To contribute to the treatment of spent solution discharged from industry, decomposition reaction of cyanide solution containing Ag(I) by the photocatalytic and/or ozone oxidation route was investigated. The main findings obtained were as follows:
1) Ag(CN)
2- ion in cyanide solution is photocatalytically reduced to elemental Ag by TiO
2 or ZnO catalyst powder, but exhibits an induction period at the initial stage under the air bubbling condition. By contrast, there was no induction period under N
2 gas bubbling condition. Precipitation of Ag powder was far slower than that under air bubbling. Simultaneously CN
- ion is oxidized to CNO
-, and subsequently to NO
3- and CO
32-. Oxidation of CNO
- ion was significantly slower under N
2 gas bubbling than under air bubbling.
2) ZnO is a more efficient photocatalyst for Ag( I ) cyanato complex, however limited consumption of the ZnO catalyst is unavoidable.
3) Using ozone as a decomposing agent for cyanide solution containing Ag(CN)
2-, AgCN is precipitated. However, complete removal of Ag( I ) is not expected by this method. In contrast, the addition of KCl to the solution leads to complete Ag( I ) removal, producing AgCl instead of AgCN.
4) Using ozone and photocatalytic reactions at the same time, production of CNO
- ion by oxidation of the CN
- ion can proceed faster than that using each reaction independently, precipitating Ag
2O
2 powder. However, complete removal of Ag( I ) is not expected. AgCl instead of Ag
2O
2 is recovered by the addition of KCl to the solution.
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