| The bauxite reserved in China,with the mineral feature of diaspore,is an important raw material for refractory and alumina industry.The impurities including K2O in bauxite can degrade the performances of refractory,but there are relatively few studies on the impurity removal and purification of bauxite.D-I type bauxite(diaspore-illite)has high Al2O3 content and impurities are primarily potassium-containing illite minerals.By removing potassium and impurities from D-I type bauxite,the high value-added utilization of this type of bauxite as a refractory material can be realized.The thesis takes D-I type bauxite and monomineral illite as the research objects.Starting from the mineral properties and the presence of potassium,tht dissolution behavior of elements in the "roasting-leaching" impurity removal process is studied.Through thermodynamic criteria,mineral structure evolution,crystal chemistry and impurity removal,dissolution kinetics,etc.,the basic theory and technology for removing potassium and impurity of D-I type bauxite by the "roasting-leaching "method have been formed.The sintering behavior of D-I bauxite after impurity removal was studied,and the impurity removal effect was investigated.The mineralogy of D-I type bauxite and monomineral illite was studied.Through testing methods such as rock and mineral identification,XRF,XRD,SEM and energy spectrum,the embedded particle size,element composition,mineral phase,microscopic morphology and the distribution of impurities in the bauxite samples are analyzed.The contents of Al2O3,K2O and Fe2O3 in bauxite are 57.34%,3.23%and 3.81%respectively.Among them,the content of soluble impurities is low,and K is present in illite.Following crystal chemistry calculatoin,the molecular formula of illite is obtained,which lays the foundation for the analysis of the element dissolution in[SiO4]tetrahedron and[AlO6]octahedron.The impurity removal test of D-I type bauxite sample was carried out by direct acid leaching method.The influence of concentration,temperature,time and liquid-to-solid ratio on the removal of impurities was investigated,and the composition,phase and morphnology of the leached bauxite were analyzed.The results show that under the action of direct acid leaching,the removal rate of K is less than 20%,and the difficulty of effective removal of K in illite is the main reason for the low removal rate of K.The removal of potassium in illite minerals is the key to the removal of impurities in D-I bauxite.The illite was selected to study the mechanism of removal of potassium,and the influence of the evolution of the mineral structure of illite on the removal of potassium was systematically studied.Through thermogravimetry,phase analysis,infrared spectroscopy and nuclear magnetic resonance analysis,the effects of calcination temperature on illite hydroxyl removal,interlayer spacing,functional group and Al and Si coordination changes were obtained.The results showed that illite removed hydroxyl groups at 550～950℃ and transformed into dehydrated illite,and the interlayer force was weakened;the six-coordinate AlⅥtransforms into four-coordinate AlⅥ,with increasing crystal defects and reactivity to benefit the removal of potassium.Based on the evolution of the mineral structure of the illite during the potassium removal process,a roasting process for potassium removal in illite is proposed.Theroasting-acid leaching method,roasting-Ba2+exchange method and roasting-high temperature hydrothermal method of potassium removal process were studied,and the influence of the system temperature,liquid-solid ratio,charge ratio and other parameters on the potassium removal rate was investigated.In the potassium method,the order of potassium removal rate is:hydrothermal method>Ba2+ exchange method>roasting-acid leaching method.During the potassium removal process,the[AlO6]octahedron and[SiO4]tetrahedral crystal structures are not significantly damaged.The removal of potassium is mainly realized by the exchange between layers.The high temperature hydrothermal effect promotes the exchange between H+ and K+,and Ba2+ enlarges the interlayer spacing,and produces vacancy effects between the layers to promote the release of K+.A kinetic model for potassium removal was constructed,and the reaction rate of the potassium removal process was controlled by the chemicalreaction[1-(1-x)-/3=k2t].The roasting thermodynamics,acid leaching thermodynamics and impurity removal process of D-I type bauxite were studied.The order and criteria for the reaction of the multi-component system in the acid leaching process have been established.ΔGT resulted from the reaction between the impurities and the acid is less than 0.The reaction is thus spontaneous.Based on thermodynamics and phase transition theory during bauxite roasting,the "roasting-acid leaching" impurity removal process was systematically optimized.The results showed that when roasting above 550℃,D-I type bauxite would undergo a solid phase reaction,which hindered the leaching process and was not conducive to the removal of potassium;The impurities in the D-I type bauxite are removed by roasting at 550℃ followed by acid leaching.The removal of impurities is controlled by interfacial mass transfer and residual solid film diffusion.After purification,the K2O content in the sample is reduced from 3.83%to 2.09%,which improves the quality of bauxite used for refractory materials.The sintering performance and impurity removal effect of the purified bauxite were studied.The changes in the properties of refractory materials such as apparent porosity,bulk density,and compressive strength at room temperature were investigated.After the removal of impurities,the load softening temperature of refractory materails increased from 1203.5℃ to 1421.5℃,and the high temperature performance was significantly improved.The present wrok provides techncial guidance on the use of D-I type bauxite as raw materials of high-quality refractory materials. |
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