硅在铝酸钠溶液分解过程中的行为

采用离子膜电解强化铝酸钠溶液分解,考察硅在分解过程中的行为,并用扫描电镜和电子能谱分别对自发分解产品的表面形貌及表面元素进行了表征。结果表明:二氧化硅的浓度变化在分解过程中分三个阶段,即前期迅速减少,中期基本不变,后期又缓慢减少;在分解温度不同时,二氧化硅的浓度在高温时变化较低温快。种分温度为70℃与60℃时,在分解6 h后,分解率都在50%左右。种分温度为70℃时,在前1 h分解率就达到40%左右,明显比60℃时快,说明溶液分解显著地由化学反应控制。二氧化硅使10μm以下的粒子数增加,同时二氧化硅在60℃时相比70℃更能影响粒度分布。纯铝酸钠溶液自发分解产品表面光滑,含硅铝酸钠溶液自发分解产品表面有细小粒子和不规则絮状物,表面元素分析表明絮状物为硅铝酸钠晶体之间的簇合。

Behavior of SiO2 in the Precipitation of Caustic Aluminate Solutions

The behavior of SiO2 in the precipitation of Gibbsite in caustic aluminate solution has been investigated by ion membrane electrolysis.The microstructure of unseeded precipitation of aluminum hydroxide and its surface elements were characterized by using scanning electronic microscope(SEM) and Electron Spectrometer.The results show that silicon dioxide influenced on precipitated process obviously.The concentration change of SiO2 upon 0.60 g/L in the precipitation process was thought to be undertaken there-step: decrease quickly at first,a lag period step secondly and a slow step thirdly.The precipitation ratio are up to 50% after six hours in pure solution or sodium aluminate solution with SiO2.The precipitation rate was faster at 70℃ comparing with 60℃,especially at the first hour its precipitation ration almost 40%,which indicates that the decomposition of supersaturated sodium aluminate solution is controlled by chemical reaction.The number of particle size under 10 μm was increased in the present of SiO2,and the effecting of SiO2 on the number of fine particle size at 60℃ was more than at 70℃.The SEM present that the surface of Al(OH)3 from unseeded precipitated pure solution were lubricity,but there were some fine particle size in the surface of Al(OH)3 from solutions with SiO2,especially some foreign colloid-like crystal was appeared.In colloid area,four elements (Si,Al,O and Na) was detected by Electron Spectrometer,it is speculated that sodium aluminum silicate may be exist.