Thermochemical properties of hydrothermal alkaline solutions and their application to metal extraction.

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1. <Dissolution mechanism of Tin and Zine in NaOH Solutions at elevated Temperatures and its application to scrap recycling of surface coated steel plates>The dissolution behavior of metallic tin plate in aqueous sodium hydroxide solutions was investigated. The dissolution rate was mainly controlled by the diffusion of dissolved oxygen at temperatures higher than 30ﾟC and NaOH concentration higher than 0.1 mol/1-H20. It increase with the increase in temperature and in rotation speed, while a maximum rate was observed as incresing NaOH concentration. These results were applied to the recycling treatment of surface coated steel plates.2. <Enhanced Dissolution of Copper in Cupric Ammine Solutions at elevated Temperatures and its application to removal of Cu from steel scraps.>The dissolution rate of metallic copper plate in aqueous cupric ammine solutions was mainly controlled by chemical reaction at temperatures below 30ﾟC,and by diffusion of cupric complex at temperatures higher than 40 … More ﾟC.It increase with an increase in temperature and rotation speed, while a maximum rate was observed for increasing Cu (II) concentration. The effect of different anion showed significant results on dissolution rate of copper and iron, and carbonate ion was found to prevent the corrosion of iron. From the result, a method to remove Cu from steel scraps was proposed.3. <Solubility of Nb205 and leaching behaviors of Nb and Ta from niobite in KOHsolutions have been investigated in order to develop an alkali hydrothermal leaching prcess of Nb and Ta.>The solubility of Nb 205 was measured in the range of 40ﾟC to 200ﾟC at various molar ratios (K/Nb) of K20 to Nb205. Nb205 shows the maximum solubility at the solution composition of K/Nb=4/3 at a given temperature. The rise of temperature causes the solubility of Nb205 to increase at the temperatures below 120ﾟC,but decrease above 120ﾟC.The maximum leaching degree of about 90% was obtained at 200ﾟC.It was proved that the alkali hydrothermal leaching process is effective for the recovery of Nb and Ta from the niobite concentrate. Less