The Resource Utilization Of Solid Waste Coal Fly Ash

This study was aimed to settle the utilization problem of solid waste coal fly ash. Taking fly ash from Hangzhou thermal power plant and banshan power plant, firstly the characterization of two different ashes, namely desulfurization ash derived from circulating fluidized bed boiler (CFB ash) and pulverized coal ash (PC ash) were studied. Then, the dry process iron removal and wet process carbon separation were conducted based on the characterization of the PC ash. Its comprehensive utilization was studied at last, which included the preparation of precipitated silica and aluminium, synthesis of zeolite molecular sieves and the preparation of glass-ceramic. The main contents and results were as follows:(1) The characterization of CFB ash and PC ash were comparatively studied and the results were as follows:The loss on ignition (LOI) and CaO contents of CFB ash were higher than that of PC ash. The main phase of PC ash was mullite and quartz, including large quantity of amorphous phase. As compared, the main phase of CFB ash was quartz, calcite and anhydrite with small amount of glass phase. The SEM observation revealed that the PC ash manifested as regular sphere-like particle, while the regular particle was rare to be observed in the CBF ash.(2) The results of iron removal by magnetic separation experiment showed that the magnetic separation efficiency was higher when the dip angle and current intensity of the analyzer was 30°and 2.5A, respectively. Compared to roughing dressing, the iron removal efficiency of roughing-scavenging dressing was higher than that of roughing-fine dressing. The main phases of magnetic particle were quartz, mullite and maghemite. The study of wet process carbon separation indicated that the carbon removal efficiency attained 82.53% when the dosage of light diesel oil collector was 800g/t. The removal efficiency was 80.03% when the amount of sec-octyl alcohols was selected as 600g/t. The phase analysis of floated product showed that carbon was the prevailing phase with little amount of mullite. The carbon was an intergrowth of glass and silicate manifested as spherical porous shape.(3) The results of alkaline fusion study showed that the phase transformation temperature decreased after adding sodium carbonate and sodium chloride into the coal fly ash. Thereafter, the precipitated silica andγ-Al2O3 were prepared using the alkaline fused product as material through hydrochloric acid extracting and ammonia precipitation method, respectively. The TG-DTA and SEM analysis indicated that the y-MPS showed good modification effect on precipitated silica compared with that of stearic acid. At last, the titania-silica composite was successfully prepared using precipitated silica as the silica source by chemical coating method.(4) The sodalite and kaliophilite were prepared using coal fly ash as material by hydrothermal and fusion method, respectively. The synthesized sodalite was regular sphere shape. As compared, there were many plate-like crystals developed on the surface of kaliophilite particle. The TG-DTA analysis showed that the synthesized zeolites had remarkable thermal stability. The leaching test confirmed that the kaliophilite possessed high potassium retention rate. The hydrothermal treatment of coal fly ash in LiOH·H2O alkaline solution was also studied and the Li-ABW zeolite was synthesized by fusion method.(5) The glass-ceramic with major phase Li2Al2Si3O10 was prepared through sintering coal fly ash with LiOH·H2O powder. SEM observation revealed that the product particle interlocked together with dense well-sintered microstructure. The a-cordierite glass-ceramic was also prepared by solid state sintering method using coal fly ash and (MgCO3)4·Mg(OH)2·5H2O powder as precursors. As the LiOH·H2O additive amount reached 10%,β-spodumene and spinel phases developed. SEM observations revealed that the contour of crystal grains became smooth with the doping of Li+ion. In addition to this feature, the densification process improved and the sample's porosity and grain size decreased notably. As the TiO2 contents increased from 4% to 10%, low quartz and rutile were formed. Simultaneously, the amounts of indialite and spinel decreased.