| Shortage of iron ore resource has seriously restricted the development of iron and steel industry in China recently. It is significant to utilize the secondary resources which are rich of iron, such as pytite cinder, comprehensively. Pyrite cinder, also containing considerable nonferrous metals, is a kind of important secondary resources which are difficult to upgrade and smelt. Tens of millions of tons of pyrite cinder are discharged in chemical industry annually. In addition, there are more than100million tons of the accumulated waste cinder in storage that cannot be efficiently utilized. However, there are some limitations for comprehensive utilization of the pyrite cinder containing nonferrous metals. As an example, it is required that FeO content of cinder is less than5%with traditional technology of high temperature chlorination roasting for pyrite cinder. The iron grade of oxidized pellet which is prepared by high temperature chlorination roasting is low for the blust furnace. Furthermore, the nonferrous metal elements, such as copper, cannot be removed by the traditional reduction technology. Therefore, This paper developed a "one step" technology of preheating chorination-direct reduction. The raw material used is namely pyrite cinder mixture from Lingbao with Cu, Pb, Zn and high FeO content. Moreover, the mechanism was studied, which supplied the theory basis and effective process for the comprehensive utilization of pyrite cinder containing nonferrous metals.The study of this thesis focused on the preparation of green balls, preheating and chloridizing roasting of pellets and reduction roasting of pre-heated pellets. It is shown that blast furnace burdens of high quality, which possess high grade of iron, good mechanical strength, some metallization degree and low content of copper, lead and zinc, have been acquired by "one step" technology of chloridizing and reduction roasting from pyrite cinder containing nonferrous metals. Based on the above research, the tests, using the pyrite cinder mixture contaning Fe61.24%、 Cu0.22%、Pb1.79%and Zn0.20%, were conducted in a grate-kiln at a pilot scale. The main quality results of pre-reduced pellets were as follows:total iron content of73.17%、metallization degree of46.18%、the Cu、Pb and Zn content of0.18%,0.16%and0.065%, the compressive strength of1069N per pellet, tumbler strength of64%, the reducibility index of30.12%, the reduction swelling index of-3.7%, reduction disintegration index of (RDI+3.15)98.83%。The test results show that this new process can effectively separate copper, lead, zinc form iron, and greatly increase the iron grade. The mechanical strength and metallurgical property of pre-reduced pellets and the content of copper, lead and zinc in them also can meet the requirement of blast furnace burden.The chloridizing roasting behaviors of pyrite cinder pellets were investigated.①It can be seen from the research of chlorination thermodynamics that it is easy for oxides, sulfides, ferrite and silicates of copper, lead and zinc to chloridize with the addition of CaCl2in pellets, but hard for the iron oxide and the gangue like silicon and alumina. This is the basis for separation of copper, lead, zinc from iron.②It is shown from the research of chlorination kinetic that the chlorination reactions of CuO, Cu2O, ZnO and ZnFe2O4are controlled by interface chemical reaction from1025℃to1175℃, while PbO is controlled by diffusion. The chlorination reaction rates of copper, lead and zinc are very fast, which support the removal of copper, lead and zinc inside pyrite cinder well at the chain grate in preheating.③Form the chlorination behavior of copper, lead and zinc, it is found out that it is the easiest to remove sulfides in the chloridizing roasting, then the oxides. Furthermore, it is most difficult for ferrites and silicates to remove. The gangue has a great effect on the removal of copper, lead and zinc.④The microstructure change of preheated pellets shows that oxidizing and chloridizing roasting can pomote the crystallization of iron oxides.It was further investigated of the reduction mechanism of pyrite cinder pellets and reduction volatilization behaviors of lead and zinc. The following results are obtained.①It can be seen from the research of reduction thermodynamics that the copper oxides are the easieat to reduce, zinc oxides are most difficulty to reduce, lead oxides are middle. Metallic zinc and lead volatilize into flue gas, while the metallic copper is remained in pellets.②It is found out from the research of reduction kinetic that reduction of iron oxides is controlled by interface chemical reaction inside pyrite cinder pellets within the temperature range of800-1100℃, and the reduction reaction rate is fast. The reduction reactions of zinc ferric and lead oxide are also controlled by interface chemical reaction at950-1100℃. The lead oxide is the fastest to reduce, iron oxides are the slowest to reduce, and zinc oxides are in the middle.③From the research of solidification mechanism pyrite cinder pellets and microstructure feature in reduction, it is proved that fully solidification of pellets and sufficient crystallization of iron oxides are the premise to obtain high strength of reduced pellets.④The reduction volatilization behaviors of lead and zinc show that the high reduction temperature and the high concentration of CO promote the removal of zinc and lead. |
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