Research On Physicochemical Fundamental And New Technology Of Tin, Zinc-Bearing Complex Iron Concentrate Pellets By Weak Reduction Roasting

With the rapid development of iron & steel industry of China, it is of significance to intensify utilization of domestic complex iron ore resources. The complex iron ores containing fin and zinc are typical intractable ones, great reserves of which are found in China. In this research, tin, zinc-containing iron concentrate, taken from Huanggang in Inner Mongolia Autonomous Region, was used to investigate the physicochemical fundamental and new technology of preparation of pellets for blast furnace by weak reduction masting and recovery of tin and zinc.Based on the investigation of basic physicochemical properties of the tin, zinc-bearing iron concentrates, the process mineralogy of them were detailedly researched by using advanced testing methods, such as optical microscope, SEM, XRD and electron probe. It was found that magnetite in the concentrates was closely symbiotic or enwrapped by cassiterite and sphalerite, which mostly existed in the shapes of superfine monomer or anomalistic granules. So it was difficult to separate fin and zinc from the iron concentrates.The analytical results of reduction thermodynamics of iron, fin and zinc oxides showed that, tin and zinc could be separated from iron when reduction temperature was between 974℃and 1250℃, moreover, CO% in the gas wasless than 16.8% but above 7.6%. SnO₂ was reduced and volatilized as gaseous SnO, ZnO could be reduced into Zn_g and Fe₂O₃ or Fe₃O₄ were only reduced to FeO under the conditions.The isothermal and non-isothermal reduction kinetics of Fe₃O₄→FeO stage was investigated using CO as a reduction agent. The results indicated that the controlling mechanism of isothermal reduction reaction was similar to that of the non-isothermal reaction. Under the non-isothermal conditions, the reaction of Fe₃O₄→FeO stage was controlled by interfacial chemical reaction when reduction temperature was between 600～920℃, however, it was controlled by a mixed chemical reaction and diffusion when the temperature was above 920℃. The isothermal reduction kinetics of SnO₂ and ZnO in the concentrate pellets containing tin and zinc were carded out and it was found that the reduction of SnO₂ was controlled by interfacial chemical reaction when temperature was at 950℃and 1000℃, whereas, it was controlled by a mixed mechanism of chemical reaction and diffusion when the temperature was at 1050℃and 1100℃. As far as the reduction of ZnO was concerned, it was controlled by interfacial chemical reaction when the reduction temperature was between 950～1100℃.On a basis of investigations of preparation, drying, preheating and roasting characteristics of tin, zinc-bearing iron concentrate pellet, a new process of comprehensive utilization of tin, zinc-containing iron concentrate by weak reduction roasting was fast put forward. Technological parameters of the scale-up experiment were performed on an analog equipment of a grate-kiln. Under the optimal experimental conditions, 1～2% anthracite, which was added inside the pellets, had a little effect on the volatiliTation of tin and zinc. Compared with the pellets without internal anthracite, the volatilization rate of tin and zinc was improved by 0.5～1.5%, which was respectively more than 80% and 70%, and the remaining contents of tin and zinc in the roasted pellets were less than 0.06%. The compression strength of the finished pellets was in excess of 2480 N/P, the ISO tumbling index over 97% and the abrasion index less than 2%. The results obtained from scale-up experiments showed that the new process could effectively realize the separation of tin and zinc from iron. The compression strength of roasted pellets and residual tin and zinc in them also met the requirement of the blast furnace production.The factual acreages of all the main minerals in the artificial pellets were measured by using Leica Figure Analytical Software—Qwin. By the application of optical microscope, SEM, XRD and X-ray energy spectrograph, the main minerals were approved and the factual mass percentage of them in. the roasted pellets were calculated based on the chemical analytical results. From the above research, the bonding mechanism of the pellets by weak reduction roasting was performed for the first time. The investigations disclosed that the weak reduction roasted pellet was mainly bonded by the recrystallization of wustite at high temperature, and the wustite particles were connected with each other and incrusted closely by the olivine crystallized imperfectly between them. So the pellets have high strength.This investigation provided a new approach for the comprehensive utilization of fin, zinc-bearing complex iron concentrate and credible technological parameters for the industrial production of the new process.