| 摘要 |
<p>PROBLEM TO BE SOLVED: To solidify impurities in a residue by introducing an oxygen contg. gas such as air into a slurry after leaching with chlorine so as to control the pH of the leaching liquid. SOLUTION: In a leaching process with chlorine, chlorine having strong oxidation power is introduced, and during the process, sulfur is oxidized to produce a little amt. of sulfuric acid which decreases the pH of the leaching liquid to almost 0 and stabilizes a minute amt. of impurities such as Fe as ions. Therefore, it is necessary to increase the pH of the leaching liquid to fix the impurity ions as insoluble hydroxides or oxides in the residue and to remove the fixed matters. In order to carry out this process, an oxygen-contg. gas such as air which is rather inexpensive is introduced into the slurry to neutralize protons in the leaching liquid. Namely, protons are decreased in number by the reaction of O2 +4H<+> +4e<-> =2H2 O. However, if the pH increases too much, Ni is also distributed as a hydroxide in the residue to decrease the recovery rate of Ni. Therefore, the pH is controlled to 0.5 to 1.</p> |
