540SR98500
x°/EPA
United States
Environmental Protection
Agency
EPA/540/SR-98/500
June 1998
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology
Summary
Simultaneous Destruction of
Organics and Stabilization of
Metals in Soils
A. Bruce King, Stephen Paff, and Randy Parker
The Center for Hazardous Materials
Research (CHMR), through a Coopera-
tive Agreement with the U.S. Environ-
mental Protection Agency's National
Risk Management Research Laboratory,
conducted a laboratory evaluation of
the Sulchem Process for treatment of
soils contaminated with organic hydro-
carbons and heavy metals.
The Sulchem Process mixes the ma-
terial being treated with elemental sul-
fur at elevated temperatures in an inert
reactor system. Organic hydrocarbons
react with the sulfur to form an inert
fine solid of carbon and sulfur, hydro-
gen sulfide gas, and modest amounts
of carbon disulfide. Heavy metals react
to form sulfides or sulfide-coated par-
ticles which are less soluble. The acid
gases formed may be scrubbed or
treated to recover elemental sulfur us-
ing an auxiliary process unit.
At processing temperatures of 250°
to 350°C, destruction and removal effi-
ciencies for aromatic hydrocarbons
from phenanthrene to benzopyrene
were all in excess of 99%.
Using the EPA Method 1311, Toxicity
Characteristic Leaching Procedure
(TCLP), cadmium, copper, lead, nickel,
and zinc were significantly reduced fol-
lowing treatment of the soil by the
Sulchem process. Copper TCLP values
were reduced most effectively; lead was
reduced below regulatory targets when
concentrations in the original soil were
below about 10,000 ppm. Cadmium was
reduced below TCLP limits when the
concentration in the original soil was
below several thousand ppm.
Process economics for remedial soil
treatment were estimated to be in the
range of $105 to $181/ton depending
on the size of the site and the process-
ing rate.
This Summary was developed by
EPA's National Risk Management Re-
search Laboratory, Cincinnati, OH, to
annnounce key findings of the SITE
Emerging Technology that Is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
This research and development fo-
cussed on the application of the Sulchem
Process to contaminated soils at
Superfund sites to provide destruction of
hazardous organics while stabilizing met-
als in contaminated soils. The Sulchem
Process uses elemental sulfur, which re-
acts with the carbon in organic materials
at moderately elevated temperatures to
form an insoluble, inert carbon-sulfur amor-
phous solid (CS056). The contained heavy
metals are immobilized through formation
of insoluble metal sulfides.
Printed on Recycled Paper
-------
The Sulchem Process's main process
components include a pre-reaction mixer
where the soil and sulfur are mixed; an
externally heated rotating solids reactor; a
vapor phase reactor where desorbed or-
ganics from the first reactor are further
reacted with elemental sulfur; the off-gas
handling system, which collects and treats
condensable byproducts and scrubs acid
gases from the effluent vapors; and a
post-reaction treatment unit that recovers
excess reagent and prepares the treated
product to comply with on-site disposal
requirements. A general block flow dia-
gram for the Sulchem Process is shown
in Figure 1.
The Sulchem Process, as applied to
treatment of soils and sludges, consists of
two reactors: one for treating the solid
phase material and a second for treating
the gases emitted from the first reactor,
including desorbed organic vapors. The
second reactor is required because, for
the more volatile organic compounds, de-
sorption effectively competes with reac-
tions with liquid phase sulfur.
The feed soil, possibly after some de-
watering, is fed into a pre-reaction mixer
where elemental sulfur (and other re-
agents, if used) are added to the feed soil
and lightly mixed. The feed mixture (soil
and reagents) is next fed to the first reac-
tor, which consists of an indirectly heated,
rotary reactor. A controlled atmosphere is
produced in the reactor with the flow of
inert gases over the tumbling solids, which
Makeup
sulfur
Reactor
Treated soil
Figure 1. Sulchem process schematic.
acts to exclude oxygen from the reactor
and remove off-gases released by the pro-
cess.
Batch Reactor Experimental
Procedures
Three different small batch test reactors
were employed for the initial screening
studies. Each was sized to heat batches
of approximately 200g of soil in an inert
atmosphere from ambient temperature to
nominal reaction temperatures ranging
from 250° to 450°C. For the initial tests,
two unstirred reactors were employed. One
of these was designated as the closed
mode reactor (high pressure) and the
other, the vented mode reactor (low pres-
sure). These two reactors were heated by
immersion in a heated fluidized sand bath.
Subsequently, an autoclave was modified
to provide an auger mixed reactor. The
autoclave was heated with a cylindrical
furnace jacket which could be lowered
after the run for rapid cooling of the reac-
tor.
Organics Destruction
The Sulchem Process is a two-stage
process in which the soil reacts with sulfur
in the first stage. Unreacted organics des-
orbed from the first stage react with sulfur
in the vapor phase in the second stage.
The purpose of these tests was (1) to
establish the soil treatment temperatures
and other process conditions necessary
to achieve organic compound destruction
in the soil reactor; (2) to estimate the
boiling range of volatile organics that will
be desorbed during the heatup of the soil
reactor before reaction temperatures are
reached; and (3) to evaluate process con-
ditions for a second-stage vapor reactor
to treat the volatile organics desorbed from
the soil reactor.
So/7 Batch Reactor Tests
In batch reactor tests of the reaction
mixture, the soil and sulfur are heated,
while mixing, from ambient temperature to
the desired reaction temperature and then
held at the run temperature for the de-
sired time interval. The temperature at
which significant reaction first occurs was
estimated, based on small batch tests with
mineral oils in the closed and vented mode
reactors, to begin in the range of 200°C to
250°C for the more reactive saturated hy-
drocarbons. Therefore, the initial screen-
ing tests were run at temperatures of
250°C and higher.
A comparison of the boiling range of
the organics in the feed soil with the boil-
-------
ing range of the desorbed vapors col-
lected in downstream traps and the scrub-
ber (i.e., overhead) indicated the
approximate temperature range over which
desorption and reaction compete in the
solids reactor. For example, those com-
pounds with high recoveries in the over-
head represent the boiling range where
desorption takes place before any reac-
tion occurs. Those compounds not found
in the overhead represent the boiling range
above the reaction temperature regime.
An intermediate boiling point regime, where
only partial recovery is found, represents
the boiling range where reaction and des-
orption processes compete.
Several scoping tests were performed
using a series of organic compounds of
successively higher boiling points to 1)
establish the boiling range where desorp-
tion occurred before reaction (thereby es-
tablishing the approximate threshold
reaction temperature) and 2) provide an
initial screening of the level of destruction
and effect of process variables for the
higher boiling components where desorp-
tion is not important.
Tests of Desorption Versus
Boiling Range
Nine aromatic compounds (2000 ppm
each, except pyrene at 1000 ppm) with
boiling points from 165° to 393°C were
mixed into a 75/25 Synthetic Soil Matrix
(SSM) topsoil blend. Several series of
three sets of runs were carried out at
250°C, 350°C, and 440°C for 2 hours with
200g soil and 30g sulfur. Analysis of the
recovered samples for the spiked organic
compounds was compared with a sample
of the original spiked soil. The results are
Table 1. Effect of Boiling Point on Destruction and Removal
Compound
BP
1a. Reactor run at 250°C and
mesitylene
durene
naphthalene
2-Me Naphthalene
biphenyl
bibenzyl
hexachlorobenzene
anthracene
pyrene
165
197
218
241
254
285
322
340
393
Charge
(mg)
Reactor
Residual
Recovery in
Ice Trap
Recovery in
Scrubber
Total
Percent
Recovered
Percent
Destroyed
Destruction
and Removal
Efficiency (%)
2 Hour Residence Time
276.9
276.2
343.7
353
368.5
356.8
327.5
306.1
175
0.15
0.15
0.65
1.07
3.11
3.87
8.60
7.32
2.56
225.5
249.3
287.9
276.9
295.8
229.2
204.4
64.0
6.9
0.35
0.08
0.17
0.06
0.06
0.00
0.36
0.00
0.00
226
249.53
288.72
278.03
298.97
233.07
213.36
71.32
9.46
81.6
90.3
83.8
78.5
80.3
64.2
62.5
20.9
3.9
18.4
9.7
16.0
21.2
18.9
34.7
34.9
76.7
94.6
99.9
99.9
99.8
99.7
99.2
98.9
97.4
97.6
98.5
1b. Reactor run at 350°C and 2 Hour Residence Time
mesitylene
durene
naphthalene
2-Me Naphthalene
biphenyl
bibenzyl
hexachlorobenzene
anthracene
pyrene
165
197
218
241
254
285
322
340
393
1c. Reactor run at 440°C and
mesitylene
durene
naphthalene
2-Me Naphthalene
biphenyl
bibenzyl
hexachlorobenzene
anthracene
pyrene
165'
197
218
241
254
285
322
340
393
276.9
276.2
343.7
353
368.5
356.8
327.5
306.1
175
1.13
0.27
0.2
0.15
0.32
0.28
17.66
9.15
2.71
220.3
245.6
296.3
281.8
298.4
221.5
96.5
23.3
2.3
2.98
5.09
8.25
7.24
7.68
4.67
2.11
0.59
0.04
224.41
250.96
304.75
289.19
306.4
226.45
116.27
33.04
5.05
80.6
90.8
88.6
81.9
83.1
63.4
30.1
7.8
1.3
19.0
9.1
11.3
18.1
16.9
36.5
64.5
89.2
97.1
99.6
99.9
99.9
>99.9
99.9
99.9
94.6
97.0
98.5
2 Hour Residence Time
276.9
276.2
343.7
353
368.5
356.8
327.5
306.1
175
0.27
0.08
0.09
0.08
0.15
0.08
0.49
0.35
0.67
243.8
245.8
280.2
269.2
282.5
228.8
205.4
69.0
12.7
4.24
10.15
12.48
8.22
7.64
4.87
3.56
1.22
0.14
248.31
256.03
292.77
277.5
290.29
233.75
209.45
70.57
13.51
89.6
92.7
85.2
78.6
78.7
65.5
63.8
22.9
7.3
10.3
7.3
14.8
21.4
21.2
34.5
36.0
76.9
92.3
99.9
>99.9
>99.9
>99.9
>99.9
>99.9
99.9
99.9
99.6
-------
presented in Table 1. Surrogate recover-
ies for all recovered fractions were in the
60 to 90% range.
The combined recovery from the prod-
uct fractions was compared with the ana-
lytical results from the extraction of the
feed soil (based on a 200g charge that
nominally contains 400mg of each com-
pound except pyrene which was loaded at
200mg) to arrive at a total recovery for
each compound. This procedure corrects
for losses in the experiment, sampling,
and analysis. Absolute recoveries of mesi-
tylene and durene in both the soil charge
and the product analyses were about 70%
and below the values of 85 to 90% ob-
served for the higher boiling compounds
spiked in the soil. These compounds are
technically not semivolatile organics (de-
fined as BP > 200°C) and are outside the
method range for the Soxhlet extraction
(Method 3540) used for the sample
workup; therefore recoveries were lower.
Table 1 shows three different measures
of process performance: recovery from the
overhead, destruction, and destruction and
removal efficiency (ORE) of the treated
soil. These measures are discussed fur-
ther.
Recovery from Overhead
The percentage recovered from over-
head is a measure of the amount of a
compound that is desorbed from the soil
rather than reacted. It is calculated as the
ratio between the total amount of the com-
pound recovered in the ice traps and
scrubber to the amount originally present
in the soil.
Destruction
The percentage destroyed is a mea-
sure of the effectiveness of the sulfur in
the reactor. The percentage destroyed was
calculated simply as the difference be-
tween the amount originally present in the
soil and the amount recovered both in the
overhead and soil fractions, divided by
the amount originally present in the soil.
Destruction and Removal
Efficiency
The ORE is a measure of overall re-
moval of each compound from the soil.
The DRE is calculated by subtracting the
ratio of the amount of residual compound
left in the soil to the amount originally
present from one. For the lower boiling
point compounds, it reflects primarily the
effect of desorption. For the higher boiling
compounds, it reflects reaction efficiency.
Reaction temperature does not greatly
affect the recoveries as the desorption
step removes the compound from further
opportunity to react in the simple batch
reactor system. The residual content of
the treated soil is nonetheless greatly re-
duced, corresponding to DRE values of
better than 99% at the higher reaction
temperatures.
Metals Stabilization
A series of batch screening runs were
made on several soil blends containing
various heavy metals. The purpose of
these initial tests was to find how well
each of the various heavy metals re-
sponded to the sulfur treatment of the
Sulchem Process. A priori one might ex-
pect that the stabilization mechanism might
be the formation of metal sulfides as an
insoluble coating. If this is the case, then
the heavy metals whose sulfides are
soluble in acid (e.g., chromium, cobalt,
iron, nickel, and zinc) might not be ren-
dered immobile as much as other metals
(e.g., lead) with the Sulchem treatment
since the TCLP test leaches the sample
with a buffered acetic acid solution. It was
for the purpose of examining this premise
that the initial metal screening tests were
made.
For the screening studies to compare
the behavior of different heavy metals re-
ported here, the process parameters were
sulfur-to-soil ratio, reaction temperature,
and reaction time. Generally one sulfur-
to-soil ratio was used (typically 0.15), a
range of reaction temperatures were used
(i.e., 250°C, 300°C, and 350°C), and the
reaction time was typically one-half hour.
The initial metal screening tests were
done on soil samples of Standard Analyti-
cal Reference Matrix (SARM-III) and pre-
pared blends of metals spiked in either
Synthetic Soil Mixture (SSM) or a 75/25
blend of SSM and horticultural topsoil. The
SARM samples had been prepared with
arsenic trioxide (As2O3), cadmium sulfate
(CdSO4), chromium nitrate (Cr(NO3)3), cop-
per sulfate (CuSO4), lead sulfate (PbSO4),
nickel nitrate (Ni(NO3)2), and zinc oxide
(ZnO).
Screening studies of various metals
were made with a series of closed-mode
reaction runs made on five separate metal/
SSM mixtures. These individual blends
were made using lead oxide (PbO), cad-
mium oxide (CdO), arsenic oxide (As2O3),
chromium (III) oxide (Cr2O3), and nickel
hydroxide (Ni(OH)2) to contain 1000 ppm
of each of the metals. TCLP analyses
were made of the soil blend as well as the
three raw reactor products from each pro-
cessing temperature. Two-hour reaction
runs were used in these tests, which were
conducted in the closed mode unstirred
reactor. These data are listed in Table 2.
It was concluded that both lead and cad-
mium responded to the treatment, the lat-
ter more at elevated temperatures. The
results on the arsenic and nickel were
inconclusive.
Tests using SARM-III were conducted
to evaluate the performance of the differ-
ent contained heavy metals. These runs
were carried out in the stirred reactor au-
toclave to ensure that adequate mixing
was used. Since the objective was to de-
termine metals stabilization, no analyses
were made on these runs for the con-
tained organic compounds also present in
the SARM-III.
Table 3 shows the results for the SARM-
III feed. For the main metals present in
the SARM-III TCLP leachate (i.e., all but
arsenic and chromium), copper responds
the most effectively to the Sulchem Pro-
cess, decreasing the TCLP value 100-fold
at the mildest conditions and to the detec-
tion limit at the highest temperature, pre-
sumably because of insoluble sulfide
formation. A continuous reduction of TCLP
nickel leachate levels for the treated soils
is shown at successively higher tempera-
tures. The results for cadmium, lead, and
zinc also demonstrate some temperature
effect, but not as extensive as observed
for nickel.
Based on these results, additional test
blends were prepared using the oxides or
hydroxides of lead, cadmium, nickel, and
zinc to further evaluate the process condi-
tions necessary to improve the TCLP re-
sults. The objective was to evaluate the
stabilization of these metals in soils with a
higher organic carbon content than those
employed in the previous tests. There-
fore, the next series of tests used the 75/
25 SSM/top soil blend.
Tables 4-7 show runs on various blends
of Cd, Pb, Ni, and Zn as a function of
temperature. The first three test blends,
listed in Tables 4-6, contained a relatively
high loading of metals to evaluate pos-
sible process limits for reduction of the
leachate to TCLP limits. The cadmium
results demonstrate the previously ob-
served effect of process temperature on
the reduction of TCLP, although the effect
of process temperature is much less for
lead in this case. Substituting the more
soluble nitrate at the same lead loading
demonstrates how the more soluble form
can prevent reaching the TCLP regulatory
limit of 5 mg/L in this case. Although some-
what higher TCLP levels are observed for
the starting soil blend using more soluble
salts, the response of the soil to the
Sulchem treatment shows comparable re-
duction in TCLP values. The nickel- and
zinc-spiked SSM topsoil blend did not dem-
onstrate as great an effect from process
temperature that was previously noted for
-------
Table 2. Tests of Various Metals vs. Reaction Temperature
Temp
°C
250
300
350
Sulfur/
Soil
0/1.0*
.251.75
.25/75
.25/75
Pb
TCLP
(mg/L)
14.4
0.69
0.58
0.20
Cd
TCLP
(mg/L)
38.9
8.34
4.43
0.62
As
TCLP
(mg/L)
3.07
5.97
8.23
11.7
Cr
TCLP
(mg/L)
<0.05
<0.05
<0.05
<0.05
Ni
TCLP
(mg/L)
1.51
0.89
1.21
1.16
* Denotes untreated SSM.
Table 3. Metal Treatment Results with SARM-III Soil*
Untreated
Soil
Metal/
Concen-
tration
(ppm)
AS/500
Cd/1 ,000
Cr/1 ,500
Pb/1 4,000
Ni/1 ,000
Cu/9,500
Zn/22,500
Run Numbers
27-77
TCLP
mg/L
0.21
36.8
<0.05
35.5
22.2
153
791
Temp
°C
250
250
250
250
250
250
250
TCLP
mg/L
0.16
22.5
0.07
25.5
17.3
1.13
628
Run Numbers
27-78
Temp
°C
300
300
300
300
300
300
300
TCLP
mg/L
0.23
15.1
0.12
22.7
6.71
0.05
361
Run
Temp
°C
350
350
350
350
350
350
350
Numbers
27-79
TCLP
mg/L
0.37
12.4
<0.05
21.2
3.72
0.03
162
Run Numbers
27-84
Temp
°C
400
400
400
400
400
400
400
TCLP
mg/L
0.21
6.02
<0.05
16.1
0.72
0.03
58.1
Run
Temp
°C
440
440
440
440
440
440
440
Numbers
27-92
TCLP
mg/L
<0.05
3.66
<0.05
12.2
0.4
<0.01
32.4
*AII test runs were 0.5-hr, duration with 13% sulfur content in the feed soil.
Table 4. Metal Treatment Results with 75/25 SSM/Topsoil Blend*
Untreated Soil
Metal/
Concen-
tration
(ppm)
Cd/5000
Pb/1 0,000
Salt
Added
CdO
PbO
TCLP
mg/L
144
61.7
Run Numbers
27-69
Temp
°C
250
250
TCLP
mg/L
28.3
4.08
Run Numbers
27-71
Temp
°C
300
300
TCLP
mg/L
42.0
1.22
Run Numbers
27-70
Temp
°C
350
350
TCLP
mg/L
22.4
1.21
Run Numbers
27-76
Temp
°C
400
400
TCLP
mg/L
4.41
2.21
Run Numbers
27-91
Temp
°C
440
440
TCLP
mg/L
0.54
2.03
*AII tests were 0.5-hr, duration with 13% sulfur content in the feed soil.
Table 5. Metal Treatment Results with 75/25 SSM/Topsoil Blend*
Metal
Cd
Pb
Salt
Added
CdCI2
Pb(N03)2
Untreated
Soil
Metal
Concen-
tration
(ppm)
1,000
10,000
Run Numbers
33-40
TCLP
mg/L
30.1
96.4
Temp
°C
250
250
TCLP
mg/L
4.98
29.2
Run Numbers
33-41
Temp
°C
440
440
TCLP
mg/L
0.31
7.61
*AII tests were 0.5-hr, duration with 13% sulfur content in the feed soil.
-------
Table 6. Metal Treatment Results with 75/25 SSM/Topsoil Blend*
Untreated
Soil
Metal
Ni
Zn
Salt
Added
Ni(OH)2
ZnO
Metal
Concen-
tration
(ppm)
2,000
2,000
TCLP
mg/L
0.54
36.3
Run Numbers
27-95
Temp
°C
250
250
TCLP
mg/L
1.95
25.6
Run Numbers
27-96
Temp
°C
300
300
TCLP
mg/L
2.5
22.6
Run Numbers
27-97
Temp
°C
350
350
TCLP
mg/L
4.7
24.8
*AII tests were 0.5-hr, duration with 13% sulfur content in the feed soil.
Table 7. Metal Treatment Results with 75/25 SSM/Topsoil Blend*
Metal
Cd
Pb
Ni
Zn
Salt
Added
CdO
PbO
Ni(OH)2
ZnO
Untreated
Soil
Metal
Concen-
tration
(ppm)
200
2,000
500
500
Run Numbers
33-12
TCLP
mg/L
2.37
2.40
0.097
6.76
Temp
°C
250
250
250
250
TCLP
mg/L
0.33
0.38
0.28
3.49
Run Numbers
33-13
Temp
°C
300
300
300
300
TCLP
mg/L
0.17
0.41
0.35
4.60
Run Numbers
33-14
Temp
°C
350
350
350
350
TCLP
mg/L
<0.01
<0.10
0.08
0.80
Run Numbers
33-15
Temp
°C
400
400
400
400
TCLP
mg/L
<0.01
<0.10
<0.01
0.11
*AII tests were 0.5-hr, duration with 13% sulfur content in the feed soil.
these metals in the SARM blend (Table
3).
Based on the results from these three
tests with high levels of added metals in
the 75/25 SSM/topsoil blend, a fourth blend
was prepared at intermediate concentra-
tions of Cd, Pb, Ni, and Zn and run at
various temperatures. This blend was pre-
pared to more fully challenge the process
at the highest concentrations possible and
yet still achieve a passing TCLP for the
treated soils.
However, the results in Table 7 show
that the fourth blend did not adequately
challenge the process for all of the met-
als. These experiments demonstrate sig-
nificant reduction of TCLP values for the
treated soils for lead and, at elevated tem-
peratures, for cadmium. Zinc was not
greatly reduced and the nickel results were
inconclusive due to a too-low TCLP value
for the starting soil. Tests of additional
blends with higher metal contents are
needed to arrive at a more suitable dem-
onstration test mixture.
Finally in Table 8, a soil blend was then
spiked to 10,000 ppm by weight of cobal-
tous (II) oxide and run at several tempera-
tures. In contrast with the other metals,
lower treatment temperatures actually en-
hanced the leachability of the cobalt from
the added cobaltous oxide. This may be
due to formation of a more acid soluble
surface on the particles.
Summary of Metals Tests
Preliminary results of the screening tests
on different spiked soil mixtures provide
Table 8. Metal Treatment Results with 75/25 SSM/Topsoil Blend
Metal
Co
Salt
Added
CoO
Untreated
Soil
Metal
concen-
tration
(ppm)
10,000
Run
Numbers
23-40
TCLP
mg/L
15.0
Temp
°C
350
TCLP
mg/L
65.8
Run
Numbers
23-42
Temp
°C
440
TCLP
mg/L
11.3
'All tests were 0.5 hr. duration with 13% sulfur content in the feed soil.
the opportunity to assess the response of
the different heavy metals to stabilization
by the Sulchem Process. Each metal re-
sponds differently, but in general there
will be a maximum metal content that can
be processed to achieve passing TCLP
leachate values. The maximum metal con-
tent that can be reduced to the TCLP
regulatory limit by the process will vary
somewhat, based on the reaction tem-
perature, reaction time, sulfur stoichiom-
etry, or organic content of the soil. In
general, however, a batch screening test
at 250°C, using sulfur content on the or-
der of 10 to 15% and reaction time of one
half hour will define an approximate upper
limit of the content of each metal that can
be processed. Higher levels of metals can
be processed to give passing TCLP val-
ues by increasing the temperature and/or
adding soluble sulfide, particularly for cad-
mium, nickel, cobalt, and zinc. Increasing
the stoichiometry or reaction time provides
only a marginal improvement.
Recognizing that actual soil composi-
tion will affect the results, treatability stud-
ies are required to more precisely define
the metal concentration that can be pro-
cessed for a particular soil to give accept-
able TCLP leachate values. Based on the
very limited tests to date, lead limits of
approximately 10,000 ppm and cadmium
of several thousand ppm would seem to
-------
be generally feasible. Copper responds
very well and nickel and zinc appear to be
processed although the results are mixed.
No definitive information on arsenic or
chromium could be developed from the
SARM-III tests.
Rotary Soil Reactor Tests
CHMR conducted six tests for organic
compound destruction using a rotary soil
reactor. The tests were conducted using
manufactured gas plant (MGP) site soils.
The MGP sample was selected for the
larger-scale rotary soil reactor runs be-
cause 1) these soils typically have high
levels of higher boiling aromatic hydrocar-
bons but very few VOCs and 2) there are
over 1500 MGP sites across the United
States. Approximately 15 gallons of the
material was obtained from the site. Table
9 summarizes the characterization of the
MGP sample.
The objectives of the tests were to dem-
onstrate organic destruction at a larger
scale using Superfund soil and the
Sulchem configuration present in the ro-
tary reactor, and to determine the appro-
priate process conditions for optimal
destruction. Four runs were conducted
using the soil as it was obtained from the
site. Two runs were conducted with soil
that was dried to reduce the moisture con-
tent and thereby reduce the vapor flow
rate.
Table 9. Characterization of MGP Sample
Runs were made at 300° and 350°C at
reaction times of 0.5 and 1.0 hours. A
one-hour residence time at reaction tem-
perature was used initially because it was
thought to provide sufficient time for the
reaction to proceed completely. A half-
hour residence time was used for two of
the six runs to determine whether a half
hour was sufficient for the reaction to pro-
ceed.
The sulfur/soil ratio was generally 10%,
but runs were also conducted at 6 and
20%. Four of the runs were conducted
with the soil as it was obtained from the
site. Before conducting two of the runs,
the soil was dried to reduce the moisture
content and thereby reduce the vapor flow
rate.
Analyses were conducted using EPA
Methods 3550, 3660, and 8100 which in-
volve extraction with methylene chloride,
followed by analysis using gas chromato-
graphic methods. The GC/FID results were
quantitated by calibrating for four major
constituents (2-methyl naphthalene,
acenaphthene, phenanthrene, and pyrene)
which covered the boiling point range for
the contaminants in the soil. In addition to
quantifying the recovery of these com-
pounds, semi-quantitative recoveries for
other constituents in the GC (which had
been identified by GC/MS) could also be
determined from the ratio of GC/FID peak
areas for both the starting soil and the
Moisture Content
Total Extractable Organics
Particle Size Distribution
Organic Compound Types
Napthalene, and C,-,C2-, C3-substituted
Dibenzothiophene, and C,-,C2-, C3-substituted
Fluorene, and C,-,C2-, C3-substituted
Phenanthrene, and C,-,C2s C3-substituted
Pyrene, and C,-, and C2-substituted
Chrysene, and C,-, and C2-substituted
Dibenzoanthracene
Benzopyrenes and Benzofluoranthenes
Pristane
Phythane
<4 mesh
4-10 mesh
10-20 mesh
20-60 mesh
>60 mesh
20.1%
2.8%
51.1%
20.7%
14.7%
11.2%
2.2%
1253
423 \iglg
623 ng/g
1626ng/g
1343ng/g
605 (ig/g
30 ng/g
543 ng/g
366 fig/g
256 ng/g
product fractions based on their relative
quantities and dilutions as were done for
the four compounds that were quantitated.
These other constituents showed similar
behavior of recovery as a function of boil-
ing point.
Quantitative Results
Table 10 shows the run conditions and
quantitative results from the experimental
runs, including individual product fractions.
Several of the caustic traps were also
extracted for organics, but very low quan-
tities were found. Therefore the summary
table only lists the reactor solids, conden-
sate trap (trap #1), and the ice trap (trap
#2). The percent recovered from the over-
head, percent destroyed, and DRE for six
compounds are given. The results for the
two highest boiling compounds are based
on initial concentrations measured by GC/
MS analysis.
The lowest boiling compounds (me-
thyl naphthalenes) showed very little de-
struction, although the ratio of 1-methyl
naphthalene to 2-methyl naphthalene de-
creased by a factor of two to three. In
addition, naphthalene, not found in the
original soil, was produced in the pro-
cess, presumably by partial reaction of
higher homologs. Differences in reac-
tion rates are also observed for the in-
termediate boiling aromatics (dimethyl
naphthalenes, acenaphthene, fluorene,
phenanthrene, in the boiling point range
between 260° and 340°C.) These com-
pounds show destructions ranging from
about 50 to over 90%, whereas some of
the saturated hydrocarbons in the same
boiling range (pristane and phytane) are
generally present in the products at
about 50% of the feed content.
Higher boiling aromatic hydrocarbons
(pyrene, chrysene, benzopyrene, etc., with
BP>340°C) are nearly completely de-
stroyed with only very low levels, or non-
detect levels, observed in any of the
product fractions. This indicates that the
process works well for the high boiling
point compounds, even at temperatures
below their boiling points.
The recoveries of the four compounds
that were quantified by the analytical
method are representative of the yields
observed semi-quantitatively for the other
hydrocarbons with similar boiling ranges
in the test soil. The effect of boiling range
on the fate of the hydrocarbon contami-
nant in the soil, whether desorbed into the
overhead, chemically destroyed, or left as
trace residuals on the treated soil, are
similar to the initial screening studies on
the effect of boiling range on the fate of
contaminants in the process.
-------
Table 10. Rotary Reactor Tests-Recoveries
BP
°C
Run 46-6: 350°C,
1 hour, 6.9% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
Run 46-10: 350°C,
1 hour, 20% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
Run 46-14: 300°C,
1 hour, 11% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
Run 46-18 350°C,
1 hour, 9.1% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
Run 46-22 300°C,
0.5 hour, 9.1% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
Run 46-26 350°C,
0.5 hour, 11.1% Sulfur,
mg recovered/kg feed
2-methyl naphthalene
acenaphthalene
phenanthrene
pyrene
chrysene
benzopyrene/benzofluoranthene
241
278
340
393
448
M50
241
278
340
393
448
>450
241
278
340
393
448
>450
241
278
340
393
448
>450
241
278
340
393
448
>450
241
278
340
393
448
>450
Fraction
mg/kg feed
58.9
257.9
380.0
633.6
323
680
58.9
257.9
380.0
633.6
323
680
58.9
257.9
380.0
633.6
323
680
58.9
257.9
380.0
633.6
323
680
58.9
257.9
380.0
633.6
323
680
58.9
257.9
380.0
633.6
323
680
Reactor
0.09
0.00
0.09
0.08
0.00
0.00
0.00
0.00
0.00
0.08
0.00
0.00
0.00
0.44
1.07
0.58
0.00
0.00
1.90
1.56
5.74
1.99
0.00
0.00
0.88
0.00
0.89
0.00
0.00
0.00
0.69
0.38
0.96
0.55
0.00
0.00
Trap 1
49.03
19.87
46.09
3.90
0.00
0.00
24.96
9.79
13.54
0.00
0.00
0.00
71.08
21.91
60.50
0.00
0.00
0.00
18.00
11.20
50.22
0.00
0.00
0.00
115.57
0.00
59.09
0.00
0.00
0.00
106.71
16.69
165.34
6.53
0.00
0.00
Trap 2
6.84
0.74
5.30
0.00
0.00
0.00
0.30
0.05
0.34
0.00
0.00
0.00
1.04
0.15
2.37
0.00
0.00
0.00
0.79
0.00
2.12
0.00
0.00
0.00
1.93
0.00
2.99
0.00
0.00
0.00
2.47
0.00
7.64
0.00
0.00
0.00
Overhead
Recovery
94.8
8.0
13.5
0.6
0.0
0.0
42.9
3.8
3.7
0.0
0.0
0.0
122.4
8.6
16.5
0.0
0.0
0.0
31.9
4.3
13.8
0.0
0.0
0.0
199.4
0.0
16.3
0.0
0.0
0.0
183.5
6.5
45.5
1.0
0.0
0.0
Destruction
%
5.0
92.0
86.5
99.4
>99.9
>99.9
57.1
96.2
96.3
>99.9
>99.9
>99.9
-22.4
91.3
83.2
>99.9
>99.9
>99.9
64.9
95.1
84.7
99.7
>99.9
>99.9
-100.9
>99.9
83.4
>99.9
>99.9
>99.9
-86.4
93.4
54.2
98.9
>99.9
>99.9
ORE
%
99.8
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
99.8
99.7
>99.9
>99.9
>99.9
96.8
99.4
98.5
99.7
>99.9
>99.9
98.5
>99.9
99.8
>99.9
>99.9
>99.9
98.8
99.9
99.7
>99.9
>99.9
>99.9
-------
The soil reactor showed nearly com-
plete conversion for chrysene and ben-
zopyrene, two compounds with boiling
points above 400°C, and 99% conversion
for pyrene. For lower boiling compounds,
as anticipated, the soil reactor showed
the effects of competition between reac-
tions with sulfur, and desorption for the
organic compounds.
Conclusions and
Recommendations
The Sulchem process was shown to
destroy certain polynuclear aromatic com-
pounds in soil (particularly higher boiling
compounds such as pyrene, chrysene and
benzopyrene) in a reactor when operated
at temperatures between 300° and 350°C.
However, a reactor configuration capable
of efficient destruction of a broader range
of compounds was not obtained. This limi-
tation may have been due more to limita-
tions of the laboratory study, rather than
inherent limitations of the technology. Spe-
cific conclusions from this laboratory study
of the Sulchem Process are as follows:
Destruction within the soil reactor
was strongly correlated with com-
pound boiling point:
- Organic compounds with boil-
ing points above 350°C are es-
sentially completely destroyed in
the process (destruction >
99.5%);
- Organic compounds with boil-
ing points in the range of 250°
to 350°C are partially destroyed.
However, a significant quantity
volatilize before destruction oc-
curs;
- Organic compounds with boil-
ing points below about 250°C
primarily volatilize from the soil
reactor before reaction can oc-
cur;
A second stage sulfur/vapor reac-
tor was shown to destroy a signifi-
cant percentage of the organics
desorbed from the soil reactor,
thereby requiring subsequent treat-
ment of the condensate produced;
Metal stabilization in the treated soil
(as measured by TCLP) is achiev-
able for certain metals (particularly
lead, cadmium, zinc, copper, and
nickel) due to sulfide formation, with
performance limits depending on
the chemical form and concentra-
tion (e.g., typically lead below
10,000 mg/kg, cadmium below 1000
mg/kg).
Remediation costs employing the
Sulchem Process are estimated at $105
to $183/ton based on site size, reactor
configuration, and processing rate.
Only very limited testing of reactor con-
figurations or techniques to destroy vola-
tilized organics was employed. CHMR
recommends additional testing of vapor-
phase organic reactors at higher tempera-
tures (^00°C or higher) and longer
residence times. From this, the destruc-
tion efficiency (and its limits) can be de-
termined for an integrated soil/vapor
reactor system.
-------
A. Bruce King and Stephen Paff are with the Center for Hazardous Materials
Research, Pittsburgh, PA 15238. The EPA Author, Randy A. Parker (also the
EPA Project Officer, see below) is with the National Risk Management Re-
search Laboratory, Cincinnati, OH 45268.
The complete SITE Emerging Technology report, entitled "Simultaneous Destruc-
tion of Organics and Stabilization of Metals in Soils," (Order No. PB98-133150,
Cost: $25.00, subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-605-6000
The EPA Project Officer can be contacted at
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
10
-------
-------
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/540/SR-98/500
BULK RATE
POSTAGES FEES PAID
EPA
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