碳热还原-磁选-酸浸法去除粉煤灰中的杂质

Removal of impurities in fly ash by carbon thermal reduction magnetic separation and acid leaching

粉煤灰中除含有分子筛所需要的硅铝相之外,还含有大量的莫来石、石英相、磁铁矿、赤铁矿、石膏等杂质,不但影响分子筛的色泽,更对分子筛的合成、吸附、催化等性能有严重影响.在合成分子筛之前需要对粉煤灰进行除杂处理.本文首先以碳热还原的方法降低粉煤灰中铁的价态,该过程同时将硫酸钙还原为氧化钙,然后用磁选的方法去除部分磁性铁,最后用盐酸酸洗将剩余铁以及氧化钙溶于酸中,过滤除去.实验结果表明,最佳还原条件为:48μm粉煤灰、碳-氧摩尔比2.0,氩气气氛,在1 000℃下反应1 h;经过碳热还原和盐酸酸洗后,粉煤灰中Si O2和Al2O3的质量比达到5.65,TFe含量质量分数达到0.49%,Ca O含量质量分数达到2.08%.基本达到下一步合成的要求.

Composition of fly ash is very complex. It contains large amounts of impurities such as mullite,quartz,magnetite,hematite,gypsum,etc. These impurities not only affect the color of molecular sieve,but also have bad impact on synthesis,adsorption,catalysis properties etc. The impurities have to be removed before synthesis of zeolite.In this paper,the ferric iron in the fly ash was reduced by carbon thermal reduction. Meanwhile,the calcium sulfate was reduced to calcium oxide. And then,a part of magnetic Fe was removed by magnetic separation method. Finally the residual and calcium oxides were acidified with hydrochloric acid into dissolved Fe Cl2 and Ca Cl2,and then were filtrated. The experimental results showed that the optimum reduction conditions are size of fly ash is 48 μm,carbon-oxygen mass ratio is 2,argon atmosphere,reaction temperature is 1 000 ℃,time is 1 h,Si / Al（ mass of Si O_2 to Al_2O_3） ratio is 5. 65,the content of TFe drops to be 0. 49%,the content of Ca O is 2. 08%. The purified species can be taken as a material for the molecular sieve.