Study On The Behavior Of Mineral Phase Reconstruction During Suspension Roasting Of High-iron Red Mud

The comprehensive utilization of red mud from the waste residue of aluminum industry is a worldwide problem.This subject is a comprehensive utilization technology of industrial solid waste resources,and basic research is carried out around the bottleneck problems and key technical problems that need to be solved in the process of suspension roasting of high iron red mud resources.the purpose of this paper is to clarify the differences and influence rules of physicochemical properties such as reaction behavior,microstructure and magnetic characteristics of iron minerals in alkaline environment during suspension roasting of high iron red mud,and to reveal the reaction and transformation mechanism of minerals in the roasting process.It provides theoretical support for the transformation and enhanced separation of iron minerals in the suspension roasting process of red mud.In this paper,the red mud of Bayer process in Weiqiao,Shandong Province was taken as the research object,and the systematic basic research work was carried out by means of chemical analysis,X-ray diffraction analysis(XRD),magnetic analysis(VSM),scanning electron microscope and energy spectrum analysis(SEM-EDS),time-of-flight secondary mass spectrometry(TOF-SIMS)and the combination of theoretical analysis,experimental research and mechanism research.It provides a strong theoretical basis for the recovery and utilization of iron minerals from alkaline wastes such as high-iron red mud.The chemical multi-element analysis,XRD and iron phase analysis of the raw ore show that the TFe grade of the red mud is 47.47%,FeO content is 0.02%,Al2O3 content is 12.14%,TiO2 content is 4.14%,the SiO2 content of 1.94%,and the other impurities are less.The main crystal minerals in the red mud ore are hematite,limonite,goethite,ilmenite,diaspore and iron-aluminum oxide.The study of process mineralogy shows that the iron elements in the red mud are mainly found in limonite,hematite and iron-aluminum oxides,with distribution rates of 38.35%,39.06%and 20.05%,respectively,and aluminum elements are mainly found in limonite,iron-aluminum oxides and boehmite,with distribution rates of 26.92%,58.64%and 5.36%,respectively.Titanium mainly occurs in iron-titanium oxide,iron-aluminum oxide,rutile and hematite,with distribution rates of 64.85%,16.72%,8.36%and 7.92%,respectively.Sodium is mainly found in limonite,iron-aluminum oxide and sodium aluminosilicate,with distribution rates of 26.26%,51.43%and 11.90%,respectively.The results of thermodynamic analysis show that the chemical reaction during the suspension roasting of red mud is complicated.In addition to the reduction reaction of iron minerals,iron minerals and other minerals may also react during the roasting reaction to form complex iron compounds such as sodium ferrite(Na2O ·Fe2O3),calcium ferrite(2CaO·Fe2O3),ilmenite(2FeO·TiO2).hinders the reduction of iron minerals.Secondly,the more components of the system,the more complex the phase composition of the reaction equilibrium,indicating that the reduction reaction of iron minerals is greatly affected by the interaction between other minerals.The kinetic analysis of suspension magnetization roasting reaction of hematite without alkali,1.0%sodium hydroxide and 2.0%sodium hydroxide shows that the three kinetic models all conform to Avrami-Erofeev equation.Under the three conditions,the apparent activation energies are 26.745kJ/mol,80.912kJ/mol and 83.482 kJ shock mol,respectively,and the pre-exponential factors are 3.658min-1,5192.030min-1,and 6987.433min-1,respectively.The addition of sodium hydroxide leads to a sharp increase in the activation energy needed for hematite reduction roasting reaction,and the higher the sodium hydroxide content,the longer the reduction reaction time,the stronger the hindrance of the phase transformation from hematite to magnetite in the roasting process.The experimental study on roasting and reduction of iron minerals in alkaline environment shows that in the experiment of adding single alkali,with the increase of the amount of NaOH and Na2SiO3,the phase transformation of Fe2O3 to Fe3O4 in the suspension roasting process of hematite is hindered,and the higher the alkali content is,the more obvious the hindrance is.With the increase of the addition of CaO,the phase transformation from Fe2O3 to Fe3O4 is enhanced at first in the process of hematite suspension roasting,but when the addition of calcium oxide is more than 1.5%,it is not conducive to the phase transformation.The suspension roasting test results of adding mixed alkali and mixed alkali to iron ore respectively show that the phase transformation from Fe2O3 to Fe3O4 is first promoted during the roasting process,and when the addition of mixed alkali is more than 1.0%and 0.5%,it is not conducive to the phase transformation.The experimental results of adding mixed alkali to artificial mixed ore show that mixed alkali and other gangue minerals in hematite will affect the reduction reaction of iron mineral,and when mixed alkali and gangue mineral act together,mixed alkali plays a major role in the phase transformation of iron minerals,but the artificially added gangue minerals will participate in the reaction between iron minerals and alkali to a certain extent and consume part of the alkali.The study on the behavior of mineral phase reconstruction in the suspension roasting process of red mud shows that hematite,limonite and goethite in red mud are transformed into magnetite,and diaspore and gibbsite are dehydrated into alumina.Iron alumina spinel,ilmenite and sodium aluminosilicate have not changed.After magnetic separation,the minerals enriched in the magnetic separation concentrate are mainly magnetite and strong magnetic iron-aluminum spinel,while the minerals entering the magnetic separation tailings are mainly ilmenite,alumina,some weak magnetic iron-aluminum spinel,sodium aluminosilicate,quartz and so on.Mass spectrometric analysis and ion deep sputtering analysis showed that the signals of Na,Al,Fe and Ti in red mud samples were significantly enhanced before and after reduction roasting,indicating that roasting could activate these elements.After roasting,the signals of some elements in the samples were significantly enhanced,indicating that roasting can activate some elements.Secondly,with the deep sputtering inside the particle,the ion signal of each element of the particle increases at first and then stabilizes from the surface to the interior,indicating that the distribution of each element in the particle is uniform,and the signal of sodium element is weakened.it shows that part of sodium is attached to the mineral surface and exists in the form of free sodium.TOF-SIMS secondary ion image analysis and SEM-EDS analysis show that Fe and Al elements have close affinity behavior(iron-aluminum oxide form);Fe and Ti elements have close affinity behavior(ilmenite form);Fe and Na elements have certain affinity behavior)free alkali attached to magnetite crystal surface);Fe has no affinity behavior with Si,K,Ca,Mg and other elements.Al and Fe elements have close affinity behavior(iron-aluminum oxide form);Al and Si,Na elements have certain affinity behavior(sodium aluminosilicate form);Al has no affinity behavior with Ti,K,Ca,Mg and other elements).The research content of this paper enriches the basic theoretical system of resource utilization of red mud and provides technical support for the recovery and efficient utilization of iron minerals in red mud.