Rhenium (Re) is an industrially important metal because of its use in catalysts and additives in alloys. Due to the rarity and maldistribution of Re, stabilization of its price and supply by recycling is quite important. Therefore, it is necessary to develop Re recovery methods from acid leach solutions of spent catalysts and alloys. In this study, we present a new Re recovery method using primary amines from Re-containing hydrochloric acid (HCl). Re was successfully recovered from HCl solutions as precipitates using 4-hexylaniline (HexAni). Separation of platinum (Pt) and Re was achieved using 2-ethylhexylamine and HexAni as precipitants, respectively. We also succeeded in the selective and quantitative precipitation of Re using HexAni from the HCl solution containing Re, aluminum, vanadium, cobalt, and nickel. Precipitation recovery method of Re using HexAni from HCl solutions is a promising candidate for Re separation and recycling.

Use of pulsed electric field and non-thermal plasmas generated using compact pulsed power generators has been widely expanded. In our research group, gas treatment such as decomposition of toxic and odor components and removal of aerosols using streamer discharges, and water treatment using discharges generated over water surface have been studied. The study of agricultural applications has been conducted for three purposes; to improve productivity of plants in pre-harvest applications, to keep freshness of fruits and vegetables in post-harvest applications, and to improve safety and productivity in food processing applications. In this article, some applications and development of pulsed power systems are introduced.

Ion solvation extraction has been used as a separation techniques for gold (Au(III)) from various metal ions in a hydrochloric acid media. Dibutyl carbitol (DBC) has been used as the most popular solvent to extract Au(III), while no better solvent has been found for many years. In the present review, the results of recent investigations by the authors to find valid solvents for ion solvation extraction are summarized. Ethers and ketones are suitable in view of the high extractability for Au(III) as well as the good properties including chemical stability. Ethers and ketones which have a smaller side chains and relatively higher polarity showed higher extractability, however, polar solvents would leak into the aqueous phase. Therefore suitable solvents with moderate polarity are narrowed down based on the balance between high extractability and low aqueous solubility. As the polarity affects the extractability, the logP value (octanol/water partition coefficient) and the Hansen solubility parameter would be one of the indexes for the Au(III) extractability. Solvents used in industrial processes are required to have not only high extractability but also good properties such as a low aqueous solubility and a high flash point. The comprehensive research revealed the requirements for solvents to extract Au(III) based on ion solvation. Additionally, several potential solvents which might replace DBC were suggested.