In the present work, thermal decomposition of ASs in air was characterized by a combination of TG-DSC, XRD, and TG-FTIR. The treatment of generated toxic (CN)2 gas was investigated as well. The result showed that the decomposition of Zn2Fe(CN)6 in ASs preferentially reacted with CuSCN leading to the early decomposition of ASs, in which a part of CuSCN decomposed into Cu5FeS4 or Cu2S followed by being oxidized to sulfates and oxides as the temperature increased to 420 °C. For Zn2Fe(CN)6·3H2O in ASs, the decomposition products below 500 °C include ZnS, ZnSO4, CuxFeySz, iron oxides and Zn(CN)2; instead, Fe3O4, ZnSO4 and ZnFe2O4 were formed. The FTIR and chemical quantitative analysis showed that nitrogen-containing gaseous products predominately contained (CN)2, HCN and small amounts of NH3 and NOx. In view of toxic gases released, catalytic oxidation employing in-situ generation of roasting slag at 600 °C (AS1) can be effectively used for the conversion of (CN)2 to N2 under the optimal conditions of airflow rate of 0.7 L/min and AS1/ASs mass ratio of 0.5. Significantly, the ZnFe2O4 phase in AS1 completely disappeared and was converted to ZnSO4 after the experiment, which facilitated the subsequent acid leaching, thereby achieving the synergistic treatment of exhaust gases and slag.
Keywords: Catalytic oxidation; Cuprous thiocyanate; Cyanogen; TG-FTIR; Zinc ferrocyanide.
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