X-Ray and Electron Microscope Studies of Calcined and Sulfated Limestones

    Published: Jan 1970

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    Calcitic limestone and Iceland spar were shock calcined at temperatures in the range 750 to 1300 C, and the products were examined by electron microscopy and X-ray diffraction to determine the pore size, structure, and crystallite size of the calcines. The calcination took place in two stages: dissociation of the calcium carbonate and recrystallization of the oxide.

    Samples of the same materials, with and without prior calcination, were treated with a gas containing 4 percent sulfur dioxide at 750, 1050, and 1200 C, and examined as before to determine the degree and manner of sulfation. The limestone calcines were consistently more reactive with sulfur dioxide than were those of the Iceland spar; the difference is attributed to the larger crystallite size of the initial Iceland spar and an unfavorable distribution of pores in the spar calcines. Sulfation occurs in two stages: a general surface reaction of the sulfur dioxide and oxygen with the calcium oxide, and a subsequent diffusion-controlled reaction through the sulfatecovered outer surface to the unreacted lime core.

    Calcite calcines react best with sulfur dioxide at temperatures below 1050 C. Simultaneous calcination-sulfation, as in the injection into the furnace of a coal-burning power plant, takes place best at temperatures of 1050 C or higher.


    calcite, limestone, calcium carbonates, calcium oxides, calcium sulfates, electric power plants, flue gases, sulfur dioxide, air pollution, injection, X-ray diffraction, electron microscopes, roasting, sulfation, crystallites, density (mass/volume), porosity, evaluation, tests

    Author Information:

    McClellan, G. H.
    Research chemists, Tennessee Valley Authority, Muscle Shoals, Ala.

    Hunter, S. R.
    Research chemists, Tennessee Valley Authority, Muscle Shoals, Ala.

    Scheib, R. M.
    Research chemists, Tennessee Valley Authority, Muscle Shoals, Ala.

    Committee/Subcommittee: C07.05

    DOI: 10.1520/STP41934S

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