Preparation of Alumina from Heated Kaolin Leached by Citric Acid with AACH as an Intermediate

Abstract

Because the supply of bauxite ores in many countries is becoming deficient, a process of preparing alumina from an alternative resource, namely, kaolin, is proposed in this work. First, kaolin was heated at 600 °C for 2 h before being leached with 1 M citric acid solution, about 75% of the Al in kaolin entered the leachate as aluminum citrate (AlCit) solution. Then, about 50% of the Al(III) in the leachate could be precipitated as ammonium aluminum carbonate hydroxide (AACH) by addition of NH4HCO3 at pH 9.00 ± 0.50. The morphology of AACH characterized by SEM and TEM was spherical particles composed of many nanorods with sizes of about 500 × 25 nm. Finally, mesoporous γ-Al2O3 was obtained by roasting AACH at 700 °C. The Fe and Na contents in the obtained γ-Al2O3 product determined by XRD and ICP-AES were 2 and 0.1 ppm, respectively. The obtained γ-Al2O3 had a morphology similar to that of AACH, and its BET surface area was as high as 235.2 m2/g.