Ionic liquids have unique properties that are quite different from conventional molecular liquids, and have therefore attracted much attention in various fields as novel functional media. When ionic liquids are used as extraction media in solvent extraction, they can also act as “liquid ion exchangers”, and it is thus expected to exhibit superior extractability and separability compared with those in conventional organic solvent systems. The authors have focused on these characteristics of ionic liquids, and have studied on the extraction separation of metal ions using ionic liquids as extraction media, with the aim of developing highly efficient solvent extraction systems. This article presents the evaluation of the solvent properties of ionic liquids in metal ion extraction, the separation of rare earth metals by the synergistic effect in ionic liquid systems, and the development of a macrocyclic extractant and the structure analysis of the metal complex extracted into the ionic liquid.

A frequency of cyanobacterial blooms appearance in lakes has been increasing as a consequence of eutrophication together with global warming. Although cyanobacterial blooms have been removed/collected by a suction method, there are few ways to effectively use the cyanobacterial biomass. If added values such as adsorptive function for pollutants in aqueous solution can be provided to the cyanobacterial biomass, it would be contributed to solve problems on cyanobacterial blooms and water pollution. This study aimed to prepare adsorbent from cyanobacterial bloom sample collected in a eutrophic lake for the removal of pollutants, and attempted to remove Cd²⁺ by cyanobacterial blooms-originated adsorbent (CBA) prepared via dehydration treatment using a concentrated sulfuric acid. As a result, CBA possessed smaller specific surface area (13.1 m²/g) and higher amount of total acidic functional groups (8.29 mmol/g), and the maximum amount of Cd²⁺ adsorption was 1.43 mmol/g, which was higher than oxidized activated carbons. From these values, the number of carboxy groups per unit surface area was calculated to be 1.51 × 10²⁰ number/m², and the distance between carboxy groups was estimated to be 8.14 × 10⁻² nm, which would be one of the major reasons of higher amount of Cd²⁺ adsorption. Furthermore, adsorption/desorption experiments were repeatedly conducted 3 times, and the results showed that the adsorption amount and recovery rate were not largely varied, indicating that CBA can be reused for the Cd²⁺ adsorption. These results suggest that the preparation of adsorbent for the removal of Cd²⁺ would be one of the effective ways for the effective utilization of cyanobacterial biomass.