Environ. Sci. Technol. 1994, 28, 1801-1807
Thermal Treatment of Fuel Oil-Contaminated Soils under Rapid Heating Conditions Ver6nica Bucal6, Hiroshi Saito, Jack B. Howard, and Willlam A. Peters' Department of Chemical Engineering, Energy Laboratory and Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Batch samples (-50 mg) of 63-125-w.m particles of a U.S. EPA synthetic soil matrix, neat or contaminated with 4 or 7 wt % of no. 2 fuel oil, were subjected to preselected temperature-time histories. Effects of heating rate, final temperature, heating time, and contamination level on extents and apparent global rates of contaminant removal were studied. At 1000 "C/s, the percent fuel oil removal approached 100% in about 0.7 s (final temperature = 700 "C). Most of the oil can also be eliminated by heating the sample to final temperatures of 300 and 500 "C at 1000 "C/Sand then continuing heating for about 25 s. Heating rate affects the details of oil release but heating to 300 "C at 200 or 1000 "C/s each gave oil decontamination efficiencies that approached 100% in about 25 s. For the same peak temperature and heating rate, soils with initial contaminant levels of 4 or 7 wt % required about the same total heating time for essentially complete removal of the oil. Products generated during the heating of selected soil samples were collected and analyzed. The results imply that significant chemical transformations of the fuel oil probably occur during higher temperature, e.g., 500 "C, thermal treatment.
contaminated soil samples, time of contaminant adsorption, and contaminant type on the desorption rate have been also investigated ( 4 , 5). Temperature emerges as perhaps the single most important variable in the thermal decontamination of soil (e.g., refs 4 and 8-10). However, its effects are usually better understood by also evaluating the collateral impact of heating rate and total heating time. To these ends, this paper focuses on temperature and related effects on soil decontamination under rapid heating conditions (e.g., 1200 "C/s) pertinent to thermal treatment of finely divided (e.g., 0.05-0.25 mm diameter) soil particles. Data are provided on how independent variations in temperature, heating rate, and treatment time, as well as initial concentration of contaminant, affect the removal of no. 2 fuel oil from a US. EPA synthetic soil matrix. Selected volatile products composition data are also provided. These results are pertinent to a number of current and emerging thermal technologies for above-ground or in situ treatment of soil, e.g., fluidized bed and plasma heating, air stripping, thermal desorption, and the early stage of heating smaller soil particles in rotary kilns. Methods and Materials
Development and implementation of reliable, publicly acceptable technologies to clean up Superfund and other hazardous waste sites is a major focus of modern environmental science and technology. Thermally based soil treatment methods are of interest in this regard ( I , 2). To achieve the desired decontamination efficiencies while minimizing undesired byproducts, there is a need for a better understanding of the basic physical and chemical processes that occur during soil treatment, e.g., adsorption and desorption of organic contaminants by soil particles during heating. There have been many pertinent studies. Among these, Wu et al. (3) used chromatographic response analysis to study mass transfer mechanisms and equilibrium behavior of organic contaminants in soil matrices. Lighty et al. ( 4 ) found that the rate of p-xylene evolution from various materials (sand, glass beads, clay, and peat) is a strong function of sorbent properties, with nonporous materials exhibiting a faster rate of xylene removal. An electrodynamic thermogravimetric analyzer was used by Tognotti et al. (5)to analyze contaminant adsorption and desorption rates on or from montmorillonite clay and two powdered chars (Spherocarb and Carbopack). The results indicate that adsorptionfdesorption phenomena depend on sorbent characteristics such as surface area and size distribution of micropores. Adsorption experiments indicated that moisture sharply reduces the soil sorption capacities for organic compounds (6, 7). Lighty et al. (8) observed a faster desorption of contaminant with moisture present and attributed this to steam distillation of the contaminant. Effects of the method of preparation of
A US. EPA synthetic soil matrix was prepared elsewhere to reflect the attributes of soils at Superfund sites. Its makeup was guided by an extensive review of 86 records of decision and an independent study of the composition of eastern US. soils (11). Small particles (63-125 pm, obtained by sieving) were studied to reduce intraparticle temperature and concentration gradients during rapid heating. Heat transfer calculations imply that internal temperature gradients are small (112 "C) for a monolayer of particles of this size, except possibly for the highest heating rate studied here (6100 "C/s) where a gradient of several tens of K could exist between the particle surface and its center, but only for about 12 ms. Chemical analysis of this size fraction found 0.3 wt % organic carbon and 3.7 wt % carbonate carbon. The samples were conditioned in a desiccator with drierite for 2 days. The moisture content (typically 1wt % ) was then determined by drying a portion of the sample in a 110 "C oven until it reached constant weight. Using a technique similar to method 2 described by Lighty et al. (41, the soil was contaminated with 4 or 7 wt % of a no. 2 fuel oil that had been extensively chemically analyzed (12). A desired amount of oil was placed directly onto a soil sample of about 1cm in depth using a syringe. The soil was then carefully shaken by hand for 1 h and allowed to sit for approximately 24 h. The contamination level of soil was routinely determined as the weight difference between contaminated and neat soils. These values compared well with contamination levels determined by extraction of selected contaminated samples with methylene chloride. A 7% oil loading is relevant to sites with high contamination levels and to rapid response cleanups of oil spills on soil.
0 1994 Amerlcan Chemical Society
Environ. Sci. Technol., Vol. 28, No. 11, 1994 1801
Introduction
0013-936X/94/0928-'1801$04.50/0
Reactor vessel
Vacuum
I
Sunken reaim to hold soil
Aluminum liner
LE?!?!?
Aluminum liner
Side view
4 He feed
Figure 1.
Front view of the capme sample reactor showing the foil hot stage end various stations for collection of tars and other condensables.
'\Mounting
Aluminum liner
\
He feed
Flange
I
\
Figure 2. Side view 01 the captive sample reactor showing the loading rod posltloned to drop soil particles onto the foil.
Captive soil samples of known weight (-50 mg), contaminated or neat in control runs, were heated by passing electrical current through a hot stage. The apparatus (Figures 1 and 2) is similar to the electrical screen heaters of Suuberg (18,Suuberg et al. (14),Caron (15),Hajaligol ( I @ , Hajaligol et al. KO (18),and KO et al. (19),amongothers,butwas modifiedintworespects. To prevent the loss of friable soil particles, the heating screen was replaced with a 0.001 in. thick stainless steel foil with a 0.79 in. i.d., 0.11 in. deep cylindrical well to confinethe soil (Figure 1). The foil was mounted between two large aluminum electrodes within a cylindrical Pyrex chamber. Before heating the soil, the reactor was flushed (evacuated with a mechanical vacuum pump and refilled) with helium several times (four times for weight loss experiments and seven for runs that included products collection). The second modification was implemented to inhibit the evaporation of fuel oil during this flushing. A movable cylindrical loading rod (Figure 2) was used to add soil to the foil after purging the reactor. This rod consists of three 0.75 in. diameter aluminum sections connected hy on-axis screws and threads. Soil is placed in the middle (0.75 in. long) section of the rod in a 0.125-
(In,
1802 Envkon. Scl. Tschnol., Vd. 28. No. 11. 1994
in. blind hole drilled along a diameter of the rod to a depth of 0.63 in. Soil was added to the foil by pushing the rod into the reactor chamber through two seals mounted on a side flange (Figure 2), until the rod was directly above the depression in the foil, and then rotating the rod about itsaxistodump thesoilontothefoilwell. Thesoilparticles were then spread into approximately a monolayer by agitating the foil using a vibrator contacting the chamber top. The middle section of the rod is relatively light and is separable from the other sections for weighing. The amount of soil used in a run was determined as the weight reduction in this piece due to dumping the soil. Heating rate, final temperature, and time at final temperature were independently selected for each experiment by adjusting variable transformers and timers that determined power levels and heatup and holding times. Figure 3 defines peak temperature and various experimental times. Samples cooled down naturally, mainly by radiation and/or convection at initial rates between 400 and 600 OC/s depending on peak temperature. Soil temperaturetime histories (Figure 3) were measured throughout each experiment, by using a rapid response (0.0005-in. thermocouple junction thickness), type K thermocouple placed beneath the foil. Heat transfer calculations imply that the thermocouple closely tracks the bulk mean temperature of the soil particles (e.g., conservativelyto within about 10 "C at a nominal heating rate of 1000 Ws). For runs that included products collection, the reactor was purged with a constant helium flow rate of 0.5 L/min for 90 min, beginning a few seconds before the start of heating. Tars were collected (Figures 1 and 2) on aluminum reactor liners, on a stationary aluminum funnel at the reactor exit, on a small microfilter held firmly in a fitting at the reactor exit, and directly on (unlined)reactor walls. The funnel facilitates tar collection by helping direct tar vapor andaerosolstoward themicrofilter (18,I9).The totaltaryieldwasdeterminedgravimetricallyastheweight increase of the liners, funnel, and filter plus the weight of material obtained by a solvent (CHzClz) wash of unlined surfaces within the reactor. Downstream of the tar filter at the reactor exit was a condensable product trap, which consisted of 3 in. of 3% OV-17 on SO/lOO mesh Gas Chrom Q followed by about 3 in. of50/80meshPorapakQpackedintoa6mmdiameter U-shaped Pyrex glass tubing. This trap was cooled in a -40 O C alcohol-dry ice bath. The material collected in this trap was also measured gravimetrically. Further downstream was a trap to collect light gases, e.g., CO, COz, and C1- Czhydrocarbons. This consisted of a 15 in. long,
e I
Peak Temperature
Holding Time
i
J
+-
-1
-1
41 /
i
o
Flgure 3. Schematic showing typical temperature-time profiles obtainable in the captive sample reactor and defining heatup, holding, and heating times.
1/4 in. 0.d. U-shaped stainless steel tube packed with Porapak Q. This trap was immersed in a Dewar flask of liquid nitrogen at -196 "C. Yields of light gases were quantified by analyzing the trap contents by gas chromatography. Soil weight loss was determined as the weight difference between the soil loaded from the rod and the soil residue on the foil after the run. The fuel oil removal was calculated from the expression: removal (% ) =
WL, - WLJ1- L,) LC
h
1
5
0
$ 1
A
a
801
N
x 100
(1)
where WL, (mg of volatilized/mg of initial contaminated soil) and WL, (mg of volatilized/mg of initial neat soil) are the fractional weight losses of the contaminated soil and neat soil, respectively, under closely similar heating conditions, and L, is the fractional contamination level (mg of fuel/mg of contaminated soil). This calculation assumes that the fuel oil in the contaminated soil does not affect the volatiles release from the neat soil.
Results Effects of peak temperature on the weight loss of neat and contaminated (7 wt 7%) soil samples and on the corresponding percentage removals of fuel oil calculated according to eq 1are shown in Figures 4 and 5, respectively. These are zero holding time experiments in which the soil was heated to the indicated peak temperatures at a nominal rate of 1000 "Cis, followed immediately by the cooling of the sample. Likely contributors to weight loss from neat soil (Figure 4) are moisture and possibly some tar at low temperatures and tars, CO, and COZ at higher temperatures. Products yields for 25-5 holding time experiments are presented in Tables 1and 2. Calculated oil removals approach a nominal value of 100% at 700 "C (Figure 5). A propagation of error analysis on eq 1implies 100 f 6 % However, selected samples of contaminated soils from experiments showing the high extents of oil removal (i.e., approaching 100% by thermal treatment were extracted with methylene chloride after cool down. The resulting extract yields were comparable to those from control runs on cooled residues of uncontaminated soil. This finding further supports the picture that thermal treatment
.
z0
1
50 200
300
400
500
600
700
800
Peak Temperature ("C) Flgure 5. Percentage removal of no. 2 fuel oil as affected by peak temperature calculatedfor the data of Figure 4 using eq 1 (heating rate = 1000 OC/s; zero holding time; initial contamination level 7 wt %). The curve is a free-drawn trend line.
efficiently removed the fuel oil with little or no oil residues on the soil and also reinforces confidence in the use of eq 1. The weight loss behavior of neat and contaminated soil samples for temperatures above 700 "C was also studied. However, the data are not detailed here because of poor reproducibility in the results for contaminated soils, Figures 6 and 7 present the effect of holding time on the weight loss exhibited by neat and contaminated soil samples heated at 1000 "C/s to final temperatures of 300 and 500 "C,respectively. These figures show the following: the precision in weight loss data for neat and contaminated soils; the significant amount of weight loss that occurs during heatup to final temperature; the significant weight loss from neat soil; and thus the importance of correcting for neat soil devolatilization in interpreting weight loss data for contaminated soil. For example, oil removal at 300 and 500 "Cis about the same after about 10-15 s ofheating at either temperature (Figure Envlron. Scl. Technol., Vol. 28, No. 11, 1994 1803
Table 1. Volatile Products from Heating Soil Samples to 300 and 500 "C at 1000 "C/s; Holding Time = 25 s
peak temp, 300 "C neat soil" wtloss ( % ) condensables (mg) tars (mg)
co (PP) coz ( P d
CH4 (rg) CzHz (rg) CZH4 (Pg) CZH6 (Pg) no. 2 fuel oil removal ( % )c condensables tars as % of fuel oil removedd light hydrocarbon gases as % of fuel oil removedd
contaminated soil 7 w t
0.80 0.00 0.44 16.84 99.02 0.87 0.31 0.69 0.90
%b
7.60 2.30 1.26 17.23 64.00 2.31 0.31 5.23 1.02
3.23 0.41 0.72 24.01 286.36 2.88 0.42 2.90 1.68
97.9 91.1 0.18
+
peak temp, 500 "C contaminated soil 7 wt % ' b
neat soil"
10.00 2.64 1.62 32.00 320.00 58.00 2.55 204 17 99.9 89.5 7.83
0 Basis = 46.5 mg of neat soil. Basis = 50 mg of contaminated soil = 46.5 mg of neat soil 1. After correction for contribution of neat soil.
+ 3.5 mg of fuel oil.
Removal calculated by eq
Table 2. Volatile Products from Heating Soil Samples to 300 "C at 200 "C/s for Initial Contaminant Level of 7 wt % and at 1000 "C/s for Initial Contamination Level of 4 wt %; Holding Time = 25 s
heating rate, 200 "Cis heating rate, 1000 "Cis neat soil" contaminated soil 7 wt % b neat soilc contaminated soil 4 wt wtloss(70) condensables (mg) tars (mg) co (Pg)
0.66 0.00 0.60 22.61 102.24 0.85 0.31 0.33 0.60
con (PLP)
CH4 (Pg) CzHz (fig) CZH4 (Pg) CZH6 (Pg) no. 2 fuel oil removal
(%)e
condensables + tars as 70 of fuel oil removedf light hydrocarbon gases as 70 of fuel oil removedf
7.52 1.60 1.42 25.61 107.35 1.24 0.30 0.96 0.45
0.80
0.00 0.45 17.39 102.21 0.90 0.32 0.71 0.93
98.7 70.1 0.03
%d
4.75 0.56 0.65 17.17 78.04 1.44 0.32 1.67 1.28 99.6 38.2 0.09
0 Basis = 46.5 mg of neat soil. b Basis = 50 mg of contaminated soil = 46.5 mg of neat soil + 3.5 mg of fuel oil. Basis = 48 mg of neat soil. Basis = 50 mg of contaminated soil = 48 mg of neat soil + 2 mg of fuel oil. e Removal calculated by eq 1. f After correction for contribution of neat soil.
d
i
1
1
"
6
2i 0:
,
-
0.0
0
0.3
10
20
30
Holding Time ( s )
Heatup Time ( s )
-0 0.0
0
05
t 3
10
__ 20
-I. -
30
r
Holding Time ( s )
Heatup Time ( s )
Flgure 6. Weight loss data for neat (0)and contaminated soil (a7 = 300 OC; heating rate = 1000 "Cis). Curves are free-drawn trend lines.
Flgure 7. Weight loss data for neat (0)and contaminated soil (a, 7 wt % fuel oil) (peak temperature = 500 "C; heating rate = 1000
8) even though casual comparison of the closed squares of Figures 6 and 7 could lead to the false conclusion that oil removal at 500 "C is higher than at 300 "C for all heating times studied. Figure 8 also shows that most of the oil
(i.e., approaching 100%) can be eliminated a t a lower temperature (300 "C) by longer heating (about 25 9). Heating rate effects were studied by heating neat and contaminated soil specimens to a final temperature of 300
wt % fuel oil) (peak temperature
1804 Environ. Sci. Technol., Vol. 28, No. 11, 1994
"Us). Curves are freedrawn trend lines.
10
r/
3
,
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Heating Time (s) Figure 8. Average percent removal of no. 2 fuel oil as affected by total heating time, calculated from the data of Figures 6 and 7 using eq 1 (heating rate = 1000 "CIS; initial contamination level = 7 wt % fuel oil; 0, peak temperature = 300 "C; H, peak temperature = 500 "C). Curves are free-drawn trend lines.
,
I
10
Figure 10. Weight loss data for neat and contaminated soil (7 wt % fuel oil) as affected by holding time at final temperature for different heating rates (peak temperature = 300 "C; 0,neat soil heated at 1000 "C/s; W, neat soil heated at 200 "C/s; 0, contaminated soil heated at 1000 "CIS; 0, contaminated soil heated at 200 OC/s).
' 7
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1 7
70-
k-
e:
60-
M
4
0 100
1000
H e a t i n g Rate ("C/s)
10000
Figure 9. Average percent removal of no. 2 fuel oil as affected by heating rate (peak temperature = 300 "C; initial contamination level = 7 wt O h fuel oil; zero holding time). The curve is a freedrawn trend line.
"C at 200, 1000, and 6100 OC/s and then immediately allowing the cooling to begin. The corresponding percentage fuel oil removals (Figure 9) show that more oil is evolved with decreasing heating rate. This is qualitatively consistent with the proposition that slower heating provides more time for oil removal during heatup. To further investigate this hypothesis, experiments were performed to determine if continued heating at final temperature produced, for higher heating rates, oil removals comparable to those obtained at lower heatup rates and shorter holding times, i.e., fuel oil removal was determined for samples heated to 300 "C at 200 or 1000 "C/s and then maintained at that temperature for an additional time up to 25 s. Figures 10 and 11respectively show the weight loss and corresponding oil removal. Figure
I
to
20
30
Holding Time ( s ) Figure 11. Average percent removal of no. 2 fuel oil as affected by holding time at final temperature (peak temperature = 300 "C; Initial contamination level 7 wt %; 0, heating rate = 200 "CIS; 0, heating rate = 1000 "C/s).
11 shows that for either heating rate the fuel oil can be virtually eliminated at 300 "C by continuing heating for about 25 s. This figure also shows higher oil removal at zero holding time at 200 "C/s as would be expected, since more time is available during heatup (see Figure 9). However, the additional oil removal between 0 and 15 s is more rapid and extensive for the 1000 "C/s case. This suggests that the oil remaining at zero holding time is more resistant to removal (or destruction) for 200 "C/s heating, e.g., it is richer in less volatile components or is chemically more stable. Supporting this reasoning, Tables 1 and 2 show that, despite similar oil removals from 25-9 heating at 300 O C for 200 OC/s or 1000 "C/s heating rate experiments, liquids with a greater content of more volatile components (i.e., condensables vs tars) were more prevalent in the products from faster heating (Table 1). Envlron. Scl. Technol., Vol. 28, No. 11, 1994 1805
104
i I
4
I
AM
1
E
4-1
. 04
r
1
I
0 0.3
0.0
c _ _ _
-1
I
10
30
2o
P
Holding Time ( s )
Heatup (s)
Time
Figure 12. Weight loss data for neat and contaminated soil as affected by heatingtime for different initialcontaminationlevels (peaktemperature = 300 "C;heating rate = 1000 "CIS;H, neat soil; 0, contaminated soil, 7 wt % fuel oil; 0 ,contaminated soil 4 wt % fuel oil). Curves are free-drawn trend lines. i h
w
v
are presented in Tables 1and 2. The typical distillation range for no. 2 fuel oil is 160-390 "C. Thus most or all of the oil, in the absence of chemical reactions, would be expected to collect in the tars and condensables fractions of the present products recovery system. In two of the three 1000 OC/s cases (Tables 1 and 2), the material in these two fractions accounts for about 90% of the oil evolved. However in the third case (Table 2), heating the soil with 4 wt % oil contamination to 300 OC, tars plus condensables account for onlyabout 38% of the oil evolved. This result, which was confirmed in two replicate experiments, may reflect lower oil collection efficiencies in the tars and condensables traps a t smaller initial loadings of contaminant. This would explain the high tar and condensables accountabilities for oil removal for identical thermal treatment of a soil sample with 7 wt % oil contamination (Table 1). For a 1000 OC/s heating rate, the small yields (absolute and, as a percentage of oil removal0.09-0.18 % ) of light hydrocarbon gases for a final temperature of 300 OC suggest that little or no oil is converted to gases for this relatively mild thermal treatment schedule. However, at a final temperature of 500 OC, light hydrocarbon gases are estimated to account for almost 8% of the oil evolved (Table 11, suggesting that more significant chemical transformations of the oil occur at or during heating to this temperature. As discussed above, Figure 11plus Tables 1and 2 suggest that for slower heating, Le., 200 "C/s, physicalprocesses, e.g., preferential evaporation of more volatile components, or chemical reactions of the oil may modify oil composition a t a much lower temperature (i.e~,300 "C). Discussion
X I
80
50
~
I
0
0.0
0.3
c---d
I
10
20
30
Holding Time ( s )
Heatup Time ( s ) Flgure 13. Average percent removal of no. 2 fuel oil as affected by holding time for different initial contamination levels (peak temperature = 300 "C;heating rate = 1000 " U s ; 0,contamination level = 7 wt % fuel oil; . , contamination level = 4 wt % fuel oil).
Effects of initial contaminant loading (4 and 7 wt % ) were studied by heating soil specimens to 300 "C at 1000 "C/s and holding there for up to 25 s. Figures 1 2 and 13 respectively present the resulting weight loss and oil removal data. Figure 13shows little or no impact of initial contamination level on percentage oil removal a t different holding times. Volatile product distributions were measured for selected experimental conditions that in prior runs gave high or nearly complete oil removal after 25 s of thermal treatment. Results for different combinations of heating rates, final temperatures, and initial contamination levels 1806 Environ. Sci. Technol.. Voi. 28, No. 11, 1994
The present results (e.g., Figure 5) show that peak temperature strongly influences the extent of contaminant removal from the soil. For samples heated a t 1000 OC/s, essentially all of the fuel oil can be removed in under 1 s (peak temperature about 700 "C). Comparison of Figures 5 and 8 shows that, for samples heated at the same heating rate (1000 O C i s ) , almost complete removal of fuel oil can be achieved at lower peak temperatures (e.g., 300 vs 500 "C) by continuing heating for an additional 15-25 s. Qualitative observations, i.e., of the color of evolving tar vapors, indicate that the fuel oil undergoes some chemical modification a t treatment temperatures higher than 700 "C. More quantitative inferences are possible from products composition data. Methane and ethylene yields are somewhat different for neat vs contaminated soil samples heated for 25 s a t 300 "C after heating up to this temperature a t 1000 "Cis, but these and other light hydrocarbon gases account for little of the evolved oil (0.090.18%) (Tables 1and 2). These results suggest that there is little chemical modification of the fuel oil during or after heating the soil at 1000 OC/s to relatively low temperatures (300 "C). However, for the same heating rate and holding time at 500 "C, all four of the light hydrocarbon gases, i.e., CH4, CzH2, CzH4,and C2H6, were detected in much higher yields from contaminated vs neat soil (Table 1). The estimated increased gas production from the oil, i.e., the total gas make less the contribution from the soil itself, is sufficient to account for 7.83% of the evolved oil. This suggests that the fuel oil undergoes nonnegligible chemical transformations during thermal treatment at temperatures of 500 "C or perhaps even lower. Figure 9 shows that for a peak temperature of 300 "c, more oil is evolved with decreasing heating rate, Le., 77.5 9%
at 200 "C/svs 56.4% at 6100 "Us. Aplausible explanation is that, since more time is required for the specimen to obtain final temperature at low heating rates, slower heating provides greater opportunity for oil desorption during heatup. Figure 11 presents the oil removal for samples heated to 300 "C at 200 and 1000 "C/s and then maintained at that temperature for an additional time. If complete or high removal is required, the results indicate that it is necessary to heat samples for about an additional 25 s after first reaching 300 "C, regardless of the heating rate used. Tables 1 and 2 show that there are few differences in the light hydrocarbon gas yields (other than CzH4) from heating contaminated soil to 300 "C at 1000 and 200 "Us, respectively, but do suggest compositional differences in the liquids boiling range volatiles, i.e., those evolved at 1000 " U s , are enriched in more volatile components, Le., condensables. For slower heating (200 "C/ s), there may be preferential evaporation of more volatile components or some chemical transformations of the oil even for low final temperatures (300 "C). Conclusions
Laboratory-scale studies imply that prescribed thermal treatment can substantially eliminate no. 2 fuel oil contamination in soils. Rates and extents of oil removal can be manipulated by adjustments and to a certain degree by tradeoffs in treatment time, temperature, and heating rate. Peak or final temperature is the variable that most influences the extent of fuel oil removal and the propensity of the oil to undergo changes in chemical composition during thermal treatment. However, temperature effects should be scrutinized in light of potential collateral impacts of heating rate and total treatment time. As the peak temperature is increased, significantly shorter residence times are required for complete (i.e., approaching 100%) removal of the oil (e.g., about 0.7 s at 700 "C vs about 25 s at 300 "C). Comparisons ofvolatile product distributions from thermal treatment of neat and contaminated soils indicated that, for heating at 1000 "C/s, the fuel oil does not undergo significant chemical transformations at lower temperatures, i.e., around 300 "C, but that at 500 "C the oil does experience nonnegligible chemical modification. More detailed chemical analyses are needed to determine the yields and identities of fuel oil reaction products during thermal treatment of soil. Essentially complete removal of no. 2 fuel oil appears to be feasible under rather mild heating conditions, e.g., by heating to 300 "C at 200 "Us, and then continuing heating at this temperature for about 25 s. Mild changes in initial contamination level, from 7 to 4 wt % ,show little effect on the fractional extent of decontamination for 1000 "C/s heating to 300 "C for various holding times. Solvent extraction of cooled soil residues confirmed high extents of thermal removal of oil inferred from gravimetric measurements. Thus, the present methodology including the use of eq 1 is considered an accurate tool to predict the oil removal from soil, provided the presence of the oil does not affect the decomposition behavior of the soil itself. However, it is essential to correct for weight loss of the soil
itself in order to reliably determine rates and extents of oil removal from contaminated soils. Acknowledgments
We thank Dr. Seymour Rosenthal from Foster Wheeler Enviroresponse Inc. and Dr. Raymond M. Frederick from the U.S.EPA for providing the soil samples. Financial support of this research by NIEHS Grant ES04675-06 (MIT-Superfund Hazardous Substances Basic Research Program) and by the Northeast U.S. EPA Hazardous Substance Research Center is greatly appreciated. V.B. gratefully acknowledges the fellowship support of the Consejo Nacional de Investigaciones Cientlficas y TBcnicas (CONICET) of Argentina. We also thank Mr. Eric Freeman, Prof. Patrick Gilot, and Dr. Mathias Koch for technical contributions. Literature Cited (1) Oppelt, E. T.Environ. Sci. Technol. 1986,20 (4), 312-318. (2) Oppelt, E. T. JAPCA 1987, 37 (5), 558-586. (3) Wu, Y.G.;Dong, J.; Bozzelli, J. W. Combust. Sci. Technol. 1992,85, 151-163. (4) Lighty, J. S.;Pershing, D. W.; Cundy, V. A.; Linz, D. G. Nucl. Chem. Waste Manage. 1988,8, 225-237. (5) Tognotti, L.; Flytzani-Stephanopoulos, M.; Sarofim, A. F.; Kopsinis, H.; Stoukides, M. Environ. Sci. Technol. 1991,25 ( l ) , 104-109. ( 6 ) Chiou, C. T.; Shoup, T. D. Environ. Sci. Technol. 1985,19 (12), 1196-1200. (7) Pennell, K. D.; Rhue, R. D.; Rao, P. S. C.; Johnston, C. T. Environ. Sci. Technol. 1992, 26 (4), 756-763. (8) Lighty, J. S.; Silcox, G. D.; Pershing, D. W.; Cundy, V. A. Presented a t the Air Pollution Control Association, 81st Annual Meeting, Dallas, TX, 1988; Paper 88-17.5. (9) Lighty, J. S.;Silcox, G. D.; Pershing, D. W.; Cundy, V. A.; Linz, D. G. Environ. Prog. 1989, 8 ( l ) , 57-61. (10) Lighty, J. S.;Silcox, G. D.; Pershing, D. W.; Cundy, V. A.; Linz, D. G. Environ. Sci. Technol. 1990, 24 ( 5 ) ,750-757. (11) Esposito, P.; Hessling, J.; Locke, B. B.; Taylor, M.; Szabo, M.; Thurnau, R.; Rogers, C.; Traver, R.; Barth, E. JAPCA 1989, 39 (3), 294-304. (12) Leary, J. M.S. Thesis, Department of Chemistry, MIT, Cambridge, MA, 1982. (13) Suuberg, E. M. Sc.D. Thesis, Department of Chemical Engineering, MIT, Cambridge, MA, 1977. Peters, W. A.; Howard, J. B. Ind. Eng. Chem. (14) Suuberg, E. M.; Process Des. Dev. 1978,17, 37-46. (15) Caron, R. Batch Reactor Manual, In-House Report; Department of Chemical Engineering, M I T Cambridge, MA, 1979. (16) Hajaligol, M. R. Ph.D. Thesis, Department of Chemical Engineering, MIT, Cambridge, MA, 1980. (17) Hajaligol, M. R.; Howard, J. B.; Longwell, J. P.; Peters, W. A. Ind. Eng. Chem. Process Des. Dev. 1982,21, 457-465. (18) KO,G.H. Ph.D. Thesis, Department of Chemical Engineering, MIT, Cambridge, MA, 1988. (19) KO, G.H.; Sanchez, D. M.; Peters, W. A.; Howard, J. B.
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Received for review October 4, 1993. Revised manuscript received May 23, 1994. Accepted May 24, 1994.' .a Abstract
published in Advance ACS Abstracts, July 1, 1994.
Envlron. Scl. Technol., Vol. 28, No. 11, 1994
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