Study On The Kinetics Of Typical Metallurgical Reactions By Gases On-Line Analysis Technique

The kinetic study of redox reaction in metallurgical process is the core issue of metallurgical physical chemistry research. It can provide a theoretical basis for the optimization of metallurgical process, improvement of production efficiency and exploration of new metallurgical processes. At present, the common method for the kinetics study of metallurgical reactions is thermogravimetric method. In order to get other methods, and achieve dynamic study of metallurgical reactions, the gases on-line analysis mass spectrometry technique was used to study the kinetics of metallurgical reactions. Through on-line monitoring in the process of the reaction gas ion intensity with time, qualitative and quantitative analysis of reaction can be done by using gases on-line analysis mass spectrometry technique. The method used common reaction gases in gases on-line analysis mass spectrometry technique is named gas mass mass spectrometry method. And the method used isotopic gases and combined with gases isotope exchange technique is named isotope exchange method. Due to the importance on the metallurgical process, the reaction between CO2-CO and iron oxides has been attracted the ateention by many researchers and got many results. However, there is some issues. First, most work focuses on the reaction between CO2-CO and melts contained iron oxides, or between CO2-CO and iron oxide powder, there is less study on the CO2-CO and solid-state iron oxide. Second, the iron oxides are concentrated on FeO and Fe3O4, but Fe2O3has less attention. Third, most studies use carbon isotope exchange method to obtain accuracy rate constant, less studies use oxygen isotope exchange method. To recycle CO2gas, domestic metallurgy reaearchers blowing CO2-O2mixed gas in converter steelmaking process. There is many advantages for this blowing way. But the oxidation reaction rule, mechanism and the utilization of CO2in melt with CO2-O2gas are still unkown. The kinetics study of reaction using CO2-O2gas in melt is necessary. In this work, the kinetics of reaction between CO2-CO and solid-state iron oxides (pure iron, FeO, Fe2O3), the reaction between CO2-O2and Fe-C system in melts are studied by using gases on-line mass spectrometry analysis technology.The kinetics of reaction between CO2-CO and solid-state pure foil iron is studied by using gas mass spectrometry method. The calculation of reaction rate has been deduced. Also, the calculation of reaction rate constant equation has been obtained by combining with the reaction mechanism. The oxidation reaction contains three parts. Reaction in the first part and the second part is interface chemical reaction controlling, in the third part is mixed model controlling. The results showed that the oxidation between CO2-CO and solid Fe contains three stages, the controlling step is CO2dissociation. Compared with results obtained by thermogravimetric method, this on-line mass spectrometry method can be used to study the reaction kinetics between CO2-CO and solid-state iron.The kinetics of reaction between CO2-CO and solid-state Fe2O3is studied by using carbon isotope exchange method. The calculation equation of apparent reaction rate constant has been amended, and the real reaction rate constant was evaluated. All the results showed that the rate constant decreased with increased oxygen parcial pressure. This work perfected the interface kinetic data of oxygen transfer in solid-state iron oxides. It found that the variation of rate constant with oxygen parcial pressure in different iron oxide phase had different slope.The kinetics of reaction between CO2-CO and solid-state FeO is studied by using18O isotope exchange method. All the results showed that the controlling step within approximately30s is interface chemical reaction, after30s is diffusion reaction. The CO2dissociation k1, re-formation rate constant k2, and mass transfer coefficient k3were obtained. k1and k2increased with increasing oxygen parcial pressure, while k3linearly decreased with increasing oxygen parcial pressure. Also, the activation energy for k1, k2and k3with92.92kJ/mol,43.21kJ/mol and82.03kJ/mol were obtained. The value of oxygen diffusion coefficient has been obtained in this study. The diffusivity of oxygen linearly decreased with increasing oxygen parcial pressure. The oxygen diffusivity activation energy of151.26kJ/mol was obtained. It is concluded that the oxygen diffusion in wustite occurs through an oxygen vacancy.The kinetics of decarburization with CO2-O2in Fe-C melts has been studied by using gas mass spectrometry method. Through the thermodynamic calculation of surplus heat, it found that the utilization of CO2was much less, the CO2percentage conformed to thermodynamic condition became bigger. The effects of gas sampling locations, blowing distances, initial carbon content, flow rates, CO2percentage and temperature on decarburization rates have been investigated. The results showed that the rates increased with bigger flow rates and initial carbon content. The rates decreased with increasing blowing distances and CO2percentage. The decarburization with CO2-O2mixed gases in Fe-C melts satisfied apparent zero order reaction, and the decarburization reactions with CO2, O2were parallel. The utilization of CO2in different CO2percentage was calculated. In the range of0%～60%, the utilization of CO2decreased with increasing CO2 percentage. In the range of70%～100%, the utilization of CO2increased with increasing CO2percentage. The kinetic model of decarburization with CO2-O2was deduced. The reaction mechanism changed in the all CO2/O2ratio range. In the range of0%～60%, the decarburization reaction controlling step is mass transfer. In the range of70%～100%, the controlling step is mixed model (decarburization with O2is mass transfer controlling, decarburization with CO2is interface chemistry controlling). At last, the optimum CO2percentage was obtained within the range of30%.