S-EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-062 July 1981
Project Summary
Chemical Speciation of
Flue Gas Desulfurization (FGD)
Sludge Constituents
James Lu
This project studies the problem of
flue gas desulfurization (FGD) sludge
disposal to land. Specifically, the
chemical species of FGO sludge con-
stituents are thermodynamically mod-
eled using the equilibrium constant
approach in an attempt to predict the
constituent concentrations in fresh
and aged FGD wastewater and sludge.
This method involves solving the
stoichiometric equations of various
chemical species subject to constraints
imposed by the equilibrium constants
as well as mass balance and charge
balance relations. Diagrams such as
Eh-pH plots, ion-ratio plots, concen-
tration pH figures, and species distri-
bution figures are then used to display
the stability field and speciation re-
sults.
The thermodynamic model used in
this study was verified for suitability
and accuracy by the analytical results
of various FGD sludge samples taken
from the Kansas City Power and Light
(La Cygne plant)'. The model was also
operated over a wide range of opera-
tional and chemical changes to theo-
retically determine their impacts on
the concentration and speciation of
various solid and soluble species. The
impacts of (1) changes in pH and ionic
strength; (2) addition of lime, silicates,
hydrogen sulfide, and phosphates to
the sludge; (3) variation of chloride,
sulfate, and borate levels; (4) addition
of magnesium to the sorbent; and (5)
sulfite oxidation were all estimated
using the model.
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
A conventional environmental impact
assessment of flue gas desulfurization
(FGD) sludge disposal would include
chemical analysis and identification of
the total concentrations of constituents
in the sludge and its leachate. However,
public health effects of FGD waste
disposal depend on which chemical
forms or species of the constituents are
released to surrounding waters and not
necessarily on their total concentration.
Thermodynamic modeling is the only
feasible means to obtain contaminant
species information of FGD sludge. A
thermodynamic model can also be used
to predict migration trends of constit-
uents when FGD wastes age; estimate
final concentrations of constituents in
FGD leachate (aged wastewater) without
conducting expensive field monitoring;
and predict effects of operational and
chemical changes in FGD wastes.
Many available techniques can be
used to construct and interpret a chemi-
cal thermodynamic model. In this study,
the equilibrium constant approach is
used.
-------
Methodology of Species
Analyses
Two principal graphical treatments,
Eh-pH plots and the ion-ratio method,
are used to describe the stability fields
of constituents in FGD sludge. The Eh-
pH plot is used for constituents with
different redox species such as iron,
manganese, mercury, arsenic, and
selenium. The ion-ratio method is used
for constituents with only one redox
state or for reactions involving no
electron transfer.
The speciation model is constructed
by the equilibrium constant approach.
The actual mathematical equilibrium
model involves a series of simultaneous
equations that describe the various
interactions among components of the
system. Seven general equations are
involved (Table 1). To solve these equa-
tions simultaneously, the information
on metal and ligand species, overall
formation constants, solubility products
(and/or Henry's constants), and activity
coefficients must be compiled from the
literature. A computer solution is neces-
sary, as the expanded equations number
in the hundreds. The resultant nonlinear
equations are solved by Newton-
Raphson iteration.
Because the chemical composition of
FGD sludge can vary over an extremely
wide range, this study focused on
speciation at the lowest levels (ionic
strength (I) =0 05) and the highest levels
(I = 0 8). All possible distributions of
species are expected to be within this
range.
Speciation of Solid and
Soluble Chemical Species
Fresh FGD Sludge
Thermodynamic modeling of the fresh
FGD wastewater system can be per-
formed as if no solid was formed or
dissolved because (1) the equilibrium
conditions among soluble species can
easily be reached and (2) the rates of
nucleation and dissolution of the solid
species are very low. A summary of the
predominant soluble species shows
that the major ions (i.e., calcium, mag-
nesium, potassium, and sodium) and
the manganese species exist as free
ions in fresh FGD wastewaters(Table2).
Other trace metals, however, can be
complexed considerably in the same
wastewaters. Chloride complexes may
under certain conditions become the
predominant species for cadmium,
copper, lead, mercury, and zinc; borate
Table 1. General Models Used for Speciation Calculation
Mpfi)
fi) • L*(j)
h a b
III *M(i)»L(Jk = 1
j = 1 p = 1 q = 1
g c d
III *M(i)uL(j)v - 1
i = 1 u = 1 v = 1
k I h
[M(ih] = [Mm + I I I m[M(i)mL(j)n}
m=1n=1j=1
h a b
+ I I I p[M(i)fUj)q]
j=1 p=1q=1
h c d
+ 1 I I n(M(i)mL(j)n]
k I g
[L(jh] = (L(j),] + I I I n[M(i)mL(j)n]
m = 1 n = 1 j = 1
gab
+ I I I
i = 1 p = ; q = 1
g c d
+ I I I [M(i)aL(M
j= 1 u = ; v = 1
12)
(3)
(4)
15)
(6)
(7)
where:
[M(i)mL(j)n] = concentration of complex M(i)mL(j)n (in
moles/ liter)
[M(i)t] = free metal ion concentration of ith metal
(in moles/ liter)
[L(j)<\ = free concentration ofjth ligand (in
moles/liter)
[M(i)i] - total concentration of ith metal in the
system (in moles/ liter)
and
nM(i)uL(j}y = mole fraction of solid or gas species for
metal or ligand solids
i = metal species
-------
Table 1. (continued)
j - ligand species
g = total number of metals
h = total number of ligands
k = maximum number of metals Mfi) coordinating
ligands L(j)
I = maximum number of ligands Lfj) coordinating
metal Mfi)
a, b, c, and d = positive integer showing maximum number
of metals or ligands in the solids or gases
- overall formation constant of complex
M(i)mL(j)n
Xx = thermodynamic activity coefficient of soluble
species x
fi = thermodynamic activity coefficient of solid
for gas) species x (in this study, assume fx =* 1)
K - solubility products or Henry's constants
complexes may become the predominant
species for copper and lead; sulfite
complexes may become the predominant
species for cadmium and iron; and
hydroxide complexes may become the
predominant species for mercury, zinc,
and the trivalent metals such as chromi-
um and iron. In fresh FGD wastewater,
arsenic and selenium exist primarily as
arsenate and selenite species. The pre-
dominance of a given species can be
affected significantly by the pH level of
the wastewater. The ionic strength (or
more specifically, the soluble levels of
the related ligands) also plays an im-
portant role in the speciation of most
constituents:
Aged FGD Sludge
The speciation of constituents in the
solid and soluble phases of aged FGD
sludge was computed assuming that
the equilibrium condition among all the
soluble and solid species had been
reached. Because of the long contact
period, equilibrium conditions between
solid and liquid phases probably can be
reached in aged FGD wastes. The calcu-
lated results are summarized in Table 3.
Results show that sulfur dioxide re-
moved from the flue gas reacts to form
CaSO< • 2H20(s) and CaS03 • 1 /2H20(s)
in the FGD sludge. In the aged sludge,
carbonate solids may become the pre-
dominant species for cadmium, calcium
(when pH isgreaterthan?), copper, lead
(at pH greater than about 9), manganese
(at pH greater than about 7.5), and zinc
(at high ionic strength and pH around 8).
Hydroxide solids are the predominant
species for chromium, iron, cadmium (at
pH greater than 9), magnesium (at pH
greater than 9), manganese (at pH
greater than about 9), and zinc (at low
ionic strength and pH greater than
about 9) in the aged sludge. Arsenic,
mercury, and selenium exist primarily
as elemental metals in the aged sludge.
Aluminum forms predominantly phos-
phate solids at low pH and oxide solids
at high pH. In aged sludge, the molybdate
and silicate solids are usually the pre-
dominant species for lead and zinc,
respectively
The predominant soluble species of
constituents in aged FGD leachates are
similar to those found in fresh FGD
wastewater. However, the concentra-
tions of these soluble species are gen-
erally decreased through aging because
of the nature of solids found. The pre-
dominant soluble species and their
concentrations for each individual con-
stituent at two different ionic strengths
are shown in Table 3. In most cases, the
predominant species alone will account
for a major portion of the concentration.
Therefore, knowing the predominant
solid and soluble species, the total
soluble concentration of a constituent in
FGD leachate can be easily calculated
without the aid of the computer.
Model Verification
The thermodynamic model was veri-
fied by checking the model results
against both analytical data and certain
theoretical considerations.
The model, in relation to analytical
data, was evaluated by comparing the
known soluble concentrations of con-
stituents in aged FGD wastes to those
predicted by the model. The calculated
results for aluminum, arsenic, boron,
cadmium, cobalt, copper, iron, manga-
nese, mercury, potassium, selenium,
sodium, and zinc either approach or are
very close to the concentration levels
experienced in the field (Table 4). For
other elements (specifically calcium,
chromium, fluoride, lead, and magne-
sium), the model was not as effective.
The low levels of calcium predicted are
due primarily to the interaction of calcite
with Ca-COa and CaSOa complexes in
the model. The high levels of chromium
and lead calculated are due to the
inclusion of hydroxide and carbonate
complexes in the model For fluoride
and magnesium, the discrepancy may
be caused by certain unsuitable solids
included in the model. The discrepancies
also may be due to (1) errors in the
stability constants and activity coeffi-
cients; (2) effects of other mechanisms
such as adsorption by hydroxide solids
or clay minerals; and (3) effects of
kinetic constraints.
According to scientific considerations,
in general, the model results behave in
accordance with basic chemical and
thermodynamic principles, including
the effects of changing pH, Eh, and
ligand levels
Effects of FGD System and
Sludge Variables on Chemical
Speciation
To select a sludge treatment or dis-
posal procedure, observing the possible
beneficial or adverse effects of opera-
tional or chemical changes in a FGD
system on sludge speciation is useful.
The chemical changes studied here
include those of pH, ionic strength,
chloride concentration, borate concen-
tration, sulfate concentration, and
sulfite oxidation (Table 5). The opera-
tional changes were limited to the
addition of lime, silicates, hydrogen
sulfide, phosphates, and magnesium
(Table 6).
A change in pH can influence the
direction of the alteration processes
(dissolution, precipitation, adsorption,
or complexation) in any chemical system.
In general, a pH increase in the FGD
sludge system tends to dissolve more
-------
Table 2. Predominant Species of Soluble Constituents in Fresh FGD Wastewater
Predominant Species"
Ionic
Constituent Strength pH - 5 pH = 7
pH =
Al
As
Cd
Ca
Cr
Co
Cu
F
Fe
Pb
Mg
Mn
Hg
K
Se
Na
Zn
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
AIF2+(34),AI(OH}2+(20),
AIF2(17)
AIF2(55)
H2As04'(98)
H2As04-(95)
Cd2+(50)CdC03(aq)(40)
AI(OH)idOO)
AIF2(38),AIF3(31>
HAs02'(68)
HAs042~(78)
Cd2+(49),CdCr(40)
Ca2+(83)
Cr(OHr<79)
Cr(OHf*(65)
Co2+(69)
Co2*(40>. CoSO4(aqj(26]
Ca^(89)
Ca2+(71)
Cr(OH)2<85)
Cr(OH)2*(81)
0.05 Cu2*(54)
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
CuB(OH)4(35), CuCf(26)
F(25),SnF*(52)
CaF+(40),F~(38)
Co2+(40J, CoSO4aq)(26)
Cu(B(OH)4)2faq)(5J)
CufBfOHMaqMSSi
FeS03(97)
Pb2+(55)
F~(40).MgF+(44)
Fe(OH)2(100)
Fe(OH)2(84)
PbSO*(22),Pbz*(21)
Pb2+(19)
Pb(B(OH)A)2!aq)<87)
Mn2*(79)
HgCI3-(47),HgC/42-(26)
HgCI,(aq)(27)
IC(97)
HSe03'(97)
HSe03(97)
Na*(95)
Na"(95)
Zn2+(74)
Zn2+(47),ZnCr(34)
Mn2+(78)
Mn2+(55)
HgCI2laq)(62)
HgCI3-(46),
K+(97)
K"(89)
Se03*-(74)
SeO32'(74)
Na+(95)
Na*(95)
Zn2+(74)
AI(OHU'dOO)
AI(OH)4-(100)
HAs02'(100)
HAs042~(97)
CdC03(35),Cd2*(21).
CdCI(OHFf20)
Ca2+(81)
Ca2+(71)
Cr(OH)A'dOO)
Cr(OH)4-(100)
CoCO3(aq)(44).Co^(26)
CoCr<20)
z+(25).
Cu(B(OH)4)2faq)(100)
MgF+(47),F~(45)
Fe(OH)4'(93)
Fe(OH)2(93)
PbfBfOHJMaqjOS).
Mn2*(54)
HgCIOH(aq)(52)
IC(98)
K*I89)
SeO3 (99)
Se02-(99)
Na+(97)
Zn(OH)2faq)(68)
Zn(OHMaq)(42).
ZnCIOH(aq)(26)
Note: Values in the parentheses indicate the percent of the total concentration.
alf one species accounts for less than 50 percent of the total concentration, then more than one species will appear.
elemental constituents such as As°(s),*
Hg°(l), and Se°(s) and to transform some
of the carbonate, phosphate, or other
sol ids into hydroxide solids, thus affecting
the concentration of soluble constituents.
A pH change may also affect the ligand
concentrations and, thereby, change
the concentration of soluble constituents.
The overall effects of pH on total
constituent concentration depend on
*s = solid
I = liquid
the solubility constants of the new
solids formed, the new ligand concen-
trations, and the formation constants of
the complexes. For example, a high pH
level can increase total soluble mercury
and selenium and yet decrease most of
the other bivalent trace metals. For
trivalent metals such as chromium and
iron, the minimum soluble constituent
concentrations occur in the neutral pH
region.
Although a change in ionic strength in
the FGD sludge can affect the stability
constants, its effects on the soluble
levels of constituents or on the stability
fields of various solids are usually
negligible if their related ligand levels
are unchanged. The soluble chloride
concentration of FGD waste is a very
important factor in determining the total
soluble level of cadmium, copper, lead,
mercury, and zinc. Variations in borate
concentration have an impact primarily
on total soluble copper and lead concen-
trations. The soluble sulfate concentra-
tion may affect the total soluble calcium,
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Table 3. Predominant Species of Constituents in Aged FGD Sludge
Predominant Solid Species'
Predominant Soluble Species'
Ionic
Constituent Strength
pH=7
pH =
pH=7
Al
As
Cd
Ca
Cr
Cu
Fe
Pb
Mg
Mn
Hg
K
Se
Na
Zn
005
0.8
0.05
08
0.05
0.8
0.05
0.8
0.05
08
005
08
005
0.8
005
08
0.05
0.8
0.05
08
0.05
08
005
0.8
005
0.8
005
08
0.05
0.8
AI(H2PO,)(OHUs)
AHHtPOJIOHMs)
As°(s)
As°(s)
CdCOds)
CdCOa/s)
CaSOyl /2H10(s).
CaSO*-2H20(s)
CaS03-H,0(sl.
CaSOt-2H20(s)
Cr(OHMs)
CrfOHMsl
CuiCOdOHkls)
CutCOalOHMsl
Fe(OHMs)
Fe(OHMs)
PbMoOtls)
PbMoOtfsi
b
b
b
b
Hg°(D
Hg°(D
b
b
Se'fst
Se°(s/
b
b
b
ZnSiOa/s)
AlfHtPOdtOHMs)
AlfHiPOtMOHMs)
As°(s)
As°(s)
CdCOils)
CdCOJs)
CaSOyl /2H,0(s),
CaSOt-2HzO(sl
CaSOyHiO(s),
CaSOt-2H20/s)
Cr(OHMs)
CrfOHMs)
CuiCOJOHMs)
CutCOJOHMs)
Fe(OHMs)
Fe(OHMs)
PbMoOJs)
PbMoOtls)
b
b
b
b
Hg°(1)
Hg°(1)
b
b
Se°fs)
Se°(s)
b
b
ZnSiOifs)
ZnSiOJs)
Zn(OHMs)
AlzOvSH&ls)
AlzOy3HtO(s)
As'fsl
As°(s/
CdfOHMs)
Cd(OHUs).
CdCOJs)
CaCOJsl,
CaS03-1 /2H20(s).
CaS04-2H,0{s)
CaCOz/sl,
CaSOi-1 /2HiO(s).
CaS04-2HiO(sl
Cr(OHUs)
CrlOHMs)
Cu2COJOHMs>
CuiCOJOHMs)
Fe(OH)Js)
FefOHMsl
PbMoOJs)
PbMoOJsl.
PbCOJs)
Mg(OH)^s)
MglOHMs)
MnCOJs)
MnfOH/M,
MnCOifsl
Hg°(D
Hg°ID
b
b
Se°(s)
Se°(s)
b
b
ZnfOHMsl
ZnSiOJsl,
ZnCOifsj
AIF*(6 04)
AlFi (5.051
HaAsO,~(8 03)
HaAsO,~(75J/
Cd**(5.23>
cdcris 121
Ca^fO 211
Ca** 10.25)
Cr/OHf*(4. 13)
Cr(OHk"(5.0)
CuBtOH)t*(15.38)
(16 78)
CuB(OH)S(1499)
(1609)
FetOHk"(7 16)
FeS03(6.98)
Pb2t(5.80)
PbCr(5.67)
Mg**(391)
Mg**(0.95)
Mn**l3 49)
Mn2t(3.56)
HgCUaqX22. 1)
HgCli(19 9)
K*(1.89)
K*(1 87)
HSeO3-(28.6)
HSeO,~(28.6)
Na*(1 36)
Na*(0.83)
Zn**(3.63)
Zn*+(3.84)
AI(OH)Jaq)(6 26)
Al(OHMaq)(6 89)
HAsO '-(11.231
HAsO*~(1087)
C^(6.03)
CdCr<5 13)
Ce2*<0 53)
Ca*(0.32)
Cr(OH>2*(4. 76)
Cr(OHk''(4 72)
CulB(OH)Maq)
(16.9)
CutBIOHMdaq)
(164)
Fe(OHk*(9 16)
Fe(OH)i(9. 12)
PbB(OH)S(5.82)
PbB(OH)t*(5 44)
Mg*(3 92)
Mg**(0.95)
Mn*(3.49)
Mn2*(3.56)
HgCUaqlVO 4)
HgCk'118.2)
ICI1.89)
IC(1.87)
Se03*-(18.2)
Se03"-(182)
Na'd.Se)
Na'(0.83)
Zn2t(3.65)
Zn**(4 06)
AI(OH)3(aq)(5.95)
A/(OHMaq)(5.36i
HAsOt2~(8.82)
HAs02'(10.91)
CdtS03)2*-(7. 72)
CdCIOH(aqK6.07)
Ca2t(2. 19)
Ca2*(2 0)
Cr(OH)t-f4 03)
Cr(OHk'(3.99)
Cu(B(OH)^aq)
CufB(OH)Maq)
Fe(OH)t'(10.07)
Fe(OH)t-(8.96)
Pb(B(OH).l3-(7 14)
PbfBfOHMitS.SSI
Mg2tf4. 16)
Mg2*(1. 13)
MnSO,laq)(4. 10)
Mn2tl4.33)
Hg(OH)daq)(17 9)
HgCIOH(aq)(1 7 0)
IC(1.93)
1C Y; 91)
SeO32~(6. 19)
Se032-(6. 19)
Na '(1.37)
N a* (0.85 )
ZnSOJaq)(5 67)
Zn(OHMaq)(5.9i
Note. Values in parentheses indicate the -log molar concentration.
'If one species accounts for less than 50 percent of the total concentration, then more than one species will appear for each condition
"—indicates that there is no stable solid or that the stable solid is in complex forms (e.g., complex silicates)
magnesium, cadmium, and zinc concen-
trations. In general, if the total soluble
levels of the above-mentioned ligands
(e.g., chloride, borate, and sulfate) are
known, the total soluble metal concen-
trations in the aged'FGD leachates can
be approximated without extensive
computation.
For operational changes, sulfite oxi-
dation may reduce the concentration of
sulfite complexes and increase the
concentration of sulfate complexes but
have very little impact on the total
soluble concentration of most metals.
The most significant effect of sulfite
oxidation is the transformation of
CaSO3-1 /2H20(s) to CaS04-2H20(s) or
CaCO3(s), depending on pH levels. This
transformation may affect the soluble
levels of arsenic, mercury, and selenium
if the redox potential is controlled by
sulfate/sulfite species.
Adding lime to FGD sludge is used in
pozzolanic fixation processes to improve
the engineering properties of dewatered
sludge. The model shows, however that
adding lime may adversely affect con-
stituent solubility. Adding lime may
reduce the total soluble levels of certain
constituents such as arsenic and manga-
nese; however, the total soluble levels
of most other trace toxic metals such as
cadmium, chromium, copper, lead, mercu-
ry, selenium, and zinc, increase in aged
FGD sludge following lime addition.
This may actually increase the potential
for environmental damage should the
concentration increase outweigh the
dilution factor decrease that results
from permeability reduction.
Adding silicates may reduce the total
soluble aluminum and zinc concentra-
tions, but other elements studied are
virtually unaffected.
Phosphate addition will only reduce
two soluble major ions (calcium and
magnesium) while increasing the soluble
cadmium level. Phosphate itself is also a
water pollutant, so adding phosphates
is not recommended for the treatment of
FGD wastewater.
The addition of hydrogen sulfide may
reduce the soluble concentrations of
trace metals substantially (Table 6). This
operational change, however, may not
be desirable for an FGD system because
(1) hydrogen sulfide itself is a pollutant,
and (2) the diffusion of oxygen into the
sludge, followed by the oxidation process,
will eventually return the soluble metals
to their original concentration.
Magnesium improves the efficiency
of wet FGD systems; therefore, use of
high magnesium reagents could become
commonplace. The model shows that, in
general, adding magnesium will not
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Table 4. Validity of the Thermodynamic Model for the Prediction of FGD Sludge
Speciation*
Constituent
Al
As
B
Cd
Ca
Cr
Co
Cu
F
Fe
Pb
Mg
Mn
Hg
K
Se
Na
Zn
Validity of
Modef
Excellent
Good
Excellent
Excellent
Not applicable
Not applicable
Good
Excellent
Not applicable
Good
Not applicable
Not applicable
Excellent
Excellent
Good
Good
Good
Excellent
Reason for Discrepancy
Form strong CaCOafs) when pH >7
Form strong Cr-OH complexes
Solubility-controlling solid unknown
Form strong Pb-COs and Pb-OH complexes
Solubility-controlling solid unknown
'Based on comparison of modeling results with Kansas City Power and Light FGD
sludge analysis.
^Excellent means that the migration trends of the constituent follow those predicted by
the model and that measured levels in the aged leachate are within 30 percent of
those estimated by the model; Good means that both estimated and calculated levels
of constituents show the same migration trends when FGD waste ages.
significantly affect the total soluble
levels of most constituents.
The full report was submitted in
fulfillment of Contract No. 68-03-2471
by SCS Engineers under the sponsor-
ship of the U.S. Environmental Protec-
tion Agency. This Project Summary was
authored by James Lu of Cal Science
Research, Inc. for SCS Engineers.
-------
Table 5. Effects of Chemical Changes on the Speciation of Constituents in FGD Sludge
Constituent
pH
Ionic Strength
Chloride
Concentration
Borate
Concentration
Sulfate
Concentration
Sulfite
Oxidation
Al
As
Cd
Ca
Cr
Co
Fe
Pb
Solid: High pH levels
favor the formation of
AI^>,-3H,0(s); low pH
levels favor the for-
mation of AI(HiPOt)
(OHMs)
Soluble: When pH is
higher than about 6,
the predominant
species will change
from AlFt to Al3' -OH'
complexes
High pH levels tend to
dissolve As°(s) and
form arsenate species
Solid. When pH is
higher than 10.5,
CdCOstst may grad-
ually transform to
Negligible (when re- Negligible
lated ligand concen-
trations are unchanged)
Negligible
Negligible
Negligible
The relative distri-
bution of Cd2* and
Cd-CI complexes can
be altered by ionic
strength changes
Soluble- High pH
level can lower the
total Cd level
Solid CaCOa/s) Negligible
may greatly increase in the
sludge when pH>7
Soluble. WhenpH>7
the total Ca and Ca"
are reduced signifi-
cantly
Solid: Cr(OHJ3ts) is Negligible
significant when pH
ranges from 6 to 9
Soluble: When pH is
higher than about 4,
the predominant species
will change from Cr3*
to Cr-OH complexes
Solid: Negligible Negligible
Soluble. WhenpH
>4. 8, the predominant
species will change
from Co2* to Cu-
B(OH)t complexes
Solid. Negligible Negligible
Soluble: High pH
levels fpH >8.5) tend
to increase Fe-OH~
complexes but reduce
the total Fe levels
Solid: When pH <9, Negligible
PbMoOtls) is predomi-
nant. otherwise. PbCOi/sl
is predominant
Soluble: At high pH
levels, Pb-COj may
increase the total Pb
levels
Negligible
Can greatly affect
the total soluble
Cd levels when chlo-
ride is higher than
certain levels
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
WhenpH<4.7.
Cu-CI com-
plexes may become
predominant when
the chloride
level is higher
than 2,000 ppm
Negligible
When the bor-
ate level in-
creases from
5 ppm to 2OO
ppm, the solu-
ble lead level
can be increased
about 2,000
Negligible
Negligible
Cd-S0t complex
may become predom-
inant when Cl~,
SO,2', or OH'
complexes are not
significant
When pH > 5. and the
sulfate level is
higher than about
5.000 ppm. the CaSOt
fag) species may
become predominant
Negligible
Negligible
Negligible
Negligible, if the
redox potential is
not controlled by
sulfate/suHite species
Will reduce Cd(SOJt~
and increase CdSOt/aq)
levels. However.
effects on total solu-
ble Cd and Cd solids
are negligible
Will convert the sul-
fite solid into sulfate
or carbonate solids.
Will have very little
effect, however, on
soluble Ca
Negligible
Negligible
Negligible
Negligible
When pH >7, Pb-
Cl complexes may
become predominant
when the chloride
level is higher
than J,500 ppm
When the bor-
ate level in-
creases from
5 ppm to 200
ppm. the solu-
ble lead level
can be increased
about 10.OOO
times
Negligible
Will transform FeSOS
to FefSOti. but the
solid phase will remain
unchanged
Negligible
-------
Table 5.
Mg
Mn
Hg
K
Se
Na
Zn
(continued)
Solid: High pH levels Negligible
(pH >9) favor the for-
mation of Mg(OH)ifs)
Soluble. When pH is
increased, the MgSOt
(aq) species may be-
come significant
No significant effect Negligible
on predominant solu-
ble species. However.
the total soluble level
will be decreased at
high pH levels because
of the formation of
more solid
Low pH levels favor the Negligible
formation of Hg°(1) in
the sludge. High pH
levels tend to increase
the soluble levels of
HgCI,, HgCI*
HglOHkfaq). and
HgCIOHfaql
Slightly reduces the K' Negligible
levels when pH is
increased
High pH levels tend to Negligible
dissolve Se°(sj and
form selenate species
Will slightly reduce Negligible
the Na* levels when
pH increases
Solid: High pH levels Negligible
favor the formation of
Zn(OHMs). When pH
decreases, ZnSiOsfs)
will replace Zn(OHMs>
Soluble: Will reduce
total levels when pH
increases
Negligible Negligible
May affect the Negligible
levels of
Mn-CI com-
plexes, but will
not change the
total soluble
levels signifi-
cantly
When the chloride Negligible
level varies from
50 to 6,OOO ppm, the
total soluble Hg can
be increased for
more than four orders
of magnitude
Negligible Negligible
Negligible Negligible
Negligible Negligible
When pH <9, the Negligible
total soluble Zn
exists predomi-
nantly as ZnCr if
the chloride level
is higher than
3.00O ppm
When the soluble
sulfate level is
raised to as high
as 3.000 to 5.000
ppm, the level of
MgSOJaq) may
exceed the Me?*
level
Negligible
Negligible
Can affect the
K2SOtlaq) level.
Will not, however.
affect the total
soluble level of K
Negligible
Can affect the
NaxSOt/aq) level.
Will not, however.
affect the total
soluble level of Na
ZnSOtlaq) may
become predominant
at a pH around 9
when Cl ~and OH'
complexes are not
significant
Negligible
Negligible
If the redox poten-
tial is controlled
by sulfate/sulfite
species, sulfite oxi-
dation can increase
the soluble Mg level
Will increase the
KiSOtfaq) level
and reduce the K*
level, but will not
have a significant
effect on total
soluble K
If the redox potential
is controlled by sul-
fate/sulfite species.
sulfite oxidation can
increase the soluble
Se level
Will increase the
NaiSOtlaq) level and
reduce the Na* level.
but will not have a
significant effect on
total soluble Na
Negligible
-------
Table 6. Effects of Adding Chemical Compounds on the Speciation of FGD Sludge Constituents
Constituent
Addition of
Lime
Addition of
Silicates
Addition of
Hydrogen Sulfide
Addition of
Phosphates
Addition of
Magnesium
At
As
Cd
Ca
Cr
Cu
Fe
Pb
Effect on total soluble
A I is negligible
Lime addition can cause
more
form, so reduce the
total soluble As
slightly
When the lime dosage is
higher than 1,500 ppm,
soluble Cd can be
increased from 0.01 ppb
to 1.45 ppb
When the dosage of lime
is from 100 to 1O,000
ppm, the total soluble
Ca will increase from
200 ppm to 400 ppm
Lime addition tends to
increase the total
soluble Cr because of
hydroxide complexes
formation
Lime addition tends to
increase soluble Cu but
will not raise the
soluble Cu above the
detectable level
When the lime dosage is
higher than 1,500 ppm,
the soluble Fe level will
be increased from 0.012
ppb to 22 ppb
Lime addition tends to
increase the total sol-
uble Pb because of car-
bonate complex formation
The soluble Al level can
be greatly reduced when
silicate addition is
higher than 280 ppm as
Si
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
Cd can be reduced to
trace levels when sul-
fide addition is higher
than 0.2 ppm
Negligible
Negligible
Cu can be reduced to
trace levels by adding
as little as 0.001 ppm
of sulfide
Negligible
Pb can be reduced to
trace levels by adding
as little as 0.001 ppm
of sulfide
Effect on total soluble
AI is negligible
Negligible
When phosphate addition
is higher than 310 ppm
fas PI, the soluble Cd
can be increased about
2 times
If phosphate addition is
higher than 310 ppm
(as P), soluble Ca can
be reduced slightly
Negligible
Negligible
Negligible
Negligible
Will not affect the total
soluble AI
Will not affect the total
soluble As
Will not affect the total
soluble Cd
Magnesium addition may
decrease the Ca-S04
and Ca-F complexes but
will not change the total
soluble Ca
May affect the total solu-
ble Cr through the CrF1*
reduction
Will not affect the total
soluble Cu
Will not affect the total
soluble Fe
Will not affect the total
soluble Pb
Mg
Mn
Hg
K
Se
Na
Zn
Lime addition will only
affect the total soluble
Mg slightly but will
significantly transform
Mg-C03 complexes
Lime addition tends to
reduce the soluble Mn
to the 20-36 ppb range
Lime addition tends to
increase the total sol-
uble Hg slightly because
of an increase in pH
Negligible
Lime addition will in-
crease the total soluble
Se because of an
increase in pH
Negligible
Lime addition may
increase the total
soluble Zn to ppm
levels
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
The soluble Zn level
is reduced when sili-
cate addition exceeds
280 ppm as Si
Negligible
Negligible
Hg can be reduced to
trace levels by adding
as little as 0.001 ppm
of sulfide
Negligible
Negligible
Negligible
Zn will be reduced to
trace levels when sul-
fide addition is higher
than 0.5 ppm
Soluble Mg will be
reduced about 2 5
times as the phos-
phate level is
increased from 0.3
to 3,100 ppm (as PI
Negligible
Negligible
Negligible
Negligible
Negligible
Negligible
Will cause the increase of
soluble Mg
Will not affect the total
soluble Mn
Will not affect the total
soluble Hg
Magnesium addition may
decrease the KiSOJaql
level but will not affect
the total soluble K
Will not affect the total
soluble Se
Magnesium addition may
decrease the NaiSOJaql
level but will not affect
the total soluble Na
Will not affect the total
soluble Zn
-------
James Lu is with Cal Science Research, Inc., Huntington Beach, CA 92647.
Donald E. Sanning is the EPA Project Officer (see below).
The complete report, entitled "Chemical Speciation of Flue Gas Desulfurization
(FGD) Sludge Constituents," (Order No. PB 81-187 205; Cost: $24.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
10
ft U.S. GOVERNMENT PRINTING OFFICE: 1W1 -757-01Z/7218
-------
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