| Superfine aluminum hydroxide is applied in many fields because of its special performance. Ion-exchange membrane electrolysis of sodium aluminate solution, which is a new method and has the advantage of simple process, was introduced in this paper. The influence of process conditions on the particle size distribution of Al(OH)3 products and the effect of different surfactants on the agglomeration of Al(OH)3 particles in sodium aluminate solution were studied. Conclusions are drawn as follows:The process conditions such as alkaline concentration of sodium aluminate solution, stirring rate, decomposition temperature and reaction time play an important role in the size distribution of Al(OH)3 particles. The optimum experimental condition was determined. When sodium aluminate solution with 150 g/L alkaline is treated by ion-exchange membrane electrolysis and then decomposed at 35℃and 400 r/min for 1 h, Al(OH)3 product with the minimum particle size and a narrower size range is gained.The dosage and molecular weight of polyethylene glycol (PEG), a nonionic surfactant, can greatly affect the sizes and morphology of Al(OH)3. The particle size of Al(OH)3 is greatly decreased by the addition of PEG with the molecular weight of 1000 (PEG1000) or 4000 (PEG4000) in the solution. The average size of Al(OH)3 particles is reduced to 5.977μm with the addition of PEG1000 at the dosage of 0.25 g/L, and reduced to 3.900μm with the addition of PEG4000 at the dosage of 0.175 g/L. The particle size of the product with the addition of PEG4000 is smaller even at a lower dosage than that with the addition of PEG1000. Al(OH)3 appears in the shape of sheets with the addition of PEG1000, and in the shape of thin columns with the addition of PEG4000, while Al(OH)3 is an irregular glomeration without any additives in the solution.Anionic surfactants of sodium dodecyl sulfonate and lauryl sodium sulfate have similar effect on the particle size distribution and morphology of Al(OH)3. The agglomeration among Al(OH)3 particles is markedly restrained by both anionic surfactants. The optimum dosages of sodium dodecyl sulfonate and lauryl sodium sulfate are 0.15 g/L and 0.05 g/L, respectively, and the average sizes of corresponding Al(OH)3 products are 6.971 urn and 6.659μm. The two anionic surfactants have a great effect on the morphology of Al(OH)3 and sheet-shaped Al(OH)3 is produced in the experiments.Nonionic PEG, anionic sodium dodecyl sulfonate and lauryl sodium can inhibit the agglomeration among Al(OH)3 particles by their absorption on the Al(OH)3 particle surface. The addition of all the above surfactants cannot affect the crystalline structure of Al(OH)3 products from ion-exchange membrane electrolysis and decomposition of sodium aluminate solution. All the products are bayerite with or without additives. |
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