The influence of additives on the crystal habit of gibbsite

Organic compounds in the processing of lateritic bauxites to alumina Part 2: Effects of organics in the Bayer process

“…King (1973) interpreted the square law in terms of a proposed pre-equilibrium between the predominant [Al(OH) 4 ] − species and a dimeric species at the gibbsite surface; using a linear growth model, the slowness of the reaction was interpreted as due to a very low equilibrium concentration of the dimer at the growing solid surface. This appears to be consistent with the hypothesis of a dimeric "growth unit" which has been proposed (Paulaime et al, 2003;Seyssiecq et al, 1999) based on molecular modelling and crystallographic considerations (the "growth unit" concept in crystallization hypothesises the formation in solution of a fundamental building block of the crystal which can readily be incorporated into the crystal surface (Li et al, 1999;Zhong et al, 1994)). However other authors have proposed different growth units for gibbsite.…”

“…This is consistent with observations on the importance of the stereochemistry of the inhibitor, in particular that compounds with three adjacent hydroxyl groups alternating either side of the carbon backbone are the most potent inhibitors. It is also similar in principle to the proposal by Seyssiecq et al (1999) based on binding of alcohol groups to a dimeric aluminate "growth unit" which was predicted by molecular modelling to exist at low concentrations in aluminate solutions. The inter-atomic distances between pairs of oxygen atoms in the growth unit were found to be quite similar to the distances between alternate OH groups in polyols (polyhydroxy carboxylic acids and alditols), leading the authors to propose the general structure shown schematically in Fig.…”

“…6. The shapes of the individual crystals within the agglomerates are consistent with theoretical predictions (Seyssiecq et al, 1999;Sweegers et al, 2001Sweegers et al, , 2002. Crystals become elongated in pure sodium aluminate solutions because the rate of growth on the hexagonal (001) basal plane is mainly by a relatively fast birthand-spread mechanism, whereas the side faces are characterised by slower spiral growth.…”

Relationship between Crystallite Size and Bond Lengths in Boehmite

“…Aluminas are commonly obtained from four precursors: two hydroxides, gibbsite (11) and bayerite (12); and two oxyhydroxides, diaspore (13) and boehmite. Although this last phase has been widely used for preparing aluminas, a detailed characterization of boehmite is lacking.…”

Uticaj Dodatka Glukoze Na Specifičnu Površinu I Teksturalne Osobine Nano Kristalne Mezoporozne Alumine

“…Temperatura sinteze od 70°C je izabrana da bi se minimiziralo taloženje amorfnih faza [4]. Seyssiq i ostali [19] su pokazali da dodatak aditiva (polikarbonske kiseline) ima uticaj na kristalnu strukturu istaloženog gibsita. Isto tako Nikolić i ostali [23,24] su pokazali da dodatak oksalne kiseline smanjuje brzinu rasta i povećava stepen aglomeracije gibsita u Bayer-om procesu.…”