MOBILITY OF CADMIUM IN COAL FLY ASH - Management of Hazardous Residues Containing Cd - page 176

5. E VALUATION OF C D A MOUNT O BTAINED
FROM S EQUENTIAL E XTRACTION

Sum of Cd contents in appropriate chemical fractions for various
sequential extraction methods were compared (Figure 1).
It was found, that applied methods extract Cd from coal fly ash to

n

[ ] i

∑ Cd

solutions to a various extent. Summary concentration of Cd ( ) for

i = 1

individual sequential extraction appropriately equaled: 17.5 (Tessier), 15.1
(Psenner), 14.3 (Kersten i Förstner), 13.1 (Gatehouse), 13.1 (Rudd), 9.5
(Sposito) and 6.9 (BCR) mg · kg -1 .
Taking into account the total contents of Cd in coal fly ash (19.0 mg · kg -
1 ), the percentage contents (%) of cadmium in coal fly ash according to applied
methods can be put in order:

BCR (36.5%) < Sposito (50.0%) < Gatehouse (68.9%) = Rudd (68.9%) <<
Kersten i Förstner (75.3%) < Psenner (79.5%) < Tessier (92.1%)

The results indicate that the most reliable method for determination of
chemical fraction of Cd in coal fly ash are Tessier's as well as Psenner's
method (Figure 1).

6. C HEMICAL F RACTION OF C D IN C OAL F LY A SH

Distribution of Cd in coal fly ash indicate that its content in various
fractions is variable (Figure 2). It was found that Cd occurs first of all in the
organic and sulfide fraction (3.2 mg · kg -1 - BCR, 3.7 - Sposito, 7.2 - Rudd)
and the residue (3.9 mg · kg -1 - Gatehouse, 4.7 - Kersten i Förstner, 6.5 -
Tessier), acid soluble, carbonate and adsorbed fraction (2.0 - mg · kg -1 -
Tessier, 1.9 - BCR, 4.5 - Rudd, 4.4 - Sposito), oxide fraction (3.0 mg · kg -1 -
Tessier, 1.8 - BCR, 2.8 - Gatehouse, 3.0 - Kersten i Förstner) as well as in
small concentrations in the water soluble and exchangeable fraction (1.3
mg · kg -1 - Kersten i Förstner, 1.4 - Psenner, 1.4 - Rudd, 1.4 - Sposito, 1.5 -
Tessier, 3.1 - Gatehouse). For Tessier, Gatehousea and Kersten and Förstner
procedures the Cd fractions can be put in order (except for 5-th fraction i.e.
residue):