| The titanium resource reserve in Panzhihua-Xichang(also known as Pan-Xi)area accounts for 90%of the total in China.The ilmenite concentrate obtained from the existing beneficiation process can only be used for producing titanium dioxide pigment by sulphate process or smelting acid-soluble titanium slag with high energy-consumping and heavy polluting.It cannot be used as raw materials for the fluidized chlorination process due to high contents of of Ca,Mg and other components.It has become an important direction to promote the sustainable development of titanium industry in China to develop a new preparation technology of titanium rich materials for fluidizing chlorination from Pan-Xi ilmenite concentrate.In this work,the process of preparing synthetic rutile from Pan-Xi ilmenite concentrate by oxidizing roasting-magnetic separation and subsequent selective chlorination was studied.Focusing on the problems existing in the above process,such as hard to regulate magnetization in oxidation process and difficult to efficient removal calcium,magnesium and other impurities in the follow chlorination process,efficient and controllable fluidized oxidation roasting and fluidized chlorination technology were adopted.The study revealed the mineral phase transformation and impurities separation rules in the oxidizing roasting-magnetic separation process and the chlorination behavior of the key impurities of calcium and magnesium during selective chlorination process,in order to established an optimized regulation.It is valuable reference for a new artificial rutile prepared process from Pan-Xi ilmenite concentrate.The following research results have been obtained.(1)The Hongge ilmenite concentrate from Pan-Xi area was used as raw material,consistsing of manganese or magnesium bearing ilmenites as main mineral phases and silicate gangue not completely dissociated,which has a high content of calcium,magnesium,aluminum,silicon and other non-iron impurities.It is show weak magnetism with the magnetic saturation point and coercive force are 2000 Gs and 270 Gs respectively.The results of thermal analysis and phase transition showed that the ilmenite concentrate begins to gain weight and exotherm in the oxidation atmosphere above 550?,Futhermore,the newly generated Fe2O3 and the unoxidized FeTiO3 can combined to generate magnetic solid solution(x FeTiO3·(1-x)Fe2O3),but its magnetism will be significantly weakened by continuous oxidizing into TiO2 and Fe2O3.(2)Based on the experimental results of fluidized oxidizing roasting,the optimal temperature range of oxidized magnetization is 650??750?,Moreover the duration for oxidization of ilmenite concentrate to reach the magnetic extremum can be shortened by raising the temperature.Finally the optimized parameters of fluidization roasting with air are oxidation at 725? for 30 min or oxidation at 650? for 90 min,with which the Fe2+/TFe content ratio in the oxidized sample was 0.51,the magnetic saturation point increased to 9500 Gs and 10000 Gs respectively,and the coercivity also increased to 500 Gs and 495 Gs respectively.The magnetism of the ore sample was significantly enhanced.The boundary of the main mineral and gangue was cracked to a certain extent in the oxidized ilmenite.Besides,with wet ball grinding for 5min,the average particle size of oxidized ilmenite can be reduced to 42.20 ?m,which can realize the gangue and the main mineral monomer dissociated is conducive to remove gangue at the subsequent magnetic separation process.(3)The results of magnetic separation under different parameters showed that the impurities removal rate increased slightly with the mineral particle size decreased or the beneficiation strength of magnetic field increased,but the titanium recovery rate decreased obviously.Under the optimized conditions:oxidation at 725? for 30 min,ball grinding time of 5 min to an average particle size of 42.20?m and the beneficiation strength of magnetic field of 0.35 T,The titanium recovery rate was 47.45%,and the contents of CaO?MgO?Al2O3 and Si?2 in the concentrate were 0.28 wt.%,2.17 wt.%,0.63 wt.%and 1.35 wt.%respectively,with the corresponding removal rates of 81.82%,76.51%,81.35%and 83.92%.It can effectively achieve the quality ilmenite concentrate improvement.And the TiO2 grade of tailings is still up to 46.50 wt.%,which can be directly used for producing titanium dioxide pigment by sulphate process or smelting acid-soluble titanium slag to realize the cascade utilization of Pan-Xi titanium resources.(4)The thermodynamic analysis shows that the impurity oxides of aluminum and silicon in the ilmenite concentrate is difficult to be removed by selective chlorination.The oxides of iron,manganese,calcium,magnesium and other impurities could be chlorinated preferentially than titanium oxide,thus achieved impurities removal by selective chlorination.Combined with the thermodynamic equilibrium region diagram,the thermodynamic equilibrium regions that can achieve selective chlorination of Fe,Ca and Mg are decrease with the increase of temperature.Compare with titanium oxide,the oxides of iron and calcium could be easily selective chlorinated,while magnesium oxide is easy to form a stable phase of magnesium dititanate(MgTi2O5),which is tough to be chlorinated.(5)In order to meet the particle size requirements of fluidization,the upgraded ilmenite by magnetic separation was used for selective chlorination after granulation and sintering.The selective chlorination process with carbon monoxide and chlorine gas can remove iron by simultaneous volatilization,while the chlorination of manganese,calcium and magnesium and other impurities reacted into nonvolatile chlorides,which can be further removed by water leached.Concretely,the removal rates of iron and manganese increased gradually increased with chlorination temperature and duration,while calcium can be removed at lower temperature and in shorter duration.But the removal rate of magnesium increased rapidly only if the chlorination temperature exceeded 900?.In addition,aluminum can be removed by chlorination at high temperature with long duration,while silicon can only be partially removed.(6)The key in the process of selective chlorination to produce synthetic rutile is efficient removal of magnesium.During the chlorination process with unreacted shrinking core model,magnesium was enriched in the unreacted core as iron chlorination and volatilization,to from the stable magnesium titanate(MgTiO3)and magnesium ferric dititanate(MgTi2O5-Fe2Ti2O7 or MgTi2O5-Fe3Ti2O10),reatarding the chlorination of magnesium and the deep removal of iron.Consequently it is require higher temperature and longer duration to effective removal of magnesium,leading to titanium revcovery decreasing synchronously.(7)With the optimized parameters of Cl2 and CO volume ratio of 1:1 and chlorination at 1000? for 60 min,the synthetic rutile with high TiO2 grade(96.34 wt.%)was obtained from selective chlorination and subsequent water leaching of the upgraded ilmenite.The contents of Fe2?3,MnO,CaO,MgO,Al2O3 and SiO2 in the synthetic rutile were 0.64 wt.%,0.01 wt.%,0.14 wt.%,0.66 wt.%,0.15 wt.%and 1.77 wt.%respectively.And the impurities removal rates of iron,manganese,calcium,magnesium and aluminum were 99.53%,99.58%,81.84%,89.46%,93.84%and 51.77%respectively.The final products with particle size over 100 ?m accounted for 56.33%.The preliminary established process of oxidation roasting-magnetic separation-selective chlorination of ilmenite concentrate provides a new method for the efficient utilization of Pan-Xi titanium resources in China. |
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