Study On Mechanism Of The Aggregation Of Ultrafine Kaolinite And Illite

The aggregation of ultrafine kaolinite and illite as functions of pH, cationic surfactant concentration, speed and time of agitating and structure of stirrer was investigated by sedimentation tests and flotation tests. The aggregation mechanism of minerals was studied by Zeta potential measurements, SEM observations and DLVO theory calculation.Results show that kaolinite particles aggregate by edge to face when the pH of system is less than 7 and disperse for electrostatic repulsion when the pH of system is more than 9. In the presence of cationic surfactants, minerals become hydrophobic because of the static adsorption and the hydrophobic aggregation occurs. Kaolinite particles aggregate by edge to face at acidic cationic surfactant suspension, while the hydrophobic aggregation of face to face occurs at neutral and alkaline cationic surfactant suspension. At pH 7, the settlement yield of minerals decrease with the increase of length of alkylamine acetate chains. Order of settlement yield of the four cationic surfactants is dodecylamine＞tetradecylamine＞hexadecylamine＞octadecylamine. Quaternary ammonium compounds have good dissolvability and ionize completely. The cationic of them can exchange and adsorb between the layers of minerals. So the hydrophobic aggregation of minerals with quaternary ammonium compounds is better than that with alkylamine acetate for stronger adsorption. The cationic of CTAB has bigger volume and better adsorption stability than 1227, so it is the best for the hydrophobic aggregation of minerals. The aggregation is progressively bigger and tighter with the increase of cationic surfactant concentration.The hydrophobic surface is the key of the hydrophobic aggregation of ultrafine particles. It's help to aggregate for hydrophobic particles to stir strongly. The optimum times for stirring strongly are 15 minute and 10 minute, respectively, for kaolinite and illite. The hydrophobic aggregation of ultrafine particles has relation with the symmetry and the obliquity of lamina, as well as the amounts of lamina. The order of settlement yield of the six kinds of stirrer is four tilted lamina＞two tilted lamina＞three tilted lamina＞three straight lamina＞four straight lamina＞two straight lamina.The research was supported by "Key Basic Research Program (973) 2005CB623701" of China.