碳酸氢钠在氧化铝熟料溶出过程中的行为

Behavior of Sodium Bicarbonate during Leaching Process of Alumina Sinter

氧化铝熟料中含有少量β-2CaO.SiO2,在溶出过程易被苛性碱分解,其分解产物与NaAl(OH)4发生相互作用,生成水化石榴石,造成氧化铝的损失;二次反应过程生成Ca(OH)2,使赤泥沉降性能下降;β-2CaO.SiO2分解产生Na2SiO3,增加了脱硅难度。为抑制二次反应,在溶出过程通过添加碳酸氢钠调节溶出液苛性比,降低苛性碱浓度。结果表明,控制碳酸氢钠质量分数为碳酸钠的0.6倍,在溶出反应20 min后开始均匀加入碳酸氢钠,能有效抑制β-2CaO.SiO2分解,改善赤泥的沉降性能,减少溶出液中硅含量,提高氧化铝溶出率。

β-Dicalcium silicate of alumina sinter is decomposed by caustic soda, and decomposition products react with sodium alumina to hydration garnet; the loss of alumina was caused; settling property of red mud was decreased when calcium hydroxide engendered in the secondary reactions; desilicification became even more difficult as sodium silicate being increased. To curb the .secondary reactions, bicarbonate was added to adjust caustic ratio in the digestion process, and caustic soda was decreased. The experimental study shows that when the percentage composition of bicarbonate is to be kept at 0.6 times sodium carbonate, and evenly added to leach liquor after reacting about 20 minutes, β-dicalcium silicate decomposed can be effectively curbed, sedimentation property of red mud is improved, silicon content is lowed, lixiviation rate of alumina is increased.