THE PRODUCTION OF SUPERPOZZOLAN FROM COAL FIRED UTILITY ASH PONDS

More than 1.5 billion tons of coal combustion bottom ash and fly ash are stored in landfills and ponds in the United States. These deposits are typically very heterogeneous, consisting of co-disposed bottom and fly ash often contaminated with coal char and, in some cases, pyrite and coal. The recovery of useful pozzolanic material requires that these materials be classified and the carbon and pyrite separated and concentrated. Processing technology is currently under development at the University of Kentucky to recover carbon, coarse aggregate, ultra fine fillers and highly reactive pozzolanic concrete additives. Although the overall process flow sheet is tailored to the nature of the substrate, the approach generally employs hydraulic classification, spiral concentrators, froth flotation and a final hydraulic classification step. Products with median particle sizes (D₅₀) in the 3 to 4 um size range have successfully been produced from ash feed stocks with D_50's in the range of 20 to 25 urn. This material has been shown to have excellent pozzolanic properties, with reduced water requirements and accelerated strength development compared to conventional ASTM Class F fly ash.

• INTRODUCTION

• MATERIAL PROCESSING

• CONCLUSIONS

• REFERENCES