添加剂强化拜耳法种分分解的工艺条件实验

Experiment of process parameters on Bayer seeds precipitation from caustic aluminate solutions added additives

研究添加剂强化拜耳法种分分解的微观机理。把改性阳离子型聚丙烯酰胺与聚丙烯酸钠混合添加剂加入铝酸钠种分溶液中,对添加剂混合比例、浓度和添加时间等影响铝酸钠溶液种分分解速率进行探讨,在分解过程进行8 h时,对氢氧化铝晶体进行扫描电镜测试。研究结果表明:加入添加剂可加快Al(OH)4-扩散到晶种表面,Al(OH)4-经化学反应产生Al(OH)3以及OH-扩散到溶液本体的过程,达到强化分解过程的目的;与未加添加剂相比较,改性阳离子型聚丙烯酰胺与聚丙烯酸钠混合(以质量比5∶1混合)加入,质量浓度为1.56×10-4g/L以及在分解初期加入效果最好;在有添加剂的情况下晶种表面会产生更多次生晶核,由于搅拌等因素脱落或互相吸附形成新的大颗粒晶种,加快了二次成核的形成。

Micromechanism of Bayer seeds precipitation intensified from caustic aluminate solutions was discussed. Mixed additives by modified positive polyacrylamide and sodium polyacrylate were added in the caustic aluminate solutions, the effects of the mass ratio of mixed additives, concentration and the added time were studied. After 8 h, the aluminum hydroxide crystals were measured by scanning electron microscopy. The results show that the intensified decomposition processings including all the Al（OH）4^- diffusing into the surfaces of seeds crystals, OH^- diffusing into the sodium aluminate solution and Al（OH）4^- changing into Al（OH）3 by chemical reactions are accelerated. In contrast to no additives, the better processing parameters are modified with positive polyacrylamide and sodium polyacrylate with mass ratio of 5：1, mass concentration of 1.56×10^-4 g/L and added in the seeds before precipitation. With the mixed additives added, surplus secondary nucleation is formed on the surfaces of seeds, and fallen off for stirring or adsorbing each other into new large seeds, so the second nucleation can be accelerated.