| 摘要 |
<p>PURPOSE:To recover Ag in the form of high-purity AgCN at a recovery percentage close to 100% by adjusting the pH of a spent silver-cyanide-plating waste liquor to strong base, by making O3 function to decompose free cyanogen in the liquor and by subjecting the resulting precipitate to separation by filtration. CONSTITUTION:An acid or alkali is added to the above silver-cyanide-plating waste liquor to adjust the pH to a strong base of >=9, preferably 9-14. Subse quently, O3 is blown into the above pH-adjusted waste liquor, which is allowed to react to decompose almost stoichiometrically to O2 and N2 as represented by a formula 2CN<->+5O3 2CO2+N2+11/2O2. Then said reaction is further progressed so that complex-ion CN existing in solution in the form of Ag(CN)<-> is oxidized to precipitate AgCN. On the other hand, Cu forming a complex ion in the form of Cu(CN)<-2> is brought into a condition dissolved in the liquor in the form of the complex of Cu(CN)4<-2> or Cu(CN)2 by the oxidation by O3. Consequently, on subjecting the reactant liquor in the above condition to filtra tion, washing and drying, recovery and refining of AgCN are simultaneously carried out, so that Ag can be recovered in the form of AgCN.</p> |
