Technology Research Of The Preparation Of Titanium-rich Material And Extraction Of Ti-Fe Alloy Based On Hydrogen-rich Reduction Of Ilmenite

Although there are abundant titanium resources in China, the productiontechnology of titanium industry falls behind at present comparatively because of theparticularity of the mineral. These special titanium ores are multi-element symbioticores and have complex compositions, especially, these ilmenite ores contain highcontents of calcium and magnesium. Thus, the ilmenite ores are difficult to utilize bytraditional metallurgical methods and enrichment routes. The method of electricfurnace smelting separation and sulfuric acid leaching does not meet the developmentrequirements of environmental protection. In the12th five-year plan of China, it isclearly pointed out that the electric furnace process and sulfuric acid leaching routemust be shut down in2015. Therefore, scientists of China are desperate to search forbreakthrough technologies which are environmentally friendly, energy-saving andefficient. In this paper, using Panzhihua ilmenite ores and hydrogen-rich gas which isobtained from reformation of coke oven gas (COG), we try to explore the possibilityof direct reduction of ilmenite by hydrogen-rich gas. Furthermore, selectiveelectrochemical extraction of titanium and its alloys from ilmenite ores by solid oxideoxygen ionic membrane (SOM) method is also studied.Ilmenite ore of Panzhihua in China is taken as main research object in this paper.Aiming to comprehensive utilization of COG, direct reduction behavior of ilmeniteusing hydrogen-rich gas is deeply discussed. Thermodynamic analysis on thefeasibility of ilmenite reduction by multi-component gas is carried out. Theinteraction reaction of different gases is also discussed by thermodynamic calculation.In addition, experiments of thermogravimetric analysis (TG), gas chromatography(GC) and mass spectrum (MS) are carried out to verify the results of thermodynamiccalculation; Ilmenite ores are reduced by pure hydrogen, pure carbon monoxide andhydrogen-rich gas, respectively. A dynamic model is created and discussedsystematically, besides, we attempt to make a computer simulation of shaft furnace reduction process; finally, extraction separation of titanium and iron is carried out bycorrosion method. The electrochemical reactions in the corrosion process areexamined; What’s more, a useful attempt is made in this paper to extract metallictitanium and its alloys directly using SOM method. The conclusions are as follows:(1) Thermodynamic analysis on the direct reduction by hydrogen-rich gas showsthat: ilmenite ores can be reduced by both hydrogen and carbon monoxide in a certainscope of temperature. Metallization rate of ilmenite increases with reductiontemperature rising. The reduction of ilmenite is according to the “fork-likemechanism”, and the transition temperature is1150oC which is calculated bytheoretical calculation. When the temperature is below this transition point, ilmenite isreduced into metallic iron and rutile. When the temperature is above1150oC, ilmeniteis reduced into ferrous pseudobrookite and metallic rion. In the temperature range of200-800oC, a lot of side reactions can occure, which mainly including methanationreaction and carbon deposition reaction. These side reactions can seriously influencethe ilmenite reduction.(2) Experiments on the direct reduction of ilmenite by pure gas show that: thereduction reaction rate increases with rising temperature and gas concentration. Themain reduction products are metallic iron, magneisan ilmenite and rutile in thetemperature range of900-1000oC. When the temperature is above1000oC, solidsolution of pseudobrookite can be formed in a short time. There are large amounts ofmicro-holes in surface of reduced ilmenite. The structure of ilmenite ores is becomingfrom compact into porous by reason of removal of oxygen. With the ilmenitereduction by hydrogen, magnesium migrates into the central part of the mineralparticle and finally forms an enrichment core. In contrast, the carbon monoxidereduction process the magnesium migration phenomenon is not very obvious.(3) Experiments on the hydrogen-rich gas reduction indicate that: at the samereduction temperature, the reduction rate and metallization rate increase with risinghydrogen content. When the temperature is below1000oC, the main reductionproducts are rutile and metallic iron. Ferrous pseudobrookite can be formed when thetemperature is more than1000oC. The enrichment phenomenon of magnesium is not observed in hydrogen-rich gas reduction process. The EDS analysis shows that thelattice-like structure is formed in the cross section of the mineral particles, which maybe the migration and enrichment of Si and Al. By dynamic calculation, a model isbuilt to discuss the hydrogen-rich gas reduction process. Interface reaction rateconstant and diffusion coefficient change with the variation of gaseous composition.Both of interface chemical reaction activation energy and internal diffusion activationenergy increase with the CO content rising.(4) Experiments of ilmenite pre-oxidation and the numerical simulation resultsdemonstrate that: the main oxidation products are hematite and rutile when thetemperature range is below800oC. With continuously rising temperature, theoxidation products are pseudobrookite and small amount of rutile. Micro-structure ofilmenite ores changes a lot in the oxidation reaction. Large amount ofnanometer-sized pores generate on the mineral surface, which can strength the masstransfer in the followed gas-based reduction process. When the temperature is above1000oC, sintering structure will form and micro-pores will gradually closed. Thereduction proceed of oxidized ilmenite includes two steps: Fe3+�'Fe2+and Fe2+�'Fe.A numerical shaft furnace model is built to discuss the reduction process of oxidizedilmenite pellets reduced by reformed COG. When the gas follow rate is130000m3/h,follow velocity of oxidized pellet is90t/h and the height of shaft furnace is10m, thereduction fraction of oxidized ilmenite pellets after reduction can reach90%.(5) Experiments of reduction-corrosion separation and SOM direct extractionmethod show that: as the main reduction products of ilmenite are metallic iron andferrous pseudobrookite, metallic iron can be separated efficiently from titaniumenrichment material. The TiO2grade of titanium enrichment material is above70%.Increasing the content of HCl can strengthen the corrosion separation process and theimpurities leaching. When the HCl content is more than4%, the corrosion reaction ofmetallic iron will change into dissolving reaction. Both of the natural ilmenite andreduced ilmenite can be used to extract metallic titanium and its alloys. In the SOMmethod, impurities, such as Ca and Mg, can be removed efficiently. Afterhydrogen-rich gas reduction, the original mineral structure has been destroyed and a lot of micro-pores generate on the surface of the mineral particles. Moreover, there arelarge amount of metallic iron embedded in the body of mineral particles. The surfaceof “Three-phase Interface” is enlarged. As a result, the electrolysis rate is improvedand the complete electrolysis time is decreased from5to3hours.