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Mechanisms Controlling the Leaching Kinetics of Fixated Flue Gas Desulfurization (FGD) Material under Neutral and Acidic Conditions

^a Dep. of Civil and Environ. Eng. and Geo. Sci., The Ohio State Univ., 470 Hitchcock Hall, 2070 Neil Ave., Columbus, OH 43210
^b School of Environ. and Nat. Res., The Ohio State Univ., 210 Kottman Hall, 2021 Coffey Rd., Columbus, OH 43210. C.-M. Cheng, current address, Institute for Combustion Science and Environmental Technology, Western Kentucky Univ., 2413 Nashville Rd., Bowling Green, KY 42101

View larger version (25K): [in this window] [in a new window]   Fig. 1. Schematic diagram of the rotating disk system.

View larger version (195K): [in this window] [in a new window]   Fig. 2. (I) SEM micrographs and (II) X-ray diffraction patterns of (A) filter cake; (B) fly ash; (C) lime; (D) 28 d-cured fixated FGD material before leaching; and (E) fixated FGD material after leaching at pH2.2 for 240 h. P = portlandite; L = lime; M = mullite; Q = quartz; He = hematite; Ma = magnetite; H = hannebachite; E = ettringite.

View larger version (24K): [in this window] [in a new window]   Fig. 3. Concentration profiles of selected elements as a function of time at pH 2.2 and angular velocity of 60 rpm.

View larger version (29K): [in this window] [in a new window]   Fig. 4. Stoichiometric ratio profiles of (a) Ca to S and (b) Al to Si during various leaching experiments.

View larger version (16K): [in this window] [in a new window]   Fig. 5. Steady-state leaching rates as a function of rotating speed at pH2.2. Ca (•); S (); Al (); Si (); Mg (); Fe (); As (); Se ().

View larger version (14K): [in this window] [in a new window]   Fig. 6. Steady-state leaching rates as a function of pH. Ca (); S (); Al (); Si (•); Fe (); As (gray circle); Se (gray upside-down triangle).

View larger version (16K): [in this window] [in a new window]   Fig. 7. The stoichiometric ratios of (A) Ca/S (•), and Al/Si (); (B) As/ettringite-Ca (•) and Se/Ettringite-Ca (); (C) As/hematite-Fe (•) and As/glass-Al () leaching rates at steady state under various acidic leaching conditions with 60rpm rotating speed. Solid reference lines represent the ratios of (A) Ca/S, (B) As/ettringite-Ca, and (C) As/hematite-Fe in the bulk of fixated FGD material before leaching. Dashed reference lines are the ratios of (A) Al/Si, (B) Se/ettringite-Ca, and (C) As/glass-Al in the bulk of fixated FGD material before leaching. The gray solid and dashed lines are the standard deviation of the black lines.