-------
en
as
        8  _
       12 _
       16
       20 -
                              pH
                                                       q 10'
                                                       _ i.o
                                                         10
  -4
                                                             Q.

                                                             CL
                                                       -  10
  -8
10
  -12
                                                       .  10
  -16
                                                     11
   Figure  40.   Speciation of soluble Mg in aged FGD wastes

               at I  =  0.05,  original [MgT] = 10'3-91M.
                             Ill

-------
     100
                                                  Mg(OH)2(aq)
      80
      60
       40
C
o
-Q


S_


I/I
•!•"•
Q
      20
                      Free Mg   (aq)
                                 7

                                PH
                                                     11
  Figure 41.  Primary distribution  of Mg in aged FGD wastes
              at I = 0.05,  original  [MgT]  = 10
                                               -3.91
                                                    M.
                             112

-------
                        Free K
                                                   10*
                                                   1.0
 ^ 6
 en
 o
                                                       £
                                                       Q.
                                                       Q.
                       10
                         -2
   10
                                                   10'
                                                   io-<
    12L
7

PH
                                                11
Figure 42.  Speciation of soluble K in  aged  FGD  wastes

            at I = 0.05, original [KT]  =  10~1'89M.
                          113

-------
 100
  80
  60
o

c
o
•r-
4->
3


5-

1/1
•r"
O
  40
  20
                        Free K1
                           7
                           pH
                                                 11
Figure 43.   Primary  distribution of K in  aged  FGD wastes
            at  I  =  0.05,  original [KT] =  10
                                             -1 .89
                                                   M.
                          114

-------
      0
o
I
       4  _
       8  _
      12  _
      16
      20  _
                              PH
                                                             Q.
                                                             Q.
                                                          -12
                                                      _ 10
-16
                                                    .11
   Figure  44.   Speciation  of  soluble  Na  in  aged FGD wastes
               at  I  =  0.05,  original  [NaT]  = 10"1-36M.
                             115

-------
   100
    80
    60
 c
 o
•£  40



 
-------
01
o
       16  _
       20  _
                                                       - 10'
                                                       I 10
                                                            -1
                                                             .a
                                                              a.
                                                              a.
                                                       - 10
                                                            -5-
  . 10
                                                            -9
  - 10
                                                            -13
       24  L_l
                                7

                                PH
11
   Figure 46.  Speciation of soluble  Cd  in  aged  FGD  wastes

               at I = 0.05, original  [CdT]  =  10"4<97M.
                             117
-------
  100
   80  -
    60  -
•o
O
M-
O
40 -
Free Cd++(aq)
                               PH
  Figure 47.   Primary  distribution  of  Cd  in  aged  FGO  wastes

               at  I  = 0.05,  original  [CdT]  =  10~4'97M.
                             118
-------
Figure 48.  Speciation of soluble Cr in aged FGD wastewater
            at I = 0.05,  original  [CrT] = 10
                                            -4.03
M.
                            119
-------
  100
                                 Cr(OH)7 (aq)
                            7
                           pH
11
Figure 49.  Primary distribution of Cr in aged FGD wastes
            at I = 0.05,  original  [CrT] = 10
                                            -4.03
  M.
                           120
-------
CD
O
                                                     -23
                                                   10
                                                     -28
                                                11
 Figure 50.
Speciation of soluble Cu in aged ™DgWastes
   I = 0.05,  original [CuT] = 10" '   M.
             at
                           121
-------
   100
*«   80
3
O
o

c
o
•^*
4->
3
J3

S_
4J
01
*^-
O
    60
40
    20
                  Cu,CO^(OH)
                             7

                             pH
                                             n
Figure  51.   Primary distribution  of  Cu  in aqed FGD wastes
             at i = 0.05, original  [CuT]  = 10
                                              -4.18
                                               M.
                            122
-------

o
                                                    -24
   Figure 52.  Speciation of Fe(III)  in  aged  FGD  wastes
               at I = 0.05, original  [FeT]  =  10
                                                -0.57
M.
                          123
-------
              FeSOt (aq)
     10,0
                              7
                              pH
11
Figure 53.  Primary distribution of Fe(III)  in  aged FGD wastes
            at I = 0.05, original [FeT] = 10"°'57M.
                              124
-------
                                                       -12
                                                       -16
                                                          CL
                                                          O.
                                                   -10-20
                                                       -24
                                                 11
Figure 54.  Specfation of soluble Hg(II) in aged FGD wastes
            at I = 0.05, original [HgT] = 10"5<83M.
                            125
-------
  100
                           7
                           pH
11
Figure 55.  Primary distribution of Hg in FGD wastes
            at I = 0.05, original  [HgT] = 10"5'83M.
                          126
-------
     Pb2+  - C0=  (aq)
                                          (aq)
   100
*«   80
                                               n
  Figure 56.   Speciation of soluble Pb in aged FGD wastes
              at I = 0.05,  original [PbT] = 10"4'69M.
                           127
-------
   2+
 PIT   -  COf  (aq)
   100
                                 Pb*   -  B(OH)4 (aq)
    80
    60
.a
a.
c
o
.a
•i—
5-
    40  D
    20
                          PH
                                                            (a
-------
   o
   I
Figure 58.
Speciation of soluble Zn in aged FGD wastes
at I  = 0.05,  original [ZnT] = 10~3-58M.
                           129
-------
  100
                               ZnSo4  (aq)
   20-
                                               n
Figure 59.   Primary distribution of Zn in aged FGD wastes
            at I = 0.05, original  [ZnT] = 10
                                            -3.58
M.
                          130
-------
     As shown in Figure 39,  the major calcium solids  at low pH
levels are CaS04.2H20(s)  and CaSOs.1/2H20(s).  These  two solids
have relatively higfi solubilities  compared  to that  of CaC03(s).
Therefore, the increase in total  soluble  calcium levels at low
pH is apparently caused by the lack  of low  solubility calcium
solids.  At a high pH,  the calcium concentrations  in  the aged
FGD wastes are substantially reduced  (Figure  33).   This is
caused by a reduction in  the free  calcium  ion through the forma-
tion of CaCO^s) (Figure  39).   Since  the  aging of  FGD wastes
usually results in a higher  pH, it is therefore expected that
the soluble calcium levels will gradually  decrease  as FGD wastes
are aging.

Magnesi urn

     Figures 40 and 41  show  the speciation  results  of magnesium
in the aged FGD wastes.  It  can be seen that  the free magnesium
ion is the most predominant  soluble  species  at a pH below 10.
The magnesium-sulfate complex  will become  significant when the
pH is between 8 and 10.  The levels  of free  magnesium ion and
magnesium-sulfate  complexes  will  decrease  at  a pH  higher than
about 10, while the Mg(OH)2(s) solid  will  begin to  form and
reduce the soluble magnesium concentration  by two  orders of
magnitude from its original  level.

     Comparing fresh and  aged  FGD  wastes  at  1=0.05, it appears
that the concentrations of soluble magnesium  species  are altered
by the aging effect.  More free magnesium  ion forms in aged
wastes than in fresh wastes  when the  pH is  less than  8.  At a pH
between 8 and 10,  an increase  in the  magnesium-sulfate complex
concentration occurs (see both Figures 40  and 41).   The distribu-
tion diagram (Figure 41)  shows that  the increase is associated
with the loss of free Mg^ + ion.

Potassi urn

     Figures 42 and 43  show  that the  free  K   ion is the predomi-
nant species of soluble potassium  in  the  aged low  ionic strength
FGD wastes.  This  species comprises  almost  100 percent of the
soluble potassium  when  the pH  is below 7.   At higher  pH (pH 7),
small amounts of K2S04(aq) can be  formed  (about 10  percent, as can
be seen from Figure 43.  No  new potassium  solid will  be formed
during the aging of the FGD  wastes due to  the slow  nucleation of
the complex potassium solids and the  high  solubility  of the
simple potassium solids.

Sodium

      In general, the distribution  of soluble  sodium in aged FGD
wastes at.  1=0.05 is quite similar  to  that  of potassium.  If the
sodium sp'eciation  in aged (Figures 44 and  45) and  fresh (Figure
19) FGD sludge are compared, the distribution of N
                               131
-------
appears to increase as the wastes age.  As with potassium, how-
ever, no new sodium solid can be formed during aging due to the
slow nucleation of the complex sodium solids and the high solu-
bility of the simple sodium solids.

Cadmiurn

     The thermodynamic model  shows that at low pH levels (pH<-6),
the+majority of the cadmium species exists as soluble free
Cd2  and CdCl+ (Figure 46 and 47).  As the pH increases, cadmium
is removed from solution through the precipitation of CdC03(s).
Due to the formation of this  solid, cadmium levels in aged FGD
wastewater can be reduced to  as low as 1  ppb (see Figure 46).
As the pH rises above 10.7, the soluble cadmium concentration
increases, again owing to the formation of the more soluble
Cd(OH)2(s).

     Comparing the fresh and  aged FGD wastes, the predominance
of soluble Cd-S04 complex appears to decrea.se with age at low.pH
levels.  The relative predominance of this complex in the soluble
phase increases when CdC03(s) is formed at high pH, which also
reduces the concentrations of both the free Cd2+ and Cd-Cl
complexes.  In fresh FGD wastes (see Figure 20) the cadmium-
carbonate complexes will become the predominant soluble species
at a pH of 9 to 11; in the aged FGD wastes, the levels of cad-
mium-carbonate complexes in the same pH range are lower than those
of the free cadmium ion, cadmium-chloride, and cadmium-sulfate
complexes .

Chromium

     The calculated results for the speciation of chromium are
given in Figures 48 and 49.  By comparing Figure 48 to the specia-
tion results of chromium in fresh FGD wastes (Figure 21), it is
found that the predominant soluble species of chromium (free
Cr3+ for pH less than about 4, and Cr-OH complexes for pH
greater than 4) are similar in both cases.  However, the concen-
tration of soluble chromium in aged wastes decreases (see Figure
48) when conditions favor Cr(OH)3(s) formation (see Figure 49).
The Cr(OH)3(s) can account for as much as 80 percent of the total
chromium in the aged FGD sludge.  Neutral pH levels favor the
formation of this solid (pH of 5.5 to 9 appears to be the optimum
range).

Copper

     Thermodynamic calculations indicate that at 1=0,05, the
predominant soluble species of copper in aged FGD wastes are free
copper ion at pH less than 4.8, and copper-borate complexes
mainly CujB (OH )at)z ( aci) » at higher pH .  Copper-chloride, copper-
hydroxide, or copper-carbonate complexes are the next most
                               132
-------
important soluble species under pH levels  as  shown in Figure 50.
Almost 100 percent of the total available  copperexists as
Cu2C03(QH)2(s)  precipitate,  however (see Figure 51).   Due to the
formation of  this solid,  the soluble copper concentration can be
reduced to extremely low  levels.   Therefore,  the aging of FGD
wastes should control copper migration into the aqueous environ-
ment.

Iron

     The speciation of Fe(III)  is shown in Figures 52 and 53.
Under the studied condition, it was found  that most of the iron
in FGD sludge will precipitate  out as  Fe(OH)j(s) (see Figure 53).
Soluble iron  (as FeS03+)  may exist in  a significant concentration
at low pH levels (pH 5).   Although Fe-OH complexes are the
predominant soluble species  when  the pH is greater than 5, their
concentrations  are typically less than 1 ppb.   Since  the aging
process increases both the pH and Eh va-lues,  the removal of iron
from the FGD  wastewaters  is  favored.

Mercury

     The speciation of mercury  in the  aged FGD wastes is repre-
sented in Figures 54 and  55.  Note that when  the pH is less than
about 8.5, the  predominant soluble species are Hg-Cl  complexes
(primarily HgCl2(*q)).  At higher pH,  Hg-OH complexes (primarily
Hg(OH)2(aq) will predominate in the soluble phase.  However, due
to the formation of Hg°(£) in aged FGD sludge, most of the mercury
in the sludge will precipitate  out of  the  FGD  wastewater.  This
mechanism can regulate the total  soluble mercury down to trace
levels (less  than 10-4 ppb,  as  can be  seen in  Figure  54).  There-
fore, the aging process will also remove mercury from the FGD
1eachates .

Lead

     Under the  aged, low  ionic  strength condition, lead can form
very strong complexes with the  B(OH)4  ion  in  the pH range of
6.8 to 8.4.  Between pH 8.4  and 11, Pb-C03 complexes  are the
principal soluble species (see  Figure  56).

     The thermodynamic model also shows that  under conditions of
low pH, PbMoO^s) can be  formed.   This solid  will  account for
about 90 percent of the total lead in  the  sludge (Figure 57).
Through the formation of  PbMoO/^s), the soluble lead  concentra-
tion can be reduced to about 10 ppb (Figure 56).  At  a high pH,
PbC03(s) is more stable than PbMoO^s).  The  soluble  lead concen-
tration can therefore be  reduced  even  further   The soluble lead
concentration in this pH  region from pH 7  to  11 is between 10 ppb
and 0.1 pj>b.   Aging would appear  to favor  the  removal of lead
from soluti on .
                               133
-------
Z i n c

     Free zinc ion is the major species in-aged FGD waste at pH
levels of less than 8.3 (Figures 58 and 59).  When pH is above
8.0, most, of the zinc precipitates as hydroxide and silicate
solids.  When the pH is higher than 9.3, the hydroxide solid is
still the predominant species, but major soluble species are con-
verted to zinc-hydroxide complexes.

     In the low pH region (pH 8), due to the lack of stable zinc
soTids in the aged FGD sludge, the soluble zinc levels may in-
crease in relation to those of the fresh FGD sludge (see Figure
26).  Therefore, if the pH level of aged FGD' sludge is less than
about 8, the aging process will tend to release zinc into solu-
ti on .

CONSTITUENT SPECIATIQN:  HIGH IONIC STRENGTH

     Speciation of constituents in the aged FGD wastes of high
ionic strength (1=0.8) was also evaluated for 20 metals and 13
ligands (155 complexes and 71 possible solids in all).  Results
of thermodynamic calculations are given in Figures 60 to 81.

Calcium

     The distribution pattern and the final total soluble concen-
trations of calcium in aged FGD waste at 1=0.8, is quite similar
to that at 1=0.05 (see Figures 38, 39, 60, and  61).  The principal
difference between these two cases is that the high ionic strengh
FGD sludge will possess more calcium solids (compare Figures 39
and 61) .

     In comparing the speciat ion calculation results for fresh
and aged FGD wastes (Figures 60 and 27), the total soluble
calcium in aged FGD wastes appears to be higher than that in
fresh FGD wastes when the pH is below 8.  When the pH is higher
than 8, the situation is reversed.  Therefore, the aging process
can cause the release of calcium into solution if the pH remains
below about 8; when the pH is higher than 8,  the soluble calcium
will gradually be removed from solution.

Magnes i urn

     In general, the distribution of magnesium species at 1=0.8
is similar to the distribution at 1=0.05 (see Figures 40, 41, 62
and 63).  Some differences can still  be found.  For example, in
the high ionic strength case, the hydroxide solid (Mg(OH)2(s))
can be formed from high pH levels down to about pH 8.  The same
solid for the low ionic strength (1=0.05) case can only be formed
above pH JO.  The relative percentage of Mg-S04 complex is
smaller i~h the high ionic strength case.  The existence of
                               134
-------
                                              11
Figure 60.   Speciation  of soluble  Ca  in  aged  FGD wastes
            at I  =  0.8,  original  [CaT]  =  10°'21M.
                        135
-------
       100
        80 _
        60
o

H-
O
-M
ZJ
•*->
LO
40 .,
20 r
                                                       11
                                pH
  Figure 61.  Primary  distribution of Ca in aged FGD  wastes
              at I  =  0.8,  original  [CaT] = 10
                                              0.21
                                          M.
                             136
-------
 o>
 o
                                                       Q.
                                                       a.
-2
                                                     -4
                                                 -icr6
                                               11
Figure 62.  Speciation of soluble Mg in aged FGD wastes

            at I  = 0.8,  original  [MgT]  = 10"°-95M.
                          137
-------
    100
  en
  O

  C
  o
   I/J
  •r"
  Q
      20-
Figure 63.
Primary distribution of Mg  in  aged  FGD  wastes

at I  = 0.8, original [MgT]  =  10"°-95M.
                             138
-------
   2  =
en
o
    8  _
   10
   12
                        Free K
                         pH
                                                     10
                                                     10'
                                                    1.0
                                                    10
                                                      -2
                                                        o.
                                                        0.
                                                    10
                                                      -4
                                                    10
                                                      -6
                                                 11
Figure 64.  Speciation of soluble K in aged FGD wastes

            at I = 0.8, original [KT] = 10"1'87M.
                         139
-------
     100
      80
      60
      40
o

o
s_
-u
en
      20
                            Free  K
                                                   11
                             pH
  Figure 65.
Primary distribution of K in aged FGD wastes

at I  = 0.8, original [KT] = 10~1-87M.
                             140
-------
    18
                                                        S
                                                        o.
                                                        Q.
                                                     -12
Figure 66.  Speciation of soluble Na in aged FGD wastes
at I = 0.8, original  [NaT] = 10
                                           "°'83
                                                M.
                          141
-------
       100,
        80 _
        60
C
O
40
        20
                                                    (aq)
                         Free  Na  (aq)
                                                     11
                             pH
  Figure  67.   Primary  distribution  of  Na  in  aged  FGD wastes
              at  I  = 0.8,  original  [NaT]  =  10"°-83M.
                            142
-------
•o
o
Ol
o
                                                11
 Figure  68.   Speciation  of  soluble Cd in aged FGO wastes
at I = 0.8, original [CdT] = 10
                                            ~4'97
                                                 M.
                          143
-------
  100
   80
   60
o
o
4->
-Q
I   40
t/>
Q
   20
         Free Cd++(aq)
             CdCl+ (aq)
                                 CdC03 (s)
                           7
                           pH
                                                -=*-Cd(OH),(s)
                                                n
Figure 69.  Primary distribution  of  Cd  in  aged FGD wastes
             at I  = 0.8, original [CdT] = 10
                                            ~4<97
                                                 M.
                          144
-------
i.
o
o>
o
        18
                                                       _  10'
                                                           -12
                                                      11
                               PH'
   Figure 70.   Speciation of soluble Cr in aged FGD wastes
               at I = 0.8, original [CrT] = 10
                                              -3.99
M.
                             145
-------
            CrCl++  (aq)
     100
      80
      60  _
o

o
3
-Q
S_
-u
      40  _
20 _
                         Cr(OH}2 + Cr(OH)4 (aq)
                                                   0.
                                                   Q.
                                                    11
                             PH
  Figure 71.  Primary  distribution  of  Cr  in aged FGD wastes
              at  I = 0.8,  original  [CrT]  =  10
                                              -3.99
                                             M.
                             146
-------
3
O
Ol
O
      5 _
     10 __
     15
     20 _
     25
     30
                               7
                               pH
                                                         ,-3
                                                         ,-8
                                                     -  10
                                                          -13
         -Q
          Q-
          O.
                                                     - 10
                                                          -18
                                                     _ 10
                                                         -23
                                                     - 10
                                                          -28
11
   Figure 72.  Speciation of soluble Cu  in  aged  FGD  wastes
               at I = 0.8, original [CuT] = 10~4<16M.
                             147
-------
     100
      80
      60
                        •Cu-.CO.(OH).
                        .  C,  O    i
      40
c
o
3

.Q
V)



a
                              PH
                                                     11
  Figure 73.  Primary  distribution  of Cu in aged FGD wastes


              at  I = 0.8,  original  [CuT] = 10~4-16M.
                             148
-------
     6   -
     12   -
zr   is   -
. 
-------
          FeSO* (aq)
     100
      80
      60
tu
u.
c
o
S_

•M
     40
      20  25
                                                    11
                             PH
 Figure 75.   Primary  distribution  of  Fe(III)  in FGD wastes

              at  I  = 0.8,  original  [Fe(III)T]  - 10"°-57M.
                             150
-------
     12
O)
O
     16
     20
'     28
     32   _
     36
                             PH
-24
                                                     11
 Figure 76.   Speciation  of  soluble  Hg(II)  in  aged  FGD  wastes
             at I  =  0.8,  original  [HgT]  =  10"5'74M.
                             151
-------
    100
    80
     60
4-
o
s_
4->
cn

O
                                                   11
                             PH
     Figure 77.  Primary distribution  of  Hg  in  FGD  wastes
                 at I « 0.8, original  [HgT]  =  10


                             152
                                                 -5.74
M.
-------
  cn
  o
                                                11
Figure 78.  Speciation of soluble Pb in aged FGD wastes
            at I = 0.8, original [PbT] = 10
                                           -4.65
M.
                          153
-------
                           PbB(OH)! + Pb(B(OH)j: (aq)
   100
                                                11
Figure 79.   Primary distribution of Pb in aged FGD wastes
            at I = 0.8,  original  [PbT] = 10
                                           -4.65
M.
                            154
-------
                                                11
Figure 80.   Speclation of soluble Zn in aged FGD wastes
            at I = 0.8,  original  [ZnT] = 10
                                           -3.57
M.
                           155
-------
                                             Zn(OH)°  (aq)
   100
            ZnCl+  (aq)     >
Figure 81.   Primary distribution of Zn in aged FGD wastes
            at I = 0.8, original [ZnT] = 10
                                           -3.57
M.
                           156
-------
hydroxide complexes (mainly Mg(OH)2(aq)  also become insignifi-
cant in the high ionic strength case.

     Due to the formation of hydroxide  solids  at  high  pH  levels
(pH 9), the available soluble magnesium  decreases  as  the  wastes
are aging.  The concentration of soluble magnesium decreases    A
only slightly with age at pH 9, but  decreases  by  a factor of  10
at pH 11 (see Fi gure 62) .

Potassi urn

     The distribution of  potassium in  aged  FGD wastes  at  1=0.8 is
also similar to that at  1=0.05.  But  due to the  tremendous
increase of the soluble sulfate concentration, the concentration
of K-S04 complex is relatively higher  in the high  ionic  strength
case.  This can be seen by comparing Figures 42 and 43 with
Figures 64 and 65.

     As mentioned previously, no significant simple potassium
solid can be formed in the sludge, so  the migration of potassium
between solid and liquid  phases is negligible.  Potassium does
exist as complex solids in nature (see  Table 4),  but  with ex-
tremely low nucleation and dissolution  rates.   Therefore, the
complex solids of potassium will not play an important role  for
regulating the soluble potassium levels.

Sodi urn

     The calculated speciation of sodium in aged  FGD  wastes  at
1=0.8, is shown in Figures 66 and 67.   The  pattern of sodium
speciation is similar between low and  high  ionic  strength wastes
(compare Figures 44 and 45 to Figures  66 and 67).   The only  dif-
ference between these two conditions is  the concentration level.

     Like potassium, there is no significant simple sodium solid
that can regulate the soluble sodium levels in the FGD sludge.
Due to kinetic constraints, the complex  sodium solid  will not
play an important role in the transformation of sodium species.
Therefore, the sodium concentration  in  both solid  and solution
phases of FGD systems will remain at a  constant • 1 eve! .

Cadmi urn

     The relative concentrations and percentage distributions of
cadmium species in the aged FGD wastes  at 1=0.8,  are  shown in
Figures 68 and 69.  In the high ionic  strength case,  the  cadmium-
chloride complexes (mainly CdCl2(acl) will become  the  dominant
soluble species.  Free cadmium ion is  the second  dominant soluble
species; this species is  the most common species  in the low  ionic
strength case (1=0.05) .
                               157
-------
     The results also show that cadmium solids are readily formed
in aged FGO waste at a pH greater than 7.  Two cadmium solids
have a stability field in this FGD waste condition:   CdCOsCs)
and Cd(OH)2(s).  The former solid is predominant in  the pH range
from 7 to TO.8.  Above pH 10.8, the hydroxide solid  can account
for more than 40 percent of the total  solid cadmium.

     Comparing Figures 31 and 68, soluble cadmium concentrations
appear to be lower in the aged wastes  than in the fresh wastes
in the pH range of 7.8 to 10.2  This pH range is in  the stability
field of CdC03(s) .

Chromi urn

     The results of the chromium  speciation calculation are
shown in Figures 70 and 71.  Since" the amount of soluble chromium
is only slightly different between low and high ionic strength
cases (Table 9), the speciation patterns of chromium are very
similar in both cases (see also Figures 48 and 49.)

     In comparing the fresh FGD sludge (Figure 32) to the aged
sludge (Figures 70 and 71), it appears that chromium is removed
from solution during the aging process.

Copper

     The thermodynamic model  shows that under the conditions
studied, the predominant species of copper are the copper-chlo-
ride complexes (mainly C u C1 2 (a q )) at pH less than 4.8, and the
copper-borate complexes (mainly Cu(B(OH)4)2(aq)) when the pH is
between 4.8 and 11 (see Figures 72 and 73).

     Results also show that copper is  readily removed from solu-
tion when Cu2C03(OH)2(s) is formed under aging conditions.  This
will decrease the soluble copper concentration to trace levels
when FGD wastes are aging.

Iron

     There is little difference in the total  iron concentration
in FGD sludge between high and low ionic strength conditions.
Therefore, the distribution pattern of iron is similar in both
cases (Figures 52 and 53 versus Figures 74 and 75).   Since the
high ionic strength sludge has higher  ligand concentrations,
however, the percentage of FeSOs"1" in the FGD sludge  appears  to
be higher in the high ionic strength case.

Mercury

     Since in both high and low ionic  strength cases  the mercury
concentration is controlled by Hg°(O, the distribution patterns
are very similar (Figures 54  and 55 versus Figures 76 and 77).
Almost 100 percent of the mercury exists in the solid phase.


                              158
-------
As described previously,  the  Hg-Cl  complexes  dominate  the
soluble levels in the low pH  region  (less  than  about 9).   Due
to the high chloride concentration  in  the  high  ionic strength
case, the soluble mercury is  higher  in  the high  ionic  strengh
FGD sludge than in the low ionic  strength  FGD  sludge.

Lead

     Comparing the aged FGD wastes  of  low  (1=0.05)  and  high
(1=0.8) ionic strengths,  the  most important soluble lead  species
at low pH (pH 6.8) will change from free  lead  ion,  Pb2+,  to  the
lead-chloride complexes,  Pb-Cl,  when ionic strength increases.
At high pH, the predominant lead  species  are  the lead-borate com-
plexes, Pb-B(OH)4, in the high ionic strength  case. Results
also show that in the high ionic  strength  case,  60  to  90  percent
of the lead can be precipitated  as1  PbMo04(s)  in  the low pH region.
At high pH (
-------
                            SECTION 6

                THERMODYNAMIC MODEL VERIFICATION


     In order to verify the suitability and accuracy of the ther-
modynamic model  used in this study, two complementary verifica-
tion procedures  were employed:

     •  Comparison of modeling results with analytical  data

     •  Evaluation of the model  itself in relation to certain
        scientific considerations.

     The comparison of model results with analytical data is
limited by the current state of analytical  procedures.   In recent
years, considerable advances in chemical  .speciation have been
made (Ref. 40-45).  No sound analytical scheme exists,  however,
that can accurately define all chemical species which exist in a
given natural system.  The difficulty is  due both to typical
system complexity and to the low concentrations of metal species
in nature.  Therefore, verification of the  model  using  analytical
data was limited to (1) comparing total liquid phase concentra-
tions with the total concentrations predicted by  the model; and
(2) comparison of the solid transformation  data to the  predicted
distribution of  stable solids.

     Evaluation  of the model according to certain scientific con-
siderations provides a general check on model behavior.  If a
certain variation of input parameters is  performed, its pertur-
bation of the model system can be checked for reasonableness
against expected trends or results.  For  example, consider the
case in which the model predicts that, for  element X, one percen-
of the total liquid phase concentration of  X exists as  the chem-
ical species Mmln.  This cannot be verified by total chemical
analysis.  However, by increasing the concentration of  ligand L
to abnormally high levels, the predicted  change in MmLn concen-
tration can be compared to scientific fact.
                              160
-------
COMPARISON OF MODELING RESULTS  WITH  ANALYTICAL  DATA

     As mentioned previously,  evaluation  of the model  using
analytical data can be approached  in two  ways:

     •  Comparison of the total  soluble  concentrations  of con-
        stituents in stabilized  leachates to the total  soluble
        concentrations of constituents,  as  predicted  by the model

     •  Comparison of the solid  transformation  data  to  the
        distribution of stable  solids  as  predicted  by the model.

Due to the lack of solid transformation  data in the  published
literature, only the first method  of comparison will  be discussed

     A comparison of the total  soluble constituent  concentrations
with the results of thermodynamic  calculation requires  analytical
data for aged F6D wastes.  Unfortunately, almost all  available
data is for relatively fresh FGD wastes,  such as scrubber liquor,
discharged slurries, or sludge  lagoon  supernatant.   Data for
aged sludge (such as interstitial  water  from the bottom of the
sludge lagoons) is still lacking.   Because  of this,  chemical
analysis of raw and aged FGD samples was  performed.

     The La Cygne Power Station  (Kansas  City Power  and  Light) was
chosen as a location from which  necessary samples could best be
obtained.  The La Cygne FGD system has been on  line  for several
years without a flue gas bypass, and the  limestone  and  coal used
by the plant are mined on the  site.   The  FGD chemistry  was there-
fore expected to approach "steady  state"  conditions  with respect
to sludge composition.  Four types of FGD siudge/wastewater
samples were obtained for analysis:

     •  Fresh FGD wastewater samples from the scrubber

     •  Fresh FGD sludge solids  samples  from the FGD  scrubber

     •  Aged FGD wastewater samples  from  the far end  (away from
        the discharge point), of the  second-stage sludge lagoon

     •  Aged FGD sludge samples  from the  far end (the oldest
        deposition of lime sludge) of the second-stage  sludge
        lagoon, 180 to 270 cm  below  the  surface of the  disposed
        siudge sol ids .

The sludge samples were further divided  into pore water samples
and solid sludge samples.  The  details of sample collection,
shipment, preparation, and analytical  methods are presented in
Appendix B.  The results of the analysis  of these samples are
presented in Table 10.
                              161
-------
TABLE 10.  ANALYTICAL RESULTS OF  FGD  SAMPLES  FROM
           KCP&L  LA  CYGNE  POWER  STATION

Constituent
Al
Sb
As
Be
Cd
Ca
Cr
Co
Cu
Fe
Pb
Mg
Mn
Hg
Mo
Ni
K
Se
Na
V
Zn
Alk. (as CaC03)
F~
S032"
so42-
Eh (mv)
P04-P
NO^-N
FW
0.48
0.086
0.66
0.005
0.045
850
0.001
0.049
Nil
1.0
Nil
170
2.52
Nil
3.0
0.40
83
0.250
73
0.19
0.71
198
707
13.6
19
675
27
0.2
4.8
SW
0.43
0.034
0.24
0.002
0.045
663
0.002
0.038
Nil
0.55
Nil
88
2.10
Nil
2.1
0.38
46
0.235
55
0.26
1.31
44
605
9.6
17
1650
130
0.1
1.4
Type of
FSP
0.30
0.066
0.20
0.003
0.010
810
0.001
0.022
Nil
0.1
Nil
174
0.55
Nil
4.7
0.23
74
0.475
73
0.16
0.06
188
760
9.4
50
925
77
0.1
2.3
Sampl e
SSP
0.20
0.038
0.12
0.001
0.010
410
0.002
0.010
Nil
0.04
Nil
7.0
0.15
Nil
5.8
0.02
82
0.425
75
0.21
0.06
60
708
5.5
93
625
94
0.06
1.5
FSS
833
13.9
32.6
0.69
51.4
3.45xl05
42.7
12.9
57
15,220
382
1,810
306
0.28
207
69.0
5,340
53.4
1,180
42.2
591
—
1,120
185
sss
856
8.24
26.7
0.34
56.7
3.18X105
26.6
11.7
54
18,990
340
2,330
303
0.23
203
70.2
4,940
48.3
1,310
35.6
534
—
1,093
154
                     162
-------
TABLE 10 (continued)
Type of Sample
Constituent FW SW FSP
Si 68 30 30
B 38.4 20 33
TOC Nil Nil Nil
TDS 3,700 3,980 3,920 4,
pH 6.54 7.14 7.65
CaS04-2H20(g/kg) -
CaS03'l/2H20
(g/kg)
CaC03(g/kg)
SSP
6.5
18.4
Nil
160
9.30
—


—
FSS ' SSS
— _ __
85 61
—
—
—
452 384
295 73.4

371 515

* FW = Fresh wastewater.
SW = Stabilized wastewater.
FSP = Pore water from 20 days aged fresh
SSP = Pore water from stabilized sludge
FSS = Fresh sludge solid.


sludge.
(about 5




years old).

SSS = Stabilized sludge solid (about 5 years old).
Units: Unless specified; for water sample
sample, the unit is mg/kg.
, the uni

t i s mg/1 ; for sol i d

                             163
-------
     The analytical  results of the total  amount of constituents
in the La Cygne Plant raw FGD wastes (see Table 11) were entered
into the computer model.  The total  soluble concentrations of
constituents in the  FGD wastes in aged condition were then pre-
dicted by-the model  at different pH  levels, and compared to the
field data.   The results are shown in Figures 82 through 98.

     In these figures, the analytical results are represented by
the numbers  0, 1, 2, and 3.  Symbol  0 represents the input data
(total levels of constituents in the fresh FGD waste).   Symbol  1
represents  the analytical results for the soluble constituents
in the fresh wastewater (0-day data).  Symbol 2 represents the
analytical  results for the soluble constituents in the  "rela-
tively" fresh sludge pore water (fresh sludge was aged  in the
laboratory  for 20 days before the pore water was analyzed).  The
analytical  results for the soluble constituents in the  fully
aged sludge  are represented by Symbol 3.   According to  the La
Cygne Plant  engineers, the aged sludge had been in the  sludge
lagoon for  about five (5) years.  Therefore, it was assumed that
the aged pore water  data represents  potential (stabilized)
leachate conditions  in the FGD sludge lagoon.

     The evaluation  of model results in relation to the analytical
data can be  performed using the migration trends of the consti-
tuents represented by Symbols 1, 2,  and 3.  If the soluble con-
centrations  indicated by the three data points approach the
concentrations predicted by the model, then the model can be
deemed an accurate prediction of aging phenomena.  The  results
of the evaluation for the 18 selected elements are summarized in
Table 12.

     It was  found that the analytical results for aluminum,
arsenic, cadmium, boron, cobalt, copper,  iron, manganese, mercury,
potassium,  selenium, sodium, and zinc are all either very close
to or approach the concentration levels predicted by the model.
Therefore,  it can be concluded that  the model serves as a valid
predictor for the final (stabilized) concentration or migration
trends of the various species of the above-mentioned elements in
the FGD wastes.  For some other elements  (calcium, chromium,
fluoride, lead, and  magnesium), prediction techniques were not
as successful.  For  calcium, the total soluble concentrations
predicted by the model are much lower than the analytical results.
The low levels predicted by the model are due primarily to the
formation of calcite, as well as the high levels of free carbon-
ate and sulfate (CO?,- and SOi", respectively) in regions of high
pH.  For chromium, the high levels of hydroxide complexes cal-
culated by  the model lead to the high soluble levels of chromium
in the aqueous phase.  For lead, the formation of Pb-COs complexes
predicted by the model is the primary reason for the discrepancy.
For fluoride, the solid phases assumed for the calculation are
apparently  not suitable.  It was also found by this evaluation
that the solid phases assumed for magnesium are too soluble.
                               164
-------
TABLE 11.  TOTAL CONCENTRATIONS OF CONSTITUENTS  IN
                LA  CYGNE  FGD  SYSTEM



Constituent
Ca
Mg
K
Na
Fe
Mn
Cu
Cd
Zn
Ni
Hg
Pb
Co
Cr
Al
Be
co32-
so42~
CT
F"
P043~
sio32-
B(OH)4
so32-
Mo042~
As043-
HV042-
Se032-
Total Concentrations in
FGD Wastes (Fresh Wastewater
and Fresh Sludge) (M)
10-0.387
10-1.53
10-2.67
10-2.50
10-1.09
10-2.77
10-3.57
10-3.86
10-2.57
10-3.44
10-6.38
10-3.26
10-4.17
1Q-3.61
10-2.03
10-4.63
1Q0.048
1Q-0.096
10-1.70
1Q-1.73
10-2-75
10-2.61
10-2.23
10-0-16
10-3.04
10-3.85
10-3.59
10-3.68
 Ionic  Strength                          0.1
                        165
-------
     200
     160
  Q.
  Q.
      120
  HI
  _J
  in
  D
  _J
  a
  ul
      80
                 0 (252 ppm)
                         ;Model
                                                        7X10
                                                        6 X 10
                                                              -4
                                                              -4
                                                        5 X 10
                                                        4 X
                                                              -4
                                            3  X  10
                                            2  X  10
                                                        1  X 10
                                                              -3
                                                  -3
                                                              -3
              1  (0.48  ppm)  V  2  (0.30 ppm)   3  (0.20 ppm)
                   I    /Si— — ^^ 1 — ^^^— ^. _ ^^__^ __ ]___   /gy ____  _j
                         3
                                                      10
Figure 82.
Total soluble Al(III)  concentration in La  Cygne  FGD
wastes (see text  for  explanation).
                               166
-------
    200
    160 -
    120 -
.a
a.
Q.
Lu
_J
CD
a
             0  (lO.S.ppm)
                        (200  ppb)
2.7 X 10
                                                              -6
                                         2,13 XTQ"6
                                         l.o X 1 0
                                                              -6
                                                       1.1 X 10"
                                                       5.3 X 10
                                                              -7
                              pH
 Figure 83.
Total  soluble As concentration  in La Cygne FGD
wastes (see text for  explanation).
                              167
-------
 Q.
 Q.
 CD

 LU
 _!
 03
      75
      60
45
30
      15
                 0  (63.6  ppm)
                1 (38.4  ppm)
                       2  (33
                                           Model
                                                 6.9  X  10
                                                               -3
                                                 5.6  X  10
4,2  X 10
                                                               -3
2.8  X 10
                                                        -3
                                                   (18.4 ppm)
                                               -1.4  X 10
                                                              -3
                                                     10
                               pH
Figure 84.
      Total  soluble B(III) concentration  in  La  Cygne FGD
      wastes (see text for explanation).
                              168
-------
 Q.
 Q.
 UJ
 _i
 CD

 _!
 a
 en
 H-
 O
                     2 (10 PPBX

                 1  (45 PPB)
       5 -
                                                     -2.2X10
                                                              -4
                                                     - 1.78X 10
                                                               -4
                                                     - 1.37 X 10
                                                   -4
                                                     - 8.9 X 10"5
                                         - 4.4X10
                                                              -5
Figure 85.
Total  soluble Cd(II) concentration  in  La  Cygne FGD
wastes (see text for explanation).
                              169
-------
                                                   -5  x  10-3
               1  (850  ppm)  2 (810 ppm)  3.  (410  ppm)
                                                   -0.5 x 10~3
                                                   1Q
Figure 86.
Total  soluble Ca concentration in La Cygne  FGD
wastes (see text for expl anat-i on).
                           170
-------
  S
  CL
  Q.
  CJ
  UJ
  _1
  03
  3
  _J
  O
  if)
  Q
  I-
       18
       12
                 0  (12.8  ppm)
                               2 (0.001  ppm)
                    1  (0.001  ppm
                              3  (0.002 ppm)
                                                        2.9 X 10
                                                                -4
                                            2.3  X 10
                                                                -4
                                            1.7  X 10
                                                   -4
                                                        1.15 X 10
                                                                -4
                                                        5.8 X 10"5
                                     8
                                          10
                                pH
Figure 87.
Total  soluble Cr(III) concentration  in La Cygne FGD
wastes (see text for  explanation).
                               171
-------
      5  -
      4  c
 S
 Q.
 Q.
3 -
 o
 C_3

 UJ
 _l
 CO
 3
 -1
 a
 en
 H
 a
 i-
2 -
                               2 (0.022 ppm)  -
                                                     - 1 X 10
                                                              -4
                                                     - 7 X 10
                                                              -5
1  X 10
                                                       -5
                                          3  (0.01  ppm)
                                             ^•^^^^•mJ
                                             9       10
Figure 88.
      Total  soluble Co(II) concentration  in  La  Cygne FGD
      wastes (see text for explanation).
                              172
-------
    150 -
    120
Q.

Q.
90
     60
m
_i
CD
3
-1
a
     30
                0  (354  ppm)
                                               -7.9 X 10
                                                             -3
                           2 (9.4 ppm)
                                                6.3 X 10
                                                             -3
4.7 X 10
                                                             -3
                                                3.15 X 10
                                                             -3
                                                1-..53 X 10
                                                             -3
               1  (13.6 ppm)
                                           3  (5.5  ppm)
                                                    10
                             pH
Figure 89.
       Total  soluble  F(I)  concentration in La Cygne FGD
       wastes  (see  text  for  explanation).
                             173
-------
    1860
                 0  (4540 ppm)
    1550 -
    1240
 CD
 a.
 a.
             1  (1  ppm)
     930
 0>
 u_

 UJ
 a
 en
  O
  I-
620
     310 -
                                                       3.3 X 10
                                                               -5
                                                  2.77 X 10
                                                               -5
                                                  2.22 X 10
                                                               -5
                                                  T.,66 X 10
                                                               -5
Y.ll X 10
                                                               -5
                                                  5.55 X 10
                                                               -6
                                              3  (0.04  ppm)
                                                      10
Figure 90.
       Total  soluble Fe(III) concentration  in La Cygne FGD
       wastes (see text for explanation).
                              174
-------
    2400
2000 -
    1600
1200
 O.

 HI
 J
 
-------
  1,000
    800
CL
Q.
    600
    400
111
_i
CD
a
en
f-
a
    200
                0  (708  ppm)
                                  Model
     1  (170  ppm)     2  (174  ppm)
                              pH
                                         4.1 X 10
                                                              -2
                                         3.2 X  10
                                                     2.9 X  10
                                                              -2
                                                  -2
                                                     2,05 X 10
                                                             -2
                                                     1.2 X 10
                                                  -2
                                                     4.1 X 10"3
                                                  (7  ppm)
                                                    10
Fiqure 92.
Total  soluble Mg(II) concentration  in La  Cygne  FGD
wastes (see text for explanation).
                             176
-------
     100
      80
 CL
 Q.
 IU
 _!
 CD
 3
 _J
 a
 i-
 a
 i-
      60
      40
      20
                 0 (.93.4 ppm)
    2  (0.55 ppm)

    1 (2.52 p-pm)
                                       iModel
                                    3
                               PH
                                          1 .8  X  10"3
                                                       1.45 X 10
                                                               -3
                                          1.1 X  10
                                                   -3
                                          7.3 X  10
                                                               -4
                                          3.6 X  10
                                                               -4
                                                3  (0.15  ppm)
                                         10
Figure 93.
Total  soluble Mn(II) concentration  in  La Cygne FGD
wastes (see text for explanation).
                              177
-------
    10
      -4
    10
      -6
                                                       10
                                                         -14
CL
a.
    10
      -8
                                         10
                                           -16
-------
    100
                1  (83  ppm)
                    Model
3 (823pm)
     ao
        _  Model
                            2 (74 ppm)
                                0
Q.
Q.
     60
LU
_J
CD

-I
O
H-
O
     20
                                          2  X 10
                                                -3
                                                      1  X 10
                                                            -3
                                                      1  X 10
                                                            -4
                                                    10
                              PH
Figure 95.
Total  soluble K(I) concentration  in  La  Cygne FGD
wastes (see text for explanation).
                             179
-------
                                                       -27
Figure 96.
Total  soluble Se concentrations in La Cygne FGD
wastes (see text for explanation).
                            180
-------
    100 -
     30
                 1  (73 ppm)  2 (73 ppm)    3 (75 PP"0
 Q.

 O.
      60
 IT3
 111
 _J
 IB
 O
 I-
 a
     40
      20
                                                       4  X  10
                                                             -3
                                                      3 X  10
                                                             -3
                                                      2 X  10
                                                             -3
                                                       1  x  10
                                                             -3
                                                     10
                               PH
Figure 97.  Total  soluble Na(I)  concentration in La Cygne FGD
            wastes  (see  text  for  explanation).
                              181
-------
                 0  (176  ppm)
                               pH
                                                     - 3.05 X 10
                                       2 (0.06 ppm)


                                          3 (0.06 ppm)
                                                               -3
                                                       2.45 X 1 0
                                                               ,-3
                                                       1.33 X 10"
                                                        .^2  X 10
                                                               -3
                                                       6.1  X 10
                                                              -4
                                                     10
Figure 98.
Total  soluble Zn(II) concentration  in  La  Cygne  FGD
wastes (see text for explanation).
                              182
-------
     TABLE  12.   COMPARISONS  OF THE ANALYTICAL RESULTS  OF  FGD
       WASTEWATER TO THE  RESULTS PREDICTED  BY COMPUTER  MODEL

Constituent
Al
As
Cd
B
Ca
Cr
Co
Cu
F
Fe
Pb
Mg
Mn
Hg
K
Se
Na
Zn
(1)
(Fresh Leachate,
pH = 6.5)
0.48
0.66
0.045
38.4
850
0.001
0.049
Nil
13.6
1.0
Nil
170
2.52
Nil
83
0.25
73
0.71
Constituent
(ppm - unless
(2)
(20-Day -Aged
Leachate,
pH = 7.7)
0.30
0.20
0.010
33.0
810
0.001
0.022
Nil
9.4
0.1
Nil
174
0.55
Nil
74
0.48
73
0.06
Concentration
otherwise noted)
(3)
(5-Year-Aged
Leachate,
pH = 9.3)
0.20
0.12
0.010
18.4
410
0.002
0.010
Nil
5.5
0.04
Nil
7
0.15
Nil
82
0.43
75
0.06
Model
(Equilibrium
Condition,
pH = 9.3)
0.14
0.0002
0.011
17.5
20
12.8
0.003
4.4xlO"13t
79
0.012
1.9
645
0.156
5xlO-9t
83
3.22#
73
0.073

* Refer to Figures 82 through 95.
t ppb.
# pH = 9.15,  Se = 0.43 ppm.
  pH = 9.3,  Se = 3.22 ppm.
                                183
-------
Many solid phases (such as dolomite, magnesite,  nesquehonite,
and other sulfate and phosphate species)  have been tried for the
calculation of the soluble magnesium in the FGD  system,  but none
gave results consistent with the experimental data.   Additional
study is necessary to improve prediction  accuracy for these
elements .

EVALUATION OF MODEL IN RELATION TO SCIENTIFIC CONSIDERATIONS

     The evaluation of the thermodynamic  model  in relation to
scientific considerations was performed during  the phase and
speciation calculations (Sections 2-5), as  well  as during the
calculation of the effects of chemical  changes  on the chemical
species (see Section 7).  In general,  the model  results  follow
the expected behavior patterns.  The following  are some  examples
which were used to test the acceptability of the model.

Effects of pH and Eh on the System

     The pH of a chemical system can influence  the direction of
the alternation process (precipitation, dissolution,  redox reac-
tion, and sorption), and will affect the  speciation  of almost  all
the constituents in the system.  Theoretically,  low  pH conditions
tend to dissolve more solids of oxide,   hydroxide, carbonate,
silicate, sulfate, and thus increase the  concentrations  of free
soluble metal ions.  High pH levels tend  to precipitate  more
solids, decrease the free metal ions,  and enhance the formation
of metal-hydroxide complexes in the system.  High pH  levels can
also increase the concentrations of metal-1igands, if such
ligands have a tendency to complex more in  the  high  pH region
(e.g., C0|", SO?', POJ-, etc.).

      The results of thermodynamic calculations  show  that the
constituents of the above-mentioned solids  have  higher free
metal concentrations in the low pH region,  and  form  more solids
in the high pH region (refer to Figures 60-81).   The  predicted
levels of metallic hydroxide, and of carbonate,  sulfate,
and phosphate complexes, also represent tremendous increases in
the high pH region (if the decrease of the  free  metal ions is
taken i nto account) .

     The Eh (redox potential) of a chemical system will  affect
the valence and chemical forms of many constituents  in the system.
Owing to the redox change, the solubility of some solids, as well
as the transformation of solids, wiTl  be  affected.  An increase
in Eh usually results in a transfer of reduced  solids to either
higher oxidation state solids (e.g., CaSOa-1/2H20(s)  transforms  to
CaC04-2H20(s); MnC03(s) transforms to  MnOOH(s),  or to other Mn
oxides), or more elemental solids will  be dissolved  (e.g., As°(s),
Hg°(M, and Se°(s)).  These transformations can  affect the solu-
bility of affected solids.
                               184
-------
     The results derived from the  model  usually  follow  the  trends
mentioned above.  For example,  as  the  La Cygne  FGD  wastes  age,
the redox potential  increases (Table  10).   This  change  should
result in a significant increase in  soluble mercury and selenium
levels in the system (Figures 94 and  96),  which  agrees  with  the
model  results .

Effects  of Ligand Concentrations on  the  Levels of Metallic  Com-
p 1 ex e s

     It  is known that ligand  concentration  can affect the  soluble
level  of metallic complexes.   Based  on previous  related studies
(Ref.  6-8, 23-25, 27),  it  is  known that  the chloride ligand  is
important to the solubility of  cadmium,  copper,  lead, and  zinc.
In  accounting for soluble  copper and  lead  levels, the borate
ligand may also become  significant'.   The hydroxide  ligand  is
important to the dissolution  of three-valence metals (e.g.,
Fe  and Cr).  The results calculated  by the  model  (see Sections
4 and  5) do follow these general  trends.  A more  detailed  discus-
sion of  the effects  of  ligands  on  the  soluble levels of metals
is  presented in Section 7.
                               185
-------
                            SECTION  7

                EFFECTS OF OPERATIONAL (CHEMICAL)
             CHANGES ON FGD SLUDGE CHEMICAL  SPECIES


     The principal  goals of FGD sludge disposal  are  to  minimize
the concentration of toxic constituents  in  the  liquid  phase
(leachate),  and/or to allow such impurities  to  exist only in  a
chemical form which is nontoxic and/or readily  adsorbed by soils.
In order to  assess the potential of  contaminant  species modifi-
cation to achieve these goals,  the model  was operated  over a
wide range of conditions to determine the impact of  various
operating changes on the various chemical  species.   In  this
study, the effects of 11 operational  (chemical)  changes were
studied.  The results are discussed  in the  following pages.

EFFECTS OF pH ON SPECIATION

     As was  discussed previously, change in  pH  level in any
chemical system can influence the direction  of  the  alteration
process and  the speciat ion of almost all  the constituents in
both solution and solid phases.  In  this study,  the  effects  of
pH on the speciation of constituents in  the  FGD  sludges have
been quantitatively estimated in Eh-pH and  ion-ratio diagrams
(Figures 1 through 15) and in the primary distribution  diagrams
(Figures 39  through 81).  The effects of pH  on  the  speciation
of constituents in the FGD wastewaters (leachates)  can  be viewed
in the resultant speciation diagrams (Figures 16 through 37  and
38 through 80).  The effects of pH on soluble constituents can
also be seen in Figures 82 through 98.

Effects on Solid Species

     The results of thermodynamic calculations  show  that the  pH
level can have a significant effect  on the  stability field of
FGD sludge constituents.  Figures 3, 10,  and 13  indicate that
the decrease of pH values favor the  formation of elemental  As°(s),
Hg°U), and  Se°(s).  However, for constituents  which can form
hydroxide or carbonate solids such as iron  (Figure  8)  and man-
ganese (Figure 11), an increase in pH levels instead favors
solids formation .
                               186
-------
     The ion-ratio diagrams shown in Section  3 also  indicate the
significance of pH on the stability field of  other consti-
tuents in the FGD sludges.   In general,  high  pH  levels  favor the
formation of oxide or hydroxide solids  instead of carbonate,
phosphate or other solids in FGD sludge.   For example,  higher pH
levels favor the formation  of Al203 • 3H20(s),  Cd(OH)2(s),
Cu(OH)2(s),  Pb(OH)2(s),  Ni(OH)2 and Zn(OH)2(s) over
Al(H2P04)(OH)2(s), CdC03(s), Cu2C03(OH)2(s},  PbC03(s),  NiC03(s)
and ZnC03(s), respectively  (see Figures  1,  4, 7,  9,  12,  and  15).

     The effects of pH on relative distribution  of primary
solids for some selected constituents  in  the  FGD  sludges  also
can be seen  in Figures 39 to 81.  These  results  show that the
most significant effect  of  pH on calcium  solids  is in the forma-
tion of CaC03(s) in high pH sludges.  This  phenomenon indicates
that, theoretically,  the soluble calcium  concentration  in FGD
sludge liquid phase decreases at high  pH  due  to  the  formation of
CaC03(s).  For magnesium, modeling results  indicate  that  high pH
levels favor the formation  of Mg(OH)2(s).  The pH effect  on  the
relative distribution of the two most  important  cadmium  solids
(CdCOaU) and Cd(OH)2(s) can be seen in  Figures  47 and  69.  It
was found that Cd(OH)2(s) may become the  predominant solid in
FGD sludges  only in the  very high pH region  (pH  >10.8).   In
actual practice, few  FGD systems will  have  such  a high  pH.  For
chromium, the data show  that Cr(OH)3(s)  is  the important  species
only in the  neutral pH region, that is,  pH  6  to  9 (Figures 49 and
71 .

     The effects of pH on copper, iron,  and mercury  is  not as
obvious due  to the tremendous amount of  Cu2C03(OH)2(s ) ,
Fe(OH)3(s),  and Hg (£) in the system (Figures 51, 53, 55, 73,
75, and 77).  The most significant effect of  pH  on the  solid
distribution of lead  is  that at a pH below  9, PbMo04(s)  will
become the predominant species.  However, high pH levels  (pH   9)
favor the formation of PbC03(s).  For  zinc, the  pH level  can also
affect the relative distribution of ZnC03(s), Zn(OH)2(s), and
ZnSi03(s) in the FGD  sludges.  High pH  levels favor  the  formation
of Zn(OH)2(s).  When  pH  decreases, ZnSi03(s)  will gradually  re-
place Zn(OH)2(s) (Figures 59 and 81).

Effects on Soluble Species

     The effects of pH on the soluble  species were discussed pre-
viously in Sections 4 and 5.  In general, most species  of major
ions will be significantly  affected by a  pH  change.   Unaffected
species include free  Ca2+,  Mg2 , K+, and  Na+, and their  sulfate
complexes.

     Typical examples of the pH effects  on  the total soluble
constituent levels were  discussed in Section  6.   In  general, a
high pH will reduce the  number and concentration of soluble
                               187
-------
species.   However,  due to the complexation  effect  in  the  high
pH region, the total  soluble levels  for some  species  may  increase
again.  Examples are  the total  soluble levels  of chromium (Figure
87),  fluoride (Figure 89),  lead (Figure 91),  mercury  (Figure  94),
and selenium (Figure  96).

EFFECTS OF IONIC STRENGTH ON SPECIATION

     The  ionic strength will affect  the solubility constants  on
various reactions in  the chemical  systems.   Through  this  effect,
the concentrations  and relative distributions  of species  may  be
altered.   However,  the calculated  results  show that  the  effects
of ionic  strength on  FGD systems are relatively small  compared
to effects such as  pH changes or ligands concentration changes.

     The  quantitative effects of ionic strength on the stability
field of  constituents have  been discussed  using ion-ratio dia-
grams in  Section 3.   The influence on the  stability  field of
solid phase by ionic  strength is usually less  than a  order of
magnitude from I =  0  to I = 1.0 (see Figures  1, 2, 4,  5,  7,  9,
12, and 15).  In FGD  systems (I =  0.05 to  0.8), the  maximum
ionic strength variation will expand or reduce the stability
field of  solids by  a  factor of no  more than four.

     The  effect of  ionic strength  variation on the speciation
of soluble constituents is  also small.  Among  the  constituents
studied,  only the relative  distribution of  cadmium between its
free metal ion, Cd2+, and its chloro complexes, Cd-Cl, can be
altered by a change  in ionic strength (Figure  100).   Other solu-
ble species, such as  sulfate complexes (a  typical  example is
given in  Figure 99),  may also be affected  by  as much  as  one  order
of magnitude.  However, these effects will  not significantly
change the relative  distribution of  various soluble  species.

EFFECTS OF CHLORIDE  CONCENTRATION  ON THE SOLUBILITIES  OF  METALS

     The  speciation  calculations show that  chloride  complexes
may be the predominant soluble species for  cadmium,  copper,  lead,
mercury,  and zinc.   For example, when the  chloride concentration
is higher than 400  ppm (Figure 101), the Cd-Cl complexes  may
become the predominant species for cadmium.  In general,  if  the
chloride  concentration is known, the total  soluble levels of
chloride-complexing  metals  can usually be  predicted  if no other
ligands dominate the  system.

     The  results of  related calculations are  shown in  Figures  101
through 105.  In this study, the assumed chloride  concentrations
ranged from 50 to 6,000 ppm.  Other  parameters used  for  calcula-
tion were based on  analysis of the La Cygne FGD wastewater.
                               188
-------
                                                     10*
                                       Free  Ca++
                                    so;
                                                     10'
                                CO:
                                                     1.0
                                                           a.
                                                           a.
   ea
   o
   o
      6-
                OH-'
                                                     10"
                   poi
                                                     io-*
     10
                                                     10
                                                       -6
     12
   I   I	I     I	1	1	\	I

0.050.1  0.2  0.3   0.4   0.5   0.6   0.7    0.8
                     Ionic Strength  (I)
Figure 99.
     Effects  of  ionic  strength on the speciation of
     soluble  Ca.
                            189
-------
   S   9
   en
   o
      12
      15
      18
           CV
                          Free Cd"
                                      SOI
                                   co:
                  I	I
                                                        10:
                                                        1.0
                                                a.
                                                a.
                                          1Q
                                                          -6
                                                        10
                                                          -9
                                                        io-12
          .05  0.1   0.2    0,3    0,4    0-5    0.6    0.7    0:8
                       Ionic Strength  (I)
Figure 100.
Effects of  ionic  strength  on  the  speciation  of
soluble Cd(II) .
                             190
-------
    cr>
    O
                   =  6,000  ppm


                          1"  =  4,000 ppm

                            •C1~ = 400 ppm

                                  1" = 3,000 ppm

                                    Cl" = 2,000 ppm
                                                           CL
                                                           Q.
                                                        -6
                                                    31Q-8
Figure 101.
Effects of chloride concentration on soluble Cd
concentration.
                             191
-------
   3
  O
      12
      1.6
      20
      24
             •Cl~ = 1,000 ppm
                  -CT = 2,000 ppm
                = 3,000 ppm



                  CT = 4,000 ppm


                     CT, - 5,000  ppm


                        CT  »  6,000 ppm
                                                      10'
                                                      1.0
                                                      10'
     £
     Q.
10
                                                        -a
10
                                                        -12
                                         10
                                                        -16
Figure 102.
Effects of chloride concentration  on  soluble  Cu
concentration.
                             192
-------
  .a
  a.
  en
  o
      2-
     10
     12
-Cl"  =  6,000 ppm.


   r-Cl"  =  5,000  ppm


               CT = 4,000 ppm


                 -Cl"  =  3,000  ppm


                         CT = 2,000 ppm
                         *-^
                                          10'
                                                      1.0
                                                           Q.
                                                           a.
                                                      10
                                                        -2
                                                      10-'
                                                      10
                                                        -6
                                                  11
                                          io-8
                              pH
Figure 103.
 Effects of chloride concentration  on  soluble Pb
 concentration.
                            193
-------
      15
      17
      19
  en
  en
  o
      21
      23
      25
      27
          I—Cl"  =  6,000  ppm

             -C1~ = 5,000 ppm
                               7


                              pH
                                                      10
                                                        -8
                                                      10
                                                        -10
                                                      10
                                                            -O
                                                            Q.

                                                        -12 <=•
                                                      10
                                                        -14
                                                      10
                                                        -16
                                                      10
                                                        -18
                                     11
Figure 104.
Effects of chloride concentration  on  soluble Ho
concentration.
                            194
-------
   cn
   o
       8
      10
      12
           Cl" = 3,000  ppm

              Cl" = 6,000 ppm

                     —Cl"  =  5,000  ppm

                           -Cl" = 4,000  ppm
                                    Cl" = 2,000 ppm
                                       1"  =  1,000  ppm
                                        10'
                                        1.0  I.
                                             Q.
                                        10'
                                                     10~a
                                                     10-12
                                                  11
Figure 105.
Effects of chloride concentration on soluble Zn
concentration.
                            195
-------
Effect on Cadmium

     It was found that a variation of chloride concentrations
from 50 to 6,000 ppm can lead to about a two order of magnitude
concentration change for cadmium in FGD wastewaters for any
given pH .  As shown in Figures 46 and 68, in any FGD sludge  free
Cd^ + is the only species which can exist at a higher concentration
than that of the Cd-Cl complexes when the pH is less than 8.7.
When the pH exceeds 8.7, species such as cadmi um-sul fa te , sulfite,
or hydroxide complexes may exist in higher concentrations than
that of Cd-Cl complexes depending on the ligand concentrations
and pH 1 eve! s .

     Therefore, in order to predict cadmium species concentra-
tions in the aged FGD wastewater, the following equations are
used :

     pH <8.7

     [CdT] = [Cd2+] +  [Cd-Cl complexes]    -                 (73)

     pH > 8. 7

     [Cdy] = [Cd-Cl complexes] + [Cd-S04 complex]

           + [Cd-S03 complex] +  [Cd-OH complexes]            (74)

Generic equations 73 and 74 can be approximated by the following
two equations:

     pH <8.7

     [CdT] *> [Cd2+]  + [CdCl+]

           , [Cd2+]  + 102-2[Cd2+]  [Cl~]                         (75)


     pH >8.7

     [Cd?] = [Cd2+]  + [CdCl+] + [CdOHCl(aq)]  + [CdS04(aq)]

            + [Cd(S03)2~]  + [CdOH+]

           *  [Cd2+]  + 102<2[Cd2+]  [Cl~]  + 107>3[Cd2 + ] [OH'] [Cl"]
            + 102'3[Cd2+] [S024~] + 105'4[Cd2 + ] [SO2"]

            + 104[Cd2 + ] [OH"]                                 (76)

The value of free cadmium ion concentration,   [Cd +], can be
solved usjng Equation 31  (Section 2) with the aid of the ion-
ratio or Eh-pH methods to identify the predominant solid species.
                               196
-------
If the Cd-Cl complexes are the most important (predominant)
species for soluble cadmium, then Figure 101 can be employed
for quick estimation of the total soluble cadmium concentration
i n aged FGD siudge .

Effect on Copper

     Figure 80 indicates that the studied range of chloride con-
centrations can cause a one order of magnitude variation in
concentrations of Cu-Cl complexes,  As shown in Figures 50
and 72, free Cu2 + ion is the only species whose concentration
can exceed the concentration of the Cu-Cl complexes at low pH
(pH 4.7).  From Figure 102, it can also be seen that this phe-
nomenon occurs when the chloride concentration reaches about
2,000 ppm in the FGD wastewater.  At a pH higher than about 4.7,
the Cu-B(OH)4 complexes will usually dominate Cu-Cl complex
'formati on .

     The  same type of equations used previously for the predic-
tion of the total soluble cadmium concentration also can be used
for copper:

     pH <  4.7

     [CuT] = [Cu2 + ] +   [CuCl+] +  [CuOHCl(aq)]

           ~ [Cu2+] + 101 -6[Cu2*] [Cl~]  + 109'1 [Cu2 + ] [OH"] [Cl~] (77)

     pH >  4.7

     [CuT] * [CuB(OH)J] + [Cu(B(OH)4)2(aq)]
                                            1 ,          1
                                                              (78)
From the above discussion, it appears that Figure 102 is a valid
predictor of the total soluble copper concentration in aged FGO
wastewater when (1) pH is less than 4.7, and (2) the chloride
concentration is sufficiently high.

Effect on Lead

     The speciation diagrams  (Figures 56 and 78 in Section 5)
indicate that the  Pb-Cl complexes may become the predominant
soluble lead species at pH  7 only when chloride is present at a
high concentration.  (Figure  103 shows this level to be a minimum
of 1,500 ppm.)  When the pH is higher than 7, the Pb-Cl com-
plexes are insignificant.  Therefore, the same types of predic-
tion equations are applicable:

     pH < 7

     [Pbf] * [Pb2+] +  [PbCl+]

           = [Pb2 + ] +  lO1'7^2*] [CT]                        (79)


                                197
-------
     The model  verification indicates  that at high  pH levels  the
calculated value for total  soluble lead may be higher than  the
analytical value.   Therefore,  it is  recommended that  the  thermo-
dynamic model  not  be used for  lead when the pH is  higher  than
about 7.

Effect on Mercury

     When the  pH is less than  about  9,  the Hg-Cl  complexes
alone can account  for all soluble mercury.  The effect of the
soluble chloride level  on the  soluble  mercury level  is shown  in
Figure 104.   When  the chloride concentration is increased from
50 to 6,000  ppm, the overall  soluble mercury concentration  will
vary by more than  four  orders  of magnitude in the  FGD wastewater.
Figure 104,  which  can be used  to e.stimate the total  soluble
mercury concentration in FGD  wastewater when pH is  less than
about 9, suggests  that  this estimation  is usually  unnecessary due
to the low concentration.

Effect on Zi nc

     The effect of soluble  chloride  on  soluble zinc  levels  is
presented graphically in Figure 105.  When chloride  concentration
is increased from  50 to 6,000  ppm, the  concentration  of soluble
zinc increases  about two orders of magnitude.  The  results  of
the speciat ion  calculation  (Figures  58  and 80) show  that  Zn-Cl
complexes may  become the predominant soluble zinc  species (1)
when pH  9,  and (2) when the  soluble chloride concentration is
higher than  about  3,000 ppm.   Conversely, when the  pH is  less
than about 9 and if soluble chloride concentration  is below
3,000 ppm, the  free metal ion, Zn2+, can account  for  all  soluble
zinc.  However, if soluble  chloride  concentration  is  higher
than 3,000 ppm  in  the same  pH  region,  the total soluble zinc  in
the aged FGD sludge will depend on the  chloride levels.  There-
fore, Figure 105 can be used  to predict soluble zinc  levels with-
in the above mentioned  pH range.

     The following equation can be used for the estimation  of
total soluble  zinc in the aged FGD wastewater at  low  pH:

     pH < 9

     [ZnT] ~ [Zn2 + ] + 101-4[Zn2 + ] [CT]                       (80)
EFFECTS OF SULFATE CONCENTRATION ON THE SOLUBILITIES OF METALS

     The speciation study thus far has  shown that sulfate com-
plexes may become significant at high pH levels for major ions
(Ca^"1", Mg^ + ,  K+, and Na + ) and several minor ions such as zinc.
Only the effects of sulfate concentration on major ions will  be
                                198
-------
discussed here,  however,  due to the  less  important  role  of sul-
fate in the speciation of minor ions.   Figures  106  to  109  show
the overall sulfate effect.

     In this study, the soluble sulfate concentration  was  varied
from 100 up to 40,000 ppm.  This variation  will  result in  an in-
crease of four orders of magnitude in  the concentration  of solu-
ble calcium-sulfate complexes (Figure  106).  Since  free  Ca^+'
ion and CaSQ^Uq) are the main soluble species  for  calcium in
FGD wastewater,  the total soluble level of  calcium  can thus be
approximated as:

     [CaT3  * [Ca2+] + 1O2 ' 3 [Ca2+] [SO2']                     (81)

     Figure 106  indicates that the sulfate  concentration will not
play an important role in the chemical behavior of  calcium in the
FGD wastewater when the pH is less than about 5.   When the pH is
higher than 5, the Ca-S04 complex, (CaS04(aq),  may  become
the predominant  soluble calcium species in  FGD  wastewater  if
S04<-5,000 ppm..  As discussed in Section 6,  'the  actual  distribu-
tion of calcium  solids in aged FGD wastewater cannot  be  accu-
rately estimated  by the model.  Therefore,  it is  suggested that
Equation 81 receive additional study.

Effect on Magnesium

     Figure 107  shows that soluble magnesium  levels,  (MgS04(aq)),
can vary by almost six orders of magnitude  for  an increase in
soluble sulfate  levels from  100 to 40,000 ppm.   When  the soluble
sulfate concentration is  raised to as  high  as 3,000 to 5,000 ppm
(depending  on the pH 1 evel ),  the level of MgSO^aq) may  exceed
the level of free Mg2+.  The following equation  best  describes
the predicted magnesium levels:

     [MgT]  * [Mg2 + ] + 1O2 '4 [Mg2 + ] [S0°]                        (82)

In this case, [Mg2+] should  be calculated from  the  solubility
controlling solids of magnesium.  As  was  the  case with calcium,
the actual  solid  phases of magensium  in aged  FGD  wastes  cannot
accurately  be estimated.   Figure 107  is therefore not  suggested
for the prediction of soluble magnesium levels.   It is expected
that Equation 82, however, will still  be  valid  for  FGD wastewater.

Effects on  Potassium and  Sodium

     The effects  of soluble  sulfate  on the  soluble  level of
potassium and sodium are  shown in Figures 108 and 109.  Although
soluble sulfate  levels can affect the  formation  of  potassium or
sodium sulfate complexes, the significance  of+these complex
species i.s  far below that of the free  ions  (K  and  Na + ).  Even
when the soluble  sulfate  level is as  high as  40,000 ppm  (FGD
sludge usually has soluble sulfate less than  10,000 ppm),  the
                               199
-------
                                                      -in*
     o

     I
                                      40,000 ppm

                                       = 20,000  ppm


                                         = 10,000 ppm
                                                            s.
                                                            Q.
                                                            a.
                                                         -6
                                                    11
Figure 106.
Effects of total  sulfate concentration on soluble
Ca concentration.
                              200
-------
          Free
    en
    o
       10
       12
                     SOJ = 20,000  ppm

    2 +   SOJ  =  40,000 ppm
                           ,,    w, www ppm


                           50= = 10,000 ppm
              SO;; = 100 ppm
                               7


                               PH
10'
                                              Q.

                                              Q-
                                                       10'
                                                       1.0
                                                       10
                                                         -2
                                                       10"
                                      11
Figure 107.
Effects of total sulfate concentration  on  soluble
Mg concentration.
                             201
-------
                                                     - in*
                                 =  40,000  ppm

                                 -S0= =  20,000 ppm

                                    SO? = 10,000 ppm
                             S07 =  5,000  ppm
                = 100 ppm
                                                           0.
                                                           a.
                                                        -6
                                                  11
Figure 108.
Effects of total  sulfate concentration on soluble
K concentration.
                             202
-------
                        SOl = 1,500 ppm
     01
     o
        a
       10
       12
                             504 = 5,000 ppm

                      SOf  =  10,000  ppm

                 S0=  =  20,000  ppm
              SOT = 100 ppm
                                          10*
                                                       10'
                                                       1.0
                                                            £ .
                                                            Q.
                                                            O.
                                                       10
                                                         -2
                                                       10-'
                                                       10
                                                         -6
                                                    11
                               pH
Figure 109.
Effects of total  sulfate concentration on  soluble
Ma concentration.
                              203
-------
free Ion concentrations of potassium and  sodium still  predomi-
nate.

EFFECTS OF BORATE CONCENTRATION ON THE SOLUBILITIES  OF METALS

     The speciation study has shown that  total  soluble copper
and lead concentrations can be greatly affected by borate con-
centration of FGD wastewater.  These effects  are summarized in
Figures 110 and 111.

     As discussed previously (refer to Equation 78), the
Cu-B(OH)4 complex may account for  almost  100  percent of the
total  soluble copper in the FGD wastewater when the  pH is
higher than about 4.7.  In this study, the soluble borate levels
were varied from 5 ppm to 200 ppm  to observe  the effects on
copper.  Figure 110 shows that a borate concentration increase
of this magnitude results in a 2,000-fold increase in the
copper-borate concentration.

     For lead, an increase from 5  ppm to  200  ppm in  borate
concentration may produce a 10,000-fold increase in  soluble
Pb-B(OH)4 (see Figure 111).

     Although it is still impossible to verify  the presence of
various soluble lead species in the FGD wastewater,  it can be
shown  on a theoretical basis that  Pb-B(OH)4 complexes can
account for a major portion of the total  soluble lead concen-
tration.  The Pb-C03 and Pb-OH complexes  are  the only species
which  may compete with Pb-B(OH)4 levels when  the pH  is higher
than about 7.  If the theoretical  evaluation  is correct, the
soluble lead level can be approximated by the following equation
for pH higher than 7 (when pH  7,  Equation 79 is followed):

     pH > 7

     [PbT] * 105'2[Pb2+] [B(OH)'] + 1011 -1 [Pb2 + ] [B(OH)^]3


             + 107<4[Pb2+] [CO'] +  1010<8[Pb2+][CO^]2

             + 105-3[Pb2+][OH~] +  1010>9[Pb2+] [OH~]2        (83)


EFFECTS OF LIME ADDITION TO FGD SLUDGE AND WASTEWATER

     The addition of lime and fly  ash to  FGD  sludge  has been
employed as a fixative process, primarily to  enhance physical
properties (permeability, load-bearing strength) through a
pozzolanic reaction.  However, if  lime addition achieves no
reductionof the total soluble levels or  any  toxic complexes of
the constituents, or if soluble trace metals  constituents
                               204
-------
 3
 O
 CT
 O
                             7

                             PH
                                                          Q.
                                                          Q.
                                    11
Figure 110.
Effects of borate concentration  on  soluble  Cu
concentration.
                           205
-------
 £   9
     12
     15
     18
               B(OH);  40 ppm


             B(OH)~  80  ppm



        B(OH)4 . 120 ppm-
                             pH
                                                    10
                                                    1.0
                                                    10
                                                      -3
                                                         a.
                                                         a.
                                                    1Q
                                                      -6
                                                    10
                                                      -9
                                                    io-12
                                                11
Figure 111.
Effects of borate concentration on soluole Pb
concentration.
                           206
-------
increase in concentration,  there will  be  little  environmental
advantage of disposing the  sludge with lime  addition.   Therefore,
it would be useful  to determine how various  kinds  of lime  addi-
tions affect the concentrations of constituents  in the  sludge
liquid phase.  Specifically,  if lime addition  does have benefi-
cial effects, it may be possible to determine  how  to achieve  the
optimum lime dosage in order  to obtain the minimum concentra-
tions of constituents in the  liquid phase.

     In this study, the Kansas  City Power and  Light La  Cygne
Plant FGD waste was used for  the evaluation.  The  amount of
lime addition used  for the  study ranged from 0 to  10,000 ppm
(as Ca(OH)2).  Figures 112  through 114 show  selected results.
As illustrated in Figure 112,  the concentrations of free CO?",
P0$~, SiO|", and OH" can be increased  significantly by  lime addi-
tion.  Free SO^'is  reduced  slightly when  lime  is added.  Other
ligands, such as SOJ", Cl", F~, B(OH)I, MoO|% AsOr', and  HVO?',
are only slightly,  if at all,  affected.  It  is expected that,
without any decrease in free  metal  ion concentrations,  the in-
crease in ligand levels will  lead to the  increase  in related
metal-ligand complex ing.

     Figure 113 displays the  results of lime addition on the
total soluble concentrations  of major  ions.   As  can be  seen from
this diagram, only  the total  soluble calcium levels may be
affected by the lime addition.   The total calcium  concentration
can be increased dramatically  by an added 100  ppm  of lime. When
the dosage of lime  is increased from 100  ppm to  10,000  ppm, total
soluble calcium will increase  steadily from  about  200 ppm  to  400
ppm.

     Most of the minor ions are affected  by  lime addition.
Although lime addition is usually accompanied  by a pH increase,
the total soluble concentrations of minor ions rather than show-
ing a decreasing trend, usually increase  in  the  FGD sludge liquid
phase.  This is due to the  formation of the  strong metallic
complexes of hydroxide or carbonate.  As  shown in  Figure 114,
total soluble cadmium can be  increased from  0.01 ppb to 1.45  ppb
if the lime addition exceeds  1,500 ppm.  Total soluble  Fe(III)
also will increase  to the level of 22  ppb from its original
level of 0.012 ppb  for a similar lime  dosage.   Total soluble
manganese is reduced from its  original level of 156 ppb to about
20 ppb as the dosage of lime  is increased from 0 to about  500  ppm
(as Ca(OH)2).  When the dosage  exceeds 500  ppm,  total soluble
manganese can reach concentrations as  high  as  36.5 ppb.  Lime
addition also may increase  the  total soluble levels of  Cu(II)  b.y
a factor of 10.  These levels,  however, are  still  in the trace
level range (<0.001 ppb).

     From,, the above discussion, it can be seen that thermodyna-
mically, the lime addition  has  a beneficial  effect only for
manganese.  The liquid phase  concentrations  of many other  soluble
                               207
-------
      en

      o
         10
         12
                                -Free C03    Free  SO!
                       Free OH'
                               Free  P0~
                                      4
                                       Free SiO:
           0   1.   2   345678    91011
              Lime Addition (in 1000 ppm as  Ca(OH)2)
Figure 112.
Effects of lime addition on the concentrations  of

free 1i gands .
                             208
-------
     1200
 £
 Q.
 Q.
 c
 o
 

 O
      800
      600
400
      200
        0	L
              Mg(II)
         0   1   2
                           6   7   8   9   10
            Lime Addition (in 1000 ppm as  Ca(OH)  )
Figure 113.
       Effects of lime addition on the total  soluble
       concentrations of major ions.
                           209
-------
   -Q
    a.
    a.
   •P
   03
   S-
   +J
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-------
constituents, such as Ca,  Fe,  Cd,  will  increase  significantly
when extra lime is added to the FGD waste,  thereby  increasing
the potential for leaching of  these constituents  from  the  sludge
disposal site.  This phenomenon,  however,  needs  additional  field
study to verify.

EFFECTS OF SILICATE ADDITION TO FGD SLUDGE

     As was the case with  lime, the addition  of  silicate  com-
pounds has been employed for the  fixation  of  FGD  sludge.   How
the concentration of metals and other  ions  in  their  various  forms
change as a function of silicate  additive  concentration was
examined in this  study.  This  examination  was  divided  into  two
sections:  (1) to evaluate the overall  effects of the  silicate
addition, and (2) to identify  the  silicate  level  where the  sili-
cate addition may become significant.   The  results  are given  in
Figures 115 through 124.

     In this study, the effects of silicate addition were  ob-
served from 10-5M to 10°M  (0.28 to 28,000  mg/1 as Si)  of  total
silicate concentrations in the FGD system.  The  results of  thermo-
dynamic calculations show  that silicate addition  may have  a  sig-
nificant effect on the levels  of  soluble aluminum (Figure  115)
and zinc (Figure  116).  However,  soluble levels  of  other  elements
studied (Figures  117 through 124)  were  not  shown  to  vary  with the
silicate addition.

     It can be observed in Figure  115  that  the level of soluble
aluminum species  is greatly reduced in  the  aged  FGD  sludge
liquor when the total silicate level  is higher than  1 0 ~ 2 M  (280
mg/1 as Si).  When silicate levels increase from  10~2M to  IQ-^M
(280 mg/1 to 2,800 mg/1 as Si), the total  soluble aluminum  con-
centration (about 2.7 ppm) can be  reduced  by  about  four orders
of magnitude.  As silicate levels  are  further  increased  (  10~'M),
however, the total soluble aluminum level  will remain  unchanged.
Therefore, if silicate is  added for the control  of  aluminum
solubility, the optimum levels of  silicate  in  the FGD  system
are about lO-^M to 10~^M,  depending on  the  final  aluminum  levels
desired.

     Zinc exhibits behavior similar to  that of aluminum when
silicate is added to the FGD sludge (Figure 116).  The total  zinc
levels will not be affected by silicate until  the silicate  level
reaches as high as 10'2M (280  mg/1 as  Si).  Between  10-2M  and
IQ-IM of silicate, the total soluble zinc  level  can  be reduced
4,000-fold.  The  same optimum  levels of silicate  addition  for
aluminum are suggested for zinc in order to control  soluble  zinc
in the FGD sludge leachate.  With  the  exception  of  aluminum  and
zinc, other elements studied (Figures  117  through 124  will  not
be affected significantly  by silicate  addition).
                               211
-------
~  8
-  12
o

I
   16
   20
              4321

         Total Soluble Silicate  Concentration

                    -log  [SiT]  (M)
 Figure  115.
Effects of silicate addition on Al in FGD
wa stewater.
                         212
-------
  3-
      C0=
  12
  15
  18
                      so-
                     Free Zn2+
                 Cl
                         PO:
                 J_
             4321

          Total  Soluble  Silicate  Concentrate
                   -log  [SiT]  (M)
Figure 116.
Effects of silicate addition on Zn in FGD
wastewater.
                        213
-------
 «3
 CJ
 CD
 O
                                             so;
                	OH"

                 003   Free Ca2+
                       PO:
   10
   12
              4        3-2         1

         Total Soluble Silicate  Concentration
                     -log [SiT]  (M)
Figure 117.
Effects of silicate addition on Ca in FGD
wastewater.
                          214
-------
      10
      12
                                               so=
                                           Free Mg2+
                                       CO-
                                  OH'
                               PO:
             J	I
                 4321
            Total  Soluble  Silicate  Concentration
                        -log  [SiT] (M)
Figure 118
Effects of silicate addition on magnesium in F6D
wastewater.
                            215
-------
      en
      o
                              SOf
                              Free  K+
               Total  Soluble Silicate Concentration

                         -log  [SiT]  (M)
Figure 119.   Effects of silicate addition on K in FGD wastewater
                              216
-------
    1-
    4-
                          Free ;Na
                         COf
                                       so;
             4321

         Total  Soluble Silicate Concentration

                    -log  [S1T]  (M)
Figure 120.
Effects of silicate addition on Na in FGD
wastewater.
                         217
-------
u
3
_ 6
s:
r— i
t— i
•o Q
0
1 — 1
CD
0
1
12
15
18
soi
cof

CT ^"^

OH"
F~
~ PO|
I i I i
             4321

          Total  Soluble Silicate Concentration

                     -log  [SiT]  (M)
Figure 121.
Effects of silicate addition on Cd in FGO
wastewater.
                         218
-------
u
3
s:
^ 6
i— «
i— i
H-«
l__l
9
o
t
12
15
18
~" OH"
F"
POZ
S04
_ Free Cr3+
Cl"
i i i i
              4321

         Total Soluble Silicate Concentration

                    -log [SiT]  (M)
Figure 122.
Effects of silicate addition on Cr in FGD
wastewater.
                         219
-------
en
0
   15
   18
                     Free Cu
                            2+
                            *
OH
   12
                PO
                  4
             4321

         Total Soluble Silicate  Concentration

                    -log  [SiT]  (M)
Figure 123.   Effects of silicate addition on Cu in FGD
             wastewater.
                         220
-------
 Ol
 O
                 Free Pb'
   10
                                         B(OH)'


                                        CO!"
                                          3
                                  so;
                            	OH;

                             CT
   12
    54321

         Total Soluble Silicate  Concentration
                    -log  [SiT]  (M)
Figure 124.  Effects of silicate addition  on Pb  in  FGD
             wastewater.
                         221
-------
EFFECTS OF HYDROGEN SULFIDE ADDITION  TO FGD  SLUDGE

     Sulfide is known to be an extremely effective  scavenger  for
removing certain trace metals  from the aqueous  solution.   Since
hydrogen sulfide may be available at  some power plants,  the
effects of sulfide addition to FGD wastes were  investigated.

     For modeling purposes, the total  sulfide  concentration was
varied from 10-7-51M to 10-3.20M (0.001 ppm  to  20  ppra).   The
results of calculation show that the  distributions  of copper,
lead, cadmium,  zinc, mercury,  silver,  and cobalt species  in the
FGD waste are significantly affected  by sulfide addition.   The
effect of sulfide addition on  other constituents is negligible.

     As shown in Figure 125, the total  soluble  concentrations  of
both lead and copper can be reduced to trace levels by  adding
as little as 0.001 ppm (10-7.5lM) of  sulfide to the FGD  sludge.
The total soluble levels of these two  elements  will be  further
reduced when sulfide addition  is increased.^   The  effect  of sul-
fide addition on the total soluble cadmium concentration  also
displays similar behavior (Cd  concentration  decreases as  sulfide
addition increases).  The total soluble cadmium concentration
will not, however, reach trace levels  until  the sulfide  concen-
tration exceeds about 0.2 ppm.  The reduction  achieved  in  total
soluble zinc concentration is  negligible if  sulfide addition  is
less than 0.1 ppm.  When the total  added sulfide exceeds  0.5
ppm, the soluble zinc can also be reduced to trace  levels.  The
reduction in levels of soluble heavy  metals  is  due  to the  for-
mation of insoluble metallic sulfide  compounds  such as  CuS(s),
PbS(s), CdS(s), and ZnS(s).  Figure 126 displays the distribu-
tion of metallic sulfides in FGD waste as a  function of  the sul-
fide concentration.  At low total sulfide levels (e.g.,  less
than 0.001 ppm), sulfide addition will  favor the formation  of
Ag2S(s) and CuS(s).  After sufficient  soluble  silver and  copper
are removed from solution, the remaining soluble sulfide  can  then
react with other soluble metals.  The  order  of  metallic  sulfide
formation with  increasing sulfide levels is  as  follows:   AggSfs)  •
CuS(s) - PbS(s) - CdS(s) - ZnS(s) - CoS(s).   This  sequence  can
be seen in Figure 126.

     Although the trace heavy  metals  can be  removed efficiently
by sulfide addition, this treatment may not  be  desirable  for  two
reasons.  First, excess hydrogen sulfide itself is  an undesirable
contaminant in  wastewater (leachate).   Second,  the  FGD  sludge
lagoon is an open pond, where  oxygen  can gradually  diffuse  into
the FGD waste and oxidize the  metallic sulfide  solids.   Diffusion
and oxidation will eventually  convert  the sulfide  solids  into  the
original predominant solids, and again release  the  soluble  metal
species.
                                222
-------
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    •T—
    u
    (U
    Q.
     
-------
EFFECTS OF PHOSPHATE ADDITION TO FGD SLUDGE

     In this study La Cygne Plant data  are used  for evaluation,
total phosphate concentrations in the FGD sludge ranged  from
10-5 to 10-lM (0.31  to 3,100 mg/1 as P).   Among  the metals
studied, it was found that only the total  levels of magnesium,
calcium, and cadmium can be significantly affected  by  phosphate
addition.  Soluble magnesium is reduced by a  factor of 2.5  as
the phosphate level  is increased from 10-5 to  lO^M (Figure 127)
This change is due primarily to the formation  of Mg3(P04)2(s)
solid in the FGD sludge.  According to  the calculation,  the
level of Mg3(P04)2(s) solid in the sludge is  increased at  the
following ratios:

     Total phosphate (M)               %  of  Mq formed
      in the FGD system                as Mg3(PQ4)2(s)

            10"5                             * 0
            10-4                             = 0
            10-3                               5
            10-2                              31.9
            10-1                              55.5
Due to the formation of Mg3(P0*)2(s),  the concentration
Mg2+ ion is significantly reduced.   This  change  also  le<
                                                        of free
                                                     leads to
a decrease in the concentration  of all  soluble  magnesium com-
plexes (except the Mg-P04 complexes,  which  shows  an increase
in concentration with the increase of phosphate addition.
     The total  soluble calcium can  also  be  reduced  slightly as
the total  phosphate level  exceeds  about  lO'^M  (310  mg/1  as  P)
(Figure 127).  In a manner similar  to  magnesium,  this  reduction
is due to  the formation of calcium  phosphate  solids in  the  FGD
sludge.  Three  Ca-P04 solids may be formed  in  the FGD  sludge:
Cas(P04)30H(s ) ,  Ca4 ( P04 ) 3H (s ) , and  CaHP04(s).   The  following
table shows the  effect of phosphate variation  on  Ca-P04 solids
formati on :

     Total  phosphate  (M)                % of Ca formed
      in the FGD system^             as  phosphate sol
            10
            10
            10
                 system^             as  phosphate solids

              '*
               ,
               ,
              "
            10"'
= 0
* 0
* 0
1
36
.5
.2
Because of the Ca-P04 solids formation, the amount of CaF2(s)
solid will decrease slightly (about 0.1 in terms  of the total
calcium l£vel in the sludge).  This effect will  lead to an in-
crease in the soluble fluoride level  of about 23  percent for a
IO*IM addition of phosphate to the sludge.
                                225
-------
 E
 Q.
 a.
 c
 o
 s=
 
-------
     The formation of calcium phosphate  solids  also  causes  a
decrease in the amount of CaSCs*!/2H20(s)  in  the  FGD sludge.
Due to this change, the free S03"  concentration is  increased
substantially (about 50 percent above  its  original  level).  This
change leads to a significant increase in  Cd(S03)i~  complexes,
and in so doing increases the total  soluble cadmium  concentration
by a factor of 2 above its original  level  (see  Figure  128).

EFFECTS OF MAGNESIUM ADDITION TO THE FGD  SORBENT

     The use of high magnesium scrubbing  reagents  could  become
widespread (Ref. 1).  This study used  the  model  to  identify the
effects of various concentrations  of magnesium  additives  on the
FGD sludge liquid phase.   In this  study,  the  magnesium concen-
tration in the FGD sorbent was var.ied  from 10~4 to  1OM (2.4 ppm
to 0.24 percent as Mg) to observe  the  effects on  the speciation
of metals.  Results for some selected  elements  are  shown  in
Figures 129 through 134.

     Figure 129 shows that an increase in  magnesium  concentration
in the FGD sorbent will also increase  the  levels  of  all  soluble
species of magnesium,  This formation  of  strong magnesium com-
plexes in the FGD sorbent is due to  th«  increase  of  soluble free
Mg2+ ion.  This phenomenon leads to  the  decrease  of  available
free ligands such as S0^~, F~, P0|", and  CO^" •   Therefore,  the
concentrations of the complexes formed by  tne above  ligands
with other metals are usually reduced  (see Figures  130 to 134).

     The effects of magnesium addition on  the speciation  of
calcium in the FGD system is shown in  Figure  130.   As  can be
seen from the diagram, the concentrations  of'Ca-S04,  Ca-F,
and Ca-P04 complexes are  greatly reduced  in the FGD  sorbent
when the total magnesium  concentration in  the system exceeds
IQ-^M (2,430 ppm as Mg).   The Ca-C03 complexes  appear  to  be un-
affected when magnesium is added to  the  system.  The most impor-
tant species for calcium  in the system is  free  Ca^*  ion,  which
will not be affected by the addition of  magnesium.   Therefore,
magnesium addition will not alter  the  total soluble  level  of
calcium in the system.

     Similar phenomena also hold true  for  sodium  and potassium.
When magnesium is added to the system, the concentrations of
sulfate complexes with sodium or potassium are  decreased, but
total soluble levels of potassium  and  sodium  remain  unchanged.

     For minor ions, the  effects of  magnesium addition are  also
confined to concentration changes  of the  S0|~,  F~,  and PQ^com-
plexes (Figures 131 through 134).   In  general,  if these  com-
plexes comprise the predominant soluble  species for  a  minor
element, *then magnesium addition may affect the total  soluble
levels of that element.  Otherwise,  the  effects are  confined
                                227
-------
     300
250-
     200-
   o.
   o.
   c
   o
   
-------
  en
  o
     10-3       1Q-2       10'1

    Total  Mg(II)  Concentration
                                                 10'
Figure 129.
Effects of Mg addition on the distribution of
soluble Mg complexes.
                           229
-------
    CD
    o
             Free !Ca2+
                   S04
                                   OH'
      10
      12
                    10-3       io~2       1Q-1        10°

               Total Mg(II) Concentration (M)
Figure 130.  Effects of Mg addition on the speciation of Ca
                            230
-------
•a
o
en
o
       4 _
       8
      12
      16
      20
      24
                         so;
                         co:
OH-
                          503
                POJ
          ,-4
,-3     1n-2
                       	CT


                        Free  Cd2+
,-1
         10"*      10~J     lO""       10  '      10°


               Total   Mg(Il)  Concentration  (M)
                                   10
 Figure  131.   Effects  of Mg addition on the speciation of Cd,
                             231
-------
  en
  o
    12
    15
    18
                    J	I
                                          10°      10
              Total Mg(II) Concentration  (M)
Figure 132.
Effects of Mg addition on the speciation of
Cr(III).
                           232
-------
      3-
     12
                          Free  Cu
                                 2 +
                                          B(OH)
                                 Cl
CO
     15
     18
                     PCT
               10~3     10~2      10-1      10°      10




               Total Mg(II)  Concentration  (M)
Figure 133.  Effects of Mg addition on the speciation of Cu
                            233
-------
  01

  O
    .10
    12
         10
           -4
                      otr
                     soi
                      POf
,-3
                                             Free Zn
                                                     21-
                                           Cl
  -1         °
10 '       10
             Total  Mg\(II)  Concentration   (M)
Figure 134.  Effects  of  Mg  addition on the speciation of  Zn.
                             234
-------
only to elements  forming  the  above-mentioned  complexes.   It  is
expected that the total  soluble  levels  of  most  minor  elements
studied will  not  be altered  by magnesium addition.  The  principal
exception is  chromium,  which  may form  strong  Cr(III)-F  complexes
(primarily Crp2+) in the  low  pH  region.

EFFECTS OF SULFITE OXIDATION

     As discussed previously,  the  aging of the  FGD  wastes  usually
results in an increase  of redox  potential  and pH.   During  this
aging process,  it is expected  that the  sulfite  species  will
gradually be  oxidized to  sulfate.   Since both sulfite and  sulfate
species are major components  in  FGD sludge, the oxidation  of sul-
fite may cause  changes  in other  constituents.  In this  study,  the
possible effects  of sulfite  oxidat.ion  on some selected  elements
were examined.   The results  are  presented  in  Figures  135 through
156.

     In this  discussion,  total  sulfite  was assumed  to be oxidized
from an original  concentration of  10-0.16^ to a concentration  of
10-4-16^  y^g  effects  on other  constituents  at the La  Cygne
Plant were used for the calculation.   Only the  results  of  two
typical pH values (pH = 6.5  and  9.0)  are discussed  here.

     Figure 135 and 136 show  the effects of sulfite oxidation  on
various sulfite species.   Due  to the  decrease of total  sulfite
concentrations  in the system,  various  sulfite complexes  are  also
decreased.  As  can be seen from  Figure  135, the decrease of  HSOo
or free $03  species approximately follow  the rate  of sulfite
oxidation.  However, tne  concentration  trends of metallic  sulfite
complexes are different from  that  of total  sulfite  concentration.
For example,  total sulfite oxidation  to  10~^  of its original
level will result in a  factor  of 10"7  decrease  in the Cd-S03
complex concentration.   Figure 136 indicates  that sulfite  oxi-
dation will cause a tremendous decrease  in the  level  of
CaS03'l/2H20(s) solid in  the  FGD sludge.   For La Cygne  Plant FGD
wastes, if the  total sulfite  level is  oxidized  to one-tenth  of
its original  level (perhaps  by aeration),  the CaS03 • 1 /2\\2§( s )
solid will disappear as shown  in Figure  136.

     Sulfite  oxidation  has only  a  minor  effect  on the speciation
of soluble calcium (see Figure 137).   It may  cause  a  tremendous
change, however,  in the level  of calcium solids in  the  FGD
sludge (see Figure 138).   The  calculations show that  the
CaSOs'l/SHgOU j solid will be  transformed  to  CaS04 '2H20(s) during
sulfite oxidation when  the pH  equals  6.5 and  to CaC03(s) when
the pH equals 9 .0 .

     The magnesium species will  not be affected significantly
during su*lfite  oxidation  (Figures  139  and  140).  For  potassium
and sodium (Figures 141-144)  sulfite oxidation  causes an increase
                                235
-------
                            pH = 6.5
pH = 9.0
ro
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           E
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         Figure  135.   Effects of sulfite oxidation on  the  concentrations  of sulfite complexes.
-------
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            100
             80-
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6 10~1>16 10~2'16 10~3'16 10~4'16 10~°'16 10"1'16 10~2-16 10~3-16 10"4
                                                                         [so|T]
       Figure 136.   Effects  of  sulfite  oxidation  on  the  primary distribution of S03= species.
-------
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o
en
O
  12
  15
                 pH =6.5
            I        1         1
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                                                8
                                              12
                                                         16
     pH =  9.0
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   j-0.16  jQ-1.16  jQ-2.16 jQ-3.16 jQ-4.16
20
n-0. 1 6
1        I         i
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       Figure 137.  Effects  of  sulfite oxidation on  the  speciation of Ca.
-------
100
         c
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                             PH =6.5
                oi
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                     ///////// /, /////// / /
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        Z Z Z Z Z Z Z Z Z / Z Z Z Z Z Z Z Z Z
       Z_///// S ////// _S //////
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             20
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                  ZZZZZZ Z/Z Z//Z Z Z/ZZZZ
                 z z/ z zzzz z _z/~z/ z z z z/ _z~z/.
                Z Z Z Z Z Z Z Z Z Z Z Z / / Z Z Z Z Z Z Z A
                 _z z z_zs z z z z z z z / z z z z z z z z
                Z Z Z Z Z Z Z Z Z Z Z Z / / Z Z Z / Z Z / Z
                                                           100
                                                  CaF2(s)-
                                                              pH = 9.0
                                                              \\ \ \ \ \ N\ V\ \ \ "V A \~\' V \ \ \ \ T7^. ~\ \ \ \\ \
                                                        s~
                                                        •*->
                                                        I/I
i-O. 16
                           16
                               1Q
                     -2.16
1-4.16
                                                                             CSO=T]
         Figure 138.   Effects of sulfite  oxidation on  the  primary distribution of  Ca  species.
-------
   0
                 pH '= 6.5
                    1        1
        so
cn
o
'   q
   y
  12
             Free  Mg+2
                               OH
 15

10
            1        I
                                                0
                                           cn
                                           2!
                                          cn
                                          O
                                               12
   -0.16
                                              15
                                                             pH = 9 . 0
                                                       n        i        r
                                                       so
                                                        Free  Mg+2
                                                                          OH
                                                         i        i
              .16  JQ-2.16 jQ-3.16 jQ-4.16   1Q-0.16  1Q-1.16  j Q-2 .1 6  j Q-3.1 6  10~4.16
                 [SO=T]
                                                               [so=T]
     Figure  139.   Effects  of sulfite oxidation  on  the  speciation of Mg.
-------
ro
           100
     pH =6.5
            80
         c.
         o
£   60
S-
        o
            40
            20
             0
                      1        I
                   Free  Mg
                          2+
                           MgSO°(aq)
1        I        i
                                  100
                                                                         pH = 9.0
                                            Free  Mg
                                   80
                               c
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$-

to

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                                                         60
                                  40
                                  20
                                                 MgSO°(aq)
   10
             -o.i6
       10-2-16 10~3'16 10~4'16
                                   0
                                                                   i        i
                                                                        10~2-16 10~3-16  10~4-16
                            [so=T]
        Figure 140.  Effects of sulfite  oxidation on the primary distribution  of Mg species.
-------
ro
             0
                           pH =6.5
                                 pH = 9.0
             3 -
             6~
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1 1 1
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-
l i i
           10
             -0.16
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                                                                  ~ l ' J 6   ~2 -1 6   "3'1 6
               Figure  141.   Effects  of  sulfite oxidation on the speciation of K.
-------
100
80
c
0
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£ 60
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a
ro
£ 40
20
0
pH '= 6.5
1 1 I
Free K+
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1 I I
100
80
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I 60
to
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Q
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20
0
pH = 9.0
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Free K*
~/^

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KSO- (aq)
_ _
I I i
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     -0.16
10-2.16  iQ-3.16  jo"4-16
                   [SO=T]
Figure 142.  Effects of sulfite oxidation  on  the  primary distribution of K species.
-------
ro
                           pH = 6.5
                     Cl
                          Free Na+
en

O
                                COf
  12
15
                      I	i
           1Q
    -0.16
                     .16  1Q
                                       -3.16
                                                        0
                                                       12
                                              15
                                                             pH = 9.0
                                                             	1	
                                                                    SOZ
                                                             Free
j	i        i
                                                              0~2 -1 6
                                                                                ~3A 6
                Figure  143.   Effects  of  sulfite  oxidation on the speciation of Na.
-------
ro
           100
            80
         c
         o
            60
            40
            20
             0
                            pH = 6.5
                               1        I
                           Free Na
                          NaSQ-(aq)
                              4
           1        1        1
                                             100
                                              80
                                                     c
                                                     o
                                             60
                                             40
                                             20
10
  -0.16
                             JQ-2.16  jQ-3.16 lfl-4.16
                                              0
	pH = 9.0
i        i        r
                                                             Free Na
                                                             NaSO-(aq)
 I        i        i
      10-2.16  1Q-3.16  10-4.16



       [SO|T]
        Figure 144.  Effects  of  sulfite  oxidation on the  primary  distribution of Na  species.
-------
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cr.
             0
          O
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            12
                            pH = 6.5
                               I        I
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                                                               pH = 9.0
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                                               12
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 15
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                                                                                     C0|
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    i        i
                                                        jQ
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                                                -0.16  jQ-1.16  }Q-2.16 jg-3.16



                                                                [SO=T]
                Figure  145.   Effects of sulfite  oxidation on the speciation  of Cd.
-------
ro
            100
                             pH '= 6.5
         c
         o
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         -M
         a
         .a
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-0.16    -1.16    -2.16
                                            100
                                                           80
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                                                       •o
                                         J_
                                         4J
                                         CO
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                                         Q
                                             60
                                                           40
                                                           20
                                                            0
                                                             pH = 9.0
                                                                 (s)
                                                  -4.16   jQ-0.16  1Q-1.16  jQ-2.16  jQ-3.16
        Figure  146.   Effects  of  sulfite oxidation on the  primary distribution of Cd  species.
-------
ro

oo
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   12
   15
               pH = 6.5
         1       I        T
              OH
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                                               12
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                                                     OH
                                                                      Free  Cr
I        i         i
                                                               10
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                  [SO=T]
       Figure 147.   Effects of  sulfite  oxidation on the  speciation of Cr.
-------
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   CrF
      pH = 6.5
             80
         C

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         £   60
 40
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                           Cr(OH)3 (s
                                              100
                       Cr(OH)t> + Cr(OH)^ (aq)
                           CrAsO,  (s)
j	i	I
                                               80
                                           c
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                                           I   60
                                    40-
                                               20
                                                0
                                                                           pH = 9.0
                                                                               Cr(OHy;(aq)
j	i	      i
JQ
  -0.16
                                                         jQ-0.16   jQ-1.16 jQ-2.16 jg-3.16 jQ-4.16
         Figure 148.   Effects of sulfite  oxidation on  the  primary distribution of  Cr  species.
-------
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                                                           pH = 9.0
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               CSO=T]
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                                                        [so;T]
Figure 149.  Effects of sulfite oxidation  on  the  speciation  of Cu.
-------
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en
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             80
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             40
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         Figure 150.   Effects of sulfite  oxidation on  the  primary distribution of Cu  species.
-------
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pH = 9.0
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Figure 151.   Effects  of  sulfite  oxidation  on the  speciation  of  Fe
-------
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80
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Figure 152.  Effects of sulflte oxidation on the primary  distribution  of  Fe  species.
-------
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 [SOIT]
                Figure 153.  Effects of sulflte oxidation on the  speciation  of  Pb.
-------
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        Figure  154.  Effects of sulfite  oxidation  on the  primary distribution  of Pb species
-------
             0
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                                              0
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ro
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 151	
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                Figure 155.  Effects of  sulfite  oxidation on the  speclation of Zn.
-------
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tn
            100
                            pH =6.5
             80
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             60
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                 [so;T]
         Figure 156.   Effects  of  sulfite oxidation  on  the  primary distribution  of Zn species.
-------
in the concentration of sulfate complexes  and the decrease  of
free ions.
                                                 2_
     Due to the oxidation of sulfite,  the  Cd(S03)2  species  will
be transformed gradually into the CdS04(aq)  species.   As  can be
seen in Figures 145 and 146, a tenfold decrease  in total  sulfite
concentration will  completely transform the  Cd(S03)£~  species to
CdS04(aq).  The sulfite oxidation,  however,  will  not  affect  the
cadmium solid phase significantly.

     Iron is similar in behavior+to cadmium  as  sulfite oxida-
tion tends to transform the FeS03 complex  to Fe(S04)2  complex.
The solid phase of  iron, however, again remains  unchanged
(Figures 151 and 152).

     Other minor elements studied,' such as chromium,  copper,
lead, and zinc, appear  to be unaffected by sulfite oxidation
(Figures 147-150 and 153-156).  This is because  of the absence
of a sulfite complex,  as well as the constant oxidation states
for these elements  in  the FGD sludges.  Although  the  concen-
trations of sulfate complexes of these elements  show  an increase
during sulfite oxidation, the changes  are  only  minor.
                               258
-------
-------
                            SECTION 8

                       SUMMARY OF FINDINGS
INTRODUCTION

     A conventional  environmental  .impact assessment of flue gas
desul furization (FGD) sludge disposal  would include chemical
analysis and identification of the total concentrations  of con-
stituents in the sludge and its leachate.  However, public health
effects of FGD waste disposal  depend on whi.ch chemical forms  or
species of the constituents are released to surrounding  waters,
and not necessarily  on their total concentration.

     The only feasible means of obtaining contaminant species
information in FGD sludge lies in  thermodynamic modeling.   A
thermodynamic model  can also be used to predict the migration
trends of the constituents when the FGD wastes  age; to estimate
the final concentrations of constituents in the FGD leachate
(aged wastewater), without conducting  expensive field monitoring;
and to predict the effects of operational and chemical changes
i n the FGD wastes .

     Many available  techniques can be  used to construct  and
interpret a chemical thermodynamic model.  In this study,  the
equilibrium constant approach is employed.  This method  involves
solving the stoichiometric equations of various chemical  species,
which are subject to constraints imposed by the equilibrium con-
stants as well as mass balance and charge balance relations.
Diagrams, such as Eh-pH plots, ion-ratio plots, concentration
pH figures, and species distriubtion figures, are then used to
display the stability field and speciation results.

     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 Power Station.  The model is also operated over a  wide
range of operational and chemical  changes to theoretically deter-
mine 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 phospiiates 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.
                               259
-------
METHODOLOGY OF SPECIES ANALYSES

     Two principal  graphical  treatments,  Eh-pH  plots  and  the ion-
ratio method,  are used to describe the  stability  fields of con-
stituents  in  F6D sludge.  The Eh-pH  plot is  employed for con-
stituents 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 con-
stant approach.  The actual  mathematical  equilibrium  model  in-
volves a series of simultaneous equations which  describe  the
various interactions among components  of  the  system.   Seven
general equations are involved, as shown  in  Table 13.  In order
to solve these equations 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
necessary,  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

     The thermodynamic modeling of the  fresh  FGD  wastewater sys-
tem can be  performed as if no solid were  formed  or  dissolved,
because (1) the equilibrium conditions  among  soluble  species
can easily  be  reached, and (2) the rates  of  nucleation and disso-
lution of the  solid species are very  low.  The  predominant solu-
ble species, based upon thermodynamic  calculation,  are summarized
in Table 14.  This table shows that the  major ions  (i.e., cal-
cium, magnesium, potassium, and sodium)  and  the  manganese species
exist as free  ions, in the fresh FGD  wastewaters .

     Other  trace metals, however,  can  be  complexed  considerably
in the same wastewaters.  As  shown in  Table  14,  chloride  corn-
pi exes may  under certain conditions become the predominant
species for cadmium, copper,  lead, mercury,  and  zinc; borate
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
                               260
-------
            TABLE 13.   GENERAL  MODELS  USED  FOR
                  SPECIATION  CALCULATION
                B(1.J)nm[M(1)f][L(J)f]
                      nm      f        f
                                             m      n
                                           M(i)mL(j)n
          KM(i)L(j)    '  RM(i)  L(j)   '  fM(1)  L(j)
[H(Df]  = - E - g - _ - p__g - B - a
                        M(1)  '   L(j)  -  [L(j)f]q
   w T                 U        V
                     YM(i)  '   L(j)  '  [M(i)f]V

 h   a  b

j'l  P=I  S-l  R«(')pUj)q =  1

 g   c  d
 Z   Z  z   RM(i)  L(j)   =  ]

                     k    1    h
[M(i)T]  = [M(1)f]  +   2    Z   _Z  m[M(1)mL(j)n]


          h    a    b
          h    c    d
       +222   n[M(i)  L(j)  ]
         j-1  u=1  v=l       m     n

                     k    1    g
[L(j)T]  = [L(j)f]  +   I    I    Z   n[M(i)L(j)n]
     1          T     m = 1  n = 1  j = 1       m    n

          gab
       +  2    Z    Z    [M(i)L(j)J
         1=1  p=1  q=]       P     q

          g    c    d
       +  2    Z    Z   [M(i) L(o)  1
                            261
-------
TABLE 13 (Continued)
where:
      [M(i) L(j) ]  = concentration of complex M(i)  L(j)   (in
               n    moles/liter)                 m    n

          [M(i)-]  = free metal  ion concentration of ith metal
                    (in moles/liter)

          [L(j),]  = free 'concentration of jth ligand (in
                    moles/1i ter )

          [M(i)j]  = total concentration of ith metal in the
                    system (in  moles/liter)


      RM(DpL(j)q
      and

      RM/.N ./ • \  = mole fraction of solid or gas  species for
           u  ^'v   metal or  ligand solids

                i  = metal species

                j = ligand speci es

                g = total number of metals

                h = total number of ligands

                k = maximum number of metals (M(i) coordinating
                    ligands L(j)

                1  = maximum number of ligands L(j) coordinating
                    metal M(1)

      a,b,c, and d = positive  integer showing maximum number
                    of metals or ligands in the solids or gases

         6(i.j)   = overall  formation constant of complex
               Y  = thermodynamic activity coefficient of soluble
                x   species x.
                               262
-------
TABLE 13 (Continued)
               f  = thermodynamic activity coefficient of solid
                    (or gas) species x (in this study, assume
                    f  * 1 ).
                     x    '

               K  = solubility products or Henry's constants.
                               263
-------
            TABLE  14.   PREDOMINANT SPECIES  OF  SOLUBLE CONSTITUENTS  IN FRESH FGD WASTEWATER
ro
cr>
                    Ionic
     Constituent   Strength
                                                             Predominant  Species
          Al
          As
          Cd
          Ca
          Cr
          Co
0.05

0.8
0.05
0.8
0.05

0.8
0.05
0.8
0.05
0.8
0.05
0.8
        pH = 5
A1F2*(34).A1(OH)2*(20),
A1F2+(17)
AlF2+(55)
H2As04'(98)
H2As04~(95)
Cd2+(50)CdC03(aq)(40)

CdCl+(66)
Ca2+{83)
Ca2+(71)
Cr(OH)2+(79)
CrOH2+(65)
Co2+(69)
Co2+(40),CoS04(aq)(26)
      pH = 7
A1(OH)4-(100)

A1F2+(38),A1F3(31)
HAs042~(68)
HAs042'(78)
Cd2+(49),CdCl+(40)

Cd(S03)22-(59)
Ca2+(89)
Ca2+(71)
Cr(OH)2+(85)
Cr(OH)2+(81)
Co2+(68)
Co2"l'(40),CoS04(aq)(26)
    pH = 9
A1(OH)4-(100)

A1(OH)4-(100)
HAs042"(100)
HAs042'(97)
CdC03(35),Cd2+(21),
  CdClOH2+(20)
Cd(S03)22"(65)
Ca2+(81)
Ca2+(71)
Cr(OH)4-(100)
Cr(OH)4-(100)
CoC03(aq)(44),Co2+(26)
CoC03(aq)(28),Co2+(25),
  CoCl+(20)
-------
     TABLE  14  (continued)
                    Ionic
     Constituent   Strength
                                                             Predominant Species
ro
CTl
en
          Cu
Fe
          Pb
          Mg
         Mn
0.05

0.8
0.05
0.8
0.05
0.8
0.05

0.8

0.05
0.8
0.05
0.8
        pH » 5
Cu2+{54)

CuB(OH)4+(35),CuCl+(26)
F~(25),SnF+(52)
CaF+(40),F~(38)
Fe(OH)2+(83)
FeS03+(97)
Pb2+(55)

PbCl+(33),
PbS04(22),Pb2+(21)
Mg2*(79)
Mg2+(66)
Mn2+(79)
Mn2+(55)
                                                        pH =  7
                                                  Cu(B(OH)4)2(aq)(51)

                                                  Cu(B(OH)4)2(aq)(83)
F~(40),MgF+(44)
Fe(OH)2+(100)
Fe(OH)2*{84)
Pb(B(OH)4)2(aq)(45),
Pb2+(19)

Pb(B(OH)4)2(aq)(87)
Mg2+(79)
Mg2+(66)
Mn2+(78)
Mn2+(55)
          pH = 9
Cu(B(OH)4)2(aq)(97),
Cu(B(OH)4)2(aq)
Cu(B(OH)4)2(aq)(100)
F~(93)
MgF+(47),F"(45)
Fe(OH)4-(93)
Fe(OH)2+(93)
Pb'(B(OH)4)2(aq)(95),
Pb(B(OH)4)2(aq)

Pb(B(OH)4)2(aq)(100)
                                                                           Mg2+(65)
                                                                           Mn2+(76)
                                                                           Mn2+(54)
-------
       TABLE  14 (continued)
                       Ionic
       Constituent   Strength
                                                                Predominant Species
en
cr>
            Hg
            Se
            Na
            Zn
0.05
0.8

0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
        pH = 5

HgCl2(aq)(87)
HgCl3-(47),HgCl42-(26)
HgCl2(aq)(27)
K+(97)
K+(89)
HSe03~(97)
HSeOo~(97)
    O
Na+(95)
Na+(95)
Zn2+(74)
Zn2+(47),ZnCl+(34)
        pH = 7

HgCl2(aq)(62)
HgCl3-(46),

K+(97)
K+(89)
Se032-(74)
Se032-(74)
Na+(95)
Na+(95)
Zn2+{74)
Zn2+(43),ZnCl+(33)
    pH = 9

Hg(OH)2(aq)(65)
HgC10H(aq)(52)

K+(98)
K+(89)
Se032"(99)
Se032~(99)
Na+(97)
Na+(95)
Zn(OH)2(aq)(68)
Zn(OH)2(aq)(42),
ZnC10H(aq)(26)
       Note:  Values in the parentheses indicate the percent of the total  concentration.
       * If one species accounts for less than 50 percent of the total  concentration, then more than one species
         will appear.
-------
chromium and iron.  In the fresh FGD wastewater,  arsenic and
selenium exist primarily as arsenate and selenite species.   The
predominance 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 important role in the speciation of most consti-
tuents .

Aged FGD Sludge

     The speciation of constituents in the solid  and soluble
phases of aged FGD sludge was computed with the assumption  that
the equilibrium condition among all the soluble and solid species
had been reached.  Due to the long  contact period, it is generally
quite possible that equilibrium conditions between solid and
liquid phases can be reached in the aged FGD wastes.  The cal-
culated  results are summarized in Table 15.

     Results show that sulfur dioxide removed from the flue  gas
reacts to form CaS04-2H2
-------
               TABLE 15.  PREDOMINANT SPECIES  OF  CONSTITUENTS IN AGED FGD SLUDGE
ro
crv
00


Ionic
Constituent Strength
A1 0.05
0.8
As 0.05
0.8
Cd 0 05
0.8
Ca 0.05
0.8
Cr 0.05
O.B
Predominant
pH -.5
A1(H2P04)(OH)2(s)
Al(H2P04MOII)2(s)
As°(s)
As°(s)
CdC03(s)
CdC03(sJ
CaS03.l/2H20(s),
CaS04.2H20(s)
CaS03.H20(s),
CaS04.2H20(s)
Cr(OH)3(s)
Cr(OH)3(s)
Solid Species
pll » 7
Al(M2P04)(OII)2(s)
Al(H2P04)(OH)2(s)
As°(s)
As°(s)
CdC03(s)
CdC03(s)
CaS03.l/2H20(s),
CaS04.2H20(s)
CaS03.H20(s),
CaS04.2H20(s)
0{OH)3(s)
Cr
HAs042-{8.82)
HAs042-(10.91)
Cd(S03)22-(7.72)
CdC10H(aq)(6.07)
Ca2*(2.19)
Ca2t(2.0)
Cr(OH)4-(4.03)
Cr(OH)4'(3.99)
-------
       TABLE  15  (continued)
ro
Predominant Solid Species Predominant Soluble Sf
Constituent
Cu

Fe
Pb
Mg
Mil
"9
Ionic
Strength
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
0.05
0.8
pH - 5
Cu2C03(OH)2(s)
Cu2C03(OI()2(s)
Fe(OH)3(s)
Fe(OH)3(s)
PbMo04(s)
PbMo04(s)
— t
— t
— t
— t
Hg°(l)
Hg°(l)
pH * 7
Cu2C03(OH)2(s)
Cu2C03(OI1)2(s)
Fe(OH)3(s)
Fe(OH)3(s)
PbHo04(s)
PbMo04(s)
--t
— t
	 1
— t
Hg°(l)
Hg°(l)
pll = 9
Cu2C03(OH)2(s)
Cu2C03(OH)2(s)
Fe(OH)3(s)
Fe(OH)3(s)
PbMo04(s)
PbMo04(s),
PbC03(s)
Hg(OH)2(s)
Mg(OH)2(s)
HnC03(s)
Mn(OH)?(s),
MnC03(s)
Hg°(l)
Hg°(l)
pH = 5
CuB(OH)/(15.38)
(16.78)*
CuB(OH)/(14.99)
(16.09)
Fe(OH)2*(7.16)
FeS03+(6.98)
Pb2+(5.80)
PbCl+(5.67)
Mg2+(3.91)
Mg2+(0.95)
Mn2+(3.49)
Mn2+(3.56)
HgCl2(aq)(22.1)
HgCU-(19.9)
pH » 7
Cu(B(Olt).)7(aq)
(16.9) * '
Cu(B(OH).)7(aq)
(16.4) * *
Fe(OH)2+(9.16)
Fe(OH)2+(9.12)
PbB(OH)/(5.82)
PbB(OH)4*(5.44)
Mg2+(3.92)
Mg2+(0.95)
Mn2*(3.49)
Mn2*(3.56)
HflCl2(aq)(20.4)
HgCl3-(18.2)
)ec1es
pH = 9
Cu(B(OH)4)2(aq)
Cu(B(OH)4)2(aq)
Fe(OH)4-(10.07)
Fe(OII)4-(8.96)
Pb(B(OH)4)3-(7.14)
Pb(B(OH)4)3-(5.55)
Mg2t(4.16)
Mg2*(1.13)
MnS04(aq)(4.10)
Mn2+(4.33)
Hg(OH)2(aq)(17.9)
HgC10H(aq)(17.0)
-------
           TABLE   15  (continued)
ro
•~-j
o

Ionic
Constituent Strength
K 0.05
o.a
Se 0.05
0.8
Na 0.05
0.8
Zn 0.05
0.8
Predominant
pH = 5
— t
— t
Se°
-------
     Evaluation of the model  in relation  to  analytical  data,  was
performed by comparing the known soluble  concentrations  of con-
stituents in aged FGD wastes  to those predicted  by the  model.
As summarized in Table 16, the calculated results  for aluminum,
arsenic, boron, cadmium,  cobalt, copper,  iron, manganese,  mercury,
potassium,  selenium,  sodium,  and zinc,  either  approach  or  are
very close  to the concentration levels  experienced in the  field.
For other elements (specifically calcium, chromium,  fluoride,
lead, and magnesium), the model was  not as effective.  The low
levels of calcium predicted by the model  are due primarily to
the interaction of calcite with the  Ca-C03 and  Ca-S03
complexes in the model.  The  high levels  of  chromium and lead
calculated  by the model 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 in-
cluded in the model.   The discrepancies also may be due  to (1)
errors in the stability constants and activity coefficients;
(2) the effects of other  mechanisms,  such as adsorption  by hydrox-
ide solids  or clay minerals;  and (3)  the  effects of kinetic con-
straints.

     An evaluation of the thermodynamic model  was  also  performed
according to scientific considerations.  In  general, the model
results behave in accordance  with basic chemical and thermody-
namic principles, including the effects of changing pH,  Eh, and
ligand levels.

EFFECTS OF  FGD SYSTEM AND SLUDGE VARIABLES ON  CHEMICAL  SPECIATION

     For the purpose  of selecting a  sludge treatment or  disposal
procedure,  it is useful to observe the  possible  beneficial or
adverse effects of operational or chemical changes in an FGD  sys-
tem on sludge speciation.  The chemical changes  studied  here
include those of pH,  ionic strength,  chloride  concentration,
borate concentration, sulfate concentration, and sulfite oxida-
tion.  Table 17 summarizes the qualitative results.   The opera-
tional changes studied were limited  to  the addition of  lime,
silicates,  hydrogen sulfide,  phosphates,  and magnesium  to  the
FGD system.  The results  are  summarized in Table 18.

     A change in pH can influence the direction  of the  alteration
processes (dissolution, precipitation,  adsorption, or complexa-
tion), in any chemical system.  In general,  a  pH increase  in  the
FGD sludge  system tends to dissolve  more  elemental constituents,
such as As°(s), Hg°(£), and Se°(s),  and to transform some  of the
carbonate,  phosphate, or  other solids 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.
                                271
-------
      TABLE 16.   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
Model Reason for Discrepancy
Excellent
Good
Excellent
Excellent
Not applicable Form strong CaCOgfs) when pH >7
Not applicable Form strong Cr-OH complexes
Good
Excellent
Not applicable Solubility-controlling solid unknown
Good
Not applicable Form strong Pb-C03 and Pb-OH
compl exes
Not applicable Solubility-controlling solid unknown
Excellent
Excellent
Good
Good
Good
Excellent

* Based on  comparison of modeling  results with Kansas City Power  and Light
  FGD sludge  analysis.

t "Excellent" means that the migration  trends of the constituent  follow those
  predicted by the model, and 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.

                                   272
-------
                                TABLE  17.   EFFECTS  OF  CHEMICAL  CHANGES  ON  THE  SPECIATION  OF
                                                         CONSTITUENTS   IN  FGD  SLUDGE
     Constituent

         Al
ro
>-j
CO
         As
         Cd
Solid:   High pH levels
favor the  formation of
A1203'3H20(S), low pH
levels  favor the for-
mation  of  A1(II,PO.)
(OH)2(s)      f  *

Soluble:   When pH Is
higher  than about 6,
the predominant
species will change
from A1F2  to A1J -OH"
complexes

High pH levels tend to
dissolve As°(s) and
form arsenate species
Solid:   When pH Is
higher  than 10.5,
CdC03(s) may grad-
ually transform to
Cd(OH)2(s)

Soluble:  High pH
level  can lower the
total  Cd level
    Ionic Strength

Negligible (when re-
lated llgand concen-
trations are unchanged)
   Chloride
 Concentration

Negligible
   Borate
Concentration

Negligible
Negligible
The relative distri-
bution  of Cdz+ and
Cd-Cl complexes can
be altered by Ionic
strength changes
Negligible
Negligible
     Sulfate
  Concentration

Negligible
Negligible
Can greatly affect  Negligible      Cd-SO.  complex
the total  soluble
Cd levels  when chlo-
ride Is higher than
certain levels
                                                                                                  may become  predom-
                                                                                                  inant when  Cl",
                                                                                                  SO
                      or OH"
                                                                                                  complexes  are not
                                                                                                  significant
    Sul f 1 te
   Oxidation

Negligible
                                                                                                                       Negligible
Negligible,  if the
redox potential Is
not controlled by
sul fate/sul flte species

Will  reduce  Cd(S03)o2"
and Increase CdSO^ faq)
levels.   However,
effects  on  total solu-
ble Cd and Cd solids
are negligible
-------
    TABLE  17   (continued)
Cons t1 tuent pll
Ca Solid: CaC03(s) may
Ionic Strength
Negligible
Chloride
Concentration
Negligible
Borate
Concentration
Negligible
Sul fate
Concentration
When pH >5, and the
Sul flte
Oxidation
Will convert the sul-
ro
         greatly Increase In the
         sludge when pH >7

         Soluble:   When pll >7,
         the total  Ca and Ca^
         are reduced signifi-
         cantly

Cr       Solid:  Cr(OH)3(s) is         Negligible
         significant when pll
         ranges from 6 to 9

         Soluble:   When pll 1s
         higher than about 4,
         the predominant species
         will  change from Cr^
         to Cr-OH complexes

Cu       Solid:  Negligible           Negligible

         Soluble:   When pll
         >4.8, the  predominant
         species will  change
         from Ctr   to Cu-
         BfOII)^ complexes
Fe       Solid:   Negligible           Negligible

         Soluble:   High  pll
         levels  (pH >8.5) tend
         to Increase Fe-OH"
         complexes, but  reduce
         the total  Fe levels
                                                                  Negligible
                                                                 When pH <4.7.
                                                                 Cu-Cl com-
                                                                 plexes may become
                                                                 predominant when
                                                                 the chloride
                                                                 level Is higher
                                                                 than 2,000 ppm
                                                                 Negligible
Negligible
                                                                                                      sulfate level Is
                                                                                                      higher than about
                                                                                                      5,000 ppm. the CaS04
                                                                                                      (aq) species may
                                                                                                      become predominant
Negligible
                                        fite solid into sul fate
                                        or carbonate  solids.
                                        However,  will  have very
                                        little effect  on
                                        soluble Ca
Negligible
When the bor-
ate level in-
creases from
5 ppm to 200
ppm, the solu-
ble lead level
can be Increased
about 2.000

Negligible
Negligible
Negligible
Negligible
Will transform FeS03*
to Fe(SO)2", but the
solid phase will remain
unchanged
-------
      TABLE  17  (continued)
Constituent pll Ionic Strength
Pb Solid: When pit <9, Negligible
PbMo04(s) is predomi-
nant; otherwise, PbC03(s)
is predominant
Soluble: At high pH
levels, Pb-CO, may
Increase the total Pb
levels
Chloride
Concentration
When ptl >7, Pb-
Cl complexes may
become predominant
when the chloride
level is higher
than 1,500 ppm
Borate Sulfate
Concentration Concentration
When the bor- Negligible
ate level In-
creases from
5 ppm to 200
ppm, the solu-
ble lead level
can be Increased
about 10,000
times
Sulfite
Oxidation
Negligible
ro
-•j
01
Mg      Solid:   High  pH  levels        Negligible
        (pH >9)  favor the  for-
        mation of  Mg(OH)2(s)

        Soluble:   When pH  Is
        increased, the MgSO
-------
      TABLE  17   (continued)
Chloride Borate Sulfate Sulfite
Constituent pH Ionic Strength Concentration Concentration Concentration Oxidation
llg Low pll levels favor the Negligible When the chloride Negligible Negligible
If the redox poten-
IV)
^4
CT>
          Se
         Na
formation of Hg°(l) In
the sludge.  High pH
levels tend to Increase
the soluble levels of
HgCl,, HgCl3-,
Hg(OH)2(aq), and
HgClOHtaq)

Slightly reduces the K*      Negligible
levels when pll Is
Increased
High pll levels tend to       Negligible
dissolve Se°(s) and
form selenate species
Will slightly reduce         Negligible
the Na  levels when
pll Increases
                                                                   level varies from
                                                                   50 to 6,000 ppm, the
                                                                   total soluble Hg can
                                                                   be Increased for
                                                                   more than four orders
                                                                   of magnitude
                                                                   Negligible
                     Negligible
Negligible
Negligible
Negligible
Negligible
                Can affect the
                KoS04(aq)  level.
                Will not,  however,
                affect the total
                soluble level  of  K
Negligible
Can affect the
Na~S04(aq) level.
Will not, however,
affect the total
soluble level  of Na
                                                          ttal Is controlled
                                                          by sulfate/sulflte
                                                          species, sulflte oxi-
                                                          dation can Increase
                                                          the soluble Mg level
Will Increase the
K2S04(aq) 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/sulflte species,
sulflte oxidation can
increase the soluble
Se level

Will Increase the
NapS04(aq) level and
reduce the Na  level.
But will not have a
significant effect on
total  soluble Na
-------
      TABLE  17  (continued)
Constituent pll
Zn Solid: High pH levels
Ionic Strength
Negligible
Chloride
Concentration
When pH <9, the
Cor ate
Concentration
Negligible
Sulfate
Concentration
ZnSO.(aq) may
Sulflte
Oxidation
Negligible
                     favor the formation  of
                     Zn(OH)2(s).  When pll
                     decreases, ZnS10->(s)
                     will replace Zn(OH)2(s)

                     Soluble:  Will reduce
                     total levels when pH
                     Increases
total  soluble Zn
exists predomi-
nantly as  ZnCl* if
the chloride level
Ishlgher than
3.000  ppni
become predominant
at a pH around 9
when Cl- and Oil'
complexes are not
significant
ro
-------
                                TABLE  18.   EFFECTS  OF  ADDITION  OF  CHEMICAL  COMPOUNDS  ON  THE
                                                SPECIATION  OF  FGD  SLUDGE  CONSTITUENTS

Addition of
Constituent Lime
A1 Effect on total soluble
Addition of
Silicates
The soluble Al level can
Addition of
Hydrogen Sulflde
Negligible
Addition of
Phosphates
Effect on total soluble
Addition of
Magnesium
Will not affect the total
ro
>~j
oo
                 Al  Is negligible
As      Lime addition can cause
        more Ba3(AsS04)2(s) to
        form, so reduce the
        total soluble As
        slightly

Cd      When the lime dosage is
        higher than  1,500 ppm,
        soluble Cd can be
        Increased from 0.01 ppb
        to 1.45 ppb

Ca      When the dosage of lime
        is from 100  to 10,000
        ppm, the total soluble
        Ca will Increase from
        200 ppm to 400 ppm

Cr      Lime addition tends to
        Increase the total
        soluble Cr due to
        hydroxide complexes
        formation
be greatly reduced when
silicate addition Is
higher than 280 ppm as
Si

Negligible
                                         Negligible
                                         Negligible
                                         Negligible
                                                                 Negligible
                        Cd can be reduced to
                        trace levels when sul-
                        flde addition is higher
                        than 0.2 ppm
                        Negligible
                        Negligible
                                                                                 Al  Is negligible
Negligible
When phosphate addition
Is higher than 310 ppm
(as P), 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
                        soluble Al
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 CrF*+
reduction
-------
         TABLE  18  (continued)
ro
                   Addition of              Addition of
Constituent           Lime                    Silicates

    Cu       Lime addition tends to    Negligible
             Increase soluble Cu,  but
             will not raise the
             soluble Cu above the
             detectable level

    Fe       When the lime dosage  Is    Negligible
             higher than 1,500 ppm,
             the soluble Fe level  will
             be Increased from 0.012
             ppb to 22 ppb

    Pb       Lime addition tends to    Negligible
             Increase the total  sol-
             uble Pb due to carbon-
             ate complex formation

    Mg       Lime addition will  only    Negligible'
             affect the total soluble
             Mg slightly but will
             significantly transform
             Mg-COj complexes
             Mn        Lime  addition  tends to    Negligible
                      reduce the  soluble Mn
                      to  the 20-36 ppb range

             Mg        Lime  addition  tends to    Negligible
                      Increase  the total sol-
                      uble  Kg slightly due
                      to  an Increase  In pll
                                                                                Addition of
                                                                              Hydrogen Sulf1de

                                                                         Cu can be reduced to
                                                                         trace levels by adding
                                                                         as little as 0.001 ppm
                                                                         of sulflde
                                                                         Negligible
                                                                         Pb can be reduced to
                                                                         trace levels by adding
                                                                         as little as 0.001 ppm
                                                                         of sulflde

                                                                         Negligible
      Addition of
      Phosphates
                                                                Negligible
                                                                llg can be reduced to
                                                                trace levels by adding
                                                                as little as 0.001 ppm
                                                                of sulfide
Negligible
Negligible
Negligible
Soluble Mg will be
reduced about 2.5
times as the phos-
phate level Is
Increased from 0.3
to 3,100 ppm (as P)

Negligible
Negligible
      Addition of
       Magnesium

Will not affect the total
soluble Cu
Will not affect the total
soluble Fe
Will not affect the total
soluble Pb
Mill cause the increase of
soluble Mg
Will not affect the total
soluble Mn
Will not affect the total
soluble llg
-------
    TABLE  18   (continued)
    Constituent
      Addition of
         Lime
      Addition of
       Silicates
ro
oo
o
        Se
        Na
        Zn
                 Negligible
Lime addition will  In-
crease the total  soluble
Se due to an increase
In pH

Negligible
Lime addition may
Increase the total
soluble Zn to ppm
1 evel s
                          Negligible
Negligible
Negligible
The soluble Zn  level
Is reduced when sili-
cate addition exceeds
280 ppm as SI
       Addition of
     Hydrogen Sulfide
      Addition of
      Phosphates
                         Negligible
Negligible
Negligible
Zn will  be reduced  to
trace levels when sul-
fide addition is higher
than 0.5 ppm
                          Negligible
Negligible
Negligible
Neglfglble
      Addition of
       Magnesium

Magnesium addition may
decrease the KoS04(aq)
level, but will  not affect
the total soluble K

Will not affect the total
soluble Se
Magnesium addition may
decrease the Na2SO.(aq)
level, but will  not affect
the total soluble Na

Will not affect  the total
soluble Zn
-------
     The overall  effects  of pH on  the  total  constituent  concen-
tration depend on the solubility constants  of the  new  solids
formed, the new ligand concentrations,  and  the formation  con-
stants of the complexes.   For example,  a  high pH  level  can  in-
crease 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  concen-
trations occur in the neutral pH region.

     Although a change in ionic strength  in the FGD sludge  can
affect the stability constants, its  effect  on the  soluble  levels
of constituents,  or on the stability fields of various  solids,
are usually negligible if their related ligand levels  are  un-
changed.  The soluble chloride concentration of the 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 concentrations.   The soluble  sulfate concentration may
affect the total  soluble  calcium,  magnesium, cadmium,  and  zinc
concentrations.  In general, if the  total soluble  levels  of the
above-mentioned ligands (e.g., chloride,  borate,  and sulfate)
are known, the total soluble metal  concentrations  in the  aged  FGD
leachates can be  approximated without  extensive computation.

     With regard  to operational changes,  sulfite  oxidation  may
reduce the concentration  of sulfite  complexes and  increase  the
concentration of  sulfate  complexes,  but will have  very  little
impact on the total soluble concentration of most  metals.   The
most significant  effect of sulfite  oxidation is the transforma-
tion of CaSOs-l/2H20(s ) to CaS04 .2H2d(s)  or CaC03(s),  depending  on
pH levels.  This  transformation may  affect  the soluble  levels  of
arsenic, mercury, and selenium if  the  redox potential  is  con-
trolled by sulfate/sulfite species.

     The addition of lime to the FGD sludge has been employed  in
pozzolanic fixation processes for  the  purpose of  improving  the
engineering properties of the dewatered sludge.  However,  the
model  shows that  lime addition may  have an  adverse effect  on
constituent solubility.  The addition  of  lime to  FGD wastes may
reduce the total  soluble  levels of  certain  constituents  such  as
arsenic and manganese.  However,the  total soluble  levels  of most
other trace toxic metals, such as  cadmium,  chromium, copper,
lead,  mercury, selenium,  and zinc,  increase in aged FGD  sludge
following lime addition.   This may  actually increase the  poten-
tial for environmental damage, should  the concentration  increase
outweight the dilution factor decrease  which results from  per-
meability reduction.

     The addition of silicates may  reduce the total soluble alumi-
num and zjnc  concentrations, but other  elements studied  are vir-
tual 1y unaffected.
                                281
-------
     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  the  addi-
tion of phosphates is  not recommended  for the treatment of  FGD
wastewater.

     Hydrogen sulfide  addition may reduce the soluble concentra-
tions of trace metals  substantially,  as  shown in  Table  18.  This
operational  change,  however,  may  not  be  desirable for an FGD
system  for two reasons:  (1)  hydrogen  sulfide itself  is a  pollu-
tant, 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 has been shown to  improve  the  efficiency of  wet
FGD systems; the use of high  magnesium reagents could therefore
become  commonplace.   The model shows  that,  in general,  the  mag-
nesium  addition will not significantly affect the total soluble
levels  of most constituents.
                               282
-------
                            SECTION 9

                 CONCLUSIONS AND RECOMMENDATIONS


     1.   Thermodynamic modeling of chemical  speciation  in  FGD
sludge has shown that  sludge constituents  can  exist in  a  wide
variety  of chemical  forms or species.  The predominance and  con-
centration of any particular chemical species  are  influenced by
chemical  factors such  as pH, Eh, ionic strength,  and  total  con-
centrations of ligands and metals in the system.   Although  the
FGO chemical  systems are extremely complex, .the  speciation  of
their elemental  constituents can be quantified by  calculation
with reasonable  accuracy.

     2.   The  thermodynamic approach indicates  that, in  most  FGD
systems  (ionic strength (I) of 0.05 to 0.8,  and  pH of 3 to  11),
the major solid  species for metals are usually sulfates,  sulfites,
carbonates, and  hydroxides.  Silicate, phosphate,  elemental
metal, and molybdate solids may also become  the  predominant
solid species under  certain conditions.   Based on  the pH,  Eh,
and various related  ligand conditions, the predominant  solid
species  of most  elemental constituents in  the  FGD  system  can be
derived.   The solids which will predominate  for  the sludge  con-
stituents of  concern are as follows:

     Aluminum -  Al 203 • 3H20 ( s ), AlPO^s) and  Al ( H2P04 ) ( OH )2 ( s )
     Antimony -  Sb(OH)3d2 (s)
     Arsenic  - As°(s)
     Cadmium  - CdCOaU) and Cd(OH)2(s)
     Calcium  - CaS04 • 2H20(s), CaSOs • 1/2H20(s )  , and CaCOsls)
     Chromium -  Cr(OH)3(s)
     Copper - Cu2C03(OHJ2(s) and Cu(OH)2(s)
     Iron - Fe(OH)3(s) and FeC03(s)
     Lead - PbC03(s),  Pb(OH)2(s), Pb3 (OH ) 2(COs ) (s  ) , and PbMo04'(s)
     Mercury  - Hg°(£)
     Manganese - MnOOH(s), MnC03(s), Mn(OH)2(s),  Mn304(s) and Mn02(s)
     Nickel - NiCO^(s) and Ni(OH)2(s)
     Selenium -Se°(s)
     Zinc - ZnSi03(s), ZnC03(s), and Zn(OH)2(s)

     3.   The  results of thermodynamics calculations also  show  that
the relative  distribution of various soluble species  in fresh  and
aged FGD  sludges are quite similar.  Stated  another way,  although
the aging process may  reduce or increase the total soluble
                              283
-------
concentration of constituents,  the primary soluble species
(specieswhich predominate,  or whose concentration  may become
significant  in the leachate)  is common  to  both  conditions.   For
each constituent,  only a  few  species  may become predominant  for
a given FGD  condition.  These soluh.le. species  are  as  follows:

     Calcium - Ca   ;  Ca-S04 complexes
     Magnesium - Mg2*; Mg-SO^ complexes
     Potassi urn - + K
     Sodium-Na2+
     Cadmium - Cd   ;  Cd-Cl  complexes; Cd-CO., complexes;
               Cd-S03 complexes;  Cd-S04 complexes
     Chromium - Cr3 + ; Cr-OH complexes
     Copper  - Cu'+; Cu-B(OH)4 complexes; Cu-Cl  complexes
     Iron -  Fe-OH  complexes;  Fe-S03 complexes
     Mercury -2Hg-Cl  complexes; Hg-OH complexes
     Lead -  Pb  ;  Pb-B(OH)4 complexes;  Pb-Cl complexes;
            Pb-C03 complexes
     Zinc -  Zn2 + ;  Zn-Cl  complexes; Zn-OH complexes

     4.  Knowledge of the relative distribution of constituent
species "in the FGD system is  useful for (1) the evaluation  of
general toxicity,  and (2) predicting  the migration of the con-
stituent in  the environment.   Although  it  was  impossible to
consider all the possible FGD conditions in this study,  the  cal-
culated results for the boundary conditions (ionic strength  of
0.05 and 0.8) do provide  a  range of the possible species concen-
trations.  Most FGD sludges are expected to fall within  these
boundary conditions.   The boundary results can  be  viewed in
Figures 1 through  81, in  the  main text  of  this  report.

     After the primary solid  and the  soluble species  are identi-
fied by the  methods of this study, the  total soluble  constituent
concentrations in  the aged  sludge can be calculated without  the
aid of a computer,  The concentrations  of  free  ions can  be
approximated by solving the mass equation(s)  of primary solid(s)
solubilities.  The concentrations of soluble primary  species can
then be solved by  the mass  equations  which, including the free
soluble ions and the  complex  formation  constraints, are  described
in Section 2.  The summation  of the primary soluble species  for
each constituent,  will provide its estimated total level in  the
sludge liquid phase.   Equations 73 through 83 are  examples  of
this type of calculation.

     5.  When assessing the potential impacts of FGD  sludge
leachate on  groundwater,  examination  of data from  aged FGD
wastes is most appropriate.  Most in  situ  FGD sludges have  a low
permeability  (10-4 to 10-10 cm/sec) (Ref.  1, 46) which provides
months to years of contact  time between leachate and  sludge.
During this  period, various chemical  species in the FGD sludge
(either fn the solid  or soluble phases) would gradually approach
equilibrium.  Unfortunately,  there is a lack of documented
                              284
-------
information relating to the chemical  species  present in  aged
FGD waste,  due to the similar lack of long-term FGD operations.
Therefore,  the thermodynamic model can be useful  for predicting
both the concentrations of various species,  and the total  solu-
ble concentrations of constituents in aged FGD sludge.   The
background  required for the calculation need  include no  more  than
the total  levels of the constituents  in the  fresh FGD waste.   This
thermodynamic approach could provide  a considerable cost saving
over the traditional field survey.

     6.   The thermodynamic model  discussed here can also be  used
to predict  solid or soluble species changes,  and  changes in  the
levels of total  soluble constituents  caused  by operational  or
chemical factors.  Examples of these  sensitivity  calculations
are presented in Section 7, and are summarized in Section  8.
The soluble constituent concentrations at the boundary conditions
(ionic strength  of 0.05 and 0.8)  are  displayed in Figures  157
through  167.  The shaded areas indicate the  ranges  of possible
total  constituent concentrations  in the aged  FGD  wastes.  These
values may  be used for rough estimation of the total soluble
constituents in  various aged FGD  leachates.   Only those  elements
for which the model projections agree with the analytical  results,
are shown.

     7.   The thermodynamic model  employed in  this study  was  found
to be  inaccurate when predicting  the  speciation of  calcium,
chromium,  fluoride, lead, and magnesium.   The disparity  may  have
been caused by several factors, including adsorption fay  various
solids or the kinetic constraints of  the  reactions.  The specia-
tion of  other constituents, such  as aluminum, arsenic, cadmium,
boron, cobalt, copper, iron, manganese, mercury,  potassium,
selenium,  sodium, and zinc, showed very close correlation  with
the analytical results.  More study is therefore  suggested  to
(1) verify  the model against different types  of FGD wastes,  or
(2) include more of the controlling factors  in the  model.
                              285
-------
        300
         250
    .a
    O.
    a.
         200
    .a
    3
    ^   '1501
         100
                                                     11
Figure 157.
Range of aluminum concentrations  in  aged  FGD
sludge leachates by thermodynamic model calcu-
lation.
                              286
-------
      12,000,
  _  10,000
  .a
   CL
   CL.
8,000
   
-------
       1200
                                                    11
Figure 159.
Range of cadmium
sludge leachates
1 a t i o n .
concentrations in aged FGD
by thermodynamic model calcu-
                            288
-------
    E
    Q.
    O.
   CO

   
-------
£
Q.
a.
o
o

a>
3


O




to


o
Figure 161.
          Range of cobalt concentrations in aged FGD
          sludge leachates by thermodynamic model calcu-
          lation.
                        290
-------
     10
     10-12
                                                   11
Figure 162.
Range of copper concentrations in aged FGD
sludge leachates by thermodynamic model  calcu-
lation.
                           291
-------
      J3
      Q.
      a.
       
-------
     E
     O.
     Q.
     C
     s

     O)
     O
     C/1
     
-------
       60
       50-
    £
    n.
    CL
    O)

    .Q
       40
       30
        2.0
        10
                                    I = 0.8
                     I  =  0.05
                                                    11
                               PH
Figure 165.
Range of potassium concentrations
sludge leachates by therraodynamic
1 at ion.
in aged FGD
model  cal cu^
                           294
-------
      3000
      2500-
      2000^
   OJ
      15006
   ITS
   -M

   O
      .10006
        500
                                                    11
Figure 166.
Range of sodium concentrations  in  aged FGD
sludge leachates by thermodynamic  model calcu
1 a t i o n .
                            295
-------
      24000
       20000-
   O.

   Q.
   £=

   M
   
-------
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     Special  Reference to  Copper, Lead,  Cadmium  and Zinc.
     Talanta, 24:151-158,  1977.

41.   Smith,  R.G.,  Jr.   Evaluation of Combined  Applications of
     Ul trafi 1 tration and  Complexation  Capacity Techniques  to
     Natural  Waters.  Anal.  Chem. 48:74-76,  1976.

42.   Florence, T.M. and  G.E.  Batley.   Trace  Metals  Species in
     Seawater -  I.  Removal  of  Trace Metals  from  Seawater  by
     a Chelating Resin.   Talanta, 23:179-186,  1976.

43.   Chan, Y.K.  and K.L.  Chan.   Determination  of  Labile and
     Strongly Bound Metals in Lake Water.   Water  Res.,  8:383-388,
     1974.

44.   Karger,  B.L., L.R.  Snyder, and C.  Horvath.   An Introduction
     to  Separation Science.   Wiley, New- York,  1973.

45.   Batley,  G.E.  and  T.M. Florence.   Determination of  the
     Chemical Forms of Dissolved  Cadmium,  Lead and  Copper  in
     Seawater.  Marine Chem., 4:347-363,  1976.

46.   Radian  Corporation.   Evaluation of the Physical  Stability
     and Leachability  of Flue Gas Cleaning Wastes.  Electric
     Power Research Institute,  November 1977.
                               300
-------
                     APPENDIX  A.   STABILITY CONSTANTS OF SOLUBLE METAL  SPECIES
OJ
o

Species Ligand
A13+ S04=
F"
OH"
Ba24" OH
Be21" S042"
Cl~
F"
OH"
Cd2+ C032"
so42~
Cl"
F"
Br"
I"
po43-
N03-
OH"
OH"
fa2+ rn
l» a LU o
so42"
F"
on 3-
Log p^
3.2
6.9
9.5
1.2
1.9
1.6
5.6
7.7
5.4
2.3
2.2
1.1
2.1
2.4
3.9
0.7
4

3.0
2.3
1.1

Log
4
13
18

3

9



2
1
2
3


7

11



p9 Log Pi Log ft, Log p^ Log pfi Log K
.8
.0 16.9 19.5 20.8 20.5
.5 27.0

.0 2.0

.7 12.7
-
tCdOM**)
! tCdr*]tCl"3[H*]

-, n 1 ' 1 r [CdClOHl.qU
*/ ^ • J. J. * D ~~ 9+ • IT
.5 2.2
.9 3.2 3.7
.5 5.2 6. 1

CCdjOM3*)
.6 8.7 8.5 [cdz*)zto»n
4 4
[Cd } [OH* I
, ft [C»COjH



(c«lP04)H(>al)
K








12. 2

-6.7





54.6
23.1
11.6


1/1 £
-------
     APPENDIX  A (continued)
o
ro
Species Li

Co2+ CO
SO
Cl
Br
PO
OH

Cu2+ CO
SO
n
U 1
F"
Br
I"

PO
PO
B(
OH
Cr3+ SO
Cl
F~
Br
PO
OH
gand

3
4
™"
-
4
—

0
J
4
-

-


4
4

2-
2-


3-


2-
2-





3-
3-
OH)4~
4
"•

-
4
~
2-



3-

Log

5.
2.
1.
0.

4.

6.
2.
i
A .
1.
1.
9.



7.
6.
2.
0.
4.
-1.

-10.
Pi

4
5
4
6

8

7
3
f.
\J
3
1
7



1
1
7
8
5
9

7
Log



1


9

9

2
C.
-0
9



12
i f\
10
1
9


19
P9 Log (3., Log (3A Log (3^ Log pfi Log K
UoCO,H*J
9
[C.^JtCo'-UH*]
lCDro4HU«))
(Co!*HPoJ"KH*l
.7


.7 10.8
CCuCOjH ]

. 9 ![CuZ*]tCOj-]tH*l
' (CuCOjIOH)'2)
tC^^JICflj^HOH-]2
0 1 0 1 A (CuClOM(.q)!
tCu JlCl JlOH J
.3 -1.8 -4.0
.5
{CuCO.NItl)))

tt«z*][ro43-KH*J
ItuPO^Hj'1]
ttMZ*]tMj*][M']*
.4
7-irrt 1£"1
15.2 16.1 [CU!*]ZCOH-JZ
.9
.1 11.3

[CrFOtH*]
[tr4*J[l>oJ-}tH*)
.2 18.2
K

12.3
15.0





12.5
-13.0
-4 9
~ • -*



16.0
21.3
n-i
. 7



21.5

-------
APPENDIX A (continued)
Species Ligand Log pt Log ^ Log {3q Log p
H+ C032-
so42-
F"
s2-
P043~
P0«
" -
P04
sio2(OH)22-
o B(OH)4-
CO o
so32-
Mo042"
As043"
HVOd2"
2
SeOo
1+ 9
Fe3+ S04^
CT
F~
Br~
I
po43-
^in-/nu\.2-
10.2
2.2
3.0
14.0
12.5



13.1
9.1

7.3
4.3
11.8
8.2

8.5
4.1 5.6
1.4 2.1 1.3
5.6 10.2 12.9
0.7 0.5
3.5 2.4


4 Log P5 Log pg Log K K
[Hzco3i.,n
[M*)2!^-) 16.5


(HgMxin
H.4!1?*-*! 21.2
, [«,»»,-)
:tM*]lc»oJ-i 19.9
{[H.ro.ito)]
T * O 1 O
fH 1 fPO 1
1 fH2slo?10H1?i oo 7




[H AtO "3
tH^tMOp 18.8

[H itO,l.q))
« J
CM )'[s«0j ] 1 1 . t





ffeP04M*)
[FeS*UfoJ*]tH'*] 20 . 7
2 ? 1 0 C
-------
APPENDIX A (continued)
Species


Fe2 +




Pb2 +











Mg2 +





Li gand
B(OH)4-
OH~
so42~
CT
P043~
OH"

co32~
co32=
so42-
Cl~
Br~
I-
B(OH)4~
OH"

All""
OH
OH~
co32-
so42-
F~
P043"

OH"
Log (3j
8.9
11.8
2.3
0.9
21.6
5.4

7.4

2.7
1.7
1.9
1.8
5.2
6.3
-7.7



3.2
2.4
1.8



Log p2 Log p3 Log p4 Log P5 Log p6 Log K
15.8
21.8 28.8 tF.VtoH-]2


23.9
24.8
(PbCO.H ]
3
10.8 [pbz*uco*-UM']
CFbtCOjIjHjItq)]
[Pbz*)iCcoi']ztM*3

CPbC10H(iaH
t.u C.O t.U tPb KC) HOH")
3.2 3.8 3.9
3.6 4.2 4.4
11.1
10.9 13.0 tPbX'J
-17.1 -28.1 CPb**]*{OH']
CPbjIOMlJ*]
CPb*^]JCflM"]4
CPbjIOHlJ*)

CM9'CO~H*]
fMa^^K COz"lfH*3


CN9iP04)H(tq|]
CM.'*][P044-KH*]
[HgOH']

CMjZ*)tOH']
K

25.1





13.2
25.4

-6.6




7.7
O f\ 1
30. 1
68.4
11.6


15.1

3.8
-------
APPENDIX A (continued)
Species Ligand
O i f\
Mn^+ C03^
so42"
Cl"
Br"
po43-
OH~
O _L O
Hg C^3
so42~
O i
£ Hgz+ Cl~
F-
Br"
I"
S2-
OH~
OH"
O 4- O
Ni2+ C032-
so42-
CT
F~
Br"
po43-
OH"
Log Pj Log P2 Log p3 Log p4 Log p5 Log pg Log K
(HnCO.H*!
J
tHr.Z*]tCof"HH*]
2.3
1.1 1.1 0.6
0.9 0.8
[Mol>04N(<4>}
tHn'*KP04J-HH*]
3.9 9.8
IMjCOjH*]

2.4 3.5
(HgClOHliqH
7f\ -\ \ c\ 1 i~ 1 1 r fl .
.2 14.0 15.1 15.4 tHdz*Kcri[M*)
1.6
9.6 18.1 20.5 24.0
13.4 24.6 28.4 30.3
IHsSjHjUql)
54 . 2 tH,z*]£iz-)
-------
      APPENDIX A  (continued)
CO
o
en
Species
K +
Ag+









Na +
Sn2 +


Zn2+







L1 gand
F~
so42"
CT
F~
Br~
I"


s2-
so32-
OH~
so4-
F~
Br~
OH"
so4-
H
ci -
F~
Br~

OH~

Log Pj
1.1
1.1
3.1
0.4
4.3
14.0



5.6
2.0
0.7
6.9
1.1
10.8
2.3

1.4
1.3
0.9

4.5

Log p2 Log P3 Log p,, Log P5


4.9 4.9 5.1

7.3 8.0 8.7
13.9

17.3

7.9
4.0

9.7 10.2
1.7 1.4



1.7 0.8 1.2

0.9 0.3 0

11.1 13.6 14.8

Log P6 Log K K






: [AgSHI.nl]

[A,*HS-HH*] 14.0
...^Ll^ 19.0







ClnClOMtial]
tz»z*ncruoiri -7.0


; [InPO.Hllq)]
-t r~ JT.

ClOjOH3*] c
                                                                                         [I«^*]Z[OM-]
-------
                           APPENDIX  B

                 CHEMICAL ANALYSIS  OF  FRESH  AND
                     AGED FGD SLUDGE SAMPLES
     In order to verify the thermodynamic  model  used  In  this
study,  chemical  analysis of fresh  and  aged FGD  wastes  were  per-
formed.  This section describes  the  sampling  procedures  and
analytical  methods used.

SAMPLING PROCEDURE

     Samples of  FGD sludges and  wastewaters  were collected  on
October 18-19,  1977,  at the Kansas City Power and Light  La  Cygne
Power Station.   The following is a description  of the  methods  used
to collect, prepare,  preserve,  and transport  the samples taken.
Sample Container Preparation
     The sample containers (1- and 4-liter capacities),  caps,  and
filtration syringes  used were made of polypropylene  material.
This equipment was soaked in a solution  of 5-percent nitric  acid.
The containers, cap,  and syringes  remained in  the  acid  solution
for 24 hours.  Upon  completion of  the acid soak,  the containers,
caps, and syringes were immediately rinsed three  times  each  with
doubly distilled deionized water.   Upon  vigorous  shaking off of
excess water, the caps  were placed on the  containers and stored.
The syringes were shaken of excess water and  then  wrapped in para-
film to prevent contamination.

Sample Col 1ecti on

     Approximately 125  ml of sludge were drawn from  the  sludge
effluent lines of each  of the eight scrubbers.  The  eight 125-ml
aliquots of  sludge were then placed into a 1-liter polypropylene
bottle and allowed to settle for 4 hours.   Upon  settling, a  150-ml
aliquot of the supernatant was then drawn  from and filtered
through a 0.45- m Millipore filter.  Two 75-ml portions  of the
filtrate were then placed in a separate  600-ml polypropylene
bottle.  The sample  container identified for  metal  determination
was then acidified with ultra-pure nitric  acid to  a  pH  of 1.
Both sample  containers  were then refrigerated  at  5°C until  the
next sampling addition.  The final volume  of  each  subset sample
was 600 ml .
                               307
-------
Fresh Wastewater--
     The composite sample was taken  six times  during  a  24-hour
period over two consecutive days.   The sample  consisted of two
subset samples (refer to Table 81).   The subset  sample  identified
as 2876-KAN-RW-l  was designated for  metal  analysis  only;  sample
2876-KAN-RW-2 was used for all other analyses.

Fresh Sludge--
     The fresh sludge composite sample was taken at the same time
intervals and fashion as the fresh  effluent.   A  2.5-liter aliquot
was taken from each of the sludge  effluent lines and  placed in a
20-liter polypropylene container.   Upon settling (4 hours), the
supernatant was discarded and approximately 500  ml  of settled
sludge was transferred to a 4-liter  polypropylene container.  The
sludge composite sample was then refrigerated  (4°C).   Part of the
sludge sample was aged for 20 days' for the study of the aging
effects on the FGD sludge.

Stabilized Wastewater--
     The stabilized wastewater composite was  sampled  from the
sludge lagoon.  The samples were taken in  an .area of  quiescence
near the point to reentry to the power plant.   Samples  were
taken once daily with a 600-ml aliquot, which  was filtered
(0.45 m) and split into two 300-ml  subset  samples.   The sample
marked 2876-KAN-SW-l was then acidified with  ultra-pure nitric
acid to a pH of 1.  Both subset samples were  refrigerated (4°C).

Stabilized Sludge--
     The stabilized sludge was also  taken  from the  sludge lagoon.
The plant engineer identified the  areas of oldest deposition of
lime sludge (about 5 years old).  These areas  had formed  sills
and were easily accessible.

     A casing was needed to take samples from  180 to  270  cm below
the surface of the sill.  The casing was fabricated from  eight-
inch diameter PVC pipe.  The original  360-cm  casing was cut into
two 180 cm sections and filled with  a connector.

     Once the casing was in place,  the sample  of stabilized
sludge was augered from a depth of 180 to  270  cm and  placed in a
4-liter container.  The auger bucket was teflon-coated  to prevent
metal contamination.

Sample Shipment

     All samples described above were placed  in  metal ice chests.
Ample amounts of  ice were included to ensure  that the sample
remained at 4°C.  The sample was airfreighted  from Kansas City to
Los Angeles and delivered to the DSC Department  of Environmental
Engineering within 10 hours.
                               308
-------
       TABLE B-l .   FGD SLUDGE SAMPLE IDENTIFICATION SCHEME
      Label                             SampleDescription

2876-KAN-RS                      Fresh sludge from scrubber mixing
                                tank (all  parameters)

2876-KAN-SS                      Stabilized sludge from lagoon
                                (all parameters)

2876-KAN-RW-l                    Fresh wastewater - from scrubber
                                mixing tank, filtered, fixed
                                (acidi fied)(metals )

2876-KAN-RW-2                    Fresh wastewater - from scrubber
                                mixing tank, filtered - not
                                fixed (all other parameters)

2876-KAN-SW-l                    Stabilized wastewater - from
                                lagoon, filtered, fixed (metals)

2876-KAN-SW-2                    Stabilized wastewater - from
                                lagoon, filtered, not fixed
                                (all other parameters)
ANALYTICAL METHODS

     Below is a discussion of the analytical  procedures imple-
mented in the parameter determination on the  samples of wastewater
and sludge taken at the La Cygne station.

General Parameters

     The determination of pH, nitrogen compounds, alkalinity,
chloride, fluoride, redox potential, and total  dissolved solids
follows the standard methods described in Ref.  1.  The procedures
and instruments used are as follows:

     •  pH                      Potentiometry (Orion 801A)

     •  NH3-N                   Brucine Method  (Perkin-Elmer 124,
                                light path 10 cm, 410  nm)

     •  Alkalinity              Potentiometric  titration
                                (Orion 801A)

     •  Chloride                Mercuric nitrate  method
                                309
-------
     •  Redox potential          Potentiometry  (Pt  electrode,
                                Orion  810A)

     •  Total dissolved          Gravimetry
        solids

     •  Boron                   Curcumin  method

     •  Silica                  Molybdosi1icate

     The determination of phosphorus was  accomplished  using  the
modified Ascorbic Method.  The procedures  of  the method  are  out-
1ined as follows:

     (a)  Measure 1  ml of slurry sample  and  put  in teflon  beaker
          (if filtrate sample, use 50-100  ml).

     (b)  Digest the sample at water boiler  temperature  using
          HF (1  ml)  and  HC104 (2 ml) with  teflon cover.

     (c)  After  solution is clear, remove  the  cover and  heat  to
          dryness .

     (d)  Cool,  add  2 ml of H?®? and heat  to  dryness  again.

     (e)  Add 20 ml  of H20 and 5 ml  of ION H2S04.

     (f)  Filter the sample through  the  glass  fiber and  dilute
          to 100 ml .

     (g)  Take 40 ml of  sample and add 3  ml  of  1.6 percent
          ammonium  molybdate and 4 ml  of  mixed  reagent.   (Mixed
          reagent =  50 ml of tartrate  +  50 ml  of 10 percent
          ascorbic  acid).  (If dilution  is required,  the reagents
          to sample  ratio should be  kept  constant.  An appropriate
          amount of  ION  H2S04 should be  used  to  keep  the final pH
          value  constant).

     (h)  Measure the sample by spectrophotometer  at  717 nm.

     The measurement of  orthosphate  on filtrates was  performed as
above without the digestion procedures.

     A refractometer (American Optical Corp.  Goldberg  T/C, Model
10419), was used for the measurement of  salinity.   The dry weight
data of the total slurry samples were  analyzed  on  both volume
and wei ght basi s .
                               310
-------
     A titrimetric method is used for dissolved sulfide deter-
mination.   Total  acid-soluble sulfide was determined by stripping
and titrimetric processes:

     (a)  Measure 5 ml  ZnAc and 95 ml distilled water into each
          of two  absorption flasks.   Connect the two absorption
          flasks  with a 1-liter reaction flask and purge the
          system  with N~ gas for 5 minutes.

     (b)  Transfer 10 - 50  ml slurry sample  into the reaction
          flask and add distilled water to 500 ml, then mix
          completely.

     (c)  Acidify the sample with 10 ml cone. H2S04 and replace
          the prepared  2-hole stopper tightly.  Pass N£ through
          the sample for approximately one hour.

     (d)  Add 10  ml of  iodine solution and 2.5 ml  cone. HC1  to
          each of the absorption flasks, sha-ke and mix  thoroughly

     (e)  Transfer contents of both  flasks to a 500 ml  flask and
          back-titrate  with 0.025N sodium thiosulfate titrant,
          using starch  solution as indicator.

     The analysis of FGD sludge for  carbonate sulfite and sulfate
followed the Palmrose Method as described below:

     (a)  Obtaining and preparing sample

          (1)  Using a  2-1/2 ml syringe, exactly 2 ml of sludge
               sample are drawn.  Care must  be taken here, for if
               excess sample is taken and if the excess is dis-
               carded by drawing the plunger back  to 2  ml, the
               solids may partially  settle and what remains  is
               no longer representative.

          (2)  The sample is then injected into a  beaker contain-
               ing 60 to 75 ml  of demineralized water.   The
               diluted  sample is redrawn into the  syringe several
               times to completely wash or purge the sample.

     (b)  CaS03 Titration

          (1)  Add 5 ml of  starch -  KI solution to the  sample.

          (2)  Estimate the expected CaC03 concentration.  Deter-
               mine the volume of H2S04 needed to  neutralize the
               CaCOs.   Add  5 ml to that volume and add  the sum
               to the sample and record the  volume added.

          (3)  Titrate  the  sample with potassium iodate (KIOs).
               Do not stir  the sample until  a blue color starts
                                  311
-------
               to  appear.   Titrate  until  one  drop  produces  an
               intense  blue color.   Premature stirring  would
               aggravate  the S02  stripping  problem.   Note  the
               volume of  KI03 used.

     (c)   Excess  Acid Titration

          (1)   To  bring the sample  back  from  the deep blue  to  a
               clear color, add  a couple  drops  of  sodium thio-
               sulfate.  If more  than  a  few drops  are required
               to  effect  the color  change,  the  KI03  end point
               was  exceeded and  the  entire  process should  be
               started  over.

          (2)   A  few drops  (3 to  5)  of methyl  purple  indicator
               are  added  to the  sample.   This will turn the  solu-
               tion blue.

          (3)   Titrate  the  sample to a greenish yellow  end  point
               with 1/8 normal  NaOH.  Recorci  the volume of
               hydroxide  titrated.   If the  ml  of NaOH is less
               than 5 ml  or greater  than  10 ml, the  entire
               analysis should  be redone  by adjusting the  amount
               of  H2S04 added in  step  (b)(2).

     (d)   Calculations

     If this procedure  is  followed  exactly  and  all reagents
are of the specified normality,  the  composition is calculated
as follows:

          gm CaC03/l =  3.125 x  (ml  H2S04  -  ml  NaOH)

          gm CaS03'l/2H20  - 4.025 x  ml KI03

     The  concentration  of CaS04-2H20 was  calcualted  by  subtract-
ing the amount of  calcium  in CaCOs  and CaS03-^H20  from  that  of
total  calcium  concentration in  sludge.

Metals

     Sludge  samples used  in the  determination of metals (except
mercury)  in  the lime slurry sludge,  were  digested  by concen-
trated hydrofluoric acid  (HF),  nitric  acid  (HNOs), and  perchloric
acid (HC103) to clear the  solution  at  175°C  in  a teflon beaker
(with  teflon cover).  Atomic absorption  spectrophotometers
(Perkin Elmer's 3058 and  4-60) were  used  in  the  analyses of metals
Both flame and heated graphite  atomizers  (HGA 2100)  were employed
in total  sample analysis.   The  choice  of  an  atomizer is dependent
on the suitable linear range (concentration)  of the  element  which
is being  determined.  The  following  table was the  guide used  in
choosing  the atomizer:


                               312
-------
          Optimum Working Range
    Fl ame
atomizer (mg/£)
0
0
0
0
0
0
0
0
10
0
0
1
0
5
2
0
.03
.1
.2
.02
.002
.05
.2
.3

.1
.3

.002


.05
1
2
- 20
2
0
2
- 10
- 10
- 300
- 10
-' 10
- 20
0
- 100
- 100
2




.02







.02



Heated graphite
atomizer (pg)*
20 -
10 -
20 -
1 -
50 -
3 -
50 -
30 -
500 -
10 -
200 -
50 -
50 -
1000 -
400 -
1 -
2000
2500
1000
40
1000
100
2000
1000
7000
500
5000
1500
1000
80000
20000
70
         £1ement

           Na
           K
           Ca
           Mg
           As
           Cd
           Cu
           Fe
           Hg
           Mn
           Ni
           Pb
           Se
           Ti
           V
           Zn

     *Based  on interrupt flow of argon gas

     The fresh and stabilized wastewater needed no  further diges-
tion since the sample had been filtered (0 .4 5 y m)  and fixed pH = l)
in the field.  Analysis  of the metals  (except mercury)  was
accomplished by direct injection into  the  HGA furnace.

     Mercury determination was accomplished  by  flameless  atomic
adsorption cold vapor method.  Samples (raw  and stabilize lime
slurry sludges) for total mercury analysis  were digested  in
teflon bombs (Parr No. 4745).  The procedures are  as  follows:

     (a)  Weight triplicate 0.1  - Ig of sample  and  place  in
          bottom of a teflon acid digestion  bomb.

     (b)  Carefully add  10 ml cone. HNOs,  3  ml  48%  HF and 1  g
          KMn04 and close the digestion bomb tightly.

     (c)  Place the digestion bomb into an  oven (or hot  plate)
          and adjust the temperature to 70°C.

     (d)  Digest the sample until solution  is clear.

     (e)  Determinations were accomplished  by flameless  atomic
          adsorption cold vapor  method.
       313
-------
     The pore water samples were withdrawn from various  sludge
samples (fresh, 20-day-old, and stabilized)  by the centrifugation
method at 5,000 g and 30 minutes of centrifugation .   After centri-
fugation, the supernatants were filtered through a 0.45  m  Milli-
pore filter, and were immediately acidified  to pH around 1 to
preserve the sample.  The procedures used for the analysis of
pore water samples are the same as those used for the analysis
of fresh and stabilized wastewaters, as  described previously.
                                314
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                       APPENDIX  B

                       REFERENCES
APHA, AWWA,  WPCF.   Standard  Methods  for  the  Examination  of
Water and Wastewater,  14th  ed.,  Washington,  D.C.  1975.
                          315
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