Abstract:When mixed rare earth is roasted with sulfuric acid at high temperature, the flue gas composition is complex, and the existing flue gas treatment system cannot effectively treat H2S gas. Based on this, the decomposition of sulfuric acid and pyrite under different conditions and the formation mechanism of H2S were investigated. Under the reduction condition and addition of concentrated sulfuric acid, the production amount of H2S and SO2 increases with the decrease of temperature, flow rate and oxygen content in the gas, but the formation condition of SO3 is opposite to that of H2S and SO2. Therefore, in order to effectively control the amount of H2S generated by sulfuric acid, the gas supply should be increased, the reaction temperature should be lowered and the oxygen content in the gas should be increased. Reducing the reaction temperature or increasing the air flow will reduce the temperature in the furnace, resulting in incomplete reaction between rare earth minerals and thorium minerals, and no target mineral phase can be obtained. Therefore, in the production, the oxygen content of the blast can be appropriately increased, that is, the oxygen-rich blast, which can effectively avoid the phenomenon of sulfuric acid reduction to produce H2S. At room temperature, pyrite and dilute sulfuric acid produce ferrous sulfate, sulfur and hydrogen sulfide gas; In concentrated sulfuric acid, pyrite produces iron sulfate, sulfur dioxide, elemental sulfur, and no hydrogen sulfide gas, which is mainly due to the strong oxidation of concentrated sulfuric acid. The reaction of iron sulfide, concentrated sulfuric acid and carbon mixture at 500 ℃ in an air atmosphere generates magnetite and hydrogen sulfide, while hydrogen sulfide and iron oxide are still generated in oxygen-rich air. Therefore, in the presence of reducing agents, the content of pyrite in raw materials should be reduced to effectively reduce the production of H2S.