United States
                    Environmental Protection
                    Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
                    Research and Development
EPA/600/SR-95/068    May 1995
vvEPA         Project Summary
                    Calcium Carbonate  Dissolution
                    Rate  in  Limestone Contactors
                   Raymond D. Letterman
                     The project summarized here inves-
                   tigated some of the parameters and
                   relationships used  to predict the per-
                   formance of limestone contactors. The
                   purpose of the project was to study the
                   effect of limestone  composition, espe-
                   cially the dolomite [CaMg(CO3)2] and
                   impurity content of the stone, on the
                   kinetics of carbonate mineral dissolu-
                   tion and to determine the effect of tem-
                   perature on the rate of dissolution. The
                   rate of dissolution  was determined by
                   using a rotating disk apparatus and
                   samples of limestone of varied compo-
                   sition.
                     The  limestone samples included a
                   white marble and a selection of sedi-
                   mentary stones. The white marble con-
                   tained  a  significant amount of silica
                   (approximately 35%). The major min-
                   eral  constituents of the sedimentary
                   limestones ranged  from approximately
                   100% calcite (CaCO3) to essentially pure
                   dolomite. The approximate  iron (Fe)
                   content of the stones ranged from 15
                   to 377 mg Fe/100g and the approxi-
                   mate aluminum content (Al) from 1 to
                   134 mg Al/100g.
                     A heterogeneous reaction model for
                   mineral dissolution effectively explained
                   the results of the rotating disk experi-
                   ments for all samples except the two
                   with the highest dolomite content. The
                   magnitude of the dissolution rate con-
                   stant for fresh stone decreased by ap-
                   proximately 60% as the calcite content
                   of the stone decreased from 0.92 to
                   0.09 g CaCO3/g stone. The rate of dis-
solution of stones with a high dolomite
content may have been enhanced by
the presence of small amounts of cal-
cite. The rate of solubilization of mag-
nesium  (Mg) was negligible in  all
samples  except the two with the high-
est dolomite content (93 and 100 mass
percent dolomite).
  The overall dissolution rate constant
decreased as the amount of calcium
dissolved from the surface of the stone
increased. For a given amount of cal-
cium dissolved  per unit area of stone
surface, the magnitude of the percent-
age decrease in the dissolution rate
constant increased as the iron and alu-
minum content of the stone increased.
The effect of sample aging on the rate
of dissolution  was lowest when the
weighted sum  of the  iron and alumi-
num content of the stone was less than
about 10 mg/g. The weighted sum is
equal to  the aluminum content in mg
Al/g plus 0.30 times the iron content in
mg Fe/g. The presence of silica as the
principal impurity in the white marble
seemed to reduce the effective (cal-
cite) surface area of the stone in pro-
portion  to the mass  of silica  in the
sample, but it did not appear to affect
the dissolution rate of the calcite sur-
face.
  The dissolution rate constant for cal-
cite increased with increasing tempera-
ture, from 0.38x10-3 cm/s at 5°C to
2.80x10'3 cm/s  at 25°C. The apparent
activation energy was 101+8 kJ/mol for
the surface reaction rate constant and

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17±0.3 kJ/mol for the mass transfer rate
constant  in  the heterogeneous reac-
tion model.
  This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key  findings of the  research  project
that is fully documented in a separate
report of the same  title (see  Project
Report ordering information  at the
back).

Background
  A  limestone contactor is a treatment
device in which water flows through and
dissolves carbonate minerals (typically cal-
cium  carbonate) from a packed  bed  of
crushed limestone. Dissolution of  calcium
carbonate (under a closed-to-atmospheric-
carbon dioxide  condition)  increases the
pH, alkalinity,  and dissolved inorganic car-
bon concentration  of the water and de-
pletes the amount of calcium carbonate in
the bed. Limestone contactors  are simple,
low-cost  devices, which usually  require
minimal maintenance and  are, therefore,
especially suitable for small water sup-
plies.
  In  an earlier study  (Letterman et al.,
1987), limestone contactors effectively re-
duced the  dissolution  of  corrosion
byproducts, such as  lead, copper,  and
zinc, from piping system surfaces. A math-
ematical model related the depth  of lime-
stone needed to reach the desired effluent
water chemistry to the influent water chem-
istry, the limestone particle size and shape,
the  limestone bed porosity, and the tem-
perature  and superficial velocity  of the
water. Limited field experiments  showed
that contactor performance decreases as
the water temperature  decreases.
  Another study (Haddad, 1986) monitored
the long-term  operation of a contactor con-
taining somewhat impure,  high-calcium
limestone. Here, the author concluded that
as the calcium carbonate  dissolved, the
rate of dissolution decreased because rela-
tively  insoluble  impurities formed a resi-
due layer. As the thickness of this layer
increased, the rate of transport of  calcium
ion from the calcium carbonate surface  to
the  bulk  solution decreased,  and,  thus,
contactor  performance  decreased with
time.
  Field  experiments   have   shown
(Letterman  et al., 1987) that the tempera-
ture of the  water flowing through  a lime-
stone  contactor can affect its performance.
For a given set  of design  and operating
conditions,  contactor performance tends
to decrease with decreasing temperature.
One of the objectives of this study was  to
obtain a better understanding of this rela-
tionship.
Experimental Materials,
Apparatus, and Methods

Limestones
  The  study was  conducted  using  13
samples  of  limestone including a white
marble (sample  WM) from a  quarry  in
Proctor,  VT, a  sedimentary limestone
(sample SL) from a quarry near Boonville,
NY,  Black River limestone  (sample  BR)
from a quarry near Watertown,  NY,  and
10 samples  (samples A-J)  from a dolo-
mite quarry near York, PA.
  A sample  of each stone was powdered
and dissolved in concentrated hydrochlo-
ric acid.  Dilutions  of this  solution were
used to determine the calcium, magne-
sium, iron, and  aluminum content  of the
stone with a direct current plasma spec-
trometer and an atomic absorption spec-
trophotometer.  For a  number of  the
samples, some translucent material, prob-
ably quartz,  remained after 2 days of dis-
solution. The  measured  calcium  and
magnesium  content of the samples was
used to estimate the calcite, dolomite, and
insoluble residue content of the  samples.
In these calculations the magnesium was
assumed, based on x-ray diffraction  and
thin-section  photomicrography results,  to
be associated only  with dolomite.
  The  results of these calculations  and
the  measured iron  and aluminum values
are  listed in Table  1. In several cases,
where the sum of the calcite and dolomite
fractions was slightly greater than 100g/
100g of stone, the  insoluble residue con-
tent was set equal to zero.
  Samples WM, SL and BR as well as a
number of the samples from the York do-
lomite quarry (samples A, B, D,  E and  F)
are  high calcium content limestones. Other
York samples (samples  C,  G,  H, and I)
are  predominately dolomite, and  sample J
is essentially pure dolomite.
  The  WM  sample had the highest in-
soluble residue  content  (36 g/100g) but
relatively low amounts of iron and alumi-
num (34 mg Al/100g and 71  mg Fe/100g
of stone). It is very likely that the insoluble
residue  in this sample is quartz. Sample I,
from York, had the highest amount of iron
(377 mg Fe/100g) and sample H  had the
highest  amount of aluminum  (134 mg Al/
100g).
  The  stone disks used in  the  rotating
disk apparatus were prepared by cutting
3.10- or2.45-cm-diameter, cylindrical cores
from pieces  of rock collected  at the quar-
ries. Each core was cut into a number of
3-mm-thick disks using a rock saw.  The
disk faces were  smoothed and polished
on a lapwheel with a silicon carbide abra-
sive. The back face and edge of the disks
were coated with plastic so that only the
polished face was  available  for  dissolu-
tion. Each disk was mounted in a Teflon-
coated1  brass holder (Figure  1). Between
dissolution rate experiments,  each stone
sample  was  "aged" by controlled  dissolu-
tion in dilute  acid solution. The cumulative
amount of calcium and  magnesium  dis-
solved  during  aging was determined by
measuring their concentrations in the di-
lute acid solution.

Rotating Disk Apparatus
  The  reactor used in the  rotating  disk
apparatus (Figure 1) was 14  cm in diam-
eter and the clearance between the  disk
and the walls  of the vessel was greater
than 4 cm. The disk was centered about 3
cm  above the bottom  of the  vessel,  and
its rotational speed was varied over the
range 200 to 1200 rpm.
  The   reactor was  constructed with
double-glass walls. A water bath was used
to circulate  water between  the walls to
maintain  the  reactor contents  at
preselected temperatures in the range 4°
  Mention of trade names or commercial products does
  not constitute endorsement or recommendation for
  use.
Table 1. Estimated Major and Minor Constituents of the Stone Samples (g/100g)

 Stone ID        Calcite       Dolomite       Insoluble          Fe
                                                                         Al
WM
SL
BR
A
B
C
D
E
F
G
H
1
J
64
92
99
89
92
17
79
71
89
23
38
9
0
1
4
2
16
4
68
18
29
9
59
53
93
100
35
4
0
0
4
15
3
0
2
18
9
0
0
0.071
0.101
0.019
0.024
0.029
0.189
0.040
0.041
0.015
0.294
0.154
0.377
0.189
0.034
0.114
0.044
0.012
0.001
0.093
0.037
0.025
0.005
0.129
0.134
0.032
0.010

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                        Plexiglass
                                           Drive shaft
                                               Drive shaft support
                                                       r   \
                                       Limestone disk
                                                               Water jacketec
                          Reactor support
                                                                          reactor
Figure 1.  Schematic diagram of the rotating disk apparatus.
to 25+0.2°C. The plexi-glass cover on the
reactor had holes for inserting the rotating
shaft, pH  electrode, and  wetted nitrogen
inlet tube. Additional holes were provided
for   measuring  the  temperature  and
pipetting  samples  for the calcium mea-
surement. The bulb of the pH electrode
was located 1.5 cm from the rotating disk
and 3 cm above the bottom of the vessel.
  All solutions used in the  rotating disk
experiments were made with distilled and
deionized water that had been boiled for a
few minutes, several hours before use, to
remove carbon dioxide. Fisher analytical
grade (ACS Certified) chemicals were used
(KCI,  N/10 HCI). The background electro-
lyte was 0.079 M KCI.

Methods
  A  free-drift  method, in  which the pH
was allowed to increase as the carbonate
minerals  dissolved  from the  stone, was
used  in all experiments. Experimental so-
lutions (600 mL) were prepared as needed
by adding potassium chloride and the re-
quired volume of acid  to boiled water and
then transferring this to the reactor.
  Each experiment began by  raising the
vessel and solution into place beneath the
rotating disk  and against  the  plexi-glass
cover. Samples of solution (either 2- or 5-
ml volume) were withdrawn from the ves-
sel at 6 or 9  min intervals for a period of
1.5 hrwith the use of an automatic pipette
(1  to  5 ml).  The samples  were stored in
polyurethane disposable test tubes at 4°C
for no longer than  2 days before the ion
concentrations were measured by atomic
absorption spectrophotometry.

Experimental Results
  The calcium concentration and pH
change with time in a  typical rotating disk
experimental  run are shown in Figures 2
and  3. In this example, the WM  stone
sample was  used,  the rotational speed
was  600 rpm, and  the initial  acidity was
0.01  meq/L. At the end of  the experiment
the pH was 9.04 and the calcium concen-
tration was about  2 mg/L. For an initial
acidity of 0.01 meq/L and with no calcium
in  the solution at  t = 0,  the  calculated
equilibrium  calcium concentration  is 11.6
mg/L  and the calculated equilibrium pH is
10.02.
  The overall  dissolution  rate  constant,
ko, was determined for each experimental
run by using  the measured calcium con-
centrations  and, in  some cases, the mea-
sured magnesium concentrations. For the
stones that  released  negligible amounts
of magnesium, the calcium concentrations
(Ct) were substituted in the relationship,

  M  = In {(Ceq - C,)/(Ceq - Co)}(V/A)    (1)

  where  Ceq  and Co  are the equilibrium
and initial calcium concentrations, respec-
tively,  and  A is the surface area of the
stone sample disk  exposed to the  solu-
tion.  Co was zero in all experiments. Vt is
the volume of the solution in the rotating
disk  apparatus.  For sample WM and
samples A-J, the limestone disk was 3.6
cm in diameter and, therefore, A was 10.17
cm2.  For the  3.1-cm diameter SL sample
and the 2.5-cm-diameter  BR  sample, A
was 7.91 cm2 and 4.71 cm2, respectively.

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       2.5
I
       1.5
       1.0
I
       0.0,
          0.0       0.2       0.4       0.6       0.8       1.0

                                        Time (hours)
                                                              1.2       1.4
                                                                               1.6
Figure 2. Calcium concentration in the rotating disk apparatus as a function of time: WM sample;
w = 600 rpm and initial acidity of 0.01 meq/L.
      9.0
      6.0
        0.0       0.2       0.4       0.6       0.8       1.0

                                      Time (hours)
Figure 3. pH versus time for the rotating disk experiment of Figure 2.
  The magnitude of Ceq was determined
for  each  experimental  run by using a
chemical  equilibrium model and effec-
tive solubility products  determined  for a
number of the  stone samples  (Table 2).
For the stone samples  that were not in-
cluded  in  the  solubility product experi-
ments, i.e., samples B, D, E, G, H and J,
the  average value of the effective solubil-
ity products (pKsp =  8.81) for the samples
from the same quarry was  used. pKsp =
8.35 was used for sample BR because of
its similarity to sample SL.

Table 2. Effective Solubility Products for Calcium
Carbonate and Calcium-Magnesium Carbonate
in Selected Limestone Samples.'
Stone sample ID
WM
SL
A
C
F
1
Negative log
of the effective
solubility product
8.20 ±0.07
8.35 ±0.06
8. 76 ±0.09
8.72 ±0.07
8.88 ±0.05
8.89 ±0.04
'Values are for 25°C and infinite dilution.
                                                                                       As  samples were withdrawn during an
                                                                                     experiment,  the magnitude  of Vt de-
                                                                                     creased. A value of Vt was calculated for
                                                                                     each value of Ct using the relationship,
                                                                                       V, = V0 - nv
                                    (2)
  where Vo is the volume of the solution
in  the  reactor at the  start  of the experi-
ment,  v is the  volume of each  sample
withdrawn  for the  calcium  and magne-
sium  measurements,  and  n  is the  total
number of samples withdrawn from the
reactor up  to that sample. In  the dissolu-
tion rate experiments,  Vo was  600 ml_ and
v was either 2 or 5 mL
  A straight line was  fitted to the M ver-
sus time points using  the method of  least
squares (M is given by Equation  1). The
slope of this line is equal  to the overall
dissolution  rate constant.
  Figure 4 is an M versus time plot  for a
fresh sample of WM stone. In this experi-
ment, the disk rotational speed was 600
rpm, the water  temperature was 25°C,
and the initial acidity was 0.01 meq/L. The
slope of the least squares line in Figure 4
yields an overall dissolution rate constant
of  3.3x10'3  cm/s.

Effect of Insoluble Residue on
the Dissolution Rate
  The overall dissolution rate constant for
fresh calcitic stones (stones with low dolo-
mite content) tended  to decrease as the

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     -10
     -12
       0.0       0.2      0.4       0.6       0.8        1.0

                                     Time (hours)
                                                           1.2
                                                                             1.6
Figure 4. Determination of the overall dissolution rate constant (ko) for the experiments of
Figures 2 and 3 (ko = o.oo33 cm/s).
estimated amount  of insoluble residue in
the stone increased. We  concluded that
the insoluble impurities reduced the area
of calcite exposed  to the solution. To test
this hypothesis, we assumed that the area
of exposed  calcite is proportional to  the
mass percent of calcite in the stone. The
rate  constants  were "corrected"  for  the
residue content by dividing  them by  the
mass percent of calcite in the stone. The
results of this  calculation,  listed  in  the
right-hand column  of Table  3, show that
this correction  reduces the  effect of  the
residue content on the overall dissolution
rate constant.
  The corrected overall  dissolution rate
constant  for the  coarse-grained WM
sample (3.12x10'3 cm/s) is somewhat less
               than the values of 3.51x10'3 and 3.75x10'3
               cm/s  for the  fine-grained SL and  BR
               samples.

               Effect of Aluminum and Iron
               Content on the Dissolution Rate
                 We observed that the extent to which
               the  dissolution of calcium from the stone
               surface reduced the overall  dissolution  rate
               constant depended on the aluminum  and
               iron content of the stone.
                 Figure 5 shows the normalized overall
               dissolution rate constant (i.e., the mea-
               sured value  divided  by the initial, fresh
               stone,  value,  ko/koi) plotted  versus  the
               amount of calcium dissolved from the  sur-
               face of the stone,  Cad, for stones A through
               H. (The results for  stones  I and J were
Table 3. Comparison of Experimental and Corrected Overall Dissolution Rate Constants (kjfor
Essentially Fresh Limestone Disks.'
          Stone
Mass %        Experimental kox103   Corrected kox103
 Calcite             (cm/s)              (cm/s)
Calcium dissolved in "aging" = 0.2 mg Ca/cm2
           WM                64
            SL                92
           BR               100

Calcium dissolved in "aging" ~ 0 mg Ca/cm2
            B                 92
            F                 89
                    1.99
                    3.26
                    3.75
                    4.39
                    3.46
3.12
3.51
3.75
4.77
3.89
'Small amounts of calcium had been dissolved from samples WM, SL, and BR before the first rate
constants were determined.
also plotted but  are not shown in  Figure
5.) For stones C, I, G,  and H,  the overall
dissolution rate  constant decreased  by
more than 60% as the  amount of calcium
dissolved  increased from  0 to 4 mg Ca/
cm2. For stones B, F, and J, the decrease
was less than 30%.
  Values  of ko/koi were interpolated from
Figure  5 at Cad = 2 mg Ca/cm2 and then
listed in Table 4  in rank order, from the
highest (ko/koi =  0.90 for stone F)  to the
lowest  (kjkj" =  0.23 for  stone  G). The
stones with the highest aluminum content
(> 25 mg Al/100g of stone) had the great-
est decrease in the overall dissolution rate
constant for this  amount  of calcium dis-
solved. For  several stones,  especially
stone I with ko/koi = 0.36, the iron content
seemed to be an  additional factor.
  Since both the  iron and aluminum con-
tent  of the stone  seem to determine how
sample aging affects the  overall dissolu-
tion rate constant, a composite parameter
that  includes a weighted  combination of
the  iron and aluminum concentrations (aC^
+ bCFe) was derived,  where  C^  is the
aluminum  concentration  in mg AI/100 g
and  CFe is the iron concentration  in mg
Fe/100  g. The highest linear  correlation
between ko/koi and the  Fe+AI  parameter
(r2 = 0.92) was obtained with weighting
factors a=1  and  b=0.3, i.e., (C^ + 0.30
CFe). The  quantity ko/koi and correspond-
ing values of (C^ + 0.30 CF) are listed in
Table 5.
  According to the results in Table 5, the
effect of iron and  aluminum on  the overall
dissolution rate constant will be minimized
if the quantity C^ + 0.30 CFe for the stone
is less  than about 10 mg/100g.
  In a special experiment, the brownish
residue layer that formed  on the SL disk
was scraped  into  concentrated nitric acid,
ultrasonicated and the  solution was ana-
lyzed for  total  soluble  aluminum. The
soluble aluminum expressed  as  the
amount per area of disk was 0.97 |omoles/
cm2 (26 |ig/cm2). The scraped residue did
not  dissolve completely in acid which sug-
gested the presence of alumino-silicates.
The  overall dissolution  rate constant  for
the  SL stone  increased  to 90% of its origi-
nal  value when  the residue  layer was
scraped from the  disk surface.

Conclusions and
Recommendations
  A heterogeneous reaction model for min-
eral dissolution, in which the rate  of disso-
lution is controlled by a surface reaction
and a cation mass transfer resistance act-
ing  in series, effectively explained the  re-
sults of the rotating disk experiments  for
all samples except the  two with the high-

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                                                   6             8
                           Ca dissolved per unit area of disk (mg/sq cm)

Figure 5. Effect of amount of calcium dissolved from disk surface on the fractional decrease in the
overall dissolution rate constant.
Table 4. Effect of the Iron and Aluminum Content on the Fractional Decrease in the Overall Dissolution
Rate Constant (kj at Cad = 2 mg Calcium Dissolved/sq cm of Limestone Surface.
Stone
ID
F
A
B
J
E
D
C
1
H
G
Calcite
88.9
88.9
92.1
0
70.7
78.9
16.5
8.8
38.3
22.9
/ro*703'
(cm/s)
3.5
4.7
4.4
0.9
3.3
4.2
2.7
2.8
3.3
3.2
W
0.90
0.74
0.73
0.70
0.65
0.67
0.43
0.36
0.35
0.23
Fe
(mgFe/100g)
15
24
29
189
41
40
189
377
154
294
Al
(mgAI/100g)
5
12
1
10
25
37
93
32
134
129
' Interpolated from Figure 5 at Cad = 2 mg Ca/cm2.* kd = value when negligible Ca dissolved from the
stone.
Table 5. Effect of the Weighted Sum of Iron and Aluminum in the Limestone on the Fractional Decrease
in the Dissolution Rate Constant at 2 mg Calcium/sq cm of Limestone Surface.
      Stone
ID  ko/ko: (mg/100g)
F
A
B
J
E
D
C
1
H
J
0.90
0.74
0.73
0.70
0.65
0.61
0.43
0.36
0.35
0.23
10
19
10
67
37
49
149
145
180
217
'kd = value when negligible Ca dissolved from the stone.
est dolomite content. For calcite  and the
experimental conditions of this study, the
surface reaction rate was relatively large
and the rate of dissolution was essentially
mass transfer controlled. The results show
that a  calcium ion diffusivity of 0.8 x  10"5
cm2/s (at 25°C, can be used in predicting
the mass transfer resistance.
  The  stone samples with the highest cal-
cite content and lowest dolomite content
had the highest initial rates of  dissolution.
The  magnitude of the overall  dissolution
rate  constant  for fresh stone  decreased
by approximately 60% as the calcite con-
tent of the stone decreased from 0.92 to
0.09 g CaCO3/g stone. The  rate of disso-
lution of stones with high dolomite content
may be enhanced by the presence of small
amounts of calcite. For example, the stone
that was essentially pure dolomite had  a
dissolution rate  constant that was  66%
less  than  the  constant for another dolo-
mitic stone with approximately  9% calcite.
When the high dolomite  content samples
were fresh,  it  appeared  that the  calcium
carbonate component of the dolomite dis-
solved faster  than the magnesium car-
bonate component. The rate of dissolution
of magnesium was negligible in  all samples
except the high dolomite content samples
(93 and 100 mass percent dolomite).
  The  overall  dissolution rate constant
decreased as  the amount of calcium  dis-
solved from the surface of the stone in-
creased.  Analysis  of several  stone
surfaces, by scanning electron  microscopy
and x-ray energy spectroscopy, indicated
that the density of  calcium atoms on the
surface of the  stone decreased and the
density of aluminum, silicon, and iron in-
creased as calcium dissolved.  For a given
amount of calcium dissolved per unit area
of stone surface,  the magnitude of the
decrease  in the  overall dissolution rate
constant increased  as the iron and alumi-
num content of the stone increased. The
results suggest that the  effect of sample
aging on the rate of dissolution is a mini-
mum if the weighted sum of the iron and
aluminum content of the stone  is less than
about 10 mg/g. The weighted sum is equal
to the  aluminum content in  mg Al/g plus
0.30 times the iron content in mg Fe/g. To
minimize the  negative  effect  of mineral
dissolution and  residue-layer  buildup on
the performance of a limestone contactor
during  long-term  operation,  the iron and
aluminum content should be less than this
weighted sum.
  The  presence of silica as the principal
impurity in the white  marble reduced the
effective  surface area  of the calcite in
proportion  to  the  mass of silica in  the
sample but did not  appear to cause  a

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reduction  in the  dissolution rate of the
calcite surface.
  The dissolution rate of calcite increased
with  increasing  temperature,  from
0.38x10-3 cm/s at 5°C to 2.80x10'3 cm/s at
25°C. The apparent activation energy de-
termined for the surface reaction rate con-
stant in the heterogeneous reaction model
was 101+8 kJ/mol, a value that is signifi-
cantly  larger than literature values (46 to
63  kJ/mol). The apparent  activation en-
ergy for the mass transfer rate constant
was 17+0.3 kJ/mol,  which is  consistent
with values in the literature for mass trans-
fer controlled kinetics.

References
  Haddad, M.,  1986.  Modeling of Lime-
stone   Dissolution  in  Packed  Bed
Contactors Treating Dilute Acidic Water.
Ph.D.  Dissertation,  Department of  Civil
Engineering, Syracuse University.
  Letterman, R. D.,  C. T. Driscoll, Jr.,  M.
Haddad and H. A. Hsu,  1987.  Limestone
Bed  Contactors for  Control of Corrosion
at Small Water Utilities.  A Report for the
Water Engineering Research  Laboratory,
Office of Research and Development, U.S.
Environmental Protection Agency, Cincin-
nati, OH (EPA/600/S2-86/099).
  Letterman, R D., M. Haddad and C. T.
Driscoll,  1991.  Limestone  Contactors:
Steady-State Design  Relationships, Jour-
nal  of  Environ. Eng.. Am.  Soc. of Civil
Engineers,  117:339-358.
  The full report was submitted in fulfill-
ment of CR 814926 by Syracuse Univer-
sity  under  the  sponsorship  of the  U.S.
Environmental Protection Agency.

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Raymond D. Letterman is with the Department of Civil and Environmental
  Engineering, Syracuse University, Syracuse, NY 13244-1190.
Jeffrey Q. Adams is the EPA Project Officer (see below).
The complete report, entitled "Calcium Carbonate Dissolution Rate in Lime-
    stone Contactors,"(Order No. PB95-222733; Cost: $27.00, subject to
    change) will be available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Risk Reduction Engineering Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, OH 45268
   United States
   Environmental Protection Agency
   Center for Environmental Research Information
   Cincinnati, OH 45268

   Official Business
   Penalty for Private Use
   $300
      BULK RATE
POSTAGE & FEES PAID
         EPA
   PERMIT No. G-35
   EPA/600/SR-95/068

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