The Bayer process is used for refining bauxite into smelting grade alumina (Al2O3), which is the precursor of aluminium. The process was developed and patented by Karl Josef Bayer 110 years ago and has become the cornerstone of the aluminium production industry worldwide. This study focuses on the characterization of the main liquor of the Bayer process, or Bayer liquor (BL) in terms of viscosity, composition and organic carbon distribution as a function of the molecular weight. It then shows that the purification of BL by nanofiltration helps to enhance the production of alumina. The organic carbon is well retained, which makes it possible to send a permeate back into the process, thus, increasing the whiteness and quality of the precipitated alumina crystals. Moreover, most of the other impurities are concentrated in the nanofiltration retentate. In view of the good results obtained on the Bayer liquor, this study is extended to the other effluent or solution of the Bayer process: nanofiltration can be used to retain more than 78% of most of the impurities present in these effluents. (c) 2006 Elsevier B.V. All rights reserved.