Hydrothermal synthesis of alumino-silicate from coal ash

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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.