Study on the preparation and structure of positive sol composed of mixed metal hydroxide

Using precipitation method mixed metal hydroxide (MMH) positive sol was prepared. The preparation process and the properties of the sol were studied with powder XRD, TEM, particle size distribution determination system and microelectrophoresis instrument. The preparation of MMH was made as follows: Diluted ammonia water was added to the mixed solution of aluminum and magnesium chlorides which was prepared in the molar ratio of 1:1 or 1:2, or 1:3; then the pH values of the suspension at different amounts of ammonia water were measured. After that, the precipitate was aged for 5 h in the mother solution at room temperature, and washed after filtering. Finally, the filter cake was peptized at constant temperature of 333 K. The results showed that 1) preparation reaction was completed in three steps, 2) pH value was decisive factor, and 3) both the contents of magnesium and the zeta-potential of MMH sol particles increased with pH values and finally remained constant. The mechanism of the reaction was that magnesium ions intercalated Al(OH)(3) crystal lattice, forming mixed metal hydroxide. The results also showed that positively charged MMPI colloidal particle belonged to hexagonal system and three-layer superposition structure.