Preparing Nanometer Al₂O₃ Powder Using Suzhou Kaolin

Using Kaolin as a raw material to prepare nanometer alumina powder can reduce the cost and improve the Kaolin's attachment value and economic efficiency in a large scale. The orthogonal testing method has been used to study some preparing factors on the dipping reaction of Kaolin with acid, such as the particle size of Kaolin, Kaolin calcined temperature, holding time, concentration of HCl, reaction temperature, reaction time, molar ratio of reactants etc. Adopting alkaline process, the concentration of impurity, such as Fe3+ and Ti4+, has been reduced. In the process, the concentrate of NaOH, molar ration of Al3+ to NaOH, reaction temperature, reaction time have been studied. Nanometer alumina powder had been acquired from boehmite xerogel and ammonium aluminum carbonate hydroxide (AACH). The influence of the concentration of reactants, ratio of reactants' concentration, pH, kinds and addition amount of dispersant agents, reaction temperature, reaction time and calcined temperature of precursor on the particle size, packing density, morphology, crystal form and purity have been discussed. The precursor and nanometer Al2O3 powder were characterized by TG-DTA, XRD, SEM, TEM, ICP-AES, FT-IR, Raman, Superficial Electric Potential Particle Size Meter, Laser Granularity Analysis, et al.According to large numbers of experiments, some conclusions have been drew: (1) After calcining at 700℃, the reactivity of the Kaolin has been improved owing to the crystal form of Kaolin transformed from crystalling phase to the amorphous phase. But the hyperpyrexia could make the amount of the quartz increase, the reactivity reduced; (2) The higher leaching rate could be achieved when Kaolin reacted within acid of a lower concentration at a higher temperature for a longer time; (3) The concentration of Fe3+ and Ti4+ in the leaching fluid could be more reduced by reacting within more amount of higher concentration of NaOH solution at a higher temperature; (4) The smaller average particle size, better dispersivity, higher purity nanometerα-Al2O3 could be achieved by calcining AACH.The results show that the leaching rate of ~93.83% could be achieved when Kaolin calcined at 700℃for 2h, reacted within HCl of 20wt% at 95-100℃for 3h. After the reaction of leaching fluid with 2.5mol·L-1 NaOH, the concentration of Fe3+ in the filtrate has be reduced by 98.19mol% as well as Ti4+ by 98.30mol%. Particle size of 10-20nm, packing density of 0.36g·cm-3 nanometerα-Al2O3 with purity of 98.21% was prepared by calcining AACH synthesized from 1.5mol·L-1 AlCl3 react with NH3HCO3 at pH=9, [NH4HCO3]/[AlCl3]=10/3 and calcined temperature 1150℃.