Toru H. Okabe’s research while affiliated with The University of Tokyo and other places

Efficient and environmentally friendly recovery of platinum group metals from secondary resources can facilitate a sustainable society. This study explores a two-step process for extracting Pt from catalyst materials: chlorination using ferric chloride (FeCl3) vapor followed by leaching using hydrochloric acid. When the catalyst sample prepared by mixing Pt black and alumina powder was leached with 1 M HCl(aq.) at 313 K (40 °C) for 10 min, Pt was hardly dissolved in the solution. By contrast, after exposure to FeCl3 vapor at 573 ± 20 K (300 ± 20 °C) for 35 min, 92% of the Pt was extracted under the same leaching conditions. Furthermore, when a commercial Pt catalyst powder was subjected to chlorination, virtually all the Pt was extracted during subsequent leaching. The reaction products of Pt and FeCl3 vapor were examined through compositional analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy, and their crystalline structures were analyzed using X-ray diffraction. The products were identified as FePtCl6 and FeCl2. By reacting with FeCl3 vapor, Pt was converted into a complex chloride that is easily soluble in low-toxicity acids. Therefore, the proposed process can potentially improve the efficiency and environmental friendliness of Pt recovery from spent catalysts.

To promote the recycling of Ti scrap, it is essential to develop new technologies that can efficiently remove oxygen impurities from the Ti scrap. However, the direct removal of oxygen dissolved in solid Ti is extremely difficult, and currently, there are no effective deoxidation methods that can be used industrially. In this study, we experimentally verified a new deoxidation technique for Ti using the vapor of rare earth metals with high vapor pressures, such as Sm, Eu, Tm, and Yb. It was confirmed that Eu did not decrease the oxygen concentration in the Ti samples below 1000 mass ppm O. On the other hand, it was shown that the vapor of Sm, Tm, and Yb decreased the oxygen concentration in the Ti samples through their oxide formation reactions. In particular, it was demonstrated that Tm vapor can deoxidize Ti at or below the oxygen concentration of the Ti sponge produced by the Kroll process (∼500 mass ppm O). Mater. Trans. 64 (2023) 61-70に掲載．Fig. 2，Table 2を修正． Fig. 4 Comparison of the oxygen concentrations in the Ti samples after the deoxidation experiments utilizing Sm metal (Ti-SS in Exp. no.: E-2, Ti-ho in Exp. nos.: AM-1 and AM-2), Tm metal (Ti samples in Exp. nos.: O-1, O-2, AK-1, and AK-2), Yb metal (Ti-SS in Exp. nos.: D-1, F-1, and G-1) and Yb metal with Yb2O3 (Ti-SS in Exp. nos.: D-2, F-2, and G-2) at 1300 K (1027℃) (cf. Table 5). The error bars show the analyzed error of the oxygen concentrations in the Ti samples. Fullsize Image

Efficient removal of oxygen (O) impurities from titanium (Ti) scrap is necessary to accelerate the recycling of Ti scrap. However, deoxidation of Ti is extremely difficult, both thermodynamically and technically. In this study, we developed a deoxidation technique that uses Yb (a rare earth metal with high vapor pressure at elevated temperatures) to directly remove O dissolved in solid Ti. Experimental results showed that deoxidation using Yb in halide salt fluxes such as LiCl and LiF produced Ti with O concentrations of 520-1400 mass ppm. The O concentration in deoxidized Ti samples was reduced to a level lower than that in Ti under the Yb/Yb2O3 equilibrium, probably owing to the decrease in the activity of Yb2O3, which was the deoxidation product, caused by its dissolution in the fluxes. In contrast, when vapor of Yb metal and halide salts were supplied to Ti samples via a gas phase, the Ti samples were deoxidized to the same O concentration as that under the Yb/Yb2O3 equilibrium. This deoxidation limit was controlled by the Yb/Yb2O3 equilibrium. The supply of halide salt vapor did not affect the deoxidation limit. The proposed deoxidation method is expected to help scale up the recycling of Ti scrap and ensure efficient utilization of resources.

Development of an efficient deoxidation method for titanium (Ti) is desired to recycle oxygen (O)-contaminated Ti scrap. In this study, the utilization of thulium (Tm) as a deoxidant for Ti in various halide fluxes was investigated. Tm is a rare-earth metal, which is a by-product of other rare-earth metals with high demand and has limited industrial uses. When NaCl or KCl flux was installed in the deoxidation experiments, the impurity oxygen in Ti was removed to the concentrations of 140–590 mass ppm O, which are lower than that achieved under the equilibrium between Tm and Tm 2 O 3 (290–530 mass ppm O). The results show that the nominal activity of the deoxidation product (Tm 2 O 3 ) was lowered by the presence of halide fluxes in the reaction systems. The combination of Tm and halide fluxes in a new deoxidation technique holds promising potential for both accelerating the Ti recycling and exploring novel applications for Tm. Graphical Abstract

This study was aimed at investigating an effective chlorination method for Rh and its oxide to develop an efficient Rh extraction process. The feasibility of using alkali-metal and alkaline-earth-metal chlorides (NaCl, KCl, MgCl 2 , and CaCl 2 ) as chlorinating agents was evaluated from the perspective of thermodynamics; the prediction results revealed MgCl 2 as a suitable agent for chlorinating metallic Rh and Rh 2 O 3 in an oxygen-containing atmosphere. The thermodynamic analysis results were then experimentally validated. Metallic Rh converted to RhCl 3 when mixed with MgCl 2 and heated at 973 K (700 °C) in an O 2 atmosphere. The Rh 2 O 3 powder was efficiently chlorinated when reacted with liquid MgCl 2 at 1073 K (800 °C) in an Ar–1 pct O 2 atmosphere. Therefore, the chlorination of Rh using MgCl 2 is feasible; its use has potential to make the extraction and recovery of Rh from various raw materials more efficient. Graphical Abstract

An efficient and environmentally friendly recovery of platinum group metals (PGMs) from secondary sources is necessary to ensure a sustainable supply of PGMs. In this study, contact with FeCl 2 vapor in the presence of metallic Fe was investigated as a useful pretreatment for leaching PGMs from spent automobile catalysts. Fe-PGM alloys were efficiently formed when Pt, Pd, and Rh wires and Rh 2 O 3 powder were subjected to FeCl 2 vapor treatment at 1050 K (777 °C) for approximately 40 min. Further, the leachability of the PGMs in spent automobile catalyst samples increased after a similar vapor treatment was applied. When the pulverized spent catalyst sample without pretreatment was leached with aqua regia at 333 K (60 °C) for 60 min, 88% of Pt, 91% of Pd, and 37% of Rh were extracted. Meanwhile, after vapor treatment at 1050 K, 98% of Pt, 97% of Pd, and 87% of Rh were extracted under the same leaching conditions. Thus, the pretreatment with FeCl 2 vapor, followed by leaching, is a feasible and effective technique for recovering PGMs from spent catalysts. Graphical Abstract

As the demand for titanium (Ti) continues to grow, so too does the use of Ti scrap, underscoring the need for innovative techniques for the efficient removal of oxygen (O) impurities from Ti scrap. Despite the immense challenge of directly removing oxygen from Ti–O solid solutions and the current lack of industrially applicable deoxidation methods, the current work explores a groundbreaking approach to address this issue. The thermodynamic analysis of a new technique for eliminating oxygen dissolved in solid Ti was conducted, leveraging the deoxidation properties of rare earth metals (REMs) such as Sc, Y, and La. This cutting-edge method relies on the in-situ production of REMs through the metallothermic reduction of REM halides. It was shown that Sc or Y metal can be synthesized via the reduction of ScCl 3 by Mg or YCl 3 by Li or Na, respectively. Ti with oxygen concentrations below 100 mass ppm can be obtained by leveraging the deoxidation properties of the Sc and Y metals produced in situ during the metallothermic reduction process, which contribute to deoxidation through their subsequent oxychloride-forming reactions. Employing REM halides in tandem with Li, Na, and Mg enables the efficient removal of oxygen impurities from Ti, even though these reactive metals have only weak deoxidation properties for Ti on their own. Remarkably, the proposed technique achieves oxygen concentrations significantly lower than those obtained using Ca metal as a deoxidant. In the future, this pioneering deoxidation method could be used to reduce CO 2 emissions and energy consumption during Ti production while promoting resource circulation as a key technology for Ti recycling.

Titanium (Ti) is an attractive material, abundant in nature and possessing superior mechanical and chemical properties. However, its widespread use is significantly hampered by the strong affinity between titanium and oxygen (O), resulting in elevated manufacturing costs during the refining, melting, and casting processes. The current work introduces a high-throughput technique that effectively reduces the oxygen content in molten titanium to a level suitable for structural material applications (1000 mass ppm, equivalent to 0.1 mass%). This technique aspires to streamline the mass production of titanium by seamlessly integrating the refining, melting, and casting processes. The developed method leverages the high affinity of rare-earth metals, such as yttrium (Y), for oxygen. This method utilizes the formation reaction of their oxyhalides (YOF) to directly remove oxygen from liquid titanium, resulting in titanium with a significantly reduced oxygen content of 200 mass ppm. This technique enables the direct conversion of titanium oxide feeds into low-oxygen titanium without requiring conversion into intermediate compounds. Additionally, this process offers a pathway for the upgrade recycling of high-oxygen-content titanium scrap directly into low-oxygen titanium. Consequently, this technology holds the potential to dramatically lower titanium production costs, thereby facilitating its more widespread utilization.

Rhenium is utilized as an additive to improve the high-temperature strength and stability of materials, such as nickel-based superalloys, which are employed in jet engine turbine blades, alloys for ultrahigh-temperature thermocouples, and platinum catalysts, which are used in oil refining. Currently, around 80% of rhenium demand is for superalloy production, and this demand has been increasing with the increase in demand for aircrafts. The abundance of rhenium in the earth's crust is only 1 ppb (10 ⁻⁹ ), which is less than those of platinum and gold. Owing to the rare and unevenly distributed nature of rhenium, there is the risk of supply disruption and rapid increases in its price. In this article, the recent situation of rhenium and its compounds are reviewed, especially with respect to their demand, distribution characteristics, smelting, and recycling. Some of the technologies recently developed for smelting and recycling rhenium are also introduced.