Study On Low Temperature Oxidation Of Magnetite And Oxidation Kinetics

In this paper,We analysed ingredient of magnetite,then we produced magnetite with different grain size with machine pulverizing and artificial synthesis methods.From the viewpoint of mineralogy we pulverized magnetite by the planet ball mill and studied the change trends of grain size,transformation,oxidation degree,magnetic susceptibility under the ball milling.We studied change of oxidation effect,transformation and magnetic susceptibility of magnetite grain with different diameter size oxidized in the different temperature and discussed kinetics of low temperature oxidation oxidation.The magnetite fine mineral which average grain size is 4μm contains about 10%Si,Ti impurity.Experiments indicated under ball milling grain size of magnetite refined gradually with pulverizing time prolonging.When rotate speed is 500r/m,reaction time is 30h,the oxidation effiency of magnetite attained 18.6%,magnetic susceptibility droped 3.8×10^-4m³kg^-1.The XRD results showed magnetite transformated into hematite partly.The oxidation degree of pulverized magnetite is obvious,magnetic susceptibility droped 10×10^-4m³kg^-1with hematite appearing when grain size is 2μm,temperature is 320℃,reaction time is 30d.A series of different size and monocrystal well-distribution products were synthesized with co-precipitation,hydrothermal, precipitation oxidation methods.The oxidation efficiency went up little,magnetite susceptibility cut down 0.2×10^-4m³kg^-1when grain size is 30nm,time is 2 month in the room temperature with a small amount of hematite producing.Grain morphology and reaction temperature are main influence factors in the oxidation reaction of magnetite,the oxidation production is decided by grain size,the mechanism is complicated.The oxidation degree is affected by temperature and grain morphology obviously.The low temperature oxidation production is hematite or mixture of hematite and maghematite.Kinetics experiment shows that the room temperature oxidation reactions of different grain size magnetite and pulverizing magnetite reaction can be linearly fitted using first order equation. The low temperature reactions of pulverized magnetite can be linearly fitted using pseudo-second order equation.Basicaly the three reactions are controlled by the process of oxygen diffusing from the surface of magnetite to the internal.Those are diffusion controlled reaction.