BENEFICIATION OF FLY ASH

Special Research Report SR-48 The results of a literature survey on the prevailing fly ash situation and a detailed laboratory evaluation of the physical and chemical characteristics ~, of a fly ash sample indicate that further utilization of this material must be ~· based upon some form of beneficiation. The growing production of fly ash with many ;;i.ttendant problems of economics and disposal suggest an urgent need for further consideration of beneficiation aspects. Fly ash is extremely variable and heterogeneous in its properties but is predominantly available as a dry, extremely fine siz~d material. It contains particles ranging in size from about two millimeters to less than one micron and in specific gravities from less than one to greater than four. The larger particles (residual carbon and hollow silicate spheres) tend to have low specific gravities while the smaller sizes (silicates and iron- bearing compounds) are mixtures of gravities ranging between·two and four. Consequently, an economic, efficient dry separation is difficult. An air classifier was designed, constructed and tested to evaluate the possibility of producing a uniformly fine-sized product low in combustibles. The results are most encouraging. A good yield of a desirable product was obtained with a one step operation. The product was essentially all minus 200 mesh and low in carbon. In addition it was established that , much of the dense, magnetic iron particles accompanied the coarse product which then becomes a superior feed for separation of the iron-bearing particles by magnetic or other methods. This secondary process would lead to recovery of a magnetic-iron concentrate and a high carbon . product for recovery of lost heating values.