The dissolution property of high-ferrite gibbsitic bauxite and the effect of ferrite content on the dissolution kinetics of gibbsitic bauxites in sodium hydroxide solution under atmospheric pressure from 50 to 90 °C were systematically investigated.The dissolution property of high-ferrite gibbsitic bauxite is increased by increasing the dissolution temperature and the Na OH concentration or decreasing the particle size of bauxite,which is easy to dissolve under atmospheric pressure.The kinetic equations of gibbsitic bauxites with different ferrite contents during the dissolution process at different temperatures for different times were established,and the corresponding activation energies were calculated.The ferrite in the gibbsitic bauxite reduces the dissolution speed and increases the activation energy of dissolution,the diffusion process of which is the rate-controlling step.
The mineral transition mechanism and physicochemical property of calcium aluminate clinker sintered at 1350 ℃ were systematically studied using analytical reagent α-Al_2O_3,CaCO_3 and SiO_2 when the molar ratio of CaO to Al_2O_3 is 1.0.The results show that the formation of Ca_2SiO_4 accelerates the diffusion of CaO and Al_2O_3,which promotes the formation of CaAl_2O_4 determined by dilatometer,X-ray diffraction,Fourier transform infrared spectroscopy and scanning electron microscopy methods.CaAl_4O_7,Ca_3Al_2O_6,Ca_3SiO_5 and Ca_2Al_2SiO_7 only exist in the initial stage of reactions,the amounts of which decrease with the increase of sintering duration.Ca_3Al_2O_6 and Ca_(12)Al_(14)O_(33) react with Al_2O_3 and CaAl_4O_7 to form CaAl_2O_4,while Ca_2Al_2SiO_7 reacts with CaO and Ca_(12)Al_(14)O_(33) to form Ca_2SiO_4 and CaAl_2O_4.The sintered clinker contains CaAl_2O_4 and γ-Ca_2SiO_4 as well as some Ca_(12)Al_(14)O_(33) when the sintering duration is longer than 1.0 h.The differential scanning calorimetry results reveal that Ca_2SiO_4,Ca_2Al_2SiO_7 and CaAl_2O_4 are formed at985 ℃,1045℃ and 1339 ℃,respectively.Increasing the sintering duration contributes to the transition of β-Ca_2SiO_4 to γ-Ca_2SiO_4,which improves the pulverization and alumina leaching property of the sintered clinker.
