Research On The Enhanced Gas-based Reduction Process By Pre-oxidation Of Ilmenite Concentrate Bearing High Calcium And Magnesium

The Pan-Xi region（Panzhihua&Xichang in China）has a world-renowned multi-metal co-associated super-large vanadium-titanium magnetite deposit.The ilmenite concentrate recovered from the tailings of the Panzhihua vanadium-titanium magnetite after primary beneficiation is the most important raw material for the titanium industry in China.Panzhihua ilmenite concentrate is a low-grade,high Ca-Mg content（Mg O+Ca O>6 wt.%）rock-type ore with a dense structure,which is difficult to reduce.Developing an economical,environmentally friendly,and efficient titanium slag production process is necessary.The current process using electric furnace for high Ca-Mg content ilmenite concentrates smelting facing the problem of high energy consumption and low efficiency.In this work,the isothermal and non-isothermal oxidation kinetics of ilmenite concentrate were studied experimentally,the influence of pre-oxidation on the isothermal reduction kinetics of ilmenite concentrate were conducted to prove the necessity and superiority of pre-oxidation of Panzhihua ilmenite concentrate.The results provide a theoretical basis for subsequent enhanced reduction of ilmenite concentrate.The main work and conclusions of this study are as follows:The surface of the raw ilmenite concentrate with high Ca-Mg content is smooth and dense.The Fe²⁺in the ilmenite concentrate is oxidised to Fe³⁺after the oxidation treatment,and ilmenite is transformed into pseudoplateletite and titanium dioxide.The oxidised ilmenite concentrate has a loose structure with a large number of protrusions and cracks,which can effectively increase the specific surface area of the mineral particles.The pre-oxidation process can significantly improve the reducibility of the ilmenite concentrate by changing the phases and surface morphology of the ilmenite concentrate.The isothermal oxidation reaction rate of ilmenite concentrates with high Ca-Mg content increases significantly with increasing oxidation temperature.The oxidation rate decreases with time.indicating that the diffusion of oxygen slows down from outside to inside.When the oxidation temperature is above 900°C,there is no significant effect of increasing temperature on the reaction rate.At low temperatures oxidation（600°C,650°C,and 700°C）,the chemical reaction is mainly controlled by three-dimensional diffusion,with the control mechanism being the diffusion of ilmenite concentrate oxidation cracks.At intermediate temperatures oxidation（700°C-900°C）,the chemical reaction gradually changes from three-dimensional diffusion control to random nucleation and subsequent growth control.The reaction is controlled by random nucleation and subsequent growth during isothermal oxidation at high temperatures（1000°C,1100°C,1200°C）.During the non-isothermal oxidation of ilmenite concentrates with high Ca-Mg content,the Fe₃O₄ starts to be oxidise first,which accounts for approximately 7.95%of the overall oxidation reaction.As the temperature continues to increase,Fe Ti O₃ is oxidises to Fe₂Ti O₅ and Ti O₂,which accounts for 92.05%of the oxidation reaction.The non-isothermal oxidation is divided into three stages.When the oxidation degree is0.05-0.3,the reaction mechanism is related to the coupling of reactions such as Fe₃O₄oxidation and Fe Ti O₃ oxidation,and the reaction is controlled by diffusion;when the oxidation degree is 0.3-0.5,the reaction is controlled by chemical reaction;when the oxidation degree reaches 0.5-0.95,the reaction mechanism is related to the coupling of Fe Ti O₃ oxidation and Mg Ti₂O₅ generation reactions,although the reaction mechanism is changed,the reaction is controlled by chemical reactions.The isothermal reduction process of ilmenite concentrates with high Ca-Mg content is divided into three stages,the first stage（reaction degree:0-0.06）is the reduction of Fe₃O₄ to Fe O,the second stage（reaction degree:0.06-0.26）is the reduction of Fe O to metallic iron,and the third stage（reaction degree:0.26-1.0）is the reduction of Fe Ti O₃to metallic Fe and titanium oxides.According to the reduction mechanism,the isothermal reduction process can be divided into two stages,the first stage is mainly the chemical reaction of Fe₃O₄ reduction to metallic Fe,the reduction is controlled by the interface chemistry;the second stage is mainly the chemical reaction of Fe Ti O₃reduction to metallic iron and titanium oxide。The partial reduction of Ti O₂ coupled with Fe Ti O₃ reduction in this stage,resulting in the reduction temperature has a significant effect on the reduction mechanism.As the reduction temperature increases from 800°C to 950°C,the reaction mechanism changes from interface chemical reaction control to random nucleation and subsequent growth control.The isothermal reduction of pre-oxidised ilmenite concentrates with high Ca-Mg content is divided into two stages.The first stage（0-0.33）being the reduction of Fe³⁺to Fe²⁺and the second stage（0.33-1.0）being the continued reduction of Fe²⁺to metallic Fe.According to the reduction mechanism,the isothermal reduction of pre-oxidised ilmenite concentrate can be divided into three stages,with the first stage reaction being controlled by the random nucleation and subsequent growth mechanism and the second stage reaction being controlled by one-dimensional diffusion control,where the reaction is mainly controlled by the diffusion of CO through the solid product layer;in the third stage,the reduction temperature has a great influence on the reaction mechanism as the reduction of Ti O₂ is coupled with the iron oxide reduction phase,and the reduction reactions at each temperature condition are controlled by one-dimensional diffusion,interface chemical reaction and random nucleation and subsequent growth mixing,respectively.In this paper,a systematic study of the pre-oxidation and gas-based reduction of Panzhihua ilmenite concentrate was carried out.The pre-oxidised ilmenite concentrate showed a significant increase in gas-based reduction rate and a 50%reduction time decrease compared to the original ore.Based on this conclusion,a new process for the efficient and clean reduction of ilmenite concentrates with high Ca-Mg content:fluidised oxidation fluidised reduction-electric furnace smelting separation.This study provides a theoretical basis for the future large-scale industrial production of titanium slag with the new process.This study provides a theoretical basis for the enhanced reduction process of ilmenite concentrate with high Ca-Mg content.