Study On Kinetics Of Coke-based Reduction Of High Phosphorus Oolitic Hematite

China is abundant in oolitic hematite resources. Because of fine crysyallzation granule size, complex mineral compositions and high content of harmful elements, oolitic hematite has not yet realized industrial development and utilization. Lots of experiments showed that the oolitic hematite with high phosphorus, processed by traditional beneficiation technology, couldn’t obtain ideal indexes. High quality iron powder could be achieved by coke-based reduction and magnetic separation technology. In this thesis, the kinetics of coke-based reduction of pure material systems and oolitic hematite from Guandian, Hubei province were investigated which established a theoretical foundation for the development and utilization of high phosphorus oolitic hematite.The technique conditions of coke-based reduction of high phosphorus oolitic hematite were optimized with coke as the reductant. The experimental results showed that metallization rate of reduction product, iron grade and the recovery of the iron powder were 90.50%,96.47% and 87.62% under the conditions that reduction temperature, reduction time and mole ratio of C/O were 1200℃,160 min and 3.5.Kinetics of coke-based reduction of Fe2O3, Fe2O3-SiO2, Fe2O3-SiO2-Al203, Fe2O3-SiO2-Al2O3-CaCO3 systems and high phosphorus oolitic hematite were studied isothermally and non-isothermally by thermogravimetric analysis.Experiments showed that coke-based reduction processes of Fe2O3, Fe2O3-SiO2, Fe2O3-SiO2-Al2O3 and Fe2O3-SiO2-Al2O3-CaCO3 systems could be divided into three stages, induction period, acceleration period and deceleration period. Reactions of four systems were in conformity with the Avrami-Erofeev equation, and were controlled by nucleation and growing up. Isothermal method determined activation energy of four systems were 192.48KJ/mol,235.33KJ/mol,248.23KJ/mol and 288.21KJ/mol, and corresponding pre-exponential factors were 9.47×105 min-1,3.22×107 min-1,4.02×107 min-1 and 1.15×109 min-1. Non-isothermal method determined activation energy of four systems were 178.75KJ/mol,238.66KJ/mol,245.41KJ/mol and 272.60KJ/mol, and corresponding pre-exponential factores were 8.82×105min-1,1.04×107min-1,2.99×107min-1 and 1.24×10 min-1.The contact area of Fe2O3 and reductant decreased with the adding of SiO2 and Al2O3, which resulted in low reduction rate of iron oxide and high content of iron oxide in reduction products. Ferric silicate, such as fayalite, hercynite and sekaninaite were produced at the process of coke-based reduction by reacting of Fe and FeO with SiO2 and Al2O3. Two reasons above decreased the fractional reduction of reaction. The reaction activity and gasification of coke were improved by CaO and CO2 respectively, which were produced by decomposition of CaCO3. The content of iron oxide in reduction products decreased for the sufficient coke-based reduction of Fe2O3. At the same time, the FeO from fayalite, hercynite could be changed to metallic iron with the action of CaO and CO, then the content of the ferric silicate in reduction products decreased, which increased the fractional reduction of reaction.The coke-based reduction process of high phosphorus oolitic hematite also could be divided into three stages, induction period, acceleration period and deceleration period. Coke-based reduction of high phosphorus oolitic hematite conformed to the Avrami-Erofeev equation and nucleation and growing up were controlled step. Activation energy and pre-exponential factor of oolitic hematite were 318.323 KJ/mol and 2.07×1010min-1 adopted by the isothermal method. The activation energy and pre-exponential factor were 309.49KJ/mol and 1.37×1010min-1 adopted by non-isothermal method.The contrasting of experients results of high phosphorus and Fe2O3-SiO2-Al2O3-CaCO3 system showed that other gangue minerals except Fe2O3, SiO2, Al2O3 and CaCO3 was low and affected less on coke-based reduction of Fe2O3. Fe2O3 in high phosphurs oolitic hematite mainly distributed in oolite and formed ringed homocentric structure with gangue minerals, which increased the difficulity of contact between reductant with Fe2O3 and activation energy of reaction. Therefore, the coke-based reduction of high phosphorus was lower in reduction rate and need long reduction time.