Synthesis of nanostructured boehmite powder by sol-gel method from industrial Na-aluminate solution

Abstract

Supersaturated Na-aluminate solution from KAP's Alumina plant Bayer process was chosen, as a precursor to synthesize low sodium content nanostructured boehmite powder. Firstly, the solution, was neutralized with strong mineral acid (HCl) to obtain a suitable solid phase-precursor for further hydrothermal treatment. The influence of sodium-aluminate neutralization parameters (final pH of the reaction, concentration of the initial Na-aluminate solution and reaction temperature), on the amount of incorporated sodium (as Na2O) in obtained solid phase was established. This solid phase further was used as a precursor for its hydrothermal treatment. The properties of synthesized sol and nanostructured xerogel properties were investigated. It was found that pH decrease of the neutralization reaction causes almost linear decrease in solid phase sodium content, to below 0.1% at pH=7. Similarly, the lower Na-aluminate solution concentration leads to lower sodium content, while a temperature increase generally decreases sodium content. The X-ray diffraction of the solid phase and hydrothermaly peptizated particles, shows the presence of pseudoboehmite (PB) phase. TEM micrographs of obtained sol show that the primary particle size is about 10 nm to 30 nm. These particles are agglomerated in bigger ones, of about 100-150 nm diameter.