Solid phase extraction

Hydrophobic contaminants are removed from a particulate matter by contacting the particulate matter with a solid organic phase. The hydrophobic contaminants have greater affinity for the solid organic phase than for the particulate matter and repartition to the solid organic phase. The solid organic phase is then separated from the particulate matter. A typical embodiment utilizes polystyrene particles to remove polychlorinated biphenyls from soil.

The present invention pertains to solid phase extraction. Solid phase 
extraction is a method of removing hydrophobic contaminants from 
particulate matter using a solid organic phase. 
The existence of chemical contamination in the environment is well 
documented. Hazardous or noxious compounds from both industrial or 
agricultural activities have found their way into landfills, waterways, 
etc. over the course of time through purposeful disposal or accidental 
discharge. Recent acknowledgement of the health and environmental risks of 
such contamination has led to a search for a solution which is both 
technically and economically feasible. 
Many of the particularly problematic contaminants in the environment are 
hydrophobic in nature. Typical hydrophobic contaminants include aromatic 
hydrocarbons, polyaromatic hydrocarbons, polychlorinated biphenyls, 
dioxin, long chain alkanes, or mixtures thereof. Examples of aromatic 
hydrocarbons are benzene, toluene, and the like. Polyaromatic hydrocarbons 
include naphthalene, anthracene, and the like. Polychlorinated biphenyls 
(PCBs) are compounds having the formula C.sub.12 H.sub.10-n X.sub.n, 
wherein X is a chlorine atom and n is greater than one and typically is 
five to six. Examples of long chain alkanes include natural gasoline 
(typically C.sub.6 -C.sub.12), kerosene (typically C.sub.12 -C.sub.18), 
gas oils, such as furnace and diesel oils (typically above C.sub.18), and 
lubricating oils (typically C.sub.20 -C.sub.30). 
The present invention relates to a method of removing hydrophobic 
contaminants from a particulate matter which involves the steps of (a) 
contacting the particulate matter with a solid organic phase, the 
hydrophobic contaminants having greater affinity for the solid organic 
phase than for the particulate matter sufficient to cause the contaminants 
to repartition from the particulate matter to the solid organic phase, and 
(b) separating the solid organic phase from the particulate matter. The 
above method, hereinafter "solid phase extraction," provides for the 
removal and concentration of hydrophobic contaminants from the particulate 
matter to an easily recoverable solid organic phase. 
Solid phase extraction is particularly applicable when the particulate 
matter is soil, sediment or a fraction thereof, for example, pebbles 
(particles with diameters greater than 2 mm), sand (particles with 
diameters from about 0.02 to about 2 mm), silt and clay (particles with 
diameters less than 0.02 mm). This method is particularly suited for on 
site application since soil which is contaminated can be treated by this 
method either with or without costly excavation. 
The first step of this method is to contact the particulate matter which is 
contaminated with a solid organic phase. The solid organic phase is such 
that the hydrophobic contaminants have a greater affinity for the solid 
organic phase than the particulate matter. The greater affinity or 
attraction of the hydrophobic contaminants for the solid organic phase is 
sufficient if it causes the hydrophobic contaminants to repartition from 
the particulate matter to the solid organic phase. Suitable solid organic 
phases include polymeric foams and rubber. Polymeric foams are preferred. 
The polymeric foams include polyurethane, polypropylene, polyethylene, 
polystyrene, natural rubber, synthetic rubber, and the like. A substance 
which expands upon solidification of the precursor can be incorporated 
into the liquid form of the foam precursor, to effect foaming. Examples of 
typical polymeric foams are polyurethane, polystyrene and polyethylene. 
Polystyrene is preferred. 
One benefit of the present method is the ability to make use of or 
"recycle" refuse such as discarded rubber tires or other discarded rubber 
products, discarded polymeric foam materials, etc. as the solid organic 
phase. As well as providing a use for materials otherwise considered 
"trash," the use of recycled materials for the solid organic phase makes 
solid phase extraction even more economical. 
The solid organic phase may take on many forms, shapes and sizes. For 
example, the solid organic phase can be in the form of a sheet, coating or 
surface, or can be block-shaped, rod-shaped, cube-shaped, sphere-shaped, 
or randomly shaped. One embodiment of the present method uses solid 
organic phase in particulate form. Preferred is the use of a solid organic 
phase of a shape which maximizes surface area to volume ratio. 
The contact between the particulate matter and the solid organic phase must 
be sufficient to cause the hydrophobic contaminants to repartition from 
the particulate matter to the solid organic phase. The amount of contact 
between the particulate matter and the solid organic phase, and thus the 
degree of repartitioning of the contaminants from the particulate matter 
to the solid organic phase, are affected by several factors. 
Clearly, the time of contact is one such factor. The longer the time of 
contact between the particulate matter and the solid organic phase, the 
larger the amount of contaminants which repartition into the solid organic 
phase until equilibrium is reached. Extended time of contact should 
particularly be considered if the desire is to merely leave the 
particulate matter in contact with the solid organic phase and rely on the 
natural flux of the hydrophobic contaminants for repartitioning without 
more, i.e., without mechanical assistance or other means of contact 
enhancement. 
The contact between the particulate matter and the solid organic phase and 
thus the repartitioning of the hydrophobic contaminants also can be 
enhanced by mechanical means such as mixing, stirring or tumbling. Such 
mechanical methods effectively increase the amount of particulate matter 
which is contacted by the solid organic phase, providing for more thorough 
and intimate contact between the two materials. 
Another way to facilitate the repartitioning of the hydrophobic 
contaminants from the particulate matter to the solid organic phase, 
particularly when shorter contact times are used, is by pretreating the 
particulate matter with a solvent for the contaminants, preferably an 
organic solvent. Extended residence times often cause hydrophobic 
contaminants to partition thoroughly into particulate matter. It is 
believed that pretreatment of the particulate matter with a solvent and 
the solvent's subsequent evaporation effects desorption of the hydrophobic 
contaminant from the particulate matter, thereby enhancing its ability to 
repartition. The amount of solvent used for pretreatment is from about 20% 
to about 90%, preferably 50%, by weight of the particulate matter 
requiring treatment. The solvent can be water-miscible or 
water-immiscible. Suitable solvents for use in pretreatment include 
ketones, alkanols, ethers, and alkanes, as for example, acetone, methanol, 
diethylene, and the like. 
In some instances, the solvent may have an undesirable effect on the 
physical consistency of the solid organic phase, particularly when the 
solid phase is polystyrene. This can be readily addressed by adding water 
to the particulate matter and solvent mixture prior to adding the solid 
organic phase. The amount of water added should be an amount sufficient to 
reduce changes in the physical consistency of the solid phase without 
significantly reducing the ability of the solvent to enhance the 
partitioning of the hydrophobic contaminants. Generally, the amount of 
water added should be sufficient to reduce the volume of the solvent in 
the liquid phase to 60% or less when the process is conducted at room 
temperature. 
Since, as discussed above, various factors affect the sufficiency of the 
contact and the resultant ability of the hydrophobic contaminants to 
repartition from the particulate matter to the solid organic phase, and 
since different particulate matter derived from different sources possess 
different characteristics and different types and levels of contamination, 
one desiring to use this method to remove hydrophobic contaminants will 
have to determine, by means of testing samples, the conditions and time 
for sufficient contact for the desired amount of removal/repartitioning to 
occur. The sampling, testing, and extrapolation of the results is 
conducted by conventional means known to those skilled in the art. 
Typically, the weight ratio of solid organic phase to particulate matter is 
from about 1:5 to about 1:100. Higher or lower ratios can be used 
depending on the degree of contamination and the reduction in 
contamination desired. For example, with high levels of contamination, 
(e.g., contamination in the range of 1,000-10,000 ppm) one can employ 
lower ratios such as 1:1. 
The second step in the solid phase extraction method involves the 
separation of the solid organic phase (to which the hydrophobic 
contaminants have partitioned) from the particulate matter. The separation 
step of the present method depends upon the form of the solid organic 
phase used in the repartitioning step. For example, if the solid organic 
phase is attached to a removal means, the removal means including, for 
example, string, rope, wire, and the like, separation can be accomplished 
by simply lifting the solid organic phase from the particulate matter by 
pulling the removal means. The particulate matter can be raked to rake out 
the solid phase, or passed through a sieve with openings sufficiently 
small to permit the passage of the particulate matter, but prevent the 
passage of the solid organic phase. When the solid organic phase is in 
particulate form, depending upon the composition of the solid organic 
phase, selective flotation alternatively can be employed. 
Selective flotation is a method of removal which takes advantage of 
differences in density between the solid organic phase and the particulate 
matter. Selective flotation is particularly useful when the solid organic 
phase is a polymeric foam. When a polymeric foam is used as the solid 
organic phase, it is possible to separate the solid organic phase after 
the first step is completed by flooding the particulate matter with water. 
While the particulate matter is too dense to float, the polymeric foam 
solid organic phase will float to the top of the flooded particulate 
matter where it can be scooped or skimmed off. 
After the solid organic phase is separated from the particulate matter, the 
solid organic phase optionally can be disposed of or treated and recycled 
for subsequent solid phase extraction use by any conventional 
environmentally-acceptable method. Such methods include, for example, 
incineration of the spent polymeric foam (resulting in little ash due to 
the organic nature of the solid phase) as a means of disposal, and 
chemical or biological remediation in order to recycle the solid organic 
phase for future use.

The following examples are provided to illustrate the nature of the present 
invention and are not to be construed as limiting the scope thereof, which 
scope is specifically defined in the appended claims. 
EXAMPLE 1 
2,000 parts by weight of soil contaminated with polychlorinated biphenyls 
is placed in a vessel with 70 parts by weight of rubber particles (from 
old car tires). The vessel holding the above materials is then tumbled for 
approximately 30 hours. The rubber particles are separated from the soil 
by sieving the contents of the vessel. 
EXAMPLE 2 
2,000 parts by weight of soil contaminated with polychlorinated biphenyls 
and other hydrophobic contaminants is placed in a vessel. To pretreat the 
soil, 500 parts by weight of acetone is added to the vessel, which then is 
shaken for 24 hours. Then 70 parts by weight of polystyrene foam beads 
(approximately 3 mm in diameter) are added and the vessel is shaken for an 
additional 6 hours. The acetone is then removed by evaporation, and the 
remaining contents are shaken for an additional 24 hours. The polystyrene 
foam beads are separated from the soil by sieving the contents of the 
vessel. 
EXAMPLE 3 
2,000 parts by weight of soil contaminated with polychlorinated biphenyls 
is pretreated in a container with 500 parts by weight of acetone. The 
resultant mixture is tumbled or shaken for 24 hours. Then 70 parts by 
weight of rubber particles from old car tires is added to the container 
along with 2 parts by weight of water to facilitate mixing. The container 
is tumbled or shaken for 6 hours. The acetone is then removed by 
evaporation, and an additional 2 parts by weight of water is added to the 
container, again to facilitate mixing. The contents of the container are 
tumbled or shaken for another 24 hours. The rubber particles are separated 
from the soil by sieving. 
EXAMPLE 4 
The soil in a lot contaminated with a variety of hydrophobic contaminants, 
including polychlorinated biphenyls, is turned and loosened using 
conventional farming equipment, while beads of polystyrene foam are 
deposited and mixed into the soil. The beads are allowed to remain in the 
soil for 60 days, during which time the soil is turned weekly. After the 
60 days, the soil is again turned and the beads are separated from the 
soil by selective flotation, i.e., flooding the soil with water causing 
the beads to rise to the surface, and then skimming the floating beads off 
the surface of the water. 
EXAMPLE 5 
2,000 parts by weight of soil contaminated with polychlorinated biphenyls 
is placed in a vessel with 70 parts by weight of rubber particles (from 
old ca tires) and 500 parts by weight of acetone. The vessel holding the 
above materials is then tumbled for approximately 15 hours after which 
time the acetone is removed by evaporation. The rubber particles are 
separated from the soil by sieving the contents of the vessel. 
EXAMPLE 6 
2000 parts by weight of soil that is contaminated with polychlorinated 
biphenyls and other hydrophobic contaminants is mechanically crushed to 
sand-sized particles. The soil is then placed in a vessel. To pretreat the 
soil, 500 parts by weight of acetone is added to the vessel, which then is 
mixed for up to 6 hours. A sufficient amount of water is added at this 
point to ensure that the volume of acetone in the liquid phase is less 
than 60%. 70 parts by weight of polystyrene foam beads (approximately 3 mm 
in diameter) are added and the contents of the vessel are mixed for an 
additional 6 hours. The acetone is removed by evaporation, and the 
remaining contents are mixed for up to 16 hours. The polystyrene foam 
beads are separated from the soil by selective flotation, i.e., flooding 
the soil with water causing the beads to rise to the surface, and skimming 
the floating beads from the surface of the water. 
EXAMPLE 7 
2,000 parts by weight of soil contaminated with polychlorinated biphenyls 
is mixed in a container with 500 parts by weight of acetone. The resultant 
mixture is tumbled or mixed for up to 6 hours. 70 parts by weight of 
rubber particles from old car tires is added to the container along with 2 
parts by weight of water to facilitate mixing. The container is tumbled or 
shaken for 6 hours. The acetone is removed by evaporation, and an 
additional 2 parts by weight of water is added to the container, again to 
facilitate mixing. The contents of the container are tumbled or shaken for 
up to 16 hours. The rubber particles are separated from the soil by 
sieving. 
EXAMPLE 8 
Sandy soils (2g) that have been contaminated with a PCB mixture for several 
years (initial concentration of contamination =300 .mu.g PCB/g soil) are 
treated with polystyrene beads in three different ways: 
1. 2g soil is mixed with 1 ml acetone for 12 hours. The mixture then is 
amended with 3 ml H.sub.2 O. 60 mg of polystyrene foam beads are added to 
the mixture which then is mixed for another 6 hours before the acetone is 
removed by evaporation. The remaining soil/water/bead mixture is mixed for 
a final 48 hours to ensure that repartitioning of PCB to the beads will be 
complete. 
2. 2g soil is treated as above but without adding acetone. 
3. 2g soil is treated as in #2 (without acetone), but the final mixing of 
the soil, water, and beads proceeds for up to 2 weeks instead of only 48 
hours. 
At the completion of the final mixing stage, the beads are separated from 
the treated soil and the two fractions are analyzed for PCB content. The 
results are shown in Table 1. 
TABLE 1 
______________________________________ 
PCB TITIONING (%) 
To Remaining 
Treatment & SPA Quantity.sup.1 
Polystyrene 
in Soil 
______________________________________ 
Acetone in premix step, 
24 hr for final mix step 
1 mg 29.7 70.3 
10 mg 58.1 41.9 
40 mg 74.6 25.4 
80 mg 62.0 38.0 
No acetone in premix step, 
24 hr for final mix step 
1 mg 1.4 98.6 
10 mg 16.0 84.0 
40 mg 23.7 76.3 
80 mg 28.7 71.3 
No acetone in premix, 
prolonged final mix step (2 weeks) 
1 mg 6.4 93.6 
10 mg 20.4 79.6 
40 mg 42.3 57.7 
80 mg 20.3 79.7 
______________________________________ 
.sup.1 SPA refers to the Solid Phase Agent, polystyrene. 
Thus there is an increased rate of repartitioning of polychlorinated 
biphenyls to the solid organic phase when a solvent is used in the process 
as compared to the rate of repartitioning in the absence of solvent, even 
when mixing times are prolonged. 
EXAMPLE 9 
The order of the process steps are altered as follows to determine the 
effect of such on the repartitioning of the hydrophobic contaminants from 
soil to the solid organic phase. 
Process #1 
Steps: 
1. soil+solvent 
2. water added 
3 solvent removed 
4. solid organic phase added 
5. solid phase separated from soil 
Process #2 
Steps: 
1. soil+solvent 
2. water added 
3. solid organic phase added 
4. solvent removed 
5. solid phase separated from soil 
The results are presented in Table 2. 
TABLE 2 
______________________________________ 
PCB REMOVAL (%) 
Solvent Process #1 
Process #2 
______________________________________ 
Methanol 54.8 58.1 
Acetone 65.8 97.5 
Dioxane 89.5 96.2 
Ether/methanol 56.2 93.7 
Ether/acetone 55.6 80.7 
______________________________________ 
Table 2 shows that removal of the solvent after the solid organic phase is 
added enhances PCB removal.