Application of Liquid Chromatography to Pollution Abatement Studies of Munition Wastes John T. Walsh, Ronald C . C h a l k , and Charles Merritt, Jr. Pioneering Research Laboratory, U S Army Natick Laboraforles, Natick, Mass 01 760
The application of liquid chromatography to pollution abatement studies of TNT waste waters is described. These studies include the characterization by liquid chromatography of the color formation occurring in TNT water, the development of a simple, direct analysis for cu-TNT and a description of how liquid chromatography was used to evaluate pollution abatement processes for the removal of nitrobodies from munition waste waters. The abatement processes investigated were the column adsorption type, which required adsorption isotherm, breakthrough capacity, saturation capacity, and column regeneration efficiency data. The acquisition of these data by liquid chromatographic means is described. The results showed that an adsorbent resin of the styrene-divinylbenzene copolymer type possessed nitrobody adsorption efficiencies at least equal to those of activated carbon and had the important added advantages of easy chemical regeneration and a significantly long life cycle.
The U.S. Army Munitions Command has, as its main mission, the development and manufacture of munitions for the Armed Forces. Production under full mobilization would make the Munitions Command the fourth largest industry in the U.S. The nature and extent of these operations also gives the Munitions Command the distinction of being the principal polluter within the Department of Defense. Large production requirements coupled with a broad variety of products result in numerous pollution problems, one of the most serious being the waste waters emanating from the manufacture of T N T . T N T waste waters consist of nitrobodies which are toxic, explosive, and frequently highly colored. It has been found that 2.5 ppm of T N T is toxic to fish. Consequently, the discharge of such wastes into nearby waterways constitutes a serious pollution hazard. There are several kinds of waste waters generated during T N T manufacture. “Red water” is the waste formed during the sellite purification of TNT, and “Pink water” is that waste formed when partially purified T N T is finally water washed following the sellite purification step. Both of these manufacturing waste waters are usually disposed of by incineration methods. One of the most serious waste water problems is that of wash waters from the T N T finishing process. In the finishing process, the T N T is dried, flaked, and packaged. Considerable amounts of wash-down water are used to clean equipment, and to clean the interior of finishing plant buildings. As much as 500,000 gallons per day of such water can be generated a t a single plant. It is usually beyond the capacity of a munitions plant to incinerate this volume of waste water in addition to the large amounts of “Red” and “Pink” waters normally incinerated. Consequently, the finishing plant waste waters are usually disposed of by discharging them into nearby rivers or streams. The finishing plant waters consist mostly of
a - T N T (2,4,6-trinitrotoluene), along with lesser amounts of other nitrobodies such as the dinitrotoluenes, and isomers of a - T N T . Also, because of sunlight exposure and to neutralization of the waste water prior to disposal, some of the nitrobodies undergo chemical change forming highly colored compounds. The identity and toxicity of these colored compounds is not known. Previous investigators (1-3) have studied the possibility of bacterial degradation of the responsible nitrobodies, while others (4, 5) have attempted removal of the pollutants by carbon adsorption techniques. The efficiency of biodegradation not only remains questionable but also has the disadvantage of requiring a long time to consume the material in the extremely large daily output of waste water. On the other hand, carbon adsorption techniques suffer the disadvantage of being difficult to regenerate by chemical means and hazardous to regenerate thermally when the concentration of explosives exceeds 8% of the total adsorbent weight. This paper describes liquid chromatographic studies of T N T finishing plant waste waters and the application of these studies to the evaluation of an amberlite resin, XAD-2 (Rohm and Haas Co., Philadelphia, Pa.), for use in an adsorption column for a pollution abatement process of T N T waters. For comparison purposes the same evaluations were made upon an activated carbon material, Filtrasorb-400 (Calgon Corporation, Pittsburgh, P a . ) , which has been used to a limited extent a t munitions plants.
EXPERIMENTAL A p p a r a t u s . A Du Pont Model 830 and a Waters Associates Model ALC-202/401 liquid chromatograph were used in these studies. Each instrument was equipped with both ultraviolet absorbance and differential refractometer detectors. A Vidar Autolab 6300 digital integrator was used for measuring peak areas and peak retention times. Chromatographic columns were 1-m length times 2.3-mm i.d. packed with Du Pont Permaphase ODS and Waters Associates Cla/Corasil, respectively. The solvent system was acetonitrile-water (10:90 v/v). All chromatographic runs were carried out a t a flow rate of 0.6 ml/min. The XAD-2 and charcoal adsorption columns were constructed of glass, 30 cm total length times 1.2-cm outer diameter. Each column had a n overhead reservoir of 1 1. and a Teflon stopcock for controlling flow rate. The actual adsorbent bed length was 11 cm and the bed diameter was 1 cm. Gravity flow was utilized for waste water throughout. Procedure. Liquid chromatographic analyses were carried out using the conventional syringe injection technique. Sample volumes of 10 ~1 of standard solutions and of actual waste water solutions were used. Waste water samples were analyzed directly as received. No sample preparation was required. In general, the types of samples analyzed chromatographically were of three Nay, P h . D . Dissertation. Virginia Polytechnic Institute & State University. Blacksburg. Va.. 1971. 12) H. J. Channon. G . T. Mills, and R. T. Williams, Blochem. J , , 38 ( 1 ) M . W.
(1938), ( 3 ) H. H. Tabak. C. W. Chambers, and P. W. Kabler. J . Water Pollut. Cont. Fed.. 35, 1 2 (1963). ( 4 ) R . W. Coughlin. lnd. Eng. Chem.. Res. Prod. Develop.. 50, 1 2 (1969). ( 5 ) G . R . Schulte, M. S. Dissertation, Virginia Polytechnic Institute &
State University. Blacksburg, Va., 1972.
ANALYTICAL CHEMISTRY, VOL. 45, NO. 7, JUNE 1973
1215
categories: standard solutions of a - T N T and other nitrotoluenes, such as the tri-, di-, and mononitrotoluenes; colorless acidic T N T waste water samples; and highly colored basic T N T waste waters. Standard plots of a - T N T concentration us. peak area and peak height were prepared over a concentration range of 1 to 100 (pprn). Results of the liquid chromatographic method for a - T N T in standard solutions were in good agreement with those obtained by the Silas Mason technique ( I , 6). Some typical parallel analyses are given in Table I. T h e Silas Mason method is a spectrophotometric method commonly used for a - T N T . With the waste water samples analyzed, the chromatographic method had the significant advantage of no interference from other nitrobodies present. The Silas Mason reagent is known to react with various symmetrical trinitro compounds. On the other hand, it does not react with mono and dinitro compounds. The analysis for nitroaromatic derivatives can also be carried out by gas chromatography (7). However, the gas chromatographic method requires extraction of the nitroaromatic compounds from the aqueous waste water medium. High temperatures are also required a t the sample injection port and upon the GC separation column. Alteration of nitroaromatics can occur a t such high temperatures (7). The liquid chromatographic method permits a n effective separation and determination of a - T N T and other nitroaromatic compounds a t ambient temperature without any extensive sample preparation. Quantities of less than 1 ppm are easily detectable. Adsorption column experiments were carried out by passing measured volumes through the columns a t a constant flow rate of 250 ml/hr. The concentration of a - T N T in the original waste waters was determined prior to passage through the column and again upon column eluates a t various through-put volumes. Knowing the a - T N T concentration of the original water sample, the total volume passed through the column and the a - T N T concentration in the eluates enabled the calculation of the total amount of a-TiiT passed through the column and also the amount adsorbed onto the column. Recovery of the adsorbed materials and regeneration of the adsorbents was carried out by washing the columns with acetone or toluene. The wash liquors were then evaporated to dryness under vacuum. In some instances, yellow crystals of a - T N T were obtained after the removal of solvent. In other instances, a redbrown residue was found, presumably a mixture of nitrobodies. In either case the material remaining was dissolved in a mixture of acetonitrile and water and made up t o a known volume. Acetonitrile-water is the solvent mixture used as the mobile phase in the chromatographic separation process; consequently, any interferences due to solvent chromatographic peaks appearing on the chromatograms were eliminated. These solutions were then analyzed for their a - T N T content. The recovery percentages were calculated from the amount of T N T absorbed and the amount removed by solvent stripping.
RESULTS AND DISCUSSIONS
TNT Waste Water Studies. Finishing plant waste water emerges from the plant in a practically colorless and acidic (pH = 3) state. Upon neutralization with sodium carbonate, the water develops an intense pink-amber color. It is then diluted with plant cooling water to diminish the color and to reduce the concentration of nitrobodies. As many as four million gallons per day of plant cooling water may be used for dilution purposes. Finally, after neutralization and dilution, the waste water is discharged into nearby waterways. Frequently, the colorless waste water develops color upon prolonged exposure to natural light prior to neutralization. Consequently, both pH and photochemical effects are factors in producing color. To simulate actual plant processing, samples of finishing plant waste water were subjected to laboratory treatment such as neutralization, exposure to UV light. and reacidification of the neutralized colored water. Liquid chromatographic analysis of the waste water samples a t various treatment stages was carried out. Figure 1 is a (61 Radford A r m y Ammunition Plant Laboratories. Department of the Army. Radford. Va. ( 7 ) R . W Dalton, J. A . Kohlbeck. and W T. Bolleter. J . Chrornatogr 50, 219 ( 1 9 7 0 ) .
1216
ANALYTICAL CHEMISTRY, VOL. 45, NO. 7, JUNE 1973
~~~~~
~
Table I. Comparison of a-TNT Concentrations Determined by the Silas Mason Method and Analytical Liquid Chromatography
Batch 1
Batch 2
Batch 3
Batch 4
Batch 5
Liquid
Silas Mason, pprn
chromatography, p p m
77.0 35.0 14.8 6.0 68.5 29.6 11.2 4.5 96.0 38.0 16.2 7.0 49.0 15.0 10.4 5.4 85.0 39.8 20.2 10.2
77.0 37.9 15.3 5.5 69.0 28.1 11.5 6.4 96.1 39.9 15.9 7.8 52.6 17.0 10.7 6.3 84.6 41.5 21.7 10.8
set of chromatograms representative of the various treatment stages. Part a of Figure 1 is a chromatogram of the waste water prior to any treatment. I t represents a chromatogram of the waste water as it emerges from the finishing plant-that is, clear, colorless and acidic. Three well-defined peaks were obtained with the second peak the predominant one. This is the a - T N T peak (2,4,6-trinitrotoluene). The third peak is that of 2,4-dinitrotoluene. These identifications were made by running known standards in the liquid chromatographs and by NMR analyses of the separated components. The first spike-like peak is unidentified and is apparently due to species which are nonretentive on the nonpolar chromatographic column employed. Part b of Figure 1 is a chromatogram of the same waste water neutralized with sodium carbonate. The water now developed an intense pink-amber color. The change from a colorless acidic to a colored neutral solution is reflected in the chromatogram by the almost complete disappearance of the a - T N T peak (No. 2 peak) and a significantly large increase in the spike-like No. 1 peak. Another portion of the original acidic T N T waste water was subjected to ultraviolet light for 12 hr to simulate exposure to natural light. Again, the intense pink-amber color developed. Part c of Figure 1 represents the chromatogram of the UV treated solution. The chromatogram is identical to that of the colored neutralized solution in part b. That is, the a - T N T peak has disappeared while the first spike-like peak has intensified. However, the significant factor here is that the pH of the UV induced colored solution was the same as that of the original colorless acidic T N T water (pH = 3). No p H change was involved in this color formation. The chromatograms obtained from both colored waste water solutions were identical even though the color was induced by two different effects. Ultraviolet spectra obtained for the neutralized and photolyzed solutions, respectively, show that the colored species are not the same. Upon reacidifying the neutralized solution to the pH of the original acidic T N T water, the pink-amber color disappeared. However, this reversion of color was not reflected in the chromatogram of the reacidified solution as seen in part c of Figure 2. The a - T N T peak did not reappear
Original-Colorless
NalCO,
Treatad
UV-Light
pH=B
pH=3
Amber-Color
Amber-Color
pM=3
I
Tiel
1ie1 Wi.1
(111 )
Figure 1. Chromatograms of TNT finishing plant wash water
Na,COJ
Original-Colorless pH=3
Treated
pH=B
YN' .
Ambar-Color
Reacidified pH-3 Colorless
I
d-TNT j2.4-DNT
2,4-DNT
GTNT /2,4-DNT
1111 I111 )
Figure 2. Chromatograms showing effect of acidity on TNT finishing plant waste water
Colorless
96.6%
Unknown
I 11.1
(mil )
II
21 11.0
II (111
)
Figure 3. Chromatograms showing conversion of a - T N T to colored species
nor did the intensity of the spike-like peak No. 1 decrease. This chromatogram is identical to that of the neutralized sample in part b where practically no a - T N T is seen. Consequently, a - T N T did not reform upon reacidification even though a reverse color change was induced. It would appear then that the initial color formation is due to a chemical change in a - T N T and that this change is irreversible. The loss of color upon reacidifying might be explained by the formation of another colorless compound, but not a - T N T . This colorless compound is apparently nonretentive on the nonpolar chromatographic column and would account for the continued appearance of the first spike-like peak in the chromatograms. The amount of conversion of a - T N T to the unidentified colored species was determined by neutralizing a standard 100 ppm a - T N T solution (initial pH 4) and comparing the chromatographic peak areas of CY-TNTand the spike-like peaks before and after color formation. Figure 3 is a chromatogram from which this determination was made. The amount of conbersion of a - T N T to colored species was about 95%. The significance of these data in regard t o pollution is that they point out that the main pollutant in the neutralized finishing plant waste water may not be a - T N T as suspected but may actually be the colored ANALYTICAL CHEMISTRY, VOL. 45, NO. 7 , JUNE 1973
1217
Colorless
pH=3 After
I(
-1Nl
Neutrolirotion
(91 ppm)
/
Bosin
pn-7
After Di:ution pn=5 Colorless
,I -TNT (2s
i
r-
ppm)
I-)
Figure 4. Chromatograms of plant treated waste water
Belore X A D - 2
Column
I
After
XAD-2 Breokthrouph
Figure 5. Chromatograms of T N T finishing plant waste water before and after passing through Amberlite X A D - 2 TNT breakthrough after 350 bed volumes of waste water
Figure 6. Chromatograms of TNT finishing plant waste water before and after passing through activated carbon F-400 TNT breakthrough after 350 bed volumes of waste water
species whose identity and, moreover, whose toxicity is unknown. Chromatographic analysis of actual plant samples are shown in Figure 4. The chromatogram in part a is that of the acidic, colorless T N T water as it emerges from the finishing plant prior to reaching the neutralization basin. The chromatogram in part b is that of the same water after neutralization. The chromatogram in part c repre1218
l
ANALYTICAL CHEMISTRY, VOL. 45, NO. 7, J U N E 1973
sents the waste water after leaving the neutralization basin and after dilution with plant cooling water. This series of chromatograms agrees well with those obtained from laboratory samples simulating plant treatment (Figure 1) by the fact that better than 90% of the a-TNT originally present is converted to colored species and also the chromatogram of the colored waste water has an intense spike-like peak.
Figure 7. Adsorption isotherms ( a ) Arnberlite resin XAD-2 and ( b ) activated carbon, Filtrasorb 400
XAD-2
% : -, /
Artivofed
1
Carbon
Resin
Recovery
F-400
l ~ T N T Z Z % Recovery
I
++- urb,_ l i l t (8ln
Figure
8.
I
1i.t
(.,I
1
Chromatograms showing adsorption column regenera-
tion efficiency (acetone eluant)
Process Abatement Studies. A direct column process was investigated for the removal of color and nitrobodies from the T N T finishing plant waste waters. A polymeric resin, Amberlite XAD-2 was used as the adsorbent. The resin is nonionic and its adsorption properties are dependent largely on Van der Waals forces. Accordingly, neutral organic molecules are readily removed from aqueous solutions. Comparison studies were also carried out with an activated carbon material, Filtrasorb-400, which has had limited use a t some munitions plants. The efficiency of the XAD-2 resin in removing a - T N T and other organics is illustrated in Figure 5. There was complete disappearance of peaks except for the initial spike-like peak. The activated carbon, Filtrasorb-400, gave identical results as shown in Figure 6. Adsorption isotherm studies were made on both adsorbents. The standard batch process technique (8) was used to acquire the necessary isotherm data. The amount of a - T N T adsorbed per known weight of adsorbent was determined. This was done chromatographically by determining the concentration of oc-TNT remaining in standard solutions which had been in contact with known amounts of adsorbent until a saturation equilibrium had been reached. The adsorption isotherms are shown in Figure 7 . Column regeneration efficiency was determined by measuring the amount of a - T N T recovered from the columns. A recovery of about 80% was achieved with the XAD-2 resin, while about 22-25% was obtained with activated carbon. A chromatogram comparing the recoveries of w T N T from the adsorbents by washing the columns with acetone is shown in Figure 8. Regeneration curves indicating the amount of a - T N T recovered from each adsorbent column per milliliter of acetone eluate are shown in Figure 9. The curves show that practically all of the o-TNT recovered from the XAD-2 resin required a total of 12 ml of acetone and that all of the a - T N T was recovered in the 6-12 ml fractions. In comparison while only approximately one-fourth the amount of a - T N T was recovered from the activated carbon, it was removed more rapidly and completely within the first 6 ml of acetone passed through the column. In other experiments with toluene, better than 95% recovery from the XAD-2 resin was achieved with toluene as regenerant. Because of the poor regeneration capability of the activated carbon, the column was usable for only one life cycle. The carbon would then have to be replaced after each cycle. In these studies a cycle was considered to be the passage of waste water through the column until a breakthrough of 1 ppm of a - T N T was reached. The breakthrough volume was the same for each adsorbent, i . e . . 350 bed volumes. Although the breakthrough volumes of the materials are the same, it should be noted that the adsorption capacities are different. As indicated in Figure 7 , the capacity of activated carbon is greater than that of the XAD-2 resin. This is probably due to the fact that the surface area of carbon is approximately three and one-half times greater than that of the resin. The density of the resin is about one and three-quarters times greater than the density of the activated carbon. After the breakthrough volume is reached, the column may be regenerated with toluene prior to passing the next volume of waste water. A continuing evaluation of the XAD-2 resin has demonstrated a capability to undergo continuous regeneration cycles without any significant decrease in adsorption
V o l u m e Effluent (ml.)
Figure 9. Regeneration curves (acetone eluanti ( a ) Activated carbon. Filtrasorb 400 and ( b l Amberlite resin XAD-2
(81 A. Weissberger and E. S. Proskaur. "Techniques of Organic Chernistry," Vol. V , "Adsorption and Chromatography," H . G. Cassidy, Ed., Interscience. New York. N . Y . , 1965.
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 7, JUNE 1973
1219
efficiency. Consequently, even though the XAD-2 resin is initially more expensive than activated carbon, the ease of regeneration plus its extended life cycle may make its use for removing nitrobody pollutants from waste waters economically feasible. The results of this work are summarized as follows. First, the color change induced in T N T solutions, whether by pH or photochemical effects, can be followed by liquid chromatography. Second, in neutral and basic solutions the chemical conversion of a-TNT may be as high as 95%. Therefore, the main pollutant in neutralized finishing plant waste water is most likely not a-TNT, but rather the
1220
ANALYTICAL CHEMISTRY, VOL. 45, NO. 7, JUNE 1973
colored conversion species. Third, the adsorptivk and regeneration characteristics of Amberlite XAD-2 resin for a-TNT and other nitrobodies indicate its advantages for potential use in pollution abatement problems involving munitions wastes. Furthermore, these studies illustrate the application of liquid chromatographic techniques to acquire both basic information and operational parameter data for use in the design and evaluation of pollution abatement processes. Received for review November 30, 1972. Accepted January 30, 1973.
