Poultice method for extracting hazardous spills

Chemicals spilled on porous surfaces may be removed therefrom by applying to the spill site a poultice in the form of a slurry or paste of finely divided particulate material dispersed in a volatile solvent in which the spilled chemical substance is soluble, allowing the solvent to be absorbed into the porous substrate. The poultice is then allowed to dry, thereby effecting a wicking action causing extraction of the chemical substance from the substrate into the poultice.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a poultice method for removing 
chemical spills from porous surfaces such as construction materials, 
including concrete, soil, road beds and the like, and more particularly to 
a method for cleaning up spills of polychlorinated biphenyls (PCBs) and 
PCB-contaminated transformer oil from such surfaces. 
In addition to accidental chemical spills, many instances of indiscriminate 
disposal of chemical wastes along road beds, in land fills and elsewhere 
have been reported over the last several years, and concern has grown over 
the potential harm to public health and the environment resulting from 
such occurences. Considerable effort is required in cleaning up chemical 
substances accidentally spilled or improperly disposed of, since the 
chemicals often become absorbed in the porous surfaces on which they are 
spilled. The situation is especially aggravated when the spilled chemical 
is a toxic material. 
Present clean-up methods for toxic chemical spills on porous substrates 
frequently involve extensive excavation or destruction of the porous 
surface. These methods are quite expensive and not always effective. 
Moreover, even when the site of the spill is cleaned up, there remains the 
problem of disposing of the toxic chemical substance and debris associated 
therewith in a safe and effective manner. 
Halogenated organic compounds are particularly difficult to dispose of 
because of the highly stable nature of the carbon-halogen bonds present 
therein. Compounds such as polychlorinated biphenyls (PCBs), 
dichlorodiphenyltrichloroethane (DDT), 
decachlorooctahydro-1,3,4-metheno-2H-cyclobuta-[c,d]-pentalen-2-one 
(Kepone.RTM.), and 2,4,5-trichlorophenoxyacetic acid, (2,4,5-T), which 
have been found to be persistent environmental toxins, are not only 
resistant to biodegradation, they cannot be degraded in a practical and 
effective manner by any of the well known chemical decomposition methods. 
In most cases, known decomposition methods such as chlorolysis, catalytic 
dehydrohalogenation, molten salt reactions, ozone reactions and alkali 
metal reduction achieve only partial dehalogenation of such compounds. 
Moreover, these prior art methods typically involve one or more drawbacks, 
such as the use of expensive reagents, extensive temperature control, 
inert atmospheres, complex apparatus and/or substantial energy consumption 
which would make it difficult to utilize these methods in disposing of 
halogenated organic compounds present in the porous surfaces described 
above. 
During the past several years, there has been developed at the Franklin 
Research Center of the Franklin Institute, Philadelphia, Pa., a system for 
stripping the chlorine substituents from various halogenated organic 
compounds, including PCBs, thus rendering them non-toxic and readily 
disposable. More specifically, Pytlewski, Krevitz and Smith, in their U.S. 
patent application Ser. No. 158,359, filed June 11, 1980, now U.S. Pat. 
No. 4,337,368, disclose and claim a method for the decomposition of 
halogenated organic compounds, which represents a significant advance over 
the aforementioned decomposition methods of the prior art. The 
decomposition reagent used in practicing the method of Pytlewski et al. is 
formed from the reaction between an alkali metal, a liquid reactant, such 
as polyglycol or a polyglycol monalkyl ether, and oxygen. This reagent 
produces substantially complete dehalogenation simply by mixing it with 
the halogenated compound in the presence of oxygen. 
In U.S. patent application Ser. No. 240,622, filed Mar. 5, 1981, now U.S. 
Pat. No. 4,400,522, there is described and claimed another invention by 
Pytlewski et al. based on the discovery that substantially complete 
dehalogenation of halogenated organic compounds may be carried out using a 
reagent produced by the reaction of an alkali metal hydroxide (rather than 
an alkali metal), a liquid reactant, such as a polyglycol or a polyglycol 
monalkyl ether, and oxygen. This decomposition reagent gives results which 
are comparable to those obtained with the method described in the earlier 
filed application of Pytlewski et al. referred to above. 
The reagents of the aforesaid patent and application are collectively 
referred to hereinafter as NaPEG reagents, or simply NaPEG. 
The development of the NaPEG reagents has made it possible to remove 
halogenated organic compounds from fluids contaminated therewith, as well 
as to decompose such compounds in concentrated form in a safe, efficient 
and effective manner. 
SUMMARY OF THE INVENTION 
The above-noted deficiencies of the prior art methods for cleaning up 
chemical spills from porous surfaces have been overcome in accordance with 
the present invention wherein a poultice is employed to effect an 
extraction of spilled material from a porous surface without doing damage 
to, or otherwise harming said surface. Briefly, the method involves 
applying to the site of the spill a poultice in the form of a slurry or 
paste of finely divided particulate material, such as clay, silica, or 
calcium carbonate, dispersed in a volatile solvent in which the spilled 
chemical substance is soluble. Upon standing, the solvent is absorbed into 
the surface to which it is applied and the poultice dries to form a 
powder. During drying, a wicking action by the solvent is produced causing 
extraction of the chemical substance from the substrate to the evaporating 
surface of the particulate material component of the poultice. The dried 
poultice, which is essentially the powder containing the chemical 
substance, is then collected and disposed of. 
The term "poultice", as used herein, refers to a soft paste-like mass 
applied to a porous surface to remove a chemical substance therefrom. 
The expression "toxic material", as used herein, refers to a material 
containing a poison in concentrations great enough to be hazardous to 
human health and the environment. 
While the present process may be used on any chemical spill, it is 
particularly useful for cleaning up spills of chemical substances 
comprising toxic materials, including various halogenated organic 
compounds, such as PCBs and PCB-contaminated transformer oils. Moreover, 
in a modification of the present invention, a chemical detoxifying 
reagent, such as the above-mentioned NaPEG reagents, may be incorporated 
in the poultice to decompose the hazardous substance drawn into the 
poultice. 
In addition to providing an efficient and effective way of cleaning up 
chemical spills on porous surfaces, the method of the present invention 
possesses other notable advantages. For example, when the chemical spill 
comprises a toxic material, such as the above-mentioned halogenated 
organic compounds, addition of a detoxifying reagent to the poultice 
obviates handling and disposal problems associated with such toxic 
materials. Further, the poultice may be kept on hand at potential spill 
sites and used quickly on a spill, thus reducing the time in which the 
affected area would be inaccessible.

DESCRIPTION OF THE INVENTION 
In accordance with the present invention, it has been discovered that 
chemicals spilled on porous surfaces such as construction materials, 
including, but not limited to concrete, blacktop, brick, sand, soil, wood 
and the like may be extracted therefrom using a poultice technique. The 
poultice of the present invention typically consists of a slurry or paste 
composed of finely divided particulate material dispersed in a volatile 
solvent. 
The poultice material of the present invention may be prepared from many 
types of particulate materials and solvents. Suitable particulate 
materials include mineral powders such as clay (sepiolite or attapulgite), 
ground silica, pumice, calcium carbonate or mixtures thereof. Cellulosic 
powders such as mechanically comminuted purified wood pulp and wood flour 
may also be used effectively as a poultice component. Use of finely 
divided particulate materials avoids the problem of shrinkage encountered 
when a material such as paper pulp is used in making the the poultice. 
Also, use of a finely divided particulate material is important to the 
wicking action which occurs during drying of the poultice. This 
thermodynamic driving force is due to the combined effect of the porosity 
and capillarity of the poultice and the porosity and capillarity of the 
porous substrate from which the spilled chemical is being removed. The 
porosity of the poultice should be less than or equal to the porosity of 
the substrate and the capillarity of the poultice should be greater than 
or equal to the capillarity of the substrate. While the porosity and 
capillarity of the poultice relative to the substrate may vary depending 
on the specific poultice constituents selected, substrate and chemical 
spilled, it is the combined effect of porosity and capillarity which give 
rise to the wicking action which occurs during drying of the poultice. The 
suitability of a given poultice for treating a particular spill may be 
easily determined by trial. 
Various organic solvents or solvent/water mixtures may be used as the 
solvent component of the poultice. In general, the choice of a particular 
solvent will depend on the nature of the chemical to be removed from the 
porous surface. Primarily, the solvent chosen as the poultice component 
must be capable of extracting the spilled material. For instance, where 
the spilled chemical is a halogenated organic compound, e.g., PCBs, the 
use of acetone, or other ketones, as the solvent has been found to produce 
particularly good results. 
The relative proportions of poultice components may vary, depending on the 
specific particulate material and solvent selected, the principal 
criterion being that its proportions be selected so as to give a poultice 
having a paste-like consistency. The optimum proportions may be easily 
determined by trial. 
In order to achieve removal of a spilled chemical from a porous substrate 
in accordance with this invention, the appropriate poultice components are 
blended into a slurry or paste and then applied to the site of the spill 
in sufficient quantity that the porous surface becomes saturated with the 
solvent component of the poultice. The site may optionally be covered with 
a polyethylene sheet (e.g. for approximately 30 minutes) to ensure 
saturation of the surface with solvent by reducing evaporation of the 
solvent. The saturated porous surface is then allowed to dry. Drying of 
the poultice provides the thermodynamic driving force or wicking action 
which transports the solvent containing the spilled chemical therein from 
the porous surface into the particulate material component of the 
poultice. The dried poultice containing the spilled chemical therein 
serves as a sacrificial surface that can be easily removed from the spill 
site and discarded. 
When the spilled chemical is a toxic material, handling problems will exist 
with regard to both the removal and disposal of the dried poultice 
containing the hazardous chemical. As previously mentioned, such 
situations may be handled in a safe, effective and efficient manner by 
including in the poultice a decomposition or detoxifying reagent which 
will specifically react with the toxic material. 
According to a preferred embodiment of the present invention, a NaPEG 
reagent is added to the poultice in order to detoxify halogenated organic 
compounds extracted from a porous surface into the poultice. As previously 
noted, NaPEG reagents include a family of chemical derivatives of alkali 
metal (or alkali metal hydroxide), liquid reactants, such as polyethylene 
glycol and oxygen. These reagents are produced from relatively low cost 
raw materials without significant manufacturing problems. 
The reaction for producing the NaPEG reagent proceeds spontaneously at room 
temperature simply by mixing the reactants in an open reaction vessel, 
preferably with stirring. It is unnecessary to bubble oxygen or air into 
the reaction mixture, though this will accelerate the reaction. No 
temperature control or specialized equipment is required for carrying out 
the reaction. If desired, the reaction mixture may be heated to accelerate 
the rate of reaction. For example, a reagent formed from sodium and 
polyethylene-glycol having an average molecular weight of 400 is 
preferably prepared by heating of the reaction mixture in air to a 
temperature in the range of about 50.degree. C. to about 80.degree. C., 
which provides a satisfactory reaction rate. Upon heating, the reaction 
becomes exothermic and the temperatue of the reaction mixture rises to 
near or above the melting point of the sodium, which is 97.6.degree. C. 
With the rise in temperature, the sodium becomes molten and reaction with 
the liquid ensues. Reactions involving alkali metal hydroxides are 
considerably less exothermic than those involving the alkali metals. 
Additional details of the procedures for preparing the NaPEG.RTM. reagents 
are set forth in the aforementioned U.S. Pat. No. 4,337,368 and patent 
application Ser. No. 240,622, and the entire disclosures thereof are 
incorporated by reference herein, as though set forth in full in the 
present disclosure. 
NaPEG may be incorporated into the poultice by mixing it with the solvent 
component of the poultice prior to addition of the finely divided 
particulate material. However, the order of mixing of the components is 
not essential to practicing the present invention and NaPEG may be 
incorporated into a poultice by any other convenient method. NaPEG is 
readily mixed with the other poultice components to form a paste. The 
amount of NaPEG, or other decomposition reagent incorporated in the 
poultice, may vary over a wide range and will normally depend upon the 
surface area to be treated. The mole ratio of NaPEG to halogenated organic 
substance should be 5 to 1, or greater. The concentration of contaminant 
at the spill site may be determined by analytical procedures well known to 
those skilled in the art. 
As disclosed in the aforementioned patent and application the by-products 
of the detoxification reaction are relatively non-toxic and safe to 
handle, the principal ones being sodium chloride and various oxygenated 
derivatives of the starting halogenated organic substance. 
As previously mentioned, the solvent chosen as the poultice constituent 
will depend on the solubility characteristics of the spilled chemical. In 
addition, where the spilled chemical is toxic and a detoxifying reagent is 
used, the selected solvent must be compatible with the detoxifying 
reagent. The expression "compatible solvent", as used herein, refers to 
any solvent which does not adversely affect the reactivity of the 
detoxifying reagent, or otherwise interfere with its function. Thus, if a 
NaPEG reagent is added to the poultice, ketones may not be used as the 
solvent, as they react with the NaPEG reagent in such a way as to 
interfere with its dehalogenating function. Suitable compatible solvents 
for use in connection with NaPEG reagents include polar solvents such as 
alcohols and ethers, e.g., tetrahydrofuran. Likewise, non-polar solvents, 
such as hexane, toluene and xylene are compatible with NaPEG reagents 
added to the poultice. 
Similarly, where the spilled chemical is toxic and a detoxifying reagent is 
used, the finely divided particulate material must also be compatible with 
the detoxifying reagent. For instance, if a NaPEG reagent is added to the 
poultice, mineral powders comprised of or containing silica particles such 
as fumed silica may not be used as the finely divided particulate 
material, since silica particles react with the NaPEG reagent in such a 
way as to interfere with its dehalogenating function. 
The poultice may further contain a binding agent such as cellulosic fibers. 
The addition of a binding agent helps to prevent premature cracking and 
drying of the poultice powder. It is believed that premature cracking 
interferes with the wicking action by which the solvent containing the 
spilled chemical dissolved therein is transported from the porous 
substrate into poultice. If clay is a major constituent of the poultice, 
mineral powders in platelet form, such as vermiculite, provide an 
excellent binding material. 
The poultice may also contain a gelling agent. Thixotropic gelling agents, 
which liquefy when agitated, are particularly suited for inclusion in the 
poultice, in that they facilitate application of the poultice to the 
contaminated porous substrate and further prevent flowing of the poultice. 
Examples of useful thixotropes are bentonite, chemically modified clay and 
hydrogenated castor oil. 
When solvent/water mixtures are used in the poultice, non-ionic wetting 
agents may be added to improve the solubility of the contaminants in the 
poultice. 
The time during which the poultice is in contact with the surface being 
treated must be sufficient for thorough drying of the poultice (e.g. 
approximately 24 hours). The poultice may be tested periodically to 
determine whether or not adequate drying has occurred. 
The presently preferred manner and process of making and using the 
invention, which embodies the best mode contemplated by the inventor for 
carrying out the invention, will now be described. 
A mixture of NaPEG 400 (i.e. formed from sodium, polyethylene glycol having 
a molecular weight of 400, and oxygen), in the proportion of 60 parts 
NaPEG to 40 parts toluene by weight is added to a dry clay/vermiculite 
powder to form a wet paste. The paste is applied over a PCB or 
PCB-contaminated dielectric fluid spilled onto a concrete surface. The 
paste is covered with a polyethylene sheet for approximately 30 minutes to 
reduce solvent evaporation. The polyethylene sheet is then removed, and 
the solvent is allowed to evaporate. The powder is left in place until the 
PCBs are destroyed and then collected for disposal. Alternatively the 
dried powder may be collected immediately and stored, allowing the PCB 
destruction to take place in the storage container. Substantially complete 
PCB destruction normally takes several days. The powder may therefore be 
tested periodically to determine whether or not substantial PCB 
destruction has occurred. 
While particular embodiments of the present invention have been described 
hereinabove, it is not intended to limit the invention to such 
embodiments, but changes and/or additions may be made therein and thereto 
without departing from the scope and spirit of the invention as set forth 
in the following claims.