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Studies On Theoretical Principle And Application Of Separation Of Zn-Pb

Posted on:2003-11-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:X Z GuoFull Text:PDF
GTID:1101360092965717Subject:Iron and steel metallurgy
Abstract/Summary:PDF Full Text Request
In the steel plants all over the world the output of dust is about 1%~2% as much as that of steel, most of which contains zinc and lead, and has been classified as hazardous waste, which can not be returned to the former procedures to be treated with. Therefore, the research on the treatment for Zn-Pb-bearing dusts has been one of the hotspots of the metallurgical field in recent years. The current disposal technologies still cannot handle the dust that contains low iron and high lead. The low-grade zinc-oxide ores contain impurities such as lead, sulphur, arsenic, etc. The development of disposal technologies for these ores is relatively slow; thus it is imperative to develop new processing techniques.In this paper a new theory and method is advanced on the basis of the characteristics and current status of disposal technologies of Zn-Pb-bearing dust and low-grade zinc-oxide ores, combined with some new techniques in metallurgical and material fields in recent years. Firstly, the theory of separation of Zn-Pb is put forward, and its theoretical basis and the choice of methods are expatiated and analyzed; secondly, the dynamics and heat conduction model of reduction of the pellets containing graphite are studied; and thirdly, on the basis of studies of the characteristics of this trial dust and ore, the experiments of separation and recovery of Zn-Pb and preparation of high-rank superfine ZnO powder directly coming from low- grade zinc-oxide ores are carried out respectively.In the separation of Zn-Pb, according to some different physico-chemical properties among zinc, lead and their oxides, zinc oxide and lead oxide were reduced, metallic zinc becomes Zn vapour and it can be volatilized and collected in the form of ZnO; and yet metallic lead remains in the residual slag and is recovered in the form of lead slag, so that separation and recovery of Zn-Pb in the dust is realized by one-time disposal. The researches of thermal analysis and vapour pressure of zinc, lead and their oxides show that in order to restrain volatilization and weight loss of Pb element, and realize separation of Zn-Pb, it is necessary for zinc oxide and lead oxide to be fast reduced at a low temperature. The reduction characteristics of pellet containing carbon and heat transfer of aluminum bath can solve the problem of fast reduction of oxides at low temperatures, and the method that realizes separation of Zn-Pb-pellet containing carbon & aluminium bath smelting reduction method (called as" aluminum bath method " in short) is advanced. In order to achieve basic theoretics of separation of Zn-Pb, the studies of kinetics of reduction of ZnO and PbO pellets containing graphite under the iso-temperature condition show that at the temperature of 1000~1150℃, the higher the temperature, the faster the reduction rate of ZnO; while that of PbO changes little or decreases; the calculated apparent activation energies are not large, when carbon gasification reaction, or surface reaction, or gasification diffusion is the controlling factor, and the activation energies of PbO are less than those of ZnO; the reducing reactions of ZnO and PbO are under the control of gasification diffusion, whose activation energies are 46.548~53.280kJ?mol-1 and 43.338~48.802 kJ?mol-1 respectively. Other test results show that the reduction rate of the ZnO pellet containing graphite increases with the improvement of condition of external diffusion and with the existence of aluminum bath; at the temperature of 1000~1250℃, aluminium almost does not participate in the reducing reaction of zinc oxide, and aluminum bath mainly plays a role in heat transfer in the reduction of ZnO. On the basis of reduction mechanism of pellet containing graphite, the studies on a mathematical model that incorporates heat transfer and chemical reaction and the experiments of internal temperature of a pellet show: at the initial stage of reducing reaction, the internal temperature of the pellet goes up fast, and when it reaches the beginning reduction temperature, the increasing...
Keywords/Search Tags:Separation of Zn-Pb, pellet containing carbon & aluminium bath smelting reduction method, Zn-Pb-bearing dusts, zinc-oxide ore, reduction, heat transfer, superfine ZnO
PDF Full Text Request
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