Beneficiation of a diasporic-bauxite ore by selective flocculation with sodium polyacrylate (PAS) was studied. Flocculation behaviors of diaspore, kaolinite, illite and pyrophyllite in the presence of PAS were also investigated by sedimentation tests. PAS shows good selectivity for the flocculation separation of diaspore from silicates in the range of pH 8-12. A concentrate with Al(2)O(3)/SiO(2) ratio 8.9 and the recovery of Al(2)O(3) 87.0% was obtained from a diasporic-bauxite ore with Al(2)O(3)/SiO(2) ratio 5.7 with the addition of sodium carbonate 5 kg/t and PAS 7 g/t. Micro-photogram, zeta potential and FTIR measurements were then performed to study the mechanisms. It was observed that the zeta potentials of diaspore shifted to negative value strongly and the isoelectric point (IEP) of diaspore was also changed from about pH 6-4, and the flocs of diaspore were larger and denser than that of kaolinite in the presence of PAS. A new band at 1640 cm(-1) was found in the infrared spectrum of the diaspore after interaction with PAS, and this new band matched the characteristic peak at 1624 cm(-1) in the infrared spectrum of the reaction products of PAS and AlCl(3). The adsorption of PAS on diaspore is concluded to be chemisorption caused by the chemical reaction between carboxylate group and the exposed Al sites on diaspore surface. (C) 2008 Elsevier Ltd. All rights reserved.