Wet oxidation characteristics of metal cyanide complexes below 423 K

Abstract

In the present study, the wet oxidation of zinc and copper cyanide complexes (cyanide concentration of 1,000 mg dm-3) was conducted in a hydrothermal reactor, under oxygen atmosphere of which the pressure was set to 1 MPa. The pH of the reaction solution was kept in the range of 11 to 12 and the reaction temperature was changed from 383 K to 423 K. In the experiments, mainly the effect of reaction time on the cyanide decomposition was investigated. As a result, it was found that cyanide decomposition increased with an increase in the temperature and cyanide decompositions of 99.9 % and 96.1 % were achieved after 8 hours at 423 K for Na2[Zn(CN)4] and Na3[Cu(CN)4], respectively. In the case of Na2[Zn(CN)4], mainly HCOO- and NH4+ were identified as the decomposition products. By contrast, in the case of Na3[Cu(CN)4], carbon of CN- was transformed either to H2CO3 or HCOO-, and nitrogen was converted to NH4+, N2 or NO2-. Based on these results, the decomposition mechanisms of Na2[Zn(CN)4] and Na3[Cu(CN)4] at a temperature of 423 K and pressure of 1 MPa were discussed.