Chemosphere 50 (2003) 1107 1114
www.elsevier.com/locate/chemosphere
Sonochemically induced decomposition of energetic
materials in aqueous media
1
Lala R. Qadir, Elizabeth J. Osburn-Atkinson , Karen E. Swider-Lyons,
2
*
Veronica M. Cepak , Debra R. Rolison
Surface Chemistry Branch (Code 6170), Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington, DC 20375, USA
Received 14 September 2001; received in revised form 5 September 2002; accepted 4 November 2002
Abstract
This study demonstrates that ultrasound rapidly degrades the energetic compounds RDX (cyclo-1,3,5-trinitramine-
2,4,6-trimethylene) and ADN (ammonium dinitramide) in aqueous microheterogeneous media. The conditions for
effective degradation of these nitramines, as monitored by UV absorption spectroscopy, were determined by varying
sonication time, the heterogeneous phase and its suspension density, and the concentration of NaOH. In the presence of
5 mg/ml of aluminum powder and at pH 12 (10 mM NaOH), 74% of the RDX and 86% of the ammonium dini-
tramide (ADN) in near-saturated solutions decompose within the first 20 min of sonication (20 kHz; 50 W; 6 5 °C).
Sonication without Al powder and base yields minimal degradation of either RDX and ADN ( 5 10%) or the nitrite/
nitrate ions that are expected byproducts during RDX and ADN degradation. Sonication at high pH in the presence of
dispersed aluminosilicate zeolite, alumina, or titanium dioxide also yields minimal degradation. Preliminary electro-
chemical studies and product analyses indicate that in situ ultrasonic generation of metallic aluminum and/or aluminum
hydride drives reductive denitration of the nitramines. Sonochemical treatment in the presence of a reductant offers an
effective and rapid waste remediation option for energetic waste compounds.
Published by Elsevier Science Ltd.
Keywords: High explosives; Ultrasound; Reductive denitration; Environmental remediation; RDX; Ammonium dinitramide;
Nitramines
1. Introduction mann et al., 1996). These hazardous waste stockpiles
present both environmental and health problems, espe-
Recent global demilitarization has created a need for cially since some explosives, such as RDX, cyclo-1,3,5
effective destruction or remediation of the high explosive trinitramine-2,4,6-trimethylene, are known carcinogens
materials used in nuclear weapons delivery systems and (Heilmann et al., 1996; Hundal et al., 1997). An ancillary
rocket propellants. An estimated 3:13 108 kg of mu- hazard is the wastewater that results after energetic
nitions waste exists in military stockpiles alone (Heil- manufacturing and washdown, explosive melting, and
steam-cleaning operations of reject warheads. Current
treatment technologies include open-air incineration,
alkaline hydrolysis, adsorption on carbon beds, and
*
Corresponding author. Tel.: [phone]; fax: +1-202-
advanced oxidation, but these methods are often capital
767-3321.
and energy intensive, and can produce concentrated
E-mail address: [e-mail] (D.R. Rolison).
1 toxic byproducts that need to be treated further (Heil-
Present address: Department of Chemistry, Linfield Col-
mann et al., 1996; Hundal et al., 1997).
lege, McMinnville, OR 97128, USA.
2
This study focuses on the ultrasonic treatment of
Present address: Eltron Research, Inc., 4600 Nautilus
Court South, Boulder, CO 80301, USA. high explosives in aqueous media with emphasis on the
0045-6535/03/$ - see front matter Published by Elsevier Science Ltd.
PII: S 00 4 5 - 6 5 3 5 ( 0 2 ) 0 0 7 7 0 - 1
1108 L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114
et al., 1999). It is therefore feasible that ultrasound
could also remediate RDX and ADN, because both
molecules are rendered non-hazardous by denitration,
i.e., cleavage of the nitramine moiety (N NO2) to form
nitrites (Owens and Sharma, 1980; Heilmann et al.,
1996; Hundal et al., 1997; Thompson and Doraiswamy,
1999). Reduction of the nitro group is one means of
Fig. 1. Molecular formulae for the energetic nitramines, RDX achieving cleavage of the N NO2 bond (Hundal et al.,
and ADN.
1997).
Previous studies indicate that Fe metal promotes
remediation of RDX in soil via reductive denitration
nitramines RDX and ammonium dinitramide (ADN) (Hundal et al., 1997). We choose to test Al powder be-
(Fig. 1). RDX, a white crystalline heterocyclic solid first cause its reducing power (with an EMF of )1.67 V) is far
synthesized in 1899 for medicinal use, is a stable ener- greater than that of Fe metal ()0.44 V) (Bard et al.,
getic material with nearly 130% of the explosive power 1985), and ultrasound can be used to generate, in situ, a
of trinitrotoluene, TNT (McLellan et al., 1988). Because fresh surface of metallic aluminum, which can then
of the inherent stability of RDX and its relative insen- function as a reducing agent. The ultrasonic degradation
sitivity to shock, it does not readily degrade by con- of RDX and ADN is probed by studying the UV ab-
ventional treatment methods. Bioremediation methods sorbance of filtrates derived from aqueous microhete-
take days and sometimes weeks at elevated temperatures rogeneous media as a function of sonication time, pH,
to achieve significant degradation of RDX (Freedman and the nature and suspension density of the dispersed
and Sutherland, 1998). ADN, another shock-resistant particulate. The effect of aluminosilicate zeolite, alu-
high explosive and effective oxidizer, is a stable, white mina, or titanium dioxide on the degradation effective-
Ź
ionic salt used in explosives and fuels (Lobbecke et al., ness was also studied as experimental controls for
o
1997). aluminum powder. Plausible mechanisms for the deni-
Previous studies have shown that the localized and tration of RDX and ADN by ultrasound in the presence
extreme conditions generated by ultrasound, as well as of Al powder are proposed on the basis of the results
the resulting formation in aqueous media of hydrogen obtained from absorbance measurements (to monitor
and hydroxyl radicals, create chemical species that can the loss of RDX or ADN), X-ray photoelectron spec-
degrade chemical contaminants in wastewater (Bhatna- troscopy, XPS (to determine nitrogen speciation in the
gar and Cheung, 1994; Cheung and Krup, 1994; Hoff- post-reaction filtrates), and electrochemical studies (as a
Ź
mann et al., 1996; Kruger et al., 1999). Sonochemical second means to generate Al(0) and aluminum hydride
u
effects are largely attributed to phenomena that result in aqueous solution).
from cavitation. During sonication, an oscillating pres-
sure field drives periodic cycles of expansion and con-
traction of gas-filled microbubbles in the liquid. The 2. Experimental procedures
implosive collapse of these microbubbles (cavitation)
generates high local temperatures and pressures (5000 2.1. Chemicals
°C and 1000 atm, respectively) that drive sonochemical
reactions directly (Suslick, 1990, 1997) or indirectly Analytical reagent grade cyclo-1,3,5-trinitro-1,3,5-
through reactants generated via these extreme condi- triamine (Naval Research Laboratory, Washington, DC
tions (Hoffmann et al., 1996). and Naval Surface Warfare Center, Indian Head, MD)
Ultrasonic degradation of organic species in aqueous and ADN (NRL-DC) were used as received. Stock so-
solutions may follow multiple reaction pathways, in- lutions of RDX and ADN (127 and 151 lM, respec-
cluding: (1) a high concentration of oxidizing species tively) were made with 18 MX cm water (Barnstead
such as hydroxyl radicals; (2) pyrolytic decomposition Nanopure) and stirred overnight to equilibrate. The
by the high localized temperatures and pressures; or (3) solid ADN and all ADN solutions were stored and
supercritical water oxidation (Hoffmann et al., 1996). studied in a dark environment to avoid photolytic
Substances that have been remediated sonochemically decomposition. Standard solutions of sodium nitrate
include pesticides, phenols, esters, TNT, and chlorinated (Fisher Scientific; 0.77 mM) and sodium nitrite (Fisher
organic compounds (Sierka, 1984; Hoffmann et al., Scientific; 0.94 mM) were prepared in order to test the
1996). stability of the nitrate and nitrite ions when exposed to
Ultrasonic degradation of chlorinated volatile or- ultrasound and Al metal. A stock solution of NaOH
ganic compounds (VOCs) and chlorofluorocarbons (1.00 M) was prepared by diluting 5.15 ml of a freshly
(CFC-11 and CFC-13) proceeds via cleavage of the opened solution of 19.4 M NaOH (Fisher Scientific) to
Ź
carbon halogen bonds (Cheung and Krup, 1994; Kruger 100 ml.
u
L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114 1109
The following powders were used as received in the sampling procedures produced the lowest minimum
heterogeneous ultrasound studies: aluminum powder replicate error ( 8%) in the absorbance at the moni-
(historical supply), c-alumina (Alfa-Aesar), sodium-ion- toring wavelength. We define a change that is <8% as
compensated synthetic type Y aluminosilicate zeolite indicating that no RDX or ADN degradation occurs.
(NaY; a gift from UOP, LLC), and titanium dioxide The samples were monitored at secondary UV absorp-
(P25; a gift from Degussa). The mean diameter of the Al tion maxima (236 nm (RDX) and 286 nm (ADN)) to
powder, as determined by scanning electron microscopy avoid interference from hydroxide, nitrate, and nitrate
(Leo model 1550 electron microscope), is <10 lm with a ions and particulate matter that also absorb between 190
wide size distribution of agglomerated primary particles. and 220 nm. Calibration curves for RDX, ADN, NO 2 ,
Aluminum hydride was prepared by electrochemically and NO 3 species were obtained using standard solutions.
charging a 0.133-mm thick strip (5:2 cm 1:2 cm) of Al Aliquots (50 ll) of nitrate/nitrate-derived standards and
foil at )4.00 V vs Pt mesh in a 10 mM NaOH solution. selected post-sonication samples were evaporated onto
1 cm 1 cm 0:1-mm indium foil (Alfa, 99.99%) for
2.2. Equipment and instrumentation XPS analysis.
The sonochemical reaction vessel consisted of a 25 ml
3. Results and discussion
pear-shaped, three-necked glass flask, into which the
ultrasonic horn (titanium alloy, 3.5-mm-diameter tip)
Aqueous solutions of RDX and ADN exhibit two
and temperature probe (Cole Palmer, Inc. model 8502-
UV absorption maxima (RDX: kmax ź 198 and 236 nm;
16 thermistor) were inserted. The reactor was placed
ADN: kmax ź 216 and 286 nm), as seen in Fig. 2.
into a circulatory bath (Neslab model RTE-110) with a
set temperature of 5 °C and irradiated with 50 W, 20
kHz ultrasound (Sonics and Materials Inc. model VC- 3.1. Effect of non-Al(0) solids on RDX degradation
50T ultrasonicator). The temperature was thermostatted
below room temperature because sonochemical reac- Microheterogeneous media containing TiO2, alu-
tions are typically not favored at high temperatures, due mina, or NaY were studied as control solids because
to cushioning of the imploding bubble by the greater
kinetic energy of the vapors within the bubble (McLel-
1.2
lan et al., 1988; Hoffmann et al., 1996). All aqueous
1.0
RDX
standards and reaction samples were analyzed by UV
 = 236 nm
vis spectroscopy (Hewlett-Packard photodiode array
max
0.8
model 8452A). A limited set of standards and samples
0.6
was analyzed by XPS (Surface Science Instrument model
SSX-100-03; AlKa X-rays).
0.4
2.3. Experimental protocol 0.2
0.0
The reaction samples consisted of 9.9 ml of the en-
200 225 250 275 300 325 350 375 400
ergetics-contaminated wastewater plus 0.10 ml of 1.00
M NaOH. Controls for neutral solutions of RDX,
Wavelength / nm
ADN, NaNO2, and NaNO3 were run with 0.10 ml of
1.2
water substituted for the NaOH stock solution to
maintain the same concentration of contaminant in the
ADN
1.0
sample. Powders of Al, Al2O3, NaY, or TiO2 were added
 = 286 nm
max
in 5-, 50-, or 500-mg portions to 10-ml samples of the
0.8
energetics wastewater.
0.6
The reaction samples were sonicated for 60 min with
300-ll aliquots taken every 5 10 min. After each run,
0.4
aliquots from RDX samples were diluted to 750 ll,
bringing the concentration to 50.8 lM (in the absence of
0.2
any molecular degradation). This dilution was based on
the molar absorptivity of the RDX chromophore. 0.0
200 250 300 350 400 450 500
Aliquots taken from the sonochemical reaction of ADN
Wavelength (nm)
were not diluted. All controls and post-reaction samples
were centrifuged for 30 min and pressure filtered
Fig. 2. UV vis absorption spectra of aqueous solutions of
through a 0.02-lm disk (Whatman Anotop). These RDX (63.5 lM) and ADN (74.8 lM).
Absorbance
Absorbance
1110 L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114
Fig. 4. UV absorption spectra of filtrates derived from an
aqueous pH 12 microheterogeneous medium containing RDX
(127 lM) and 5 mg/ml of Al as a function of sonication time;
percentage of degradation is monitored at 236 nm.
When a 127 lM RDX solution, 10 mM in NaOH, is
sonicated in combination with Al(0) powder at a sus-
pension density of 5 mg/ml, 74% of the compound de-
grades within the first 20 min of sonication (Fig. 4). No
Al powder visibly remains in the reaction vessel after 60
min of treatment. In contrast, RDX neither decomposes
Fig. 3. Percentage of RDX (127 lM) decomposed after a 60-
upon stirring alkaline RDX solutions with Al powder in
min ultrasonic treatment, as a function of dispersed solid and
pH. Degradation effectiveness is markedly enhanced for sono- the absence of sonication nor is the Al powder digested.
chemical reaction with dispersed Al(0) powder under basic pH. These results indicate that RDX is degraded by the so-
Replicate error is 8%.
nochemistry created by the combination of OH , A l
powder, and ultrasound.
similar chemical species may be generated in situ when At a lower suspension density of Al powder (0.5 mg/
sonicating an aqueous microheterogeneous medium ml), the concentration of RDX decreases by only 40%
containing Al powder with a Ti-alloy horn in a glass after 60 min of sonication, which also indicates that
vessel. Sonication of aqueous media containing any of metallic Al is a reactant. Suspensions containing more
these solids yields less than 11% breakdown of RDX than 5 mg/ml of Al powder show neither significantly
after 60 min of sonication, regardless of suspension improved efficiency nor an increased extent of degra-
density and even under alkaline pH (see Fig. 3). In ad- dation. This leveling off could arise for two reasons: (1)
dition, RDX did not degrade after exposing aqueous high suspension densities of solid would be expected to
RDX solution (127 lM) to an as-received (i.e., electro- lower the effectiveness of cavitational disruption of the
chemically uncharged) strip of Al(0) foil for 60 min passive oxide layer of aluminum oxide on the aluminum;
without sonication. and (2) at pH 12, because of Eq. (1), an insufficient
concentration of OH may be present at high suspen-
sion densities of Al powder to react at the stoichiometry
3.2. Sonochemistry of RDX
necessary to form aluminate:
As determined by UV absorption, RDX is stable to
AlðOHÞ3 þ OH AlðOHÞ 4 ð1Þ
sonication for 60 min in an aqueous solution. Despite
the expectation of   incineration in a bubble  due to the
extreme local temperatures that arise upon cavitation, 3.3. Sonochemistry of ADN
ultrasonic treatment alone does not generate and sustain
conditions sufficient to degrade RDX, even with the Experiments with ADN indicate that it behaves sim-
addition of either OH or suspended Al powder. A prior ilarly to RDX under sonochemical treatment. Insignifi-
study of RDX and TNT degradation using ultrasound cant levels of degradation are obtained when ADN is
also indicated minimal degradation of RDX (Sierka, sonicated for 60 min in the absence of NaOH and Al
1984). powder or in the presence of non-Al(0) solids. However,
L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114 1111
2.0
-
-
NO
NO
a
2
3
0 min
1.6 10 min
0 min
20 min
40 min
1.2
60 min
5 min
0.8
86%
degradation
0.4
10 min
0.0
20 min
210 280 350 420
210 245 280 315 350 385 420
Wavelength / nm
30 min
1.0
b
40 min
0.8
0.6
410 406 402 398
Binding energy (eV)
0.4
Fig. 6. N 1s X-ray photoelectron spectra of evaporated filtrate
derived from aliquots sampled during ultrasonic treatment of
0.2
NO 2 þ NO 3 =10 mM NaOH/5 mg/ml of Al powder. N 1s in-
tensity is normalized to that of Na 1s.
0.0
0 1 0 2 0 3 0 4 0 5 0 6 0
Sonication Time / min
Sonicating aqueous solutions of NaNO2 and NaNO3
for 60 min in the absence of base or Al powder produces
Fig. 5. (a) UV vis absorption spectra of filtrate sampled during
no significant change in either their UV absorption or
ultrasonic treatment of 151 lM ADN/10 mM NaOH/5 mg/ml
of Al powder; (b) change in absorbance at 286 nm as a function N 1s X-ray photoelectron spectra (which exhibit binding
of sonication time.
energies consistent with assignment as N in NO 2 and
NO 3 (Wagner et al., 1979)). This lack of direct ultra-
sonic reaction of nitrate, and especially nitrite, is in
sonicating a solution of 151 lM ADN/10 mM NaOH/5
agreement with the RDX and ADN controls in pure
mg/ml of Al powder for 60 min produces an 86% loss in
ADN concentration (Fig. 5a and b). In alkaline solutions water or at pH 12 in which no significant sonochemical
reactivity occurs.
with Al powder and a lower concentration of ADN (50
When a pH 12 solution of NaNO3/NaNO2 is soni-
lM), 100% degradation is achieved within 20 min of
cated in the presence of 5 mg/ml of Al powder, the total
sonication. As seen with RDX, increasing the suspension
density of aluminum powder above 5 mg/ml does not nitrogen content in the filtrates decreases as a function
of sonication time (Fig. 6). On the basis of the N 1s peak
improve the effectiveness of degradation.
ratios of nitrite to nitrate, the nitrite species undergoes
reaction first. The ultimate disappearance of NO 2 and
3.4. Sonochemistry of nitrite/nitrate
NO 3 species during sonication in the presence of OH
and Al indicates that nitrogen-containing product spe-
The relatively monotonic and clean loss of the UV
cies do not remain in the liquid, and escape from the
absorption features for RDX and ADN (as seen in Figs.
reaction vessel in the form of nitrogenous gases. XPS
4 and 5a) indicate that the decomposition products are
analysis of filtrate derived from RDX ultrasonic reac-
either not UV active or are active in a region masked by
tions exhibits no N 1s signal above background.
UV absorption by OH . Nitrate and nitrite ions, which
are possible RDX and ADN decomposition products,
are UV active, but in the same wavelength region as 4. Proposed reaction mechanisms
OH . The stability of NO 2 or NO 3 to ultrasound (as
analyzed by XPS) was explored using the same condi- Sonochemistry involves complex, coupled physical
tions developed for the RDX and ADN decomposition phenomena and chemical reactions that are not com-
studies. pletely understood, which makes it difficult to identify
Absorbanc e
intensity (au)
Absorbanc e
1112 L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114
the precise mechanisms that govern the ultrasonically 1999) (Eqs. (3) (5)). This chemistry is accompanied by
induced breakdown of the energetic materials RDX and dissolution of aluminum metal in the presence of hy-
ADN in the presence of OH and Al powder. Currently droxide to form water-soluble aluminate (Eq. (1)):
there is not even a mechanistic understanding of the
3NO 3 þ 2Al þ 3H2O ! 3NO2ðgÞ þ2AlðOHÞ3 ð3Þ
conflagration reactions involving RDX and similar en-
ergetic materials (Chakraborty et al., 2000). Prior de-
NO 2 þ 2Al þ 5H2O ! NH3 þ 2AlðOHÞ3 þ OH ð4Þ
composition studies show that NO 2 is the primary
byproduct of shock-induced and photolytic decomposi- 2NO 2 þ 2Al þ 4H2O ! N2ðgÞ þ2AlðOHÞ3 þ 2OH
tion of RDX (Owens and Sharma, 1980), as well as of
ð5Þ
alkaline hydrolysis (Heilmann et al., 1996).
The ultrasonic reactivity of microheterogeneous alkaline
media containing nitrate and nitrite and Al powder in-
4.1. Sonochemically induced reactions
dicates that cavitation does indeed generate fresh metal
surfaces to induce reductive chemistry. Reductive deni-
In sonolysis, the lifetime of ultrasonically generated
tration of RDX and ADN with ultrasonically generated
chemical radicals exceeds the lifetime of the cavitating
Al(0) is in keeping with these classes of reactions.
bubble, which permits radical-driven chemical reactions
to be triggered (Thompson and Doraiswamy, 1999).
4.3. Aluminum hydride mechanism
During cavitational implosion, pure water yields H
atoms and OH radicals upon the thermal dissociation of
We also explored a mechanism involving sono-
water vapor, Eq. (2)  these radicals are strong reduc-
chemically generated aluminum hydride (AlHx) as a
tants and oxidants and induce many of the sonochemical
candidate for the decomposition reaction since the Al H
reaction pathways described in the literature (Heilmann
bond has a high reductive potential and sonochemical
et al., 1996; Hoffmann et al., 1996):
generation of Al(0) and H should also generate AlHx.
H2O H þ OH ð2Þ Electrogeneration of aluminum hydride in alkaline me-
dia has been reported previously (Perrault, 1980). When
However active these ultrasonically derived reactants
we exposed an alkaline RDX solution, without sonica-
have proven to be with other organic compounds, the
tion, to a hydrided Al foil (as pre-generated by electro-
complete lack of ultrasonic reactivity in the absence of
reduction), the concentration of RDX decreased by 18%
Al with either aqueous or alkaline solutions of RDX,
after 60 min and 23% after 120 min. The ability of
ADN, NO 2 , and NO 3 indicates that an ultrasound-
electrogenerated AlHx to react with RDX indicates that
activated water/radical mechanism is insufficient to ex-
an Al H mechanism is a plausible pathway in the re-
plain our results.
action and that the direct electrochemical generation of
Al H may also be used to reduce nitramines. The fact
4.2. Aluminum(0) as reducing agent that a charged foil has a sustained temporal effect on
RDX decomposition indicates that sub-surface hydride
The reducing power of Al metal is difficult to harness forms and is available as a pool of reactant over time.
due to its passive oxide. Ultrasound can activate highly
reactive metal surfaces that are otherwise protected by a 4.4. Mechanistic assessment
passive oxide coating (Preece and Hansson, 1981; Souza
et al., 1998; Thompson and Doraiswamy, 1999), because Ultrasonically induced pyrolysis/thermal decompo-
of asymmetric cavitation near extended liquid solid in- sition of the energetics is not occurring on the time scale
terfaces (Mead et al., 1976). When a deformed cavity and at the ultrasonic power levels of our experiments.
collapses, it emits high-velocity microjets of liquid The results reported here demonstrate that ultrasound-
(nearing 100 m/s) that crack the passive oxide layer to exposed Al(0) destroys energetic compounds in an al-
expose a fresh metal surface that is briefly available for kaline microheterogeneous medium. The persistence of
reductive chemistry, including electron transfer to or- RDX degradation at electrogenerated aluminum hy-
ganic substrates (Luche, 1994). Previous research has dride implies that the ultrasonic conditions may also
demonstrated that mechanical agitation, even of the generate this reductant by exposing aluminum metal in
same power consumption, does not comparably break the presence of sonochemical reactants, such as H .
the passive oxide layer (Carvalho et al., 1995; Hagenson From our studies, we posit that ultrasound generates
and Doraiswamy, 1998). fresh Al metal, which then reductively denitrates RDX
It is already established that selective reduction of and ADN, as postulated in Fig. 7.
nitrate and nitrite by Al(0) occurs under alkaline con- The presence of OH is a necessary component of the
ditions (Murphy, 1991) to generate nitrogenous gas- mechanistic degradation pathway. Both Al(0)-driven
phase products: NOx, NH3, and N2 (Moon and Pyun, electron-transfer reactions with nitrite/nitrate and elect-
L.R. Qadir et al. / Chemosphere 50 (2003) 1107 1114 1113
Fig. 7. Representative diagram of proposed Al/sonochemical reaction pathway.
rochemical generation of AlHx require alkaline condi- Bhatnagar, A., Cheung, H.M., 1994. Sonochemical destruction
of chlorinated-C1 and chlorinated-C2 volatile organic-com-
tions, which substantiates the proposed mechanism in
pounds in dilute aqueous-solution. Environ. Sci. Technol.
which ultrasonically generated Al(0) reacts with RDX
28, 1481 1486.
and daughter products such as nitrite and nitrate via
Carvalho, L.R.F., Souza, S.R., Martinis, B.S., Korn, M., 1995.
reductive chemistry. The lack of a N 1s peak in the XPS-
Monitoring of the ultrasonic irradiation effect on the
analyzed aliquots confirms that the end products of the
extraction of airborne particulate matter by ion chromato-
ultrasonically treated alkaline microheterogeneous me-
graphy. Anal. Chim. Acta 317, 171 179.
dia are in the gas phase.
Chakraborty, D., Muller, R.P., Dasgupta, S., Goddard, W.A.,
A sonochemical approach has an advantage over
2000. The mechanism for unimolecular decomposition of
conventional treatment methods in that the target mol- RDX (1,3,5-trinitro-1,3,5-triazine), an ab initio study. J.
Phys. Chem. A104, 2261 2272.
ecule needs not be extracted from an aqueous phase, i.e.,
Cheung, H.M., Krup, S., 1994. Sonochemical destruction of
wastewater streams, as would be required in combus-
CFC-11 and CFC-113 in dilute aqueous-solution. Environ.
tion, or other remediation efforts. These field conditions
Sci. Technol. 289, 1619 1622.
are also not suitable for electrochemical processes,
Freedman, D.L., Sutherland, K.W., 1998. Biodegradation of
which can be quenched by impurities. Furthermore,
hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) under ni-
most of the RDX and ADN samples, at concentrations
trate-reducing conditions. Water Sci. Technol. 38, 33 40.
in water approaching saturation, degraded within the
Hagenson, L.C., Doraiswamy, L.K., 1998. Comparison of the
first 20 min and all samples were reacted at low tem-
effects of ultrasound and mechanical agitation on a reacting
peratures. Ultrasound may be a feasible alternative to
solid liquid system. Chem. Eng. Sci. 53, 131 148.
previous treatments, although more work is required Heilmann, H.M., Weismann, U., Stenstrom, M.K., 1996.
to determine the efficiency of the sonochemical de- Kinetics of the alkaline hydrolysis of high explosives RDX
and HMX in aqueous solution and adsorbed to activated
struction of energetic materials in aqueous waste upon
carbon. Environ. Sci. Technol. 30, 1485 1492.
scale-up.
Ź
Hoffmann, M.R., Hua, I., Hochemer, R., 1996. Application of
o
ultrasonic irradiation for the degradation of chemical
contaminants in water. Ultrason. Sonochem. 3, S163 S172.
Acknowledgements
Hundal, L.S., Singh, J., Bier, E.L., Shea, S.D., Comfort, S.D.,
Powers, W.L., 1997. Removal of TNT and RDX from water
This research was supported by the Office of Naval
and soil using iron metal. Environ. Pollut. 97, 55 64.
Research. L.R.Q. initiated this project as a participant
Ź
Kruger, O., Shulze, Th.-L., Peters, D., 1999. Sonochemical
u
from La Plata High School (La Plata, MD) in the NRL
treatment of natural ground water at different high fre-
Science and Engineering Apprentice Program (SEAP).
quencies: preliminary results. Ultrason. Sonochem. 6, 123
E.J.O.-A. was an ASEE Post-doctoral Associate (1996 128.
Ź
Lobbecke, S., Keicher, T., Krause, H., Pfeil, A., 1997. The new
o
1997) and V.M.C. was an NRC Post-doctoral Associate
energetic material ammonium dinitramide and its thermal
(1998 1999). The authors extend their thanks to Jeff
decomposition. Solid State Ionics 101, 945 951.
Hilgert (Branson Ultrasonics) for his loan of an ultr-
Luche, J.L., 1994. Effect of ultrasound on heterogeneous
asonicator to establish feasibility and to Doug Elstrodt
systems. Ultrason. Sonochem. 1, S111 S117.
(Naval Surface Warfare Center, Indian Head MD) for
McLellan, W., Hartley, W.R., Brower, M., 1988. Health
the generous gift of RDX.
Advisory for Hexahydro-1,3,5,-tetranitro-1,3,5-triazine.
Technical Report PB90-273533; Office of Drinking Water,
US Environmental Protection Agency, Washington, DC.
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