神华集团粉煤灰“一步酸溶法”提取氧化铝技术产生的副产品—白泥,主要成分 SiO2占70％以上,是很好的硅基原料.主要分析了白泥脱硅液中铁的存在状态与去除方法,研究了碳分法、锰砂滤料吸附、膜分离技术等的除铁效果.结果表明,白泥中的铁主要有两个来源：(1)“一步酸溶法”工艺过程中未溶解的Fe2 O3和FeO,这部分铁的氧化物在脱硅过程中与热碱不发生反应；(2)浸出液中的FeCl3和FeCl2,这部分铁的氯化物是脱硅液中铁的主要来源,与热碱反应生成 FeO－2和 FeO2－2.白泥经过干燥,其中的 FeCl3和 FeCl2转化为 Fe2 O3和 Fe (OH)3,少量不能与热碱发生反应,以纳米颗粒形式存在于脱硅液中.实验条件下,干燥白泥与洗涤白泥相比, SiO2溶出率稍低(＞71％)；脱硅液中SiO2浓度为150．0 g/L时,铁含量约182．2 mg/L.碳分法除铁可以降低溶液中铁离子含量至30 mg/L左右(主要是硅铁络合离子 FeOSi(OH)32＋),使之转化为 Fe(OH)3颗粒：一部分随偏硅酸沉淀除去,一部分以纳米胶粒形式留在碳分液中,粒径主要分布在1~12 nm.继续利用锰砂滤料和膜分离技术,除铁率均小于50％.二次碳分法制备SiO2粉末,产品含量为227 mg/kg.
The maj or composition of white mud by-produced from alumina extraction from coal ash “direct acid-leaching method”developed by Shenhua Group,is SiO2 which accounts more than 70%.The White Mud has been considered as potential silicon based materials.The chemical and physical properties of White Mud have been analyzed.The iron methods have been introduced including carbonation process,manganese sand filter, and membrane separation technique.It is concluded that there are two main sources of iron in White Mud,one is Fe2 O3 and FeO which is not dissolved during the“one-step acid-leaching method”process,and would not dis-solved in the hot concentrated NaOH solution.The other is FeCl3 and FeCl2 which came from the dissolved ox-ide of iron in the“direct acid-leaching method”,and would react with hot concentrated NaOH solution to FeO-2 and FeO2-2 during the desilicification from White Mud.After dehydration,FeCl3 and FeCl2 reacted to Fe(OH)3 and Fe2 O3 which react with hot concentrated NaOH solution difficultly and so partly exist in nanoparticles.In the experimental conditions,the leaching rates of SiO2 in dehydrated White Mud is above 70%,the concentra-tions of silicon and iron are about 150.0 and 182.2 mg/L respectively,which reduced to about 30 mg/L (FeOSi (OH)3 2+)by carbonation,converted into Fe(OH)3 particles.Part of Fe(OH)3 particles precipitated with sili-cate,the other part existed in the solution as nanoparticles,which could be rarely removed by manganese sand filter,and membrane separation technique.The iron concentration of SiO2 produced by two-step-carbonation is 227 mg/kg.
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