Ir(III) chlorocomplexes are poorly extracted into organic solvents, which is due to the charge of the complex as well as those inert character in chloride solutions, the formation of IrCl_6–n(H₂O)_n^(3–n)– (n = 0–6). Therefore, it is difficult to extract Ir(III) by solvent extraction, and currently Ir(III) is extracted by oxidizing to Ir(IV), which could form the extraction-active chloride complexes.

In this study, extraction of Ir(III) from hydrochloric acid solutions with 2-ethylhexylamine (EHA) and octylamine (OA) as primary amines, dibutylamine (DBA) as secondary amine and tri-n-octylamine (TNOA) as tertiary amine, were tested to clarify the extraction and the stripping of Ir(III). As a result, the extraction efficiencies of Ir(III) with EHA and OA were high, meanwhile, the extraction efficiencies of Ir(III) with DBA and TNOA were significantly lower than those with EHA and OA. Moreover, the extraction efficiencies of Ir(III) with EHA and TNOA were hardly improved by addition of Sn(II). It was also found that Ir(III) could be easily stripped from EHA with sodium sulfate solutions.

In recent years, the scientific and technological advances have led to environmental issues, including water pollution and depletion of natural resources. Palladium, a precious metal, is a limited resource, so there is a need to establish a technology for its selective and highly efficient recovery. In this study, a selective recovery method for palladium from plating wastewater (containing palladium 2 ppm and tin 200 ppm) was investigated using chitosan nanofiber hydrogel (CNF hydrogel), which is expected to exhibit high adsorption properties due to its high specific surface area. The adsorption experiments using standard palladium solutions on the gel revealed that the adsorption rate depended on the solution’s pH and initial concentration. It was confirmed that the adsorption of palladium on the hydrogel was fitted better to the Langmuir isotherm than the Freundlich, indicating monolayer adsorption. Palladium recovery from plating wastewater was attempted, and palladium was selectively recovered from a tin-rich solution. These findings imply that CNF hydrogel holds potential as a precious metal recovery material.

In the field of environmental resource engineering (resources processing), bioleaching, where microorganisms contribute to the dissolution of minerals, has long been studied and is a well-known microbial reaction. A similar phenomenon to this is microbiologically influenced corrosion (MIC), where microorganisms are involved in the corrosion reaction of metal materials. MIC has been rapidly advancing in research in recent years, with new reaction models being proposed. While both bioleaching and MIC involve microbial metabolism acting on insoluble inorganic substances, their mechanisms appear to differ. In this paper, we introduce the latest MIC research, discuss the similarities and differences between bioleaching and MIC reactions, and provide insights into the prospects for applying these reactions.

From November to December 2016, a scientific drilling cruise CK16-05 by using D/V Chikyu was performed at Hakurei Site, Izena Hole, middle Okinawa Trough to understand mainly the metallogenesis and physical property of the subseafloor sulfide body. At Hole 9026A of the deepest hole down to 180.0 mbsf, lithologies of drilling cores, in descending order, are (1) underwater debris flow deposit (pumiceous sediment), (2) hemipelagic sediment, (3) subseafloor sulfide body with two intercalated layers of hemipelagic sediment, (4) greenish hydrothermally altered clay with pyrrhotite-cubanite veins and (5) pervasive altered hydrothermally altered clay. Based on the all results of petrographic observations, chemical analyses and geophysical logging of boreholes, genesis of Northern Mound can be explained well by a classical syngeneic model, however, the subseafloor sulfide body was the most plausibly formed by “subseafloor pumice replacement mineralization”. Thus, the subseafloor replacement process (subseafloor pumice replacement mineralization) would be one of the important factors to form the large-scale seafloor hydrothermal deposit.