RECOVERY OF RARE EARTH ELEMENTS FROM COMPLEX ORES IN TURKEY AND THEIR
POTENTIAL USE IN HIGH TECH INDUSTRIAL APPLICATIONS – Acronym RETECH

Project M – ERAMIN III
Acronym: RETECH
Contract 179 / 01.09.2020
Funding Agency: UEFISCDI ROMANIA

PARTNERS

1. RARE EARTH ELEMENTS RESEARCH INSTITUTE, ANKARA, TURKEY, Coordonator
2. NATIONAL R&D INSTITUTE FOR NON-FERROUS AND RARE METALS – IMNR, ROMANIA
3. GENERAL DIRECTORATE OF MINERAL RESEARCH AND EXPLORATION, ANKARA, TURKEY
4. RUMELISIAD GIRISIM A.S., BURSA, TURKEY
5. NATIONAL R&D INSTITUTE FOR METALS AND RADIOACTIVE RESOURCES – INCDMRR, ROMANIA

      the overall objective of the project is to conduct R&D studies and develop efficient technologies for valorisation of REEs from existing complex ores, which will contribute to establish a sustainable REE supply chain in Turkey and Europe.
Through this project mineralogical, chemical and metallurgical studies related to integrating a full-scale enrichment research on industrial R&D projects will be conducted in Turkey. This project brings the opportunity to supply an alternative source of REE for Europe and Turkey.
Obtaining strategically important REE from a deposit located in Turkey nearby to Europe can reduce dependency of our country and EU to overseas markets, especially to China largest supplier by introducing an alternative source and also it can ensure to have a sustainable and competitive supply chain and/or supply security. Based on policy of EU and Turkey created for ensuring diversity in energy source reducing dependency on foreign energy, results of this study will provide socio-economic impact and it will lead important achievements in technological progress.

STAGE 1    2020

RESEARCH TO OBTAIN OXIDE MATERIALS DOPED WITH RARE EARTH OXIDES

STAGE 2    2021

DEVELOPMENT OF LABORATORY TECHNOLOGY FOR OBTAINING SYSTEMS OF OXIDE MATERIALS
DOPED WITH RARE EARTH OXIDES IN THE FORM OF THIN FILMS

ZrO2 powders co-doped with 8% gr. Y2O3 and 4, 6 and 8% gr. oxides of La, Nd, Sm and Gd were hydrothermal synthesized. The obtained powders consist of a mixture of cubic yttrium oxide and zirconium as the main phase and monoclinic ZrO2 with the typical structure of natural Baddeleyite, except for the initial powders doped with 4, 6 and 8% by weight Nd, where only the cubic phase was formed. These results confirm the previous results, showing that the hydrothermal synthesis of zirconia nanopowders doped with ytria favors the stabilization of the cubic phase at low temperatures.
The evolution of the crystalline phases depending on the composition and temperature shows a clear trend towards the formation of cubic solid solutions with different compositions. The stability of cubic zirconia with increasing temperature is well known and is explained by the lower surface energy of cubic symmetry. The cubic phases formed in 8YSZ-codopath by 4.6 and 8% by weight Ln2O3 (Ln = La, Nd, Sm, Gd) can be classified into three types of solid solutions, depending on the dopant concentration: (Ln0.07Y0.14Zr0.79)O1.90; (Ln0.11Y0.14Zr0.75)O1.88 și (Ln0.14Y0.14Zr0.72)O1.86. Increasing the dopant concentration decreases the height and widens the diffraction maxima. These results could be explained by the fact that the increase in dopant concentration favors the introduction of microtensions in the elementary cell and the formation of nanometric crystallites..
The low thermal conductivity of 8YSZ co-doped with 4, 6 and 8% by weight Ln2O3 may be related to the complex phase composition and the formation of cubic pyrochlor which have been reported as low thermal conduction materials. However, the results obtained by the hard disk method should be verified with other standardized methods, such as DSC flash.
Impedance spectrometry indicates that at approximately 600°C the migration of charge carriers occurs through various mechanisms, due to changing boundaries and bulk contributions to the dopant used, leading to a decrease in the total electrical resistance of the samples as the temperature increases. As the temperature rises, the contribution to the border becomes the limiting stage of driving. Activation energies have values of the same order of magnitude for all samples of 8YSZ-6% by weight Ln2O3 studied, with a value of less than 1.09 eV for co-doped materials with 6% by weight Gd.
The thin films obtained from these materials by RF sputtering have a very good thermal stability, with potential for use in thermal protection coatings.

Thermal properties of ZrO2 co-doped with 8% by weight Y-6% Ln (Ln=La, Nd, Sm, Gd).

Arrhenius diagram for co-doped ZrO₂ with 8% by weight Y and 6% by weight Ln at 600°C.

Publications

Radu-Robert Piticescu, Anca Elena Slobozeanu Sorina Nicoleta Valsan, Cristina Florentina Ciobota, Andreea-Nicoleta Ghita, Adrian Mihail Motoc, Stefania Chiriac and Mythili Prakasam, „ Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La, Gd, Nd, Sm): Crystalline Structure, Thermal and Dielectric Properties“, Materials 2021, 14, 7432. https://doi.org/10.3390/ma14237432

Radu-Robert Piticescu, Mythili Prakasam, Olivier Jay, Anca Elena Slobozeanu, Marian Burada, „ Innovative ideas in the design, re-use and re-fabrication of Rare Earth-based materials in the Context of Microelectronics and Renewable Energy“, CAS Proceedings pg. 25-28, 6-8 Octombrie 2021, IEEE Publisher, https://doi.org/10.1109/CAS52836.2021.9604177

STAGE 3    2022

DEVELOPMENT OF LABORATORY TECHNOLOGY FOR OBTAINING OXIDE MATERIALS DOPED
WITH RARE EARTH OXIDES IN THE FORM OF SINTERED PRODUCTS

In this phase, the importance of rare earths in obtaining materials for SOFCs (solid oxide fuel cells) were presented and the main methods of obtaining ceramic materials doped with rare earth mixtures were analyzed.
BaCeO3 powders doped with 8% Y (BCY2,BCY3) were obtained by hydrothermal method. The obtained powders were characterized morphologically, structurally in terms of phase composition and thermal behavior. The powders were calcined at 1200C for 8h and their phase compositions were analyzed. Given that Ce is the rare earth with the highest concentration in the bastnasite concentrate from Turkey, that’s why this high-tech application can have the biggest economic impact.

STAGE 4    2023

It was analyzed the possibility of developing a technology that would allow the use of rare earth mixtures with natural composition extracted from concentrate as a dopant for zirconia-based ceramics, with potential applications in solid oxide fuel cells. The availability of dopants consisting of natural EER mixtures could have a major impact on their efficient use by avoiding high costs and environmental problems during the separation of individual elements. For this purpose, ZrO2 doped with 8% natural rare earth mixture (8ZrMZ, containing as major REOs: 0.78 La, 0.68 Nd, 0.08 Sm, 0.067 Y, 0.055 Gd according to chemical analysis) were synthesized by a hydrothermal process at low temperatures (max. 2500C) and pressures (max. 200 atm.). ZrO2 doped with 4% Y2O3 (4ZrY) and 8%Y2O3 (8ZrY) used as standards in commercial SOFCs were synthesized under the same conditions.
The pellets sintered at 14000C of the three compositions were used for electrochemical studies by impedance spectrometry. Comparison of the Nyquist spectra for zirconia doped with rare earth mixture (8ZrMZ) with traditional zirconium oxide doped with 4 and 8% yttrium (4ZrY and 8ZrY) shows a clear difference between conduction mechanisms in the temperature range 500-8000C. The impedance spectra of the 8ZrMZ samples show only a semicircle related to the contribution of granules to ion conduction in the range 500-7000C and the beginning of a second semicircle formation at 8000C for the limit contribution of the granules. For standard composition 4 and 8 ZrO2 doped with Y, both limit contributions of granules and granules to ion conduction are observed in the temperature range 500-8000C and impedance decreases with increasing temperatures towards high frequencies.
Sintered pellets made of material doped with rare earth mixture (8ZrMZ) were used to obtain thin films by RF sputtering. The films deposited on the substrate of Si have a thickness of 13-22 nm and have a structure consisting of 51% cubic ZrO2 and 49% monoclinic ZrO2.

ISI Publications

1. A.N. Ghita, A.E. Slobozeanu, L. Licu, C.F. Ciobota, A. Sobetkii, B.S. Vasile, F. Micuescu, R. R. Piticescu. “Hydrothermal synthesis of Zirconia doped with naturally mixed Rare Earths Oxides and their electrochemical properties for possible applications in solid oxide fuel cells”. Acceptat pentru publicare in Manufacturing Review, mfreview230035
2. A.E. Slobozeanu, R. R. Piticescu, C. Predescu, A.I. Tudor, A.C. Matei “Efficient use of rare earths as dopants in the development of ZrO2 based materials” U.P.B. Sci. Bull., Series B, Vol. 85, Iss. 1, 2023, ISSN 1454-2331
3. A.N. Ghita, M. Zlagnean, N. Tomus, D.M. Banu, I-C. Popescu (Hostuc), F. Miculescu, R.R. Piticescu, A.C.Matei “Exploring the potential of rare earth element recovery from monazite” U.P.B. Sci. Bull., Series B, Vol. 85, Iss. 3, 2023 ISSN 1454-2331

STAGE 5    2024

Two samples of 1 kg each of bastnaesites concentrate from Turkey were chemically analyzed and processed, with the average total amount of lanthanides of 10.7%.
The TRL 3 (proof of concept) technology for the extraction of lanthanide mixtures using alkaline leaching and HDEHP extractant has been finalized. Nd separation experiments were then carried out and 8 g Nd purity 97% were obtained which was sent to the coordinator for testing in obtaining NdFeB powders for permanent magnets.
The preliminary technical-economic analysis showed that the use of lanthanides in zirconium doping and obtaining thin films by RF sputtering can be an efficient solution for their use in high-tech applications.