| Abstract:Zinc-bearing dust and pyrite cinder discharged from steel companies and chemical companies,have the characteristics of the large amount and containing many valuable metals and detrimental elements, resulting in huge waste of resources and serious environment pollution. Therefore,it has the considerable realistic significance to develop a new technology of utilizing these dusts to obtain the high quality burden for blast furnace.Three kinds of zinc-bearing dust and one kind of pyrite cinder were used in this thesis.The physical and chemical properties and mineralogy characters are systematically studied.The thermodynamic behaviors of iron oxides, ZnO, PbO and FeAsO4during the reduction roasting process are also analyzed. The results show that the metallized sintering process is a feasible process to remove Zn, Pb and As.On this basis, a new process of metallized sintering process to separate iron from Zn, Pb and As is developed,and the migrating behaviors of Zn, Pb and As,and the consolidation mechanism of pre-reduced sinter in the sintering process are also revealed.The iron content of gas ash, dry tpyed dust, converter sludge and pyrite cinder are33.45%,26.40%,56.30%and46.02%, respectively. The carbon content are33.80%,26.50%,0.57%and0.35%, respectively. The Zn content are0.66%,5.77%,2.27%and0.25%, respectively. The Pb content are0.15%,2.25%,0.49%and0.11%, respectively. The As content of pyrite cinder is0.17%. The mineralogy of raw material shows that most Zn and Pb absorb in the form of ZnO and PbO in the surface of iron oxides in the zinc-bearing dust. Zn and Pb exist in the form of sulfide in the pyrite cinder, and As exists in the form of FeAsO4in the pyrite cinder. Therefore,the Zn, Pb and As cannot be removed effectively from zinc-bearing dust and pyrite cinder by conventional beneficiation processes.Thermodynamics investigations show that when ZnO is reduced by carbon,the CO content requirement decreases sharply as the temperature increases.ZnO is harded than FeO to be reducd at the temperature lower than1085?.However, ZnO is easier than FeO to be reduced at the temperature higher than1085?. PbO is reduced to Pb easily, and the CO/(CO+CO2) requirement is only0.52%at the temperature of800?. FeAsO4can be reduced to As4O6at the week reducing atmosphere, and FeAsO4is reduced to As at the CO/(CO+CO2) higher than9.39%at the temperature of1000?. The Zn?Pb?As can be removed in the metallized sintering process because of the reducing atmosphere and high temperature in the burning and pre-reducing zone.The results of dynamics of iron oxides,ZnO and PbO reductions show that the reactions are controlled by chemical reaction,and the calculated activation energier are43.88and72.33KJ.mol-1, respectively, for the reductions of iron oxides and ZnO. The calculated activation energy of18.22KJ.mol-1is characteristic for gas diffusion controlled process in the PbO reducing reaction.The dynamic conditions of high temperature and rapid reduction meet requirements for the reductions of iron oxides,ZnO and PbO.The results of new process of metallized sintering show that the drop numbers, compressive strength and shock temperature of green balls are7.4times/0.5m,15N and461?under the conditions of balling at18%moisture for13min.The green balls are used to conduct the metallized sintering process under conditions of C/Fe of0.5,the carbon ratio of inside to outside pellets of50:50, the bed height of400mm and the air speed of0.4m/s.The pre-reduced product, assaying60.53%Fe with the metallization degree of45.23%,and the Zn,Pb and As content of0.18%,0.015%and0.025%, was obtained at the yield of85.62%, productivity of0.471tm-2h-1, tumble index of81.31%,the solid fuel consumption of309.67kg·t-1,respectively. The reducibility index and reduction disintegration index (RDI+3.15)of pre-reduced product are80.69%and96.45%,which show the pre-reduced product is the high quality burden for blast furnace.The ZnO?PbO and As2O5content of condensation dust are51.49%,3.15%and1.45%,respectively.The reducing and removing behaviors of Zn,Pb and As during the metallized sintering show that the bed can be devided five zones, including original material zone,wetting materials zone, drying and preheating zone,burning and pre-reducing zone and product zone.During the product zone,metallic iron outside the pellets is reoxided into wustite. During the burning and pre-reducing zone,the maximum temperature of bed is higher than1300?,and the duration (temperature higher than1250?) is longer than5min.The bed atmosphere is reducing atmosphere, and the content of CO2, CO and O2in the exhausted gas are12-15%,10?13%, and2?5%,respectively. The atmosphere inside the pellets is strong reducing atmosphere (C/Fe of pellets is0.33),and iron oxides are reduced into metallic iron.ZnO and PbO are reduced and volatilized in this zone, and FeAsO4is reduced to As.During the drying and preheating zone, the temperature of bed decreases sharply and the oxidized atmosphere strengthens.Zn,Pb and As are oxidized and condensed in the surface of dried and preheated pellets.As the running of sintering process, the ZnO, PbO and As2O5of the drying and preheating zone are re-reduced, re-volatilized, re-oxidized and re-condensed until the end of sintering process to the condensation dust.The pre-reduced product presents in the form of grape structure, and the pellets adhere together with liquid phase. The microstructures show that metallic iron is the major bonding connection inside the pellets, and the metallic iron content is39.82%.The liquid phase, such as wustite, FeSiO4and CaMgSiO4are the major bonding connections between pellets, and the wustite and slag content are31.95%and24.29%, respectively. The pre-reducing sinter possesses the metallic iron and luquid phase boding connections to achieve the consolidation.The new process is an effective one step process to separate iron from Zn, Pb and As,and the high quality burden for blast furnace is achieved.The new process possesses the characters of high productivity, simple equipments,low cost and material adaptability, which has the bright prospect in the industrial application.The study has opened a new way to utilize the zinc-bearing dust and pyrite cinder large scaly and efficiently. |
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