拜耳法过程中水合铝硅酸钠的析出活性

Precipitation activity of sodium aluminosilicate hydrate during Bayer process

以分析纯化学试剂NaAlO_2、NaOH和Na_2SiO_3·9H_2O为原料配制过饱和含硅铝酸钠溶液,模拟三水铝石型铝土矿溶出过程研究不同时间析出水合铝硅酸钠的活性,并通过XRD、SEM-EDS和FT-IR等手段探讨其影响铝酸钠溶液稳定性的机理。结果表明:在145℃、SiO_2初始浓度为4.9 g/L时,大部分的脱硅产物在前30min内生成,反应到60 min后,基本达到平衡;脱硅产物主要由无定型沸石、沸石、A型沸石和方钠石组成,其中A型沸石只在反应初期生成,形貌为规则的立方体晶体,晶胞体积很大,随着反应时间的延长,A型沸石消失;脱硅产物在铝酸钠溶液中的稳定性由大到小的顺序为沸石、方钠石、A型沸石、无定型沸石;延长脱硅反应时间可以增加水合铝硅酸钠的晶体尺寸和结晶度,降低其析出活性,有利于提高铝酸钠溶液的稳定性。

The activity of sodium aluminosilicate hydrates at different precipitation time in supersaturated silica-containing sodium aluminate solution prepared by analytical reagents of NaAlO_2、NaOH and Na_2SiO_3·9H_2O was investigated through simulating the digestion conditions of gibbsitic bauxite,the mechanism of which influencing the stability of sodium aluminate solution was also discussed by the XRD,SEM-EDS and FT-IR methods.The results show that most of sodium aluminosilicate hydrates can generate within 30 min and the reaction reaches equilibrium after 60 min at 145℃ when the initial SiO_2 concentration is 4.9 g/L.The desilication products mainly constitute of amorphous phase,zeolite,zeolite-A and sodalite.The zeolite-A,which is a cubic crystal with a larger unit cell volume than other desilication products,precipitates at the initial reaction stage,and disappears gradually with the extension of reaction time.The stability sequence from big to little of the desilication products in sodium aluminate solution is zeolite,sodalite,zeolite-A and amorphous phase.The increase of the desilication time can increase the crystal size and crystallinity of sodium aluminosilicate hydrates to reduce the activity,which improves the stability in sodium aluminate solution.