An accurate and tractable model of solubility is a pre-requisite for any careful study of precipitation. Reviewing the abundant literature on the sodium aluminate solutions and Bayer Liquor, the authors point out the need for a new model for the apparent solubility of aluminium in actual Bayer Liquors and propose such a model, based on the well established Wesolowski's expression for the infinite dilution solubility and extended Debye-Huckel expression including a large empirical b I term for the "activity coefficient effect". They suggest a chemical interpretation for this feature. (C) 2011 Elsevier Ltd. All rights reserved.