An innovative approach for pseudoboehmite precipitation from seeded sodium aluminate solutions

Precipitation of boehmite from seeded sodium aluminate (SA) solutions for production of smelter grade alumina by calcination is in the early stage of development. However, the reported boehmites are usually well crystallized and actually most boehmites for activated aluminas are poorly crystallized and less ordered forms, which is also called pseudoboehmite. In the present study, an attempt has been made to find the appropriate precipitation conditions of pseudoboehmite from seeded SA solutions by inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It was found that pure pseudoboehmite showing minor morphology difference with the pseudoboehmite seed can be easily obtained under hydrothermal conditions at 373 K not less than 10 h or at 398 K not less than 3 h. The hydrothermal seed precipitation is a dynamic inhibited process that approximately consists of three stages, namely a fast precipitation stage, a slow precipitation stage and an analogously apparent equilibrium stage. However, the seeded precipitation under circulation reflux at approximate 0.1 MPa is not suitable for preparing pure pseudoboehmite because of by-products formation, such as gibbsite, nordstrandite, diaspore, etc. This work demonstrates that pseudoboehmite can be efficiently precipitated from seeded SA solutions under certain hydrothermal conditions.