Rare earth elements (REEs) are essential in various industrial applications due to their high magnetic susceptibility, low density, and thermal stability. Praseodymium is used in producing yellow pigments for glass and ceramics, while Neodymium is crucial in producing powerful permanent magnets and laser applications. Technological advancements have driven the demand for Pr and Nd and increased the need for a reliable supply chain. The primary sources of Pr and Nd are minerals like monazite, bastnasite, and xenotime, which require complex separation processes due to their mixed contents. The main secondary sources include electronic waste, particularly from permanent magnets. The difficulty in the extraction of REEs lies in their closely related chemical and physical properties. Solvent extraction (SX), based on differences in ionic radii, is a widely used method for REE separation in industrial applications. Nevertheless, the similarity in Pr and Nd ionic radius complicates their separation compared to other REEs. This research examined the effectiveness of Cyanex 272 in the SX process for separating Pr and Nd, as well as its potential for improvement through the use of binary extractant combinations viz. Cyanex 572, Cyanex 801, Cyanex 923, as well as DEHPA. The synthetically prepared aqueous solution was composed of 400 ppm Pr and 800 ppm Nd. The extraction efficiency and selectivity were determined by using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The findings revealed that the loading efficiencies for Pr and Nd varied with the concentration of Cyanex 272, namely Pr loading efficiencies ranging from 5.5% to 24.4%, and Nd from 6.7% to 31.3%. Notably, binary extractant experiments indicated that mixtures incorporating Cyanex 272 with DEHPA, Cyanex 572, and Cyanex 801 exhibited enhanced extraction efficiencies compared with the sole Cyanex 272. On the other hand, the combination of Cyanex 272 and Cyanex 923 resulted in a diminished extraction efficiency. These obtained outcomes could potentially adapt to the development of domestic technology for the extraction of REEs from the Eskişehir Beylikova REE Ores.

Abstract

Rare Earth Elements (REEs) are essential for advanced technologies due to their unique properties. This study presents a pHcontrolled solvent extraction method to separate Samarium (Sm) from light REEs simulating Beylikova REE leaching liquid. The process, utilizing 0.75 M DEHPA in kerosene, showed that Sm achieved a 59% extraction efficiency at pH 0.5, significantly higher than La, Pr, and Nd. This pH optimization enhances the sustainability and efficiency of REE extraction, promoting the effective utilization of Turkey's REE resources and domestic technologies.

1. Introduction

Solvent extraction (SX) is a widely employed method for the separation and purification of rare earth elements (REEs). This technique involves the transfer of REE ions from an aqueous phase to an organic phase, facilitated by specific extractants, enriching the target elements from the solution. Due to the chemical similarities and close ionic radii among REEs, achieving high selectivity in their separation is often challenging. However, by adjusting various parameters such as pH and organic concentration, it is possible to influence the efficiency and selectivity of the solvent extraction process. In particular, optimizing the pH value can significantly impact the preferential separation of certain REEs over others.

2. Materials and Methods

This study presents a method for separating Samarium (Sm) from light REEs, namely lanthanum (La), praseodymium (Pr), and neodymium (Nd). The method involves a pH-controlled solvent extraction (SX) of the leach liquor, which was synthetically prepared according to Beylikova REE concentrate in Eskişehir, Turkey. For the investigation of the aqueous solution pH value
on the extraction efficiency of La, Pr, Nd, and Sm, the pH values were examined at different levels ranging from 0.5 to 4. SX of REEs was performed by using an organic phase consisting of 0.75 M DEHPA (Di-(2-Ethyl Hexyl) phosphoric acid) in kerosene. The concentrations of elements in the aqueous phase were quantified before and after the SX process by using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The obtained results indicated that Sm exhibits remarkable performance in terms of an extraction efficiency of 59% at a lower pH value (i.e. 0.5) compared to those of La (16%), Pr (36%) and Nd (24%) as seen in Figure 1. The exceptional chemical behavior of Sm under acidic conditions enabled the formation of complexes with the organic phase, facilitating selective separation. This optimization in pH value improved the selectivity of the extraction process and established a more sustainable approach for the separation of REEs which possibly further minimizes the environmental impact typically associated with extraction of REEs.

3. Conclusion

This research outcome potentially supports the efficient utilization of Turkey's REE resources and promotes the development of domestic technologies. The importance of pH value in separating Sm from light REEs in Beylikova REE leach liquor is highlighted which probably leads to the installation of more cost-effective and environmentally friendly REE extraction processes.
Acknowledgment
This study is coordinated and financially supported by TENMAK NATEN [Project No: A2.H1.P18].

Rare Earth Elements (REEs) are essential components of advanced technology applications such as renewable energy, electronics, and defense. Their unique magnetic, catalytic, and luminescent properties render them essential for the development of high-performance materials. However, efficient and selective separation of individual REEs is a significant challenge owing to their chemical and physical similarities. This study focuses on the selective separation of lanthanum (La) from complex mixtures of REEs as it is crucial for the sustainable extraction of Eskişehir Beylikova Rare Earth Ore.

In this study, solvent extraction (SX), a critical method for separating REEs, was carried out by using di (2-ethylhexyl) phosphoric acid (DEHPA) as the extractant. The selection of DEHPA was done based on its proven efficiency in REE SX processes, which offers a balance between selectivity and extraction capacity. For this purpose, various DEHPA concentrations in the organic phase were studied to obtain the optimal conditions for the selective separation of La from the leach liquor. The synthetically prepared leach liquor contained 5000 ppm La, 400 ppm Pr, 800 ppm Nd, and 200 ppm Sm. Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was utilized to determine the precise ion concentrations in the initial and extracted aqueous phases which ensured the accurate assessment of the extraction efficiency and selectivity. These initial findings revealed that the loading pattern is as follows: initial larger ionic radius La3+ (1.16 Å) loaded than after Pr3+ (1.13 Å), Nd3+ (1.11 Å), and Sm3+ (1.08 Å) came. The organic concentration was prepared ranging from 0.03M to 0.9M in kerosene. The loading efficiencies for La varied  from 1.95% to 84.5%, whereas those for Sm, Pr, and Nd varied  from 77.61% to 100%, from 41.69% to 99.17%, and from  27.78% to 97.68%, respectively, with increasing DEHPA concentrations. The outcomes demonstrated the feasibility of selective separation of La from other REEs using 0.03M DEHPA. The obtained results could be potentially adopted for the domestic production of REEs in the Eskişehir Beylikova Rare Earth Ores.

Thermal barrier coatings (TBC), are used to protect the base material against elevated temperature and other environmental impacts in the high-temperature applications such as gas turbine blades. The microstructure design of thermal barrier coatings directly affects the coating properties. In the microstructure of TBC; cracks, gaps, semi–melted phases are valid. Microstructural differences occur in the variation of the process parameters. Spray distance, powder particle size, feed angle and rate, base material type and temperature are the effective parameters of microstructural differences. In this study, the thermal barrier coating material used as yttria stabilized zirconia (YSZ); examined in three classes according to their particle size as finer, medium and coarse, respectively. Other process parameters are kept constant. Also commercial YSZ (Sulzer AMDRY 6643) is used as reference in the study for comparison. YSZ is stirred with 50 wt% Lanthanum zirconate (LZ). Mixed powders are coated on stainless steel with Atmospheric Plasma Spray (APS) method using 9MB plasma gun. The effects of different powder particle size on the porosit, and surface roughness are investigated with The Scanning Electron Microscopy (SEM) analyses.

Lithium-ion batteries (LiBs) are utilized in numerous applications due to advancements in technology, and the recovery of end-of-life (EoL) LiBs is imperative for environmental and economic reasons. Pyrometallurgical and hydrometallurgical methods have been used in the recovery of metals such as Li, Co, and Ni in the EoL LiBs. Hydrometallurgical methods, which have been demonstrated to exhibit higher recovery efficiency and reduced energy consumption, have garnered increased attention in recent research. Inorganic acids, including HCl, HNO₃, and H₂SO₄, as well as organic acids such as acetic acid and citric acid, are employed in the hydrometallurgical recovery of these metals. It is imperative to acknowledge the environmental hazards posed by these acids. Consequently, solvometallurgical processes, which involve the use of organic solvents with minimal or no water, are gaining increasing attention as alternative or complementary techniques to conventional hydrometallurgical processes. In the context of solvent systems that have been examined for a range of solvometallurgical methods, deep eutectic solvents (DESs) have garnered particular interest due to their low toxicity, biodegradable nature, tunable properties, and efficient metal recovery potential. In this study, the leaching process of black mass containing graphite, LCO, NMC, and LMO was carried out in a short time using the ternary DES system. The ternary DES system consists of choline chloride (ChCl), glycolic acid (GLY), and ascorbic acid (AA). As a result of the leaching process of cathode powders in the black mass without any pre-enrichment process, Li, Co, Ni, and Mn elements passed into solution with an efficiency of over 95% at 60 °C and within 1 h. Moreover, the kinetics of the leaching process was investigated, and Density Functional Theory (DFT) calculations were used to explain the leaching mechanism.

Bu çalışmada Yitriya ile kararlı hale getirilmiş zirkonya (YSZ) termal bariyer kaplamalar (TBK) partikül boyutlarına göre sınıflandırılarak atmosferik plazma sprey (APS) yöntemiyle üretilmişlerdir. Bu çalışma sayesinde seramik üst katman malzemesi olarak ticari uygulamalarda oldukça yaygın kullanılan YSZ'nin mikroyapı farklılıklarının TBK  özelliklerine etkisi incelenmiştir. Kaplama prosesinde, ticari YSZ (Sulzer Metco 204B-NS) elek yardımıyla üç sınıfa ayrılmıştır. Sınıflandırılan YSZ tozları önceden bağ katmanı HVOF prosesi ile üretilen altlık üzerine APS yöntemi ile kaplanmıştır. Aynı zamanda karşılaştırma amacıyla ticari YSZ ile de kaplama üretimi gerçekleştirilmiştir. Kaplamaların mikroyapı analizlerinde taramalı elektron mikroskobu (SEM) kullanılmıştır. SEM ile elde edilen kesit görüntülerinde APS yöntemi ile üretilen TBK'lerin karakteristik özelliklerine sahip olduğu ancak bu yapı içerisinde kullanılan toz boyut ve dağılımına göre farklılıklar gösterdiği gözlemlenmiştir. Kapalama porozite oranı görsel işleme metodu ile yapılmıştır. Her bir grup kaplama kendi içinde tutarlı olarak %15 ile %23 arasında değişim göstermiştir. Bunun nedeni ince toz olarak sınıflandırılan grubun plazma alevi içinde daha hızlı bir şekilde ısınarak ergimesi ve mikroyapıyı oluşturan yassı tanelerin daha ince olması olarak açıklanmıştır. Bunun yanında toz boyut dağılımı göreceli olarak dar olan tozların porozite dağılımının lokal olarak kaldığı ancak geniş boyut dağılımına sahip tozların porozitelerinin küçük ve tüm kaplamaya yayılmış olduğu gözlemlenmiştir. Kaplama özellikleri porozite oranı ve dağılımı ile ilişkilendirilmiştir. Bu amaçla sistematik olarak sıcak korozyon ve X-ışını difraktometresi analizi, gerçekleştirilmiştir. Sıcak korozyon deneyi 1200°C'de gerçekleştirilmiştir. Sıcak korozyon sonucunda elde edilen yapının ilerleme mekanizmasının porozite ile ilişkisi kurulmuştır. Sınıflandırılan tozların porozite ile orantılı şekilde, sıcak korozyona uğradığı ancak; ticari toz ile üretilen kaplamanın en düşük sıcak korozyon direncine sahip olduğu gözlemlenmiştir. Bu durumun açıklanabilmesi için porozite dağılımı da göz önüne alınmıştır. Küçük ve kaplama yapısına homojen dağılım gösteren porozitelerin sıcak korozyon sonucu oluşan kristallerin ilerlemesini engelleyemediği ancak; büyük porozitelerin lokal olarak oluştuğu kaplamalarda, porozitelerin kristallerin ilerlemesini engelleyici bir role sahip olabileceği fikrini oluşturmuştur. X-ışını difraktometresi analizinde poroziteye bağlı olarak pik şiddetlerinin farklılık gösterdiği gözlemlenmiştir. Sınıflandırılan tozların kendi içlerinde doğrusal bir şekilde davrandığı ve porozite oranı arttıkça pik şiddetinin düştüğü gözlemlenmiştir. Ancak; ticari tozun, sınıflandırılmış tozlardan farklı davrandığı ve en yüksek pik şiddetine ulaştığı görülmüştür. Bu durumun açıklanması için porozite dağılımının etkinliği düşünülmüştür ve tüm kaplamaya dağılmış porozitenin pik şiddetini arttırdığı ve belli bölgelerde yoğunlaşmış porozitenin pik şiddetini düşürdüğü sonucuna ulaşılmıştır. Yüzey pürüzlülüğü ile porozite arasındaki ilişki incelenmiş ve yapay sinir ağları ile modellenmiştir. Literatür incelendiğinde TBK'ların özelliklerinin YSA ile modellenmesi noktasında genellikle proses parametrelerine odaklanılmaktadır. Bu noktada proses parametrelerinin fazlalığı ve kontrol edilebilirliğinin zorluğundan dolayı üretilen kaplamaya ait bir özelliğin ölçülmesi daha güvenilir bir YSA oluşturulmasına neden olacaktır. Bu nedenle kaplama porozitesinin modellenmesi için yüzey pürüzlülüğü verileri kullanılmıştır. Bu sayede kaplamaya zarar vermeden kaplama porozitesini daha güvenilir olarak tahmin edebilen bir yapay sinir ağı oluşturulmuştur. TBK sisteminin yoğun olarak kullanıldığı gaz türbini uygulamalarındaki son gelişmeler incelenerek ana metale etki eden sıcaklığı düşürme yöntemleri araştırılmıştır. Film soğutma olarak bilinen ve TBK ile birlikte kullanılan soğutma yöntemi üzerinde durulmuştur. Gerçek SEM görüntüleri kullanılarak film soğutmanın yüzeydeki etkileri sonlu elemanlar metodu ile incelenmiş ve yüzey pürüzlülüğünün malzeme yüzeyine etki eden sıcaklığa etkisi incelenmiştir.