High Efficiency Recovery of Valuable Metals from Ceramics Scraps by Hydrothermal Mechanochemical Method

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In this project, we carried out the following experiments and obtained the following results :Hydrothermal extraction process of Co binder phase from WC-Co cermet was investigated in order to establish a novel recycling system of WC-Co cermet scraps. When the cermet chips were hydrothermally treated in hydrochloric acid above 110℃, Co binding phase was efficiently extracted and the cermet chips were disintegrated into relatively large fragments. After hydrothermal treatment, WC sintered body became very brittle and pulverized easily by ball milling and the mean particle size of thus obtained WC particle became similar to that of virginal WC particle. The recycled WC powder was a little easier to undergo oxidation than the virginal WC powder, so that the mechanical properties of recycled WC-Co cermet were degraded. However, the degradation of mechanical properties was prevented only by drying the WC powder more carefully. This hydrothermal process will be one of the recycling systems fo … More r WC-Co cermet.The WC-Co cermet specimens with various WC particle sizes and Co content were hydrothermally treated in HNO_3 aqueous solutions at temperatures of 110-200℃ for duration of 6-240h. The Co was preferentially leached out into the acidic solution, while the WC was oxidized to insoluble WO_3 hydrate which was subsequently separated by filtration. The hydrothermal treatment parameters such as solvent concentrations, treatment temperatures, holding time were optimized in respect to different kinds of WC-Co cermets. A hydrothermal oxidation treatment in 3M HNO_3 aqueous solution at 150℃ for 24h was capable of fully disintegrating the cermet chip composed of coarse WC grains of 1-5 〓m in size with 20 mass% of Co as binder. While the more oxidation resistant specimen composed of fine WC grains of 0.5-1.0 〓m in size with 13 mass% of Co, was completely disintegrated by a treatment in 7M HNO_3 aqueous solution at 170℃ for 24h. The filtered solid residues were composed of fine WO_3・0.33H_2O powder and a small amount of WO_3. The recovered WO_3・0.33H_2O powder can be easily returned to the industrial process for the synthesis of WC powder so that the overall recycling cost can be possibly lowered.The hydrothermal treatment of used Nd-Fe-B sintered permanent magnet was investigated in order to recover the rare-earth resources efficiently. Commercially available Ni-coated Nd_2Fe_<14>B sintered magnet was hydrothermally treated under the optimum conditions at 110℃ for 6h in the mixed aqueous solution of hydrochloric acid (3.0mol/dm^3) and oxalic acid (0.2mol/dm^3). As a result, more than 99% of Nd metal contained in the magnet was collected as solid precipitate of Nd_2(C_2O_4)3・xH_2O with the purity as high as 99.8%. Less