Previously, we investigated bead-type silica gel adsorbents bearing immobilized diglycolamic acid ligands for the recovery of rare earth elements (REEs). Although the ligand-bearing silica gel selectively adsorbs REEs, the ligand loading is limited by the specific surface area of the silica gel. To increase the ligand loading, we have prepared a film-type adsorbent by immobilizing diglycolamic acid ligands on a nonwoven poly(vinyl alcohol) fabric by means of grafting polymerization. Compared with the silica gel adsorbent, the film-type adsorbent showed similar selectivity for a heavy REE, but the adsorption capacity of the film-type adsorbent was 3-4 times that of the silica gel adsorbent because the ligand loading on the former was 3.81 times that on the latter.

Anodic dissolution of tungsten or tungsten carbide in a molten sodium hydroxide bath was investigated at 723K in order to simplify a tungsten dissolution step during tungsten recycling process from secondary resources like used cemented carbide (super hard material) tools. Cyclic voltammetry using tungsten and other metal wire electrodes suggested that tungsten is easily oxidized and dissolves into the melt, while nickel, iron and copper are hardly dissolved because of stable film formation on them as a result of oxidation. Cobalt was also oxidized, but the resultant oxide or hydroxide film seemed unstable. Anodic dissolution was carried out at constant voltage using throw-away tips and rotators of vibration motors. When the rotator was anodically oxidized at constant voltage of 1.0 V using a nickel plate as the cathode, tungsten was selectively dissolved at a high current efficiency of 97% and binder metals (nickel and copper) remained as residue. The amount of tungsten remained in the residue was less than 1% of initial value after the electrolysis for 9 hours. In the case of throw-away tips, both the tungsten carbide and binder metal of cobalt were anodically dissolved at constant voltage of 1.0 V, and whole the tips were dissolved by a long-term electrolysis of 20 hours. Although the dissolved tungsten remained in the melt, the greater part of dissolved cobalt deposited as metal powder on the cathode. The current efficiencies of tungsten carbide dissolution were calculated to be 86% and 96% in the cases of ceramic coated and uncoated tips, respectively. These results suggest that the proposed electrolysis is effective to dissolve tungsten from secondary resources, and indicate the possibility of selective recovery of both the tungsten and cobalt in the case of cemented carbide tools.

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