Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to several improvements in the inventions
previously disclosed and claimed in our Canadian patent application 186,020,
filed November 16, 1973.
Briefly, the inventions disclosed and claimed in our above re-
ferenced patent applications relate to methods of disposal and use of alkaline
earth metal sulfite-containing scrubber sludges.
These sludges may result from lime or limestone scrubbing of
sulfur oxide-containing gases, such as combustion stack gases for desulfuriza-
tion thereof; the scrubber underflow comprising an aqueous suspension of
alkaline earth metal sulfites. Such sludges also may be produced in the
double alkali desulfurization process wherein stack gases are scrubbed with ~ -
sodium, potassium or ammonium hydroxide solutions. The sludge is produced
when these solutions are then treated with lime or limestone to precipitate
the sulfites.
The sulfite sludges of interest in this invention may also include
some sulfate compounds. These may result from incidental chemical reactions
accompanying the desulfurization and scrubbing steps or they may result from
specific steps intended to oxidize sulfites to sulfates for some specific pur-
pose such as to improve dewatering characteristics.
Generally, these aqueous sludges are dewatered and treated, as
required, with lime and/or fly ash to produce novel cementitious compositions
having from 30 to 90%, by weight, solids, the solids comprising 0.25-70%, by
weight, alkaline earth metal sulfite, 0~25-70%, by weight, alkaline earth metal
hydroxide and 10-99.5% fly ash. This hardenable material may be used as
structural fill, road base, or in the formation of synthetic aggregate.
The sludge itself, prior to treatment, may provide some or all of
the necessary alkaline earth metal hydroxide and/or fly ash. Normally, a
stoichiometric excess of Iime or limestone used in the scrubbing operation and
the residual or remaining alkaline earth metal hydroxide is then available
for reaction in the present invention. Similarly, fly ash may not be separat-
1056409
ed from the stack gases prior to the scrubber operation and this fly ash is
available for reaction.
The further improvements which are the subject of the present
application are in the use of other waste materials to replace part or all
of the lime and fly ash additions heretoore specifically disclosed and used.
The supplementary or complementary materials which may be used in
these hardenable compositions, in accordance with the present invention,
include Portland cement, high alumina cement, waste lime, lime kiln dust,
partially calcined lime, cement kiln dust, BOF waste dust, or slag, coal
mine refuse or tailings, "red mud" resulting from the chemical reduction of
bauxite, alum waste, bottom ash and any highly amorphous siliceous or
alumino-siliceous incineration residue, such as that from petroleum refinery
waste incineration.
In some cases, these alternative waste materials are flocculent
slurries with a high proportion of physically associated water. As the
solids in these slurries react, this water becomes available. m e propor-
tion of such waste slurries in the treatment mix of the present invention
may be limited by the water content thus contributed to the mix. It should
be noted that these supplementary or complementary materials may provide
reactants for the pozzolanic cementitious reaction, or they may act as ag-
gregate or filler material. They may also contribute supplementary cementi-
tious activity, as in the case of Portland or alumina cement. Waste lime,
partially calcined lime, cement kiln dust and sOF waste dust are active
sources of alkaline earth metal hydroxides for the reaction upon which the
present invention depends.
These materials, in combination with those previously disclosed or
in combination with other sources of alkaline earth metal hydroxides or pozzo-
lanic activity may be used in treating sulfite sludges to produce hardenable
materials there from, these hardenable compositions being defined as here-
tofore with the exception that the 10-99.5% 1y ash content in the sludge
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composition solids may consist of fly ash or equivalent amounts of other
materials having pozzolanic activity, the equivalent amount being de~ermined
by ASTM Test Method C-618, "Pozzolanic Activity Index - With Lime".
Thus, the amount of a highly amorphous siliceous incinerator waste
residue, such as that from petroleum refinery waste incineration, providing
a pozzolanic activity, in accordance with the foregoing test, corresponding ~ -
to that of 10-99.5% fly ash, may be incorporated in the compositions of the
present invention and used in the methods of the present invention.
Other waste materials as described above may also be incorporated
in place of some or all of the required fly ash content, dependent upon the
pozzolanic activity thereof in accordance with the test as described above.
Similarly, the various above referenced waste materials including
alkaline earth metal hydroxides or hydratable alkaline earth metal oxides may
also be incorporated to the extent of their molar equivalency with 0.25-70%
alkaline earth metal hydroxide.
Por a better understanding of this invention, reference is made to
the following illustrative examples of this invention and particularly the
sludge treatment processes hereof and the hardenable and hardened compositions
resulting therefrom.
Example l
A sulfite scrubber sludge, produced by limestone scrubbing of
the stack gases in a full scale pulverized coal burning power generation unit
was dewatered to a solids content of 50%, by weight. The solids composition
of this sludge consisted of:
35% CaCO3
15% CaSO3 1/2 H2O
10% CaSO4-H20
40% Fly Ash
Various mixes of this sludge with Portland and alumina cement were
tested, with these added cements comprising up to 40%, by weight, of the
resultant sludge solids. The development of strength, as indicated by Pene-
tration Resistance,is shown by the test results listed in Table 1.
-- 3 --
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. '
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a ~
. ~ ~ 8 ~ ~ 8
'~ ~ ':'
~ :~ I ~ 8 8 8 8 o :
:~ I ~ ~ g o o , .
~1
E~ ~ I 1 8 8 g
~ n
~'~ 8 ~ O,
8 ~ I u , 0, 1 1 ~ e
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~0~6409
Example 2
Sludge produced in a double alkali treatment process for desul-
furizing stack gases was dewatered to a solids content of 62%, by weight. Fly
ash from the same power generating unit in which the stack gases were pro-
duced was added to the sludge in an amount equal to 150% of the total weight
of the sludge sample. In this particular sample, in view of the residual
calcium hydroxide in the fly ash and in the sludge, no additional alkaline
earth metal material was added.
This prepared mixture was then permitted to harden and tested for
penetration resistance with results as listed in Table 2.
Table 2
Penetration Resistance
Age of Test Resistance ~in PSI)
1 week 2,080
2 weeks 24,800
3 weeks 28,800
5 weeks 44,800
Examples 3 and 4
Lime kiln dust (partially calcined limestone) was admixed with a
sulfite scrubber sludge from a pilot scrubber in a full scale power generating
plant. This sludge consisted of 60% (by weight) solids, the solids consisting
of 50% calcium sulfite, 40% fly ash, 8% calcium sulfate and 2% free lime.
Blast furnace slag was admixed with synthetic sulfite scrubber sludge (by
weight~ 60% solids, solids consisting of 45% calcium sulfite, 35% fly ash, 10%
calcium sulfate, 5% calcium carbonate, and 5% calcium hydroxide).
These mixtures were permitted to harden, as indicated and tested
for penetration resistance with results as indicated in Tables 3 and 4.
~cu o oo
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OOOO
_~ ~ ~ N
a) ~ o o o o
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~ 0 ~0, C ~o
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~056409
Example 5
Sludge from the same source as that in Example 3 (in which lime
containing approximately 5%, by weight, magnesium oxide, was used in the
scrubber) was dewatered to 55% solids. The composition of the sludge solids,
after the addition of fly ash was as follows: (%, by weight):
1-3% Ca(OH)2
42-44% CaS03 1/2H20
8-9% CaS04-2H20
40% Fly Ash
5% CaC03
1-2% MgS03-1/2H20 ~ MgS04 7H2
High calcium lime and a typical type I cement was added to
various mixes of this sludge with penetration resistance test results, after
curing at 100F. in a moist atmosphere as listed in Tables 5 and 6.
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~ o g g
3 o~, ~
~1 I ~`3 N t~
3 H
h 3 o o o o
.~ , ~ ~ ~
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_ ,~, o~
~ g g
.~ ,,
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Example 6
A sludge as described above in Example 1 tsolids content, 50%)
was treated with dolomitic monohydrated lime and a typical Type I Cement.
Samples were cured in a moist atmosphere at 100 F, with test results as
shown in Table 7.
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~ ~ ,, ,ol g
.~ ,, ~ ~
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The foregoing is a description of this invention with reference
to specific embodiments, materials and examples. It should be understood,
however, that this invention is not limited thereto and the appended claims
are intended to be construed to encompass the various modifications and varia-
tions of the invention which may be made by those skilled in the art without
departing from the true spirit and scope of the present invention.
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