Investigation On Ilmenite Reduction Strengthened By Additives

Solid-state reduction reaction of ilmenite is impotant to processes of titanium-rich material production, such as two-stage reduction followed by smelting process, weak reduction followed by acid leaching process, deeply reduction followed by corrosion process and reduction-magnetic separation process. Therefore, the study on strengthening solid-state reduction of ilmenite is of great important to the innovation of present process for production of titanium-rich material processes from ilmenite and to development of new processes based on reduction technology.In this paper, the abundantly reserved Panzhihua ilmenite resources in China were taken as the main research object. Based on the thermodynamics calculation of ilmenite reduction, the effects of alkali metal additives on reduction of the pre-oxidized ilmenite and kinetics behaviors were systematically studied. The mechanism of strengthening of alkali metal additives on reduction of pre-oxidized ilmenite pellet was studied by X-ray diffraction, optical microscopy, scanning electron microscopy and other modern micro-testing techniques. The main results aquired in the study turned out to be as following:In this study, the following major results:(1) Thermodynamic studies of ilmenite reduction reaction show that ilmenite reduction needs high CO concentration, equilibrium concentration should be more than 90%. As the reduction with the 99.99% CO gas, when the temperature is higher than 167℃, TiO₂ may be reduced to Ti₃O₅; when the temperature is over 242℃, Ti₂O₃ may be generated; after the temperature reaches 703℃, TiO is also likely to generate.(2) The strengthening effects of Alkali metal additives on pre-oxidation ilmenite are differente: metallization is highest adding Na₂B₄O₇, followed by Na₂CO₃, NaF, Na₂SO₄, NaCl, Na₃PO₄. The results show that the anionic (group) of alkali metal additives have a significant impact on solid-state reduction reaction of ilmenite. Non-isothermal reduction experiment results show that borax has significant promoting role on the reduction of ferrous brookite, and other additives mainly promot the reduction of the ferric brookite to ilmenite and ilmenite to ferrous brookite.(3) The research results of the effects of additives on the phase of reduction product of pre-oxidation ilmenite show that the reduced product added sodium carbonate have Na₂Fe₂Ti₃O₁₀ emerged. Other additives havn't changed the reduction course of the ilmenite; the micro-morphological analysis results on reduction product of pre-oxidation ilmenite show that the additives can destroy the grain structure of product, promot the growth size of iron metal, the promoting role of borax is the most significant, which based on damaging the grain structure, also has the role of grain reorganization.(4) The test results of high-temperature performance of ilmenite added alkali metal additives in a weak reduction atmosphere show that the alkali metal additives on the effects properties of ilmenite soft melt are small; the soft melting of ilmenite is not the main reasons which lead to different properties of the reduction level.(5) The anionic (group) of Alkali metal salts additives has an important influence on solid-state reduction reaction of ilmenite. The roles of various additives on impurity magnesium and the effects on migration behavior of Mg, Al, Si and Ca show that the borax not only effectively eliminate adverse effects of MgO on reduction, but also eliminate richment phenomenon of other impurities. Other additives can reduce Mg, Al, Si and Ca enrichment to some extent, but their effects are weaker than the effect of borax.(6) Isothermal reduction kinetics analysis showed that the initial phase of reduction reaction of pre-oxidation ilmenite is Fe³⁺ to Fe²⁺, the process of ilmenite reduction is under the interfacial chemical reaction control. When the reaction is into the Fe²⁺ to Fe⁰ stage, when the temperature is between 1000℃and 1050℃, the reduction reaction is controlled by the diffusion of CO gas through the solid-phase product layer. When the temperature is between 1100℃and 1150℃, the reduction reaction is mainly controlled by interfacial chemical reaction. The reasons of restrictive aspects changes of pre-oxidation ilmenite reduction reaction are the reaction mechanism has changed. When the temperature is between 1000℃and 1050℃, the main reaction is that the ilmenite is reduced into ferrous brookite. When the temperature is between 1100℃and 1150℃, the further reduction of ferrous brookite and titanium oxide are main reaction. Borax can not change the kinetics disciplines, but adding Borax can raise the effective diffusion coefficient of gas and apparent rate constant of chemical reaction.