Research On Oxidation Kinetics Of Synthetic Magnetite Pellets

Especially in the last two years,the excessive competition between the domestic iron ore industry and foreign mining giant,has led a lot of domestic iron ore mine to be halted or bankrupt,therefore,in order to avoid the monopoly of the foreign iron ore business to our country,the domestic abundant reserves of weak magnetite refractory iron ore must be exploited efficiently,timely.From the current situation and thcology,magnetizing roasting-magnetic separation is one of the effective methods for processing the weak magnetite refractory iron ore,after being magnetizing roasting-magnetic separation,weak magnetite refractory iron ore will be converted into ferromagnetic artificial magnetite.Sintering agglomeration is not feasible for artificial magnetite after being fine grinding and further separation,nevertheless,pelletizing is quite applicable.Based on artificial magnetite from limonite from Datian,Fujian after being magnetizing roasting-magnetic separation,this paper mainly studied the oxidation kinetic of artificial magnetite pellets.Firstly,the optimized pelletizing technical parameters were determined,that 1.0 percent of bentonite,approximately 17.5 percent of water and 15 min of pelletizing consuming were needed,24 r/min of rotate speed of cutter was set,meanwhile,the green ball indexes were optimal with the compressive strength of 17.8 N per pellet,drop number of 15.6 times from 0.5 m and shock temperature above 350 ℃.Secondly,oxidation kinetics of artificial magnetite pellets was studied by using isothermal method,which indicated that artificial magnetite pellets was easy to be oxidized,and oxidation activity was very strong at low 1073 K because of its lower activation energy of only 8.90 k J/mol,the process was mainly controlled by gas inner diffusion,in fact,the oxidation degree of artificial magnetite pellets could reach 83.91%after being oxidized 8 min at 873 K;the oxidation process was controlled by chemical reaction at high 1073 K and the activation energy was 67.76 k J/mol,for example,the oxidation degree of artificial magnetite pellets could reach 87.38% after being oxidized2.5 min at 1273 K.The activation energy were 50.82 k J/mol or 85.41 k J/mol of the oxidation reaction of natural magnetite at low 1073 K or high 1073 K,respectively,which were both larger than that of artificial magnetite.Finally,kinetics equations of artificial magnetite pellets oxidation were worked out by using “unreacted shrinking core model”:The study found that the equations calculation values were in good agreement with the experimental measurement values,therefore,this would provide the theoretical basis for optimized heat schedule choosing and process control of preheating-roasting of artificial magnetite pellets.The results showed that not only the balling performance of the artificial magnetite and natural magnetite were different,but also the pellets preheating oxidation characters were completely different.Artificial magnetite pelletizing only needs 1.0% of bentonite,moreover,preheat temperature and time required for the oxidation of artificial magnetite pellets were lower and less time.Hence,using the artificial magnetite to produce pellets was of great significance,because it will consume lower energy than natural magnetite pellets during preheating-roasting.