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Unburned Carbon from Fly Ash for Mercury Adsorption: I. Separation and Characterization of Unburned Carbon

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ABSTRACT
In searching for a low cost adsorbent for mercury removal from flue gas, this study focuses on the utilization of unburned carbons from fly ash as the substitute material for the costly activated carbons. In this first paper of the series, various separation technologies are introduced for the extraction of unburned carbon from different sources of fly ash. The unburned carbons have been efficiently separated from clean ash, which is a value-added product for the concrete industry, with the separation technologies such as gravity separation, electrostatic separation, and froth flotation. Carbon concentrate with a LOI (Loss On Ignition) value of 67~80% has been generated from the processes. Characterization of the carbon products has been performed to determine the physical and chemical properties of the material. It has been found that the unburned carbon particles had a porous structure, which is similar to the activated carbon. The BET surface area of these materials was in a range of 25~58m2/g. The majority of the pores are in the range of macropore, and some parts of the surface were embedded with glass spheres. There is a linear relationship between the LOI value and the carbon and sulfur content in the carbon concentrate. Chemical analysis indicated that the mercury content in unburned carbon was much higher than the other separation products, which suggests that the carbon has certain ability to capture mercury from flue gas.
 
Cite this paper
J. Hwang, X. Sun and Z. Li, "Unburned Carbon from Fly Ash for Mercury Adsorption: I. Separation and Characterization of Unburned Carbon," Journal of Minerals and Materials Characterization and Engineering, Vol. 1 No. 1, 2002, pp. 39-60.
 
References
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[8]Shannon D. Serre* and Geoffrey D. Silcox ; Adsorption of Elemental Mercury on the Residual Carbon in Coal Fly Ash, Industrial & Engineering Chemistry Research; 2000; 39(6); 1723-1730.
 
[9]Tanaporn Sakulpitakphon, James C. Hower,* Alan S. Trimble, William H. Schram, and Gerald A. Thomas; Mercury by Fly Ash: Study of the Combustion of a High- Mercury Coal at a Utility Boiler, Energy & Fuels; 2000; (3); 727-733.
 
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[13]Hwang, J.Y. and Li, Z., “Control of Mercury Emissions Using Unburned Carbon From Combustion By-Products,” U.S. Patent 6,027,551 (2000).
 
[14]Hwang, J.Y., Hein, A.M., Kramer, R.S., Liu, J., Hozeska, T.J., Zhang, Q., and Scott, T.E., “Application of Characterization on Fly Ash Beneficiation to Produce Quality Controlled Products,” Process Mineralogy XI: Characterization of Metallurgical and Recyclable Products, 1991, pp. 167-180.
 
[15]Hwang, J.Y., Liu, X., Zimmer, F.V., Thiruvengadam, T.R., and Patzias, T., “Beneficiation Process for Fly Ash and Utilization of Cleaned Fly Ash for Concrete Application,” Proceedings: 11th International Symposium on Use and Management of Coal Combustion By-Products, Vol. 1, Paper 11, EPRI Publication, 1995.   eww150203lx
 
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