Improved Bayer Process To Prepare Alumina With Different Morphologies

In order to improve the value of alumina and increase the profit of metallurgical enterprises,the author try to improve Bayer method and prepare spherical and superfine alumina or schistose alumina which have higher value than the normal alumina used in electrolysis.In Bayer process,there are some problems,like hard preparation of active crystal and high content of sodium impurities.The above problems are solved by using the ball grained seed method to strengthen the process of carbon separation and deeplyremovingsodiumbyhydrothermalmethod.Theoptimum technological conditions are obtained.In order to remove the impurities of Fe and Si together,we should add industrial grade Al?OH?₃ and Ca O in sodium aluminate solution.On the condition of 80?,300r/min,2h,adding 50g/L Al?OH?₃ can reduce the content of Fe to12ppm,adding 15g/L Ca O can reduce the content of Si to50ppm.Mg²⁺and Zn²⁺have strong complexation with Oxalate as well as Ca²⁺.Adding 10g/L Na₂C₂O₄ can reduce respectively the content of Mg,Zn and Ca to 18ppm,15ppm,52ppm.Adding the trace of ball seeds to enhance the precipitation rate in the process of decomposing sodium aluminate solution by CO₂.Because of the“plie structure”in the surface of ball seeds,Al?OH?can combine with these plies and grow easily so that adding little seeds?Seed Coefficient=0.011?can improve the precipitation to 92%and decrease the particle size?D90=2.5?m?.Increasing the seed coefficient from 0.011 to 0.088,the precipitation increase and particle size reduce correspondingly.Intheprocessofdeeplyremovingsodiumbyhydrothermal method,raising the temperature to 180?,gibbsite changed into boehmite;Na₂O returned to dissolving in the water in the transformation process of gibbsite;the changing process was slow,rising temperature and decreasing p H can promote the transformation;prolonging the reaction time can enhance the extent of the transformation;boehmite`s morphology,liking"glass"shape,was hugely different from gibbsite after the hydrothermaltreatment.Compared with gibbsite,the boehmite was more loose and disordered;On the hydrothermal condition of p H=1,the content of Na<sub>2</sub>O was as low as 0.0163%,which can reduce to 187ppm after calcination.In the process of ball-milling,ball crusher`s rotation rate and diameter of grinding ball have main influence on the size of production.The best ball-condition is 500r/min,2h,?1mm,ball to power ration 20,which can lead the size to D10=0.15?m;D50=0.22?m;D90=1.34?m after calcination.To prepare high crystalline?-Al₂O₃ particles with schistose shaped structure,different coefficients of Al F₃ were added into starting material,boehmite?Al OOH?.In the paper,the likely mechanism was investigated by DSC-TG-MS for boehmite containing 2%of Al F₃,which indicated a gas-solid reaction via the generation of a transition compound?Al-O-F?.Furthermore,the efficients of coefficient of Al F₃?w?and calcinating temperature?T?on phase,morphology,size,specific surface area was investigated.It showed that light of Al F₃ could enhance the crystalline of?-Al₂O₃;increasing the coefficient from 0.5%to 10%,the phenomenon was more obvious,but it would increase the size and decrease the specific surface area.Boehmite could wholly change into high crystalline and hexagonal?-Al₂O₃ on the best condition of T=850?,W=2%,and constant calcining time 4h.