• Advances in environmental research
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• 제5권2호
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• pp.125-140
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• 2016

The paper is focused on the economic analysis of two hydrometallurgical processes for recovery of yttrium and other rare earth elements (REEs) from fluorescent phosphors of spent lamps. The first process includes leaching with sulphuric acid and precipitation of a mixture of oxalates by oxalic acid, the second one includes leaching with sulphuric acid, solvent extraction with D2EHPA, stripping by acid and recovery of yttrium and traces of other rare earths (REs) by precipitation with oxalic acid. In both cases the REEs were recovered as oxides by calcination of the oxalate salts. The economic analysis was estimated considering the real capacity of the HydroWEEE mobile's plant ($420kg\;batch^{-1}$). For the first flow-sheet the cost of recycling comes to $4.0{\euro}kg^{-1}$, while the revenue from the end-product is around $5.40{\euro}kg^{-1}$. The second process is not profitable, as well as the first one, taking into account the composition of the final oxides: the cost of recycling comes to $5.2{\euro}kg^{-1}$, while the revenue from the end-product is around $3.56{\euro}kg^{-1}$. The process becomes profitable if the final RE oxide mixture is sold for nearly $50{\euro}kg^{-1}$, a value rather far from the current market prices but not so unlikely since could be achieved in the incoming years, considering the significant fluctuations of the Res' market.

• Applied Chemistry for Engineering
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• 제17권5호
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• pp.483-489
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• 2006

The behavior of rare earth compounds such as $La_{2}O_{3}$, $CeO_{2}$, and $Ca(OH)_{2}$ on the removal of fluoride and heavy metals in the steel wastewater has been investigated. The removal mechanism of fluoride by rare earth elements has been known to be the formation of insoluble compounds between $F^{-}$ and cations such as $La^{3+}$ and $Ce^{4+}$ produced by the dissociation of rare earth compounds (To reduce the running cost of the fluoride wastewater treatment facility, their fluoride removal efficiencies were compared with those of inexpensive rare earth minerals such as natural lanthanide and cerium compound used as a glass polishing agent). All of the rare earth oxides used in this study showed a higher removal efficiency of fluoride than $Ca(OH)_{2}$ in the wastewater. In the case of artificial HF solution, the removal efficiency of fluoride showed in the order: $CeO_{2}$-mineral < $CeO_{2}$ < $Ca(OH)_{2}$ < $La_{2}O_{3}$-mineral < $La_{2}O_{3}$. However, the removal efficiency of fluoride in the wastewater increased in the following order: $Ca(OH)_{2}$ < $CeO_{2}$ mineral < $CeO_{2}$ < $La_{2}O_{3}$ mineral < $La_{2}O_{3}$. All agents showed high efficiencies for the removal of Mn and total Cr in the rare earth compounds. In the case of $Ca(OH)_{2}$, fluoride removal decreased with increasing pH while. However, the rare earth compounds showed a higher fluoride removal in higher pH condition, the optimum pH condition seemed to be around 7 considering both water quality and fluoride removal. Under the pH 7 condition, the $Ca(OH)_{2}$ was superior to rare earth compounds in Mn removal and the lanthanide was superior to others in total Cr removal.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 한국방사성폐기물학회 2003년도 가을 학술논문집
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• pp.363-367
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• 2003

Much attention has been given to an electrochemical reduction process for converting uranium oxide to uranium metal in molten salt. The process has the versatility of being adopted for reducing other actinide and rare-earth metals from their oxides. Using the metal oxide to be reduced as a integrated cathode designed originally and inert conductors as anodes, oxygen anions are removed from the cathode and oxidized at the surface of the anodes in a molten salt cell. However, the electrochemical properties of alkali and alkali-earth metal oxides in molten salt have not been investigated thoroughly, which made the process incomplete when it is considered as a unit process in a back-end fuel cycle. It is well known that cesium and strontium Isotopes in spent fuel are main contributors for head load. The properties of cesium, strontium, and barium oxides such as the dissolution rates and reduction potentials in molten LiC1 dissolving $Li_2O$ are examined.

• Economic and Environmental Geology
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• 제56권3호
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• pp.259-275
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• 2023

Pan African granitoids of Kaiama is comprised of K-feldspar rich granites, porphyritic granites, and granitic gneiss that are intruded by quartz veins and aplitic veins and dykes which trend NE-SW. In order to establish the geochemical signatures, petrogenesis, and tectonic settings of the lithological units, petrological, petrographical, and geochemical studies was carried out. Petrographic analysis reveals that the granitoids are dominantly composed of quartz, plagioclase feldspar, biotite, and k-feldspar with occasional muscovites, sericite, and opaque minerals that constitute very low proportion. Major, trace, and rare earth elements geochemical data reveal that the rocks have moderate to high silica (SiO₂=63-79.7%) and alumina (Al₂O₃=11.85-16.15) contents that correlate with the abundance of quartz, feldspars, and biotite. The rocks are calc-alkaline, peraluminous (ASI=1.0-<1.2), and S-type granitoids sourced by melting of pre-existing metasedimentary or sedimentary rocks containing Al, Na, and K oxides. They plot dominantly in the WPG and VAG fields suggesting emplacement in a post-collisional tectonic setting. On a multi-element variation diagram, the granitoids show depletion in Ba, K, P, Rb, and Ti while enrichment was observed for Th, U, Nd, Pb and Sm. Their rare-earth elements pattern is characterized by moderate fractionation ((La/Yb)_N=0.52-38.24) and pronounced negative Eu-anomaly (Eu/Eu^*=0.02-1.22) that points to the preservation of plagioclase from the source magma. Generally, the geochemical features of the granitoids show that they were derived by the partial melting of crustal rocks with some input from greywacke and pelitic materials in a typical post-collisional tectonic setting.

• Journal of Powder Materials
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• 제19권6호
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• pp.429-434
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• 2012

With increase in operating temperature of gas turbine for higher efficiency, it is necessary to find new materials of TBC for replacement of YSZ. Among candidate materials for future TBCs, zirconate-based oxides with pyrochlore and fluorite are prevailing ones. In this study, phase structure and thermal conductivities of $(La_{1-x}Gd_x)_2Zr_2O_7$ oxide system are investigated. $(La_{1-x}Gd_x)_2Zr_2O_7$ system are comprised by selecting $La^{3+}/Gd^{3+}$ as A-site ions and $Zr^{4+}$ as B-site ion in $A_2B_2O_7$ pyrochlore structures. With powder mixture from each oxide, $(La_{1-x}Gd_x)_2Zr_2O_7$ oxides are fabricated via solid-state reaction at $1600^{\circ}C$. Either pyrochlore or fluorite or mixture of both appears after heat treatment. For the developed phases along $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions, thermal conductivities are examined, with which the potential of $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions for TBC application is also discussed.

• Journal of Surface Science and Engineering
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• 제55권6호
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• pp.368-375
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• 2022

YSZ (Yttria Stabilized Zirconia) is used as a thermal barrier coating material for gas turbines due to its low thermal conductivity and high fracture toughness. However, the operating temperature of the gas turbine is rising according to the market demand, and the problem that the coating layer of YSZ is peeled off due to the volume change due to the phase transformation at a high temperature of 1400℃ or higher is emerging. To solve this problem, various studies have been carried out to have phase stability, low thermal conductivity, and high fracture toughness in a high temperature environment of 1400℃ or higher by doping trivalent and tetravalent oxides to YSZ. In this study, the monoclinic phase formation behavior and crystallinity were comparatively analyzed according to the total doping amount of oxides by controlling the doping amounts of Sc₂O₃ and Gd₂O₃, which are trivalent oxides, and TiO₂, which are tetravalent oxides, in YSZ. Through comparative analysis of monoclinic phase formation and crystallinity, the thermal conductivity of the thermal barrier coating layer according to the amount of doping was predicted.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.171.2-171.2
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• 2015

Nowadays, trivalent rare-earth ($RE^{3+}$) ions activated metal oxides have been proved to be excellent host materials due to their various applications. Facile wet-chemical technique have been considered as the best synthetic route due its intensive interest in the preparation of nanostructures. Europium ion doped lanthanum hydroxide ($La(OH)_3:Eu^{3+}$) phosphors were synthesized by the facile wet chemical method using the hexamethylenetetramine (HMTA) as a mediated surfactant. The thermal behavior for the $La(OH)_3:Eu^{3+}$ phosphors was investigated by thermogravimetric and differential thermal analysis method. The morphological studies were measured by scanning electron microscope and transmission electron microscope measurements, indicating three-dimensional (3D) flower-like $La(OH)_3:Eu^{3+}$ nanorod bundles. After subsequent annealing process, the lanthanum oxide ($La_2O_3:Eu^{3+}$) phosphor exhibited similar kind of morphology. The synthesized $La(OH)_3:Eu^{3+}$ and $La_2O_3:Eu^{3+}$ samples were characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, photoluminescence and cathodoluminescence properties were studied in details.

• Journal of Powder Materials
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• 제26권5호
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• pp.415-420
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• 2019

SiAlON ceramics are used as ceramic cutting tools for heat-resistant super alloys (HRSAs) due to their excellent fracture toughness and thermal properties. They are manufactured from nitride and oxide raw materials. Mixtures of nitrides and oxides are densified via liquid phase sintering by using gas pressure sintering. Rare earth oxides, when used as sintering additives, affect the color and mechanical properties of SiAlON. Moreover, these sintering additives influence the cutting performance. In this study, we have prepared $Yb_{m/3}Si_{12-(m+n)}Al_{m+n}O_nN_{16-n}$ (m = 0.5; n = 0.5, 1.0) ceramics and manufactured SiAlON ceramics, which resulted in different colors. In addition, the characteristics of the sintered SiAlON ceramics such as fracture toughness and microstructure have been investigated and results of the cutting test have been analyzed.

• Applied Chemistry for Engineering
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• 제33권4호
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• pp.352-366
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• 2022

Nuclear power plant operations for electricity generation, rare-earth mining, nuclear medical research, and nuclear weapons reprocessing considerably increase radioactive waste, necessitating massive efforts to eradicate radioactive waste from aquatic environments. Cobalt (⁵⁸Co) and strontium (⁹⁰Sr) radioactive elements have been extensively employed in energy generation, nuclear weapon testing, and the manufacture of healthcare products. The erroneous discharge of these elements as pollutants into the aquatic system, radiation emissions, and long-term disposal is extremely detrimental to humans and aquatic biota. Numerous methods for treating radioactive waste-contaminated water have emerged, among which the adsorption process has been promoted for its efficacy in eliminating radioactive waste from aquatic habitats. The current review discusses the adsorptive removal of radioactive waste from aqueous solutions using low-cost adsorbents, such as graphene oxide, metal-organic frameworks, and inorganic metal oxides, as well as their composites. The chemical modification of adsorbents to increase their removal efficiency is also discussed. Finally, the current state of ⁵⁸Co and ⁹⁰Sr removal performances is summarized and the efficiencies of various adsorbents are compared.

• Journal of Powder Materials
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• 제29권3호
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• pp.252-261
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• 2022

Cobalt is a vital metal in the modern society because of its applications in lithium-ion batteries, super alloys, hard metals, and catalysts. Further, cobalt is a representative rare metal and is the 30th most abundant element in the Earth's crust. This study reviews the current status of cobalt extraction and recycling processes, along with the trends in its production amount and use. Although cobalt occurs in a wide range of minerals, such as oxides and sulfides of copper and nickel ores, the amounts of cobalt in the minerals are too low to be extracted economically. The Democratic Republic of Congo (DRC) leads cobalt mining, and accounts for 68.9 % of the global cobalt reserves (142,000 tons in 2020). Cobalt is mainly extracted from copper-cobalt and nickel-cobalt concentrates and is occasionally extracted directly from the ore itself by hydro-, pyro-, and electro-metallurgical processes. These smelting methods are essential for developing new recycling processes to extract cobalt from secondary resources. Cobalt is mainly recycled from lithium-ion batteries, spent catalysts, and cobalt alloys. The recycling methods for cobalt also depend on the type of secondary cobalt resource. Major recycling methods from secondary resources are applied in pyro- and hydrometallurgical processes.