remediation of sucarnoochee soil by agglomeration with fine coal

Pergamon

0956-053X(94)00050-6

Waste Management, Vol. 14. No. 6, pp. 539-548, 1994 Copyright © 1994 Elsevier Science Ltd Printed in the USA. All rights reserved

0956-053X/94 $6.00 + .00

ORIGINAL CONTRIBUTION

REMEDIATION OF SUCARNOOCHEE SOIL BY AGGLOMERATION WITH FINE COAL

P. S. Narayanan, 1 David W. Arnold, 1. and M o h a m a d B. Rahnama 2 Depts. of 1Chemical and 2Civil Engineering, University of Alabama, Box 870203, Tuscaloosa, AL 35487-0203, U.S.A.

ABSTRACT. Fine-sized Blue Creek coal was used to remove high molecular weight hydrocarbons from Sucarnoochee soil, a fine-sized high-organic soil. Fine coal in slurry form was blended with Sucarnoochee soil contaminated with 15.0% by wt of crude oil, and agglomerates were removed in a standard flotation cell. Crude oil in the remediated soil was reduced from the original 15.0% to less than a tenth of a wt % by a two-step process. Oil removal of approx. 99.3% was obtained. An added benefit was that the low-grade coal used in the process was simultaneously upgraded. The final level of cleaning was not affected by initial oil concentration. The process compared favorably with a hot water wash technique used to recover oils from contaminated soil.

INTRODUCTION

Gross contamination of soils with crude or refined oil products is a problem often associated with pro- duction, refining, and distribution of petroleum hydrocarbons . The Exxon-Valdez accident off the coast of Alaska is a prime example of an oil spill leading to serious environmental problems. Several technologies such as supercritical water oxidation (1), subsurface remediat ion techniques including v a c u u m ex t rac t ion (2-4), inc inera t ion (5), and bioremediation are available for the remediation of contaminated soils. Bioremediation is useful as a final polishing step, while conventional mechanical techniques are better suited for the cleanup of heav- ily contaminated soils (6). A hot water wash of contaminated soils has been investigated by EPA researchers but has its limitations (7).

RECEIVED 6 AUGUST 1993; ACCEPTED 28 JUNE 1994. *To whom correspondence may be addressed. Acknowledgments--We wish to thank Dr. Robert A. Griffin for his assistance in this work, Philip Dark for his help with collect- ing the soil samples, the Mineral Resources Institute of The Uni- versity of Alabama for the loan of the Wemco ® flotation cell and for performing the proximate analyses on the coal. Bruce Ham- ilton and Jeff Powell of Jim Walter Resources, Inc. supplied the coal for this project. Hunt Refining Company provided the Maya crude. This project was supported in part by the Gulf Coast Hazardous Substance Research Center (contract number I 11UAL2075), and the authors wish to thank William A. Cawley for his interest and support. P. S. Narayanan wishes to express his appreciation to the Department of Chemical Engineering and the College of Engineering.

A well-known process for the cleaning and re- covery of coal fines is oil agglomeration. The process works by blending oil with coal fines having a high ash content, and floating the slurry. The lighter coal particles agglomerate with the oil and are obtained as a flotation product, while the heavier ash particles sink to the bot tom of the flotation cell and are rejected. However , the process has never been used on a large scale due to the prohibitive cost of oil (8). In a recent development, Pawlak et al. (9) and Ignasiak et al. (10) used this process in the remediation of coarse soils contaminated with high molecular weight hydrocarbons. Rahnama and Ar- nold (11) investigated the remediat ion of beach sand, silty loam and contaminated Kuwaiti soil (Fig. 1 is a schematic of their process) by agglomeration with fine coal. While coarse-grained soils were easily remediated by this method, it was de- sired to investigate the effectiveness of this process with fine-sized soils having a high clay content. This paper details the remediation of Sucarnoochee soil, a fine-sized, high clay, high organic soil by agglomeration with fine coal.

CHARACTERIZATION OF MATERIALS

Sucarnoochee Soil Sucarnoochee soil with an organic content of 2-7% was selected from the geological survey publica- tions of Alabama (12). The Sucarnoochee soil was obtained from a bank beside the road where State

539

540 P. S. NARAYANAN, D. W. ARNOLD, AND M. B. R A H N A M A

Fine Coal

Coal ÷ Oil

D,,-- Agglomerate

(Float Fraction)

Aqueous

Phase

Agitation

Oil Remediated Soil

Contaminated . . . . ~ (Sink Fraction)

Soil

FIGURE 1. Simplified schematic of the agglomeration process.

Road 39 crosses Factory Creek in Sumter County, AL. The area was identified on a soil survey map of Sumter County as sector T20N F2W. The soil samples were collected from a depth of 5-22" in the AB soil horizon and had a plasticity index of 27 (12).

The soil was air-dried and ground to a particle size small enough for the bulk of the material to pass through a I0 mesh sieve. A Gilson ® screen sieving machine was then used to sieve the ground soil. The oversize fraction (gravel particles retained on a 2 mm sieve) was discarded and a riffle-type sample splitter was used to form subsamples. Table 1 gives general properties of Sucarnoochee soil from a soil survey (12) and from this study. The particle size distribution (PSD) of the Sucarnoochee soil was determined by two methods. The first method was wet screening with U.S. standard sieves in the mesh sizes of 600, 300, 150, 75, 45 and 38 microns (Table 2). The second method used a Leeds and Northrup MICROTRAC ® Model II 7997- 10/20 equipped with a Standard Range Analyzer (700-0.7 ixm) and a Small Particle Analyzer (60-0.12 Ixm) yielding a PSD from 700 to 0.12 Ixm (Table 3). Triplicate runs were performed for each method.

Blue Creek Coal The State of Alabama's largest underground mine is the Jim Walter Resources, Inc. (JWRI) No. 4 mine

TABLE 2 PSD of Sucarnoochee Soil Obtained by Wet Sieving

Particle Size Mass Cumulative (~m) Fraction Mass Fraction

+ 600 0.0000 0.0000 + 300 0.0019 0.0019 + 150 0.0329 0.0348 + 75 0.0411 0.0759 + 45 0.0247 0.1006 + 38 0.0048 0.1054 - 38 0.8946 1.0000

in Tusca loosa County with a p roduc t ion of 2,398,289 short tons in 1989 (13). Since the Blue Creek coal is low in sulfur, cleaning entails only ash removal. With a Hargrove grindability of 90 +, this is an extremely soft coal. Fines are produced as inherent by-products of handling the material. Blue Creek coal undergoes enough size reduction in the mine and preparation plant such that up to 40% of the product is in the filter cake size range. This fine coal fraction from the vacuum filters is sticky and difficult to handle and at the same time is very dusty after drying. The No. 7 mine has a coal preparation plant somewhat similar to that of the No. 4 mine.

There are numerous alternatives to the present processing and marketing scheme. Simply dispos- ing of the fines in storage ponds, as was done 40 yr ago, is not an acceptable business practice today (11). This paper examines the use of coal fines in the remediation of contaminated soil. The coals used in this work were obtained from JWRI as filter cakes (FC) from the No. 4 and No. 7 mines, and these coals will henceforth be referred to individually as No. 4 FC and No. 7 FC throughout this paper. The proximate analyses (D 3172-89) were performed by the analytical section of the Mineral Resources In- stitute of The University of Alabama (Table 4). Coal PSDs were obtained on grab samples of the No. 4 and No. 7 FCs with the Microtrac ®.

The FCs were wet sieved using a vibratory screen to form + 50 mesh, and - 400 mesh fractions (50 and 400 are U.S. standard mesh numbers cor- responding to 296 p~m and 38 ~m, respectively). The - 4 0 0 mesh fraction was filtered using a pressure

TABLE 1 General Properties of Sucarnoochee Soil

Particle-size Distribution (wt %)

Source Depth Sand Silt Clay Soil Reaction Organic Matter of Data (in) (2-0.05 mm) (0.05-0.002 mm) (<0.002 mm) (pH) (%)

A 9--22 12.8 47.0 40.2 8.1 2.0-7.0* B 5-22 7.3 59.0 33.7 8.0 6.4

Source of Data: A = "Soil Survey of Sumter County, Alabama," September 1989, p. 126; B = Properties of Sucarnoochee soil determined in this study. *Applicable to top layer (0-22 in).

REMEDIATION OF SUCARNOOCHEE SOIL 541

TABLE 3 PSD of Sucarnoochee Soil Obtained With the Microtrac Over the

700 to 0.12 Itm Range

Particle Size Mass Cumulative (microns) Fraction Mass Fraction

+ 700 0.0000 0.0000 + 500 0.0000 0.0000 + 350 0.0000 0.0000 + 250 0.0005 0.0005 + 176 0.0086 0.0091 + 125 0.0134 0.0226 + 88 0.0173 0.0398 + 62 0.0187 0.0586 + 44 0.0146 0.0732 + 31 0.0106 0.0838 + 21.1 0.0156 0.0994 + 14.92 0.0180 o. 1174 + 10.55 0.0282 o. 1456 + 7.46 0.0783 0.2239 + 5.27 o. 1418 0.3656 + 3.73 o. 1496 0.5153 + 2.63 o. 1475 0.6628 + 1.9 o. 1459 0.8087 + 1.01 0.1039 0.9126 + 0.66 0.0486 0.9612 + 0.43 0.0281 0.9894 + 0.34 0.0061 0.9954 + 0.24 0.0023 0.9977 + o. 17 0.0015 0.9992 + o. 12 0.0007 0.9999 - o . 12 0 . 0 0 0 1 1 . 0 0 0 0

filter and argon-dried overnight, following ASTM D 2216-80 procedures, in a Fisher ® Scientific Isotemp Controlled Atmosphere Moisture Oven (Model 496 A). This fraction was called Treatment 1. Another fraction was formed by wet ball-milling natural - 4 0 0 mesh No. 4 FC in a steel ball-mill for 4 h (Treatment 2). The + 50 mesh fraction of the No. 4 FC was wet ball-milled in a steel ball-mill for 4 h to form a fraction passing through a 400 mesh sieve (Treatment 3). The natural - 4 0 0 mesh argon dried fraction of No. 7 FC was called Treatment 4. These different fractions were used to study the effect of coal treatment and PSD on the remediation process.

Maya Crude Oil Maya crude oil, used to contaminate the soil, was obtained from the Hunt Refining Company in Tus-

TABLE 4 Proximate Analyses of No. 4 FC and No. 7 FC

No. 4 No. 7 Filter Cake Filter Cake

(wt %) (wt %)

Moisture 0.87 0.79 Volatiles 24.24 20.10 Ash 8.65 8.49 Fixed Carbon 66.24 70.62

caloosa, AL. According to the specification sheets received from the company, the Maya crude oil had a specific gravity of 0.918 at 60°F and a flash point of <60°F (tag closed cup). Its viscosity was exper- imentally determined using a Haake ® RV-12 vis- cometer and was found to be 97 centipoises at am- b i e n t c o n d i t i o n s . T h e oil was m i x e d w i t h Sucarnoochee soil in a 15:85 wt/wt to form the contaminated soil used throughout this study.

EXPERIMENTAL

One-step Process

Figure 2 is a schematic of the one-step remediation process. In a standard run, 50 g of the contaminated Sucarnoochee soil was placed in a two-speed War- ing ® commercial blender (Model 34 BL 97) along with 30 g of coal. Approximately 500 g of water heated to 76°C was added to the blender so that the solids content was 10--20 wt %. This slurry was mixed at hi-speed (approximately 1100 rpm, loaded) for 10 min to ensure complete mixing. The temperature of the slurry after blending was found to be approximately 62°C. The intense mixing caused the oil in contaminated soil to preferentially adsorb onto the large surface area afforded by the fine coal. The slurry was then transferred to a Wemco ® flotation unit with a 2.8 L tank, about 1.5 L of dilution water (also at 76°C) was added, and the entire batch was floated without using any chemical additives. Slurry temperature in the flotation cell gradually reduced from about 62°C at the start of flotation to 58°C when flotation was ceased. The oil acted as a bridging liquid and caused the coal particles to agglomerate and float to the surface, while the heavier soil particles sank to the bot tom of the flotation cell.

The agglomerate was skimmed off the surface and washed over a 400 mesh screen to remove soil particles adhering to the agglomerates. The wash water was recycled to the blending stage of the next experimental run. The sink fraction (soil) that remained in the tank was filtered on Whatman No. 4 ashless filter paper using aspirator vacuum. The wet soil and agglomerates were dried overnight in an oven at 105-I 10°C as in the standard ASTM D 2216- 80 procedure and the dried samples were kept for weighing and analysis. Wash water from the previous run was recycled for all the one-step process experimental runs included in this paper.

Two-step Process Figure 3 is a schematic of the two-step process. The experimental procedure was similar to the one-step process, except that for the first step, 20 g of fine agglomerate from the previous run was used instead of 30 g of fresh fine coal. The first flotation gave

542 P.S. NARAYANAN, D. W. ARNOLD, AND M. B. RAHNAMA

Soil Wet Coal Hot Water Spray

:___V Agglomerate .~

k Screen i V _._ ] Riffle ~ J Sample 400 Mesh i Splitter Screen

i Dryin_g_ Oven 1 Wash

Soil Sample I Water

? ~ Crude Oil/_ Wash Water ~ DorY~:ng W W Dry Coal (from previous run)

Contaminated ~ Hot ] Dilution ; ' i j Soil L Water Water i (recycled

] Blender

i L

i

I to next run)

Flotation Cell

Cleaned Soil

Dried Agglomerate

Dried Soil

Wet Soil

Vacuum Filtration

Samples for

Weighing and

Testing

FIGURE 2. Schematic of the one-step remediation process.

large agglomerates that could be retained on a 100 mesh screen. In the second step, the sink fract ion that remained in the tank was to be blended with 20 g of fresh fine coal. Since the blender capaci ty was only 0.75 L, the sink fract ion was separated into 4 batches. Each batch was mixed with approx. 5 g of fine coal and reblended at hi-speed for 10 min. After reblending, the four batches were put into the flotation cell together and refloated. The agglomerates formed in the second step were very fine and were washed over a 400 mesh screen. The soil f rom the sink fract ion was filtered and dried in the same man- ner as descr ibed for the one-s tep process . The dried soil and agglomerate samples were kept for weighing and analysis.

ANALYSIS

Weighing was done using a Fisher ® Scientific balance (Model XD-8K) with a readabili ty of 0.1 g. The mois ture conten t of the agg lomera te was determined according to the ASTM D 3302-89A procedure. The agglomerate ash was determined according to A S T M 3174-89. T h e a sh c o n t e n t was calculated using the formula:

Percent ash of agglomerate =

(Weight of sample before ashing) - (weight of sample after ashing)

(Weight of sample before ashing) x 100

[1]

Due to the high amount of original organics in the Sucarnoochee soil, a solvent extract ion of the remediated soil using toluene was found to be a bet ter method of determining the amount of oil remaining on the soil than ashing of the soil. The entire soil sample was extracted with ACS grade toluene in a soxhlet ex t rac tor for 18 h to determine the amount of crude oil remaining in the soil. Wha tman cellu- lose ext rac t ion thimbles (33 m m I .D. x 80 m m length × 1 m m thickness and 43 m m I.D. x 123 m m length × 2 m m thickness) were used for the soxhlet extractions. 350 m L of toluene was used with the 33 x 80 m m thimbles and 400 m L of toluene was used with the 43 x 123 mm thimbles. After extract ion the thimbles were dried for 3 h in a Fisher ® Scientific I s o t e m p Control led A t m o s p h e r e Mois ture Oven (Model 496A) at 110°C to r emove toluene and then brought down to room tempera ture in a dessicator . Weighing to de termine toluene ex t rac tab les was

REMEDIATION OF SUCARNOOCHEE SOIL 543

Soil Large

_ _ _ _ Agglomerate

1 , 'Sample L splitter ,

10o Mesh !

L i Screen L

Soil Sample I Wet Coal Crude Oil Wash I~

' W a t e r _ _ y _ _ _

. . . . V V ~ [ Screen ] ~ _

Contaminated : i

Soil r - E_ J [ Drying Oven

- - 7 -

i Hot Water I - - - - DryVoal'C I i Dilution Water I

-vv . , 1st I ; 2nd

Hot Water Spray

r

- ~ 1 ~ 2nd Flotation

Blender

Fine Agglomerate

Flotation Cell

1st step Clean Soil

Blender I ; Cell

2rid step Clean Soil

Drying Oven

Vacuum Filtration

Dried Agglomerate

I

Samples - for

Weighing

J and ~i'-- Testing

i Dried Soil

Wet Soil

FIGURE 3. Schematic of the two-step remediation process.

done using a Sartorius ® balance (Model 2402) with a readabili ty of 0.0001 g. The unrecovered crude oil in the soil was calculated as follows:

Wt % Oil Remaining =

(Wt of soil before extract ion) - (wt of soil af ter extract ion)

wt of soil before extract ion x lOO [2]

RESULTS AND DISCUSSION

Table 5 presents the results obtained with the one- step process using various t rea tments of No. 4 FC and No. 7 FC. Individual run numbers shown in Column 1 are those used in the lab for identification purposes . Column 2 gives the amount of contaminated soil used in each run. This was the Sucar- noochee soil mixed with M a y a crude oil in a 85:15 wt/wt. Column 3 shows the amount of fresh fine coal used in each run and also the percentage of ash present in the coal. Column 4 gives the values for the coal-oil agglomerate obtained at the end of each run. Under ash of agglomerate , " s a m p l e " indicates

the % ash of that particular agglomerate sample. All results presented are in wt %. The average % ash of agglomerate for the triplicate runs is given as the mean, and the SD is also given. The - 4 0 0 mesh fraction of the No. 4 FC had an ash content of 13.67%, while a similar fract ion of the No. 7 FC had a higher ash content of 21.01%. The + 50 mesh fraction of the No. 4 FC had a low ash content of 6.41%, and hence Trea tment 3 coal had the same ash content. Column 5 gives the values for the remedia ted soil obtained f rom the process . The average values of wt % oil remaining for triplicate runs, and the SD are also given. The percentage of oil r emoved as compared to the amount of oil present in the original contaminated soil is calculated as follows:

Percent Oil Removal =

(Wt % of oil in contaminated soil) - (wt % of oil in remediated soil)

wt % of oil in contaminated soil x 100

[3]

Agglomerates were r emoved f rom the flotation cell by skimming, and some of the soil fines were

544 P. S. NARAYANAN, D. W. ARNOLD, AND M. B. RAHNAMA

TABLE 5 One-step Soil Remediation Process With No. 4 FC and No. 7 FC

Agglomerate Remediated Soil

Fresh Fine Coal Ash of Agglomerate Wt % Oil Remaining

Contaminated Dry Ash Dry Sample Mean SD Dry Sample Mean SD % Oil Run Soil Weight (wt Weight (wt (wt (wt Weight (wt (wt (wt Removal Number (g) (g) %) (g) %) %) %) (g) %) %) %) (g)

No. 4 FC Treatment 1. -400 Mesh Argon Dried

N40 50.00 20.00 13.67 21.40 6.54 43.10 3.21 N41 50.10 20.00 13.67 20.20 6.24 6.34 0 . 1 7 42.10 3.34 3.11 0.29 79.27 N42 50.00 20.00 13.67 20.70 6.24 42.40 2.78 N37 50.00 25.00 13.67 25.90 6.98 42.70 2.55 N38 50.00 25.00 13.67 25.30 7.12 7.12 0 . 1 4 43.00 3.27 2.99 0.38 80.09 N39 50.00 25.00 13.67 25.90 7.26 43.20 3.14 N25 50.10 30.20 13.67 31.00 8.69 43.60 0.53 N26 50.00 30.00 13.67 30.90 9.01 8.73 0 . 2 6 43.50 0.48 0.49 0.04 96.73 N52M 50.00 30.00 13.67 31.40 8.50 43.50 0.46 N34 50.10 35.00 13.67 38.10 9.48 39.70 0.49 N35 50.00 35.10 13.67 37.90 9.17 9.13 0 . 3 8 42.90 0.45 0.52 0.08 96.56 N36 50.00 35.00 13.67 38.30 8.73 42.90 0.61

Treatment 2. -400 Mesh Ground in a Ball Mill for 4 h

N31 50.10 31.00 13.67 34.60 9.22 40.70 0.45 N32 50.00 30.10 13.67 34.20 8.57 8.89 0 . 3 3 41.40 0.52 0.42 0.12 97.20 N33 50.00 30.00 13.67 33.80 8.87 40.60 0.29

Treatment 3. + 50 Mesh Ground in a Ball Mill for 4 h

N20 50.00 30.70 6.41 36.20 10.49 37.60 0.54 N21 50.20 30.80 6.41 38.30 11.10 10.39 0 . 7 7 36.50 0.52 0.51 0.04 96.60 N22 50.00 31.00 6.41 38.60 9.57 37.80 0.47

No. 7 FC Treatment 4. -400 Mesh Argon Dried

N43 50.10 25.10 21.01 27.80 6.65 39.30 1.88 N44 50.10 25.00 21.01 28.00 8.53 7.72 0 . 9 7 38.50 1.82 2.02 0.30 86.53 N45 50.10 25.10 21.01 27.90 7.99 41.80 2.36

caught wi th the agglomera tes . The agg lomera tes re- m o v e d f rom the f lo ta t ion cell were washed over a s ieve to r e m o v e these soil f ines which were then recyc led to the nex t expe r imen ta l r un a long with the wash water . Per iod ic e x a m i n a t i o n s showed that the soil f ines r ecyc led a m o u n t e d to app rox ima te ly 1.5 g. The wt of agg lomera tes g iven is the dry wt as m e a s u r e d af ter the agg lomera tes were dried in an o v e n at 105°C. Approx . 30% (2.25 g) of the M a y a c rude oil was lost dur ing drying. Similar ly , approx. 3% of the vola t i les in the soil were also lost while d r y i n g the r e m e d i a t e d soil s ample . W h e n these a m o u n t s were t aken in to cons ide ra t i on , the prod- uc t s f r o m each e x p e r i m e n t a l r un a c c o u n t e d for abou t 97% of all the feed mater ia ls . A sample material b a l a n c e on run n u m b e r N 39 is shown below:

I n p u t = ( C o n t a m i n a t e d soil + f resh f ine coal)

= (50.0 + 25.0)

= 75.0 grams

Ou tpu t = (Agglomera te + r emed ia t ed soil

+ h y d r o c a r b o n s due to e va po r a t i on

+ volat i les lost f rom soil)

= [25.9 + 43.2 + (7.5 x 30/100)

+ (42.5 x 3/100)]

= 72.6 grams

Losses a m o u n t to 2.4 g, or roughly 3.2% of the feed. The wt of agglomera te ob t a ined for all the runs

were a lways slightly higher t han the wt of f ine coal used s ince the oil f rom the c o n t a m i n a t e d soil was t aken up by the coal . The wt of agg lomera te approx- imate ly equa led the wt of fine coal and c rude oil in the feed. A cons ide rab le a m o u n t of ash in the f ine coal m o v e d to the soil dur ing process ing . The ash thus lost was rep laced by c rude oil. Also, as ex- p la ined above , a cons ide rab le por t ion of the c rude oil evapo ra t ed while drying. This is cons i s t en t wi th the mater ia l ba l ance p re sen t ed above .

R E M E D I A T I O N OF S U C A R N O O C H E E SOIL

TABLE 6 Comparison of No. 4 FC and No. 7 FC With the Two-step Process

545

Agglomerate Remediated Soil

Fresh Fine Coal Ash of Agglomerate Wt % Oil Remaining

Dry Ash Dry Sample Mean SD Dry Run Contaminated Weight (wt Weight (wt (wt (wt Weight Number Soil (g) (g) %) (g) %) %) %) (g)

Sample Mean SD (wt (wt (wt % Oil %) %) %) Removal

No. 4 FC -400 Mesh Argon Dried

N48 50.00 18.00 13.47 22.80 6.32 N49 50.00 18.00 13.47 22.20 7.93 N50 50.10 18.30 13.47 22.70 7.25

No. 7 FC -400 Mesh Argon Dried

A2 50.00 20.30 21.01 21.50 6.42 A3 50.10 20.30 21.01 21.70 6.31 A4 50.00 20.10 21.01 20.90 6.97

41.20 0.27 7.17 0.81 41.80 0.42 0.28 0.14 98.16

41.90 0.14

39.40 0.12 6.57 0.35 39.50 0.10 0.10 0.02 99.35

38.90 0.08

Table 6 presents the data obtained for the two- step process with - 4 0 0 mesh argon dried No. 4 FC and No. 7 FC. The amount of fresh fine coal indi- cated in Column 3 is the wt of fresh coal added in the second step of the two-step process. The agglomerate formed in this step (approx. 18 g) has only a small amount of crude oil adhering to the coal particles causing the agglomerate to be very fine. This agglomerate is reused as the coal input for the first step of the next experimental run. In the first step, the bulk of the crude oil is removed, and the coal particles used are saturated with oil, giving large agglomerate particles with a total wt close to 22 g. A small amount of crude oil is left behind on the soil at the end of the first step. Addition of fresh fine coal in the second step greatly reduces oil in the soil.

Table 7 compares the results obtained with the one-step process for different temperatures of the dilution water used. Cleanup became better as the temperature of water increased due to reduction in viscosity of the crude oil. The % oil removal did not improve significantly beyond 75°C.

Table 8 presents the results obtained with the one-step process for increasing blending time. A

blending time of 5 min was not entirely sufficient for the complete mixing of the contaminated soil and coal slurry. Therefore, oil remaining on soil was more than 1.3%. The optimum blending time was between 8 and 10 min. Increase in blending time beyond the optimum did not affect the remediation process significantly.

Figure 4 compares the one-step process and the two-step process using -400 mesh argon dried No. 4 FC. The amount of oil remaining on the soil was reduced from 15.0% to approx. 0.5% with the one- step process (96.7% oil removal) while the two-step process worked better giving approx. 0.3% oil remaining on soil (98.0% oil removal). The two-step process also reduced the ash content from 13.67% to about 7.2%. The one-step process gave a final agglomerate ash of about 8.7%.

The effect of different treatments of coal on the cleanup of Sucarnoochee soil is shown in Fig. 5. These runs were performed with the one-step process using the same amount of coal (30 g). Removal of oil became better as the mean particle size of coal decreased, that is, finer coal gave better results. Grinding in our ball mill did not significantly lower the particle size of the coal below that of the natural

TABLE 7 Effect of Water Temperature With the One-step Process

Run Number

Temperature of Water (°C)

Blending Time (min)

Fresh Fine Coal Agglomerate

Dry Dry Dry Contaminated Weight Ash Weight Ash Weight

Soil (g) (g) (wt %) (g) (wt %) (g)

Remediated Soil

Wt % Oil Remaining

(wt %) % Oil

Removal

N54 N53 N25 N29

55.00 10.00 50.00 30.00 13.47 30.50 8.10 45.50 1.45 65.00 10.00 50.00 30.00 13.47 30.80 8.37 45.30 0.97 76.00 10.00 50.10 30.20 13.47 31.00 8.69 43.60 0.53 81.00 10.00 50.00 30.10 13.47 31.70 8.65 43.70 0.46

90.33 93.52 96.47 96.93

546 P. S. N A R A Y A N A N , D. W. ARNOLD, A N D M. B. R A H N A M A

TABLE 8 Effect of Blending Time With the One-step Process

Run Temperature Blending Number of Water (°C) Time (min)

Fresh Fine Coal Agglomerate Remediated Soil

Dry Dry Dry Wt % Oil Contaminated Weight Ash Weight Ash Weight Remaining % Oil

Soil (g) (g) (wt %) (g) (wt %) (g) (wt %) Removal

R4 76.00 5.00 N25 76.00 10.00 R3 76.00 20.00

50.00 30.00 13.47 30.40 10.50 42.60 1.36 90.97 50.10 30.20 13.47 31.00 8.69 43.60 0.53 96.47 50.00 30.00 13.47 31.40 8.50 43.00 0.55 96.33

-400 mesh coal. Therefore, Treatment 2 coal had only a slightly smaller mean particle size than Treat- ment 1 and showed only slightly better toluene ex- tractables than the Treatment 1 coal. The mean particle size of Treatment 3 coal was not significantly different from that of the natural -400 mesh coal and hence cleanup was approximately the same.

Figure 6 compares the results obtained with the one-step process using the same amounts of -400 mesh argon dried fractions of No. 4 FC and No. 7 FC. The No. 7 FC had a much smaller mean particle size than No. 4 FC and consequently removed more oil from the soil per unit gram of coal than the No. 4 FC. The amount of oil on the soil was reduced from 15.0% to 2.0% (86.7% oil removal) using 25 g of No. 7 FC. For the same amount of coal used, the No. 4 FC reduced oil on soil from 15% to 3% (80.0% oil removal).

Figure 7 compares the effect of using - 400 mesh argon dried No. 4 FC and a similar fraction of No. 7 FC for the two-step process. The finer No. 7 FC consistently gave better results than the No. 4 FC. Wt % of oil remaining on the soil was 0.1% using No. 7 FC (99.3% oil removal), while the No. 4 FC gave results of approximately 0.3% (98.0% oil removal). Percentage ash reduction was also better for the No. 7 FC. The trends observed with these two coals are similar for both the one-step (Fig. 6) and the two-step (Fig. 7) processes.

In Fig. 8, the effect of increasing treat rate of coal on the remediation process is shown. As illustrated by experiments using -400 mesh argon dried No. 4 FC with the one-step process, cleanup became better as the amount of coal used increased. A 4:1 ratio of coal to oil seemed to be the optimum amount required for the one-step process. This translates to 30 g of coal for a batch of 50 g of soil contaminated with 15% by wt of oil. Beyond the opt imum amount, removal of oil leveled off and remained approx, the same for increasing amount of coal. The amount of ash in the agglomerate per unit wt of coal remained approximately the same for different treat rates. But the amount of oil in the agglomerate per unit of coal was higher for lower treat rates as the coal became saturated with oil. Therefore, ash % of agglomerate appeared to be lower for lesser amounts of coal used.

CONCLUSION

The PSD of the contaminated soil had a direct bear- ing on the ease of cleanup. Researchers at the Uni- versity of Alabama showed that oil recoveries of up to 99.9% could be achieved with a one-step process for a coarse-grained soil like beach sand (1 l). Soils with finer texture were more difficult to clean up. The Sucarnoochee soil used in this study had more than 90% particles smaller than 45 Ixm and also had

~9

96

• % Oil Removal [~ Wt% Oil Remaining

c~ c

o 04~

O2

One-Step Two-Step

99

i0,

• % Oil Removal O Wt% Oil Remaining

1 L-- Treatment 1 Treatment 2 Treatment 3

~ 8

F

c

o~

O2

FIGURE 4. Comparison of one-step process and two-step pro- FIGURE 5. Effect of coal treatment with the one-step process cess using -400 mesh argon dried No. 4 FC. using No. 4 FC.

REMEDIATION OF SUCARNOOCHEE SOIL

• % Oil Removal [ ] Wt% Oil Remaining

--1

Using 25g of J,00 mesh argon dried coal

100

99

98

97

• % Oil Removal [ ] Wt% Oil Remaining

-400 mesh argon dried coal

547

0 5

7~ - - - - o 96 - - - - 0 No4 FC NO7 FC

FIGURE 6. Comparison of No. 4 FC and No. 7 FC with the one-step process.

a high original organic content of 6.41%. This study attempted to show that the coal agglomeration process was not limited by the nature of soil or extent of contamination•

The most important factors affecting the remediation of Sucarnoochee soil were amount of coal used, PSD of coal, and the temperature of the water. A significant observation was that the process was not affected by initial concentration of oil. While thorough mixing of the coal-soil-water slurry was expected for the process to be effective, on a laboratory scale speed of blending did not have a large effect. Initial experiments performed using blender speeds ranging from 800 rpm to 1400 rpm

100

No4 FC NO7 FC

1 0 4 c~ c

o3 E

8

02~ &

01

FIGURE 7. Comparison of No. 4 FC and No. 7 FC with the two-step process.

(fully loaded) did not show significant differences, and hence the results have not been included in this study• It is anticipated that on an industrial level, the use of appropriate high shear mixing equipment and an increased blending time would help achieve an ad- equate degree of mixing• Blending time as a variable was also investigated and found to be a smaller factor.

It was observed that the PSD of coal was a very significant factor, being directly related to the surface area available for adsorption. This indicates that an adsorption medium similar to fine coal, such as petroleum coke, would also prove to be an effective material for the remediation of soil by this agglomeration process•

• - 5

o E n, O

#_

95 Using -400 mesh argon dried No. 4 FC

90 ~ ......................................................... • .

85

80 i

I

%.

.... "%•

% Oil Removal O

Wt% Oil Remaining

7 5 L.

0.4

% , ,

"L

t~3 t-- ¢.-

cO E

O "E

2a~ 13. t--- ._m

"%•

. . . . . . . . . .

0.5 0.6 0.7 Grams of Coal per Gram of Contaminated Soil

FIGURE 8• Effect of treat rate using - 400 mesh argon dried No. 4 FC with the one-step process.

548 P . S . NARAYANAN, D. W. ARNOLD, A N D M. B. R A H N A M A

The two-step process gave significantly better results than the one-step process. The wt % of oil remaining on soil was reduced to 0.1% (99.3% oil removal) using No. 7 FC for the two-step process. The two-step process used almost 40% less fresh coal than the one-step process for each batch of soil. The agglomerates formed with the two-step process were larger than 600 Ixm and showed great ease of handling.

A hot water wash of the contaminated soil was investigated by repeating the process without the addition of fine coal. The flotation product was an emulsion of oily water and soil fines. The Sucar- noochee soil contains about 90% fines, making sep- aration of soil from the oily water difficult. Only about 40% of the original soil could be recovered. This recovered soil constituted mostly of coarse particles and was found to have a remaining oil content of 7.0 wt % giving an oil removal of 53.0%.

REFERENCES

1. Glanz, J. New waste-destruction method takes aim at world's sludge. R & D Magazine. Feb: 98-100 (1992).

2. Kostecki, P. and Calabrese, E. Hydrocarbon contaminated soils and groundwater analysis, environmental fate and pub- lic health effects. In: Remediation, vol. 1. Lewis Publishers, Inc. (1991).

3. Kostecki, P. and Calabrese, E. Contaminated Soils, Diesel Fuel Contamination. Lewis Publishers, Inc. (1992).

4. Lyman, W., Noonan, D., and Reidy, P. Cleanup o f Petro- leum Contaminated Soils at Underground Storage Tanks. Noyes Data Corp. (1990).

5. Vance, D. B. Onsite bioremediation of oil and grease contaminated soils. The National Environment Journal 9 :26 (1991).

6. Gibbons, J. H. Bioremediation for marine oil spil ls-- background paper. OTA-BP-0-70, U.S. Congress Office of Technology Assessment, Washington, DC (1991).

7. Davis, E. L. and Lien, B. K. Laboratory study on the use of hot water to recover light oily wastes from sands. EPA/600/ SR-93/021, Robert S. Kerr Environmental Research Labo- ratory, Ada, OK (1993).

8. Xu, W., Herz, W. J., Arnold, D. W., and Alderman, J. K. Oil agglomeration of Blue Creek coal. The Journal o f Coal Quality. 10(2): 61-66 (1991).

9. Pawlak, W., Briker, Y., Carson, D., and Ignasiak, B. Novel applications of oil agglomeration technology. EPRI GS-6219 [Proceedings of the 13th Annual EPRI Conference on Fuel Science and Conversion], Electric Power Research Insti- tute, Palo Alto, CA (1989).

10. Ignasiak, T., Carson, D., Szymocha, K., Pawlak, W., and Ignasiak, B. Clean-up of oily waste material contaminated soil. The 9th lnt 'l Congress on Energy and Environment, Miami Beach, FL (December 1989).

11. Rahnama, M. B. and Arnold, D. W. Soil remediation by Ag- glomeration with Blue Creek coal. Journal o f Hazardous Materials. 35:89-102 (1993).

12. U.S. Department of Agriculture. Geological survey of Sumter County, AL. Soil Conservation Service (1989).

13. Tolson, J. S. and Rogers, E. G. Alabama coal data for 1989. Geological Survey of AL, Information Series 58K, Tus- caloosa, AL (1990).

Open for discussion until 30 November 1994.

remediation of sucarnoochee soil by agglomeration with fine coal

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