Tantalum (Ta), one of the rare metals, is mainly used for high-performance capacitors. While the increasing importance of Ta, its supply has many problems, e.g., imbalanced production and aspects such as conflict minerals. Recycling has a strong impact on the stable and responsible supply of materials, however, both hydro- and pyro-metallurgical procedures have many problems with the environmental impact and the operation cost. Considering the above situation, the authors have developed a novel recycling process of Ta using “dry aqua regia”. This is a molten salt consisting of ferric chloride (FeCl3) and potassium chloride (KCl) and has already been applied for the recycling of platinum group metals (PGMs) and rare earth elements (REEs). In this study, the authors chlorinated Ta using this dry aqua regia and recovered tantalum oxide by the hydrolysis of chlorinated Ta. As a result, we succeeded in the chlorination of Ta at 630 - 670 K, which is a relatively low temperature for the pyrometallurgical procedure. Chlorinated Ta was recovered as an oxide by hydrolysis with water or nitric acid leaching, with impurities consisting of iron oxide. The recovery rate of Ta was up to 77.5 %, and the loss was suggested as volatilization during the chlorination. These results suggest that the procedure using “dry aqua regia” can be an effective recovery process for Ta.

This study investigates the mineral diversity in placer platinum-group minerals (placer PGM) purportedly collected from the Onnebetsu area in Shibetsu City, Hokkaido. Placer particles consist primarily of native elements and alloys and can be broadly categorized into two groups, iridium-group and palladium-group. The iridium-group placer is predominantly composed of rutheniridosmine, osmium, ruthenium, and iridium, with each occurring as both primary and secondary phases. In contrast, the palladium-group placer consists primarily of isoferroplatinum as the primary phase, accompanied by tulameenite, tetraferroplatinum, and ferronickelplatinum as secondary phases. Notably, the iridium-group placer may also contain PGM typically associated with the palladium-group placer in subordinate amounts. In addition to the primary and secondary phases, other PGM occur as inclusions, within the outermost layers of particles, and in exsolution textures. A total of 41 PGM species were identified in this study, along with six unnamed species. The Onnebetsu area stands out as the region in Japan with the highest diversity of PGM discovered to date. This remarkable variety is largely attributed to the palladium-group placer, which is originated from cumulate rocks formed by partial melting of a mantle.

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.

We evaluated the absorption characteristics and phase state of a biphasic CO2 absorbent using 2-amino-2-methyl-1-propanol (AMP), diethylene glycol diethyl ether (DEGDEE), and water (H2O). We set the AMP concentration at 30 wt%, and adjusted the H2O and DEGDEE weight fractions. It was experimentally confirmed that phase separation of the absorbents occurred due to the progress of CO2 absorption. As the concentration of water decreased, it was separated into a lower phase, which consisted almost entirely of AMP, H2O and absorbed CO2, and an upper phase, which consisted of mostly DEGDEE. In the experiment, an absorbent composition of 30 : 20 : 50 wt.% (AMP:DEGDEE : H2O) was maintained in the liquid state at 313 K and a CO2 partial pressure of 0.1 atm in the absorption step and at ≥ 343 K and a CO2 partial pressure of 1.0 atm in the regeneration step. Under CO2 capture conditions, this adsorbent was separated into two-liquid states in the absorption step, whereas it exhibited a uniform single phase in the regeneration step. Therefore, it could operate under CO2 capture conditions as a biphasic absorbent. The amount of CO2 cyclic absorption of this absorbent was twice that of conventional monoethanolamine (MEA) absorbents when the regeneration temperature was set at 363 K.

Scandium (Sc) generally lacks independent deposits and is mainly recovered as a by-product of the smelting of other ores. Scandium is present in laterite ores in concentrations ranging from tens to hundreds of ppm. In the process of recovering nickel from laterite ores, Sc is recovered from sulfuric acid leachates. An ion-exchange resin method is an effective way to recover low concentrations of Sc (III) in sulfuric acid leachates. In our previous studies, the adsorption behaviors of Sc (III) and other trivalent metal ions were investigated, but the desorption behaviors of them were not. This study proposes optimal adsorption and desorption conditions for the selective separation and recovery of Sc from other trivalent cations in sulfuric acid solutions using an iminodiacetic acid chelating resin, Diaion™ CR11. The chelating resin with each metal ion adsorbed was mixed with sulfuric acid solution, and the desorption behaviors of these ions were investigated. On the other hand, adsorption tests were conducted using the chelating resin with residual Cr (III). The order of ease of desorption was Al (III) > Sc (III) > Fe (III) >> Cr (III). The desorption reaction rate of Cr (III) increased with increasing temperature, and its activation energy was estimated to be 82 - 93 kJ mol-1. Although the adsorption reaction rate and the amount of Sc (III) decreased with increasing residual amount of Cr (III) on the chelating resin, the adsorption ratio of Sc (III) was over 90% at a bed volume of 30 in a column test at 23˚C using the chelating resin with a residual amount of Cr (III) of 0.2 mmol g-1. With appropriate adsorption and desorption operations, scandium in laterite ores can be recovered continuously and efficiently, contributing to the development of the industry.

Fluoride(F-) is present in wastewater produced by various industries, such as semiconductor, glass processing, mining and smelting. Development of high-efficient and low-cost treatment processes of wastewater is desirable. In this study, Seashells sorbents for F- removal were synthesized by phosphate solution treatment of seashells (oyster, scallop, sea urchin and barnacle) waste at room temperature. The seashells sorbents could remove F- in water to below effluent standard (8 mg/L) in Japan. The optimal initial pH range for seashells sorbents synthesis was below pH6. The phosphate consumptions for synthesis could be estimated by specific surface area of seashells. F- sorption isotherms of seashells sorbents were fitted well by the Langmuir model. The synthesis reaction of seashell sorbents at room temperature was that calcium hydrogen phosphate was produced to the surface of calcium carbonate contained in seashells. Dominant mechanism of F- removal of seashell sorption was identified as to form fluorapatite from the calcium hydrogen phosphate and F-.

Copper slag (CS) granules received from a Japanese smelter were melted using an alumina crucible under Ar gas flow in an electric furnace. The melt was removed from the furnace and cooled slowly with various holding times in air and then water-quenched. The increase of cooling time in air promoted the partial crystallization of CS samples: the separation of Fe-rich and Si-rich phases, the precipitation of fayalite and magnetite phases and the formation of Al2O3- and SiO2-rich non-crystalline aluminosilicate phase. The CS melt was subdivided into smaller ones through a hand-made yttria-doped stabilized zirconia polycrystal sieve and repelled by a rotational graphite plate. After cooling crystallized CS granules were successfully fabricated. The crystallized CS granules including fayalite and magnetite phases satisfied a lower limit for the elution amounts of As and Pb fixed as ≤150 mg/kg in 1 mol/L HCl aqueous solution as specified in the guideline of JIS 0058-2:2005 as a test method for acid-extractable contents of chemicals.

The Federal Republic of Nigeria (herein after referred to as “Nigeria”) is the largest oil producing country in Africa and 13th in the world. However, community development is delayed especially in the Niger Delta where oil is produced. In this situation, many CSR community development projects of multi-national oil development companies (herein after referred to as “companies”) are implemented there.

It is obligatory to verify the performance of high-energy-absorbing pocket-type rockfall protection nets by full-scale experiments. While the performance verification by full-scale experiments can provide a practical evaluation, it requires a lot of cost and time because it is necessary to conduct the experiments under several conditions depending on the structure of the rockfall protection net. Therefore, the performance verification by combining full-scale experiments and numerical analysis may be a useful tool. In this study, a full-scale experiment of a high-energy-absorbing pocket-type rockfall protection net was conducted to evaluate the net performance with respect to the required capability, and reusability and repairability of the components by understanding the behavior of the net under the action of heavy weights. Throughout the experiment, the deformation of the net, the change of the wire rope tension with time, and the displacement of the top of the net and the top of the pillar were measured in detail. Moreover, it was confirmed that it is possible to evaluate the performance verification based on the performance requirements. Then, the full-scale experiment was replicated by numerical simulations to examine the effects of the rock shape on the behavior and performance of the simulated net. Through the thorough investigations on the deformation of the net, the relation between the maximum tension of the wire rope and the slip length of the shock absorber, the temporal change of the tension of each wire rope, and the absorbed energy of each structural member, it was judged that the reproducibility of the model predictions is adequately high. Specifically, when the impact energy is constant, the effect of the rock shape on the behavior and performance is considered to be small.

Ion-exchange process with chelating resins was investigated for recovery scandium from sulfuric acid aqueous solutions. An iminodiacetic acid type chelating resin, Diaion CR11, had a higher Sc adsorption selectivity than other elements. Diaion CR11 had high trivalent ions adsorption, and almost divalent ions other than nickel were not adsorbed. The adsorbed metal ions were eluted with sulfuric acid, and scandium was separated from aluminum, nickel and chromium. Only iron (III) showed a behavior similar to scandium and was difficult to separate with Diaion CR11. The elution behavior was related to the stability constants of the complex of iminodiacetic acid and metal ions.