Sequential Extraction Of Titanium And Iron Resources From Ironsand

Ironsands are a promising alternative resource of iron and titanium and have become increasingly attracting because of the advantage of large surface deposits,economical mining operations and available iron grades.This study takes a kind of ironsand as the research object in order to broaden the source of iron and titanium ore.The target is to extract Fe and Ti resources from ironsand sequentially.Finally the hot metal,high-Ti slag and Ti-Fe alloy are obtained as the end products through several segmental studies of mineral characterizations,magnetic separation,pre-oxidation,gaseous reduction and melt separation.The basic ore characteristics of ironsand are examined in the first part of this study.The results show that Ironsand is a kind of Ti-Fe oxide solid solution,with titanomagnetite and titanohematite being the main two phases.Ironsand also includes a little ilmenite.The solid solution system between pseudobrookite and ferro-pseudobrookite is the form with the maximum oxidation state.Ironsand has a smooth surface and a compact structure.The particle size distribution is concentrated in a small scope and most of the particle shape is spheroidicity.Considering the two problems of relative low grade and bad reducibility appearing in the process of ironsand utilization,two pre-treatment methods are proposed in this studied:(1)magnetic separation to improve the ironsand grade,(2)pre-oxidation to enhance the ironsand reducibility.The grades of Fe and TiO2 in roughing ironsand are 55 and 11 wt%respectively;however they can achieve 60 and 13 wt%after the magnetic separation.Moreover the relationship between the force and partical diameter in magnetic separation process is built through the physical mechanical model so as to obtain the minimum particle diameter of ironsand which can be recovered by the magnetic drum and supply theoretical basis for grinding size choice.The pre-oxidation of ironsand can realize the phase transformation from titanomagnetite to titanohematite and pseudobrookite.In this process,the Fe and O are separated from Ti and enriched into hematite gradually,leading to the partial separation of Ti from Fe and O.It decreases the inhibition effect of Ti on the Fe and O migration in subsequent reduction process.Thus,the ironsand reducibility increases.The results from XRD cell refinement,nitrogen adsorption and desorption,micro-structure and kinetic analysis show that pre-oxidation causes the shrink of cell sizes of main phases in ironsand,leading to the increase of mineral porosity.This change provides sufficient space for nucleation and growth of reduced products in the initial reduction stage and channels for the gas diffusion in the final reduction stage.Therefore,it changes the rate limiting mechanisms and decreases the limit steps.Thus,the ironsand reducibility increases.In a microtopography viewpoint,the micro-cracks caused by pre-oxidation make the reaction order from one core reaction pattern(center incompletely reduced core)into multi-core reaction pattern(tiny and random distributed core).Finally,the pre-oxidation enhances the apparent rate constant of reaction,reduces the reduction activation energy and improves the reduction kinetics of ironsand.Increasing the hydrogen concentration and reaction temperature can promote the gaseous reduction of ironsand.40vol%hydrogen concentration and 900℃reaction temperature are the suitable parameters for ironsand in the gaseous reduction process through comparing the gradient of reduction degree at the increase unit of hydrogen concentration and reaction temperature.A rather complicated phase change exists in this process.The phase compositions and transformations and the solid solubility changes at different reaction time are given in this work.In general,it can be summaried that the phase with low titanium content will be reduced firstly.Pre-reduction degree is an important parameter connecting the pre-reduction and the melt separation processes.The 70-100%scope of pre-reduction is studied in this thesis through In-situ infrared observation,rotary viscometer,Raman spectrum and Factsage software.90%pre-reduction degree is considered as one index that can ensure a smooth melt separation process based on the melt features,the viscosities and the structures of the primary slags.The ironsand with 90%pre-reduction degree as the raw material,the melting separation conditions are exploed through changing the CaF2 content.After the melt separation at high temperature,the ironsand at 90%pre-reduction degree can produce eligible hot metal and titanium slag with 43wt%titanium oxide content.This melt separation slag is used as the raw materials for Ti-Fe alloy.The dosage of reducing agent Al and exothermic agent Fe2O3 are confirmed through basic parameters from pre-experiments and thermodynamic calculations.The Ti-Fe alloy with content of 35wt%Ti-55wt%Fe-6wt%Al-2wt%Si is obtained through the reaction of aluminum thermal reduction,which is consistent with the FeTi30-B standard requirements and is closed to the FeTi40-A requirements.