After completion of the electrochemical reduction, crystal structure of the reaction intermediates was characterized by using an X-ray diffraction method. The results clearly demonstrate that the rare earth oxide was converted to RE-Ni intermetallics via co-reduction with NiO.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1178-1188
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• 1995

Bi4Ti3O12 (BIT) and its rare earth (Y, Nd, Sm, Gd)-substituted derivatives were synthesized using a sol-gel method to investigate their microstructures, cystal structures and electrical properties depending on the subsituted elemetns. Nd- or Sm-substitution into BIT appeared to be favorable, while Y- or Gd-substitution occurred with a pyrochlore phase. This suggests that a smaller trivalent rare earth ion may not be favorable in the structure of BIT. The rare earth derivatives showed that their particle sizes and shapes were considerably different depending on the kinds of substituted elements. Y-substitution resulted in developing a relatively even particle size and a dense microstructure. In structure, they may be similar to the pseudo-orthorhombic BIT but close to a paraelectric tetragonal phase. Their a (or b) axes were shortened, compared to the one of BIT. Such a distortion may result a decrease in the tilting of TiO6. BIT and the derivatives showed that their dielectric constants and losses were 40~120 and less than 0.03, respectively in the frequency range of 1~10 MHz. The dielectric loss of Y-substituted derivative was the lowest one and changed a little to frequency. Curie points were observed in all the derivatives like BIT to suggest that they would be ferroelectric. The temperature stability of the delectric properties of the derivatives below the Curie points were relatively better than the one of BIT.