Hydrothermal synthesis of alumino-silicate from coal ash

本课题主要研究了粉煤灰的提纯（浮选、磁选）及其水热处理制备高岭石型铝硅酸盐矿物的工艺。与zeta电位测量或水/油提取的飞灰颗粒上的结果进行了讨论。考察了pH调节、饲料粉碎和表面活性剂添加对测定结果的影响。Zeta电位的测量结果表明，碳或无机颗粒之间的静电相互作用被发现是非常小的。水/油萃取表明，pH值对飞灰表面疏油性的影响不是碳质表面的疏油性，而是无机颗粒表面的疏油性：在碱性条件下，飞灰表面的金属阳离子会增加无机颗粒对油的消耗。干法磁选可将粉煤灰中3.7%~ 0.1%的铁脱除。通过XRD和SEM-EDX分析表明，样品中的磁性组分（主要是磁铁矿）与碳质物质结合。实际上，在磁分离之后进行浮选时，提纯得到了显著改善。粉煤灰中石英的碱预处理有利于高岭石的合成。温度（高达300 ℃）、压力或矿浆条件对高岭石生长的影响很小。粉煤灰中的离子杂质（Ca、Mg、K、Na）似乎不妨碍反应。只有pH值与产率有一定的关系。合成的高岭石结晶度低，比表面积大。目前存在的问题之一是产品白度低，主要是铁杂质造成的。

The present project have been aimed at purification (flotation, magnetic separation) of fly ash and its hydrothermal treatment for synthesis of alumino-silicate as kaolinite.Flotation Carbon removal of fly ash by flotation have been investigated with the aid of kerosene bridging between bubble and the carbonaceous particles. The results were discussed in relation with the results of zeta potential measurement or water/oil extraction on the fly ash particles. Effects of pH adjustment, comminution of feed and surfactant addition on the results were examined. Zeta potential measurements revealed that electrostatic interaction among carbonaceous or inorganic particles was found to be very small. Water/oil extraction indicated it was liophobicity of inorganic surface rather than of carbonaceous one that should be affected by pH : in alkaline condition metallic cations on the surface of fly ash should increase consumption of oil by inorganic particles.Magnetic separation. Iron component in fly ash was removed in amount from 3.7% to 0.1% by dry magnetic separation. Analysis of separated samples with XRD and SEM-EDX indicated the magnetic components (mainly magnetite) should be conbined with carbonaceous materials. Indeed, purification was substantially improved when flotation was performed after magnetic separation.Hydrothermal treatment. Synthesis of kaolinite was found to be facilitated by alkaline pretreatment for decomposition of quartz included in fly ash. There were little effect of temperature (up to 300ﾟC), pressure or pulp condition on growth of kaolinite. Ionic impurities of fly ash (Ca, Mg, K,Na) did not seem to hinder the reaction. Only pH was found to have some relationship with the productivity. The synthesized kaolinite had low crystalinity and large specific surface area. One of the present problem is low brightness of the product, caused by iron impurity.