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Factsheet
February 2007
Prepared by the
National Response Team
Science & Technology Committee
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Application of Sorbents and Solidifiers
for Oil Spills
NOTE: ALL solidified oil must be removed from the environment.
No product can be left in the environment unless it is classified
as a bioremediation agent by U.S. EPA.
Regional Response Teams and Area Planners are tasked with developing
planning documents to allow for the use or prohibition of solidifiers listed on
the U.S. EPA National Contingency Plan, Subpart J Product Schedule
(Schedule) for mitigation of oil spills.
Solidifier and sorbent manufacturers often contact oil companies, response
contractors, state and federal agencies to promote the use of their products.
Most sorbents do not have to be on the Schedule, while solidifiers, classified
as a chemical agent by definition in 40CFR300.5, must be on the Schedule.
Solidifiers are considered an alternative or can be used in conjunction with
sorbents to recover small amounts of oil.
This guide will also assist product manufacturers and members of the
response community in distinguishing a sorbent from a solidifier for
purposes of listing such products on the Schedule and applying them in the
field.
Manufacturers should contact the EPA Product Schedule Manager with any
questions they have before proceeding with testing or marketing of their
sorbents and or solidifiers. For a current listing of solidifiers on the NCP
Product Schedule go to www.epa.gov/oilspill.
What Are Sorbents?
Definitions under Subpart J of the NCP
Section 300.915(g) ...materials consisting of, but not limited to the following
materials:
i) Organic products
a. Peat moss or straw; Cellulose fibers or cork; Corn cobs; Chicken,
duck, or other bird feathers.
ii) Mineral compounds
a. Volcanic ash or perlite; Vermiculite or zeolite.
iii) Synthetic products
a. Polypropylene; Polyethylene; Polyurethane; Polyester.
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Sorbents are essentially inert and insoluble materials
that are used to remove oil and hazardous materials
from water through adsorption, in which the oil or
hazardous substance is attracted to the sorbent
surface then adheres to it; absorption, in which the
oil or hazardous substance penetrates the pores of the
sorbent material; or a combination of the two.
Sorbents are generally manufactured in particulate
form for spreading over an oil slick or as sheets,
rolls, pillows, or booms.
ASTM Definitions: ASTM F726-99
Standard Method of Testing
Sorbent - an insoluble material or mixture of
materials used to recover liquids through the
mechanisms of absorption or adsorption, or both.
Absorbent - a material that picks up and retains a
liquid distributed throughout its molecular structure
causing the solid to swell (50% or more). The
absorbent is at least 70% insoluble in excess fluid.
Adsorbent - an insoluble material that is coated by a
liquid on its surface including pores and capillaries
without the solid swelling more than 50% in excess
fluid.
Type I adsorbent (roll, film, sheet, pad. blanket,
web) - a material with length and width much
greater than thickness and which has both linear
form and strength sufficient to be handled either
saturated or unsaturated.
Type II adsorbent (loose) - an unconsolidated,
particulate material without sufficient form and
strength to be handled except with scoops and
similar equipment.
Type III adsorbent (enclosed): pillows - adsorbent
material contained by an outer fabric or netting
which has permeability to oil, but with openings
sufficiently small so as to substantially retain the
sorbent material within the fabric or netting,
adsorbent booms-adsorbent material contained by
an outer fabric or netting which has permeability to
or is permeable to oil but with openings sufficiently
small so as to substantially retain the sorbent material
within the fabric or netting.
What are Solidifiers?
Most solidifiers available in today's market are
products composed of dry high molecular weight
polymers that have a porous matrix and large
oleophilic surface area. Solidifiers form a physical
bond with the oil.
Oil's viscosity increases to the point that the oil
becomes solidified into a rubber-like solid.
End product can range from a firm cohesive mass to a
non-cohesive granular material. Solidifiers are
available in various forms, including dry powder,
granules, semi-solid materials (e.g., pucks, cakes,
balls, sponge designs), and contained in booms,
pillows, pads, and socks.
Solidifiers Should Meet the Following Criteria
~ Insoluble in water;
~ Specific gravity of less than 1.0;
~ Composed primarily of polymers (with few other
additives);
~ Contain less than 5 ppm of heavy metals and
chlorinated hydrocarbons;
~ Have a physical reaction with oil whereby, at the
prescribed application rate, the oil is sorbed by the
product in a manner where the oil is resistant to
leaching;
~ Do not release solidified liquids under pressure;
and
~ Product itself is non-toxic to wildlife and other
species
What are the Mechanisms of Actions for Solidifiers?
Solidifiers are polymers that have a physical
attraction to oil that is enhanced by van der Waals
forces, which are based on the theory that molecules
are attracted to those that have similar structures.
Non-polar hydrocarbon polymers are attracted to non-
polar petroleum hydrocarbons, thus they prefer to be
oil-wet rather than water-wet. They consist of long
chains of hydrocarbons that have a loose molecular
structure and a very porous matrix. They are soluble
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in excess liquid (solvent) but with continued
application will increase the viscosity of the oil to
the point that it forms a solid mass.
One analogy is how Styrofoam behaves when mixed
into gasoline. Initially the Styrofoam pieces will
dissolve in the excess gasoline (a solvent); however,
continued addition of Styrofoam pieces will thicken
the gasoline, increase it's viscosity, and eventually
form a solid mass.
The reaction time is primarily controlled by the
grain size (and thus surface area) of the product.
Fine-grained powders solidify faster than granules
because of the higher surface area of the product
and the higher diffusion rate of the oil. Light, low
viscosity oils are solidified more readily compared
to heavy, high viscosity oils. Heavy, viscous oils
result in a lower effectiveness and longer
solidification time.
Oil bonds strongly with solidifiers but the exact
solidification mechanisms have not been studied in
depth. Experiments by Ghalambor (1996) showed
that solidifiers tend to absorb energy (endothermic
reaction) in their reactions with crude oil. This
initial decrease in temperature is due to the partial
dissolution of the polymer in the oil, and it indicates
the lack of a chemical reaction between the oil and
polymer.
It appears that most large molecules are firmly held,
implying an aggressive interaction with the
polymers. However, light compounds, such as in
gasoline, are able to vaporize, albeit more slowly,
from the solidified mass, indicating that there is
only a physical bonding and not a chemical reaction.
What are the Environmental Concerns Associated
with Solidifiers?
Whether the product and/or treated oil may sink,
either initially or over time. Solidifier products
currently listed (May 2006) on the Product Schedule
have a specific gravity less than 1.00 and should
float in both fresh and salt water. The treated oil
should float as well. Pre-authorized products should
be tested to document that they do not sink or cause
treated oil to sink initially or after 24 hours of
floating on the water surface. These tests could be
conducted with oil types to be included in the pre-
authorization.
Fate and bioavailability of unreacted product in the
environment. Under certain conditions, the product
could be released to the environment (e.g., wind-
blown powder, failure of containment booms and
pillows). Polymers degrade very slowly, thus residues
may be highly persistent. There are concerns that the
product could be ingested by wildlife feeding on the
water surface or in fauna living in sediments.
Currently, there are no standard oil-spill treating agent
toxicity tests for an ingestion pathway for birds or
mammals. Pre-authorization stipulations should
require recovery of all materials, both untreated
product and treated oil.
Fate and behavior of treated, unrecovered oil. There is
concern about exposure to solidified or partially
solidified oil that remains in the environment after
recovery efforts are terminated. Treated oil is
expected to weather more slowly, compared to
untreated oil, thus it may be more persistent. If the oil
is solidified into a cohesive mass, it will be less
bioavailable; if it is sticky, it could adhere to soils,
vegetation, and animal body parts (including skin, fur
or feathers) that come into contact with the solidified
mass.
Pre-authorization stipulations should require
application only under situations where
containment and recovery would be most effective.
Acute aquatic toxicity is not a major concern.
Solidifiers, by definition, are solids that are insoluble
in water. Thus, LC50 values are generally high, based
on nominal exposures where most of the product
remains as a solid on the water's surface; however the
NCP requires toxicity testing. Solidifiers that are left
in the water may have impacts that need to be
evaluated.
The chart on the following pages shows the
benefits and shortcomings of, and comparisons
between sorbents and solidifiers.
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What are the Benefits/Shortcomings/Comparisons of Using
Solidifiers versus Sorbents?
Issue
Benefits
Shortcoming
Comparison with
Sorbents
Effectiveness with Light
Oils
Work best with light oils.
None
Effective in recovering
light oils spread into thin
slicks and are difficult to
recover with sorbents.
Effectiveness on Sheens
Can remove even light
sheens.
Tend to over-apply on
sheens.
Effective in recovering
sheens that are very
difficult to pick up with
sorbents.
Effectiveness with Heavy,
Viscous Oils
Little
Longer solidification time
with emulsified, viscous
oils due to poor mixing.
Not very effective.
Sorbent effectiveness is
dependant on type; oil
snare is very effective
with viscous oil.
Low Temperature
Could be applied in ice
conditions.
Longer solidification time
or reduced effectiveness
at low temperatures due
to increased oil viscosity.
Temperature has little
effect on most sorbents.
Flash Point
Treated oil is less
flammable.
None
Both solidifiers and
sorbents may lower
flammability.
Worker Training
Increases effectiveness
Need training in proper
use of new products.
Sorbents are a very
familiar product, but there
is often overuse.
Access Limitations
NA
NA
Same requirements for
access to deploy/retrieve.
Application
Considerations
Likely to be used by
trained individuals in
specific response
conditions.
General broadcasting of
loose material could be a
problem in open areas
and in high wind
conditions that would
inhibit effective
containment and
recovery.
In contained form
(booms, pillows and
socks), would be the
same as for sorbents. In
loose form, both have
problematic containment
and recovery issues.
Recovery Methods
Manual recovery of both
contained and loose
product from effective
containment should be
straightforward.
Effective containment of
loose product is an issue-
especially in conditions of
currents, tides, and wind.
Recovery of all material is
highly desirable due to
product persistence.
In contained forms,
recovery of solidifiers
should be the same as
sorbents.
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Monitoring
Considerations
Can monitor visually for
effectiveness during both
tests and application.
When used in loose form,
constant visual
monitoring should
ensure: 1) proper and
complete containment
and recovery; 2) no
adverse wildlife or fish
impacts. Use should be
modified or stopped if
either condition is not
met.
Basically similar to
sorbents, but less
passive, especially when
using loose material. All
material should be
recovered as soon as it is
no longer effective at
removing oil.
Pickup Time for Treated
Oil
NA
Can be slow with loose
product.
About the same when
products are contained
as booms, socks, etc.
Application on Solid
Surfaces
Effective on solid
surfaces (land); treated
oil is a dry solid that can
be swept up. Also can
form a containment
barrier.
None
Likely more effective than
sorbents.
Waste Volume
Will increase volume
proportional to application
rate.
None
Sorbents create large
waste volumes.
Waste Weight
NA
Generates waste weight
equal to the weight of
added solidifier.
When properly applied,
sorbents themselves add
little to the waste weight,
but can pick up water.
Waste Disposal - Landfill
More likely to pass leach
test for landfill.
None
Sorbents less likely to
pass leach test for
landfill.
Waste Disposal -
Incineration
High BTU value; Need
preplanning to assess
waste to energy options
and management as
separate waste stream.
None
Sorbents can also be
incinerated but may have
lower BTU compared to
solidifiers, depending on
the product.
Waste Disposal Industrial
intermediate for recycling
of encapsulated product
and oil
Can be recycled via
introduction into other
industrial processes,
including: asphalt
modification; rubber
additive, etc.
Must meet TCLP and
EPA/state testing
procedures.
Not applicable for most
traditional sorbents.
What are Application and Monitoring Issues with
Use of Solidifiers?
Application Rate: Recommended rates are from 10-
50 percent by weight of the liquid to be recovered.
In practice, even higher application rates are used
because of the difficulty of estimating oil spill
volume, use on thin sheens, worker unfamiliarity
with the product (particularly if solidification is not
immediate), and general attitude that more is better.
Higher application rates can lead to increased
wastes and product costs; similar to what occurs
when sorbents are overused.
Application Method: Application of loose product
by hand or blowers under even light wind conditions
can result in product being blown out of the
treatment area. This issue is particularly true for fine
powders. Thus, product in some sort of containment
is preferred.
Mixing Energy: Most solidifiers require some
degree of physical mixing with floating oil, which
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can be achieved with water spray, boat wakes, or
hand-held devices. Booms, pillows, pads, and filter
packs can be used like similar sorbent products.
Solidification Time: Most solidifiers act quickly,
solidifying the oil in less than 1 minute up to 1 hour.
Some products continue working for over a number
of hours. Fast-acting products can be problematic
because they react with that portion of the oil they
first contact, potentially resulting in a mix of
solidified and un-solidified oil. This behavior can be
beneficial where the solidifier can be applied to the
perimeter of the oil, forming a solidified barrier to
prevent further spreading, rather than treating the
entire spill volume.
Oil Type: Solidifiers work best with light to
moderate oils. For highly volatile oils such as
gasoline, it should be noted that the oil will continue
to evaporate, albeit slowly. Solidifiers are less
effective on heavy or emulsified oils. At a spill,
preliminary tests should be conducted with the
spilled oil to determine overall application rate,
effectiveness, and character of the treated oil
(consistency, cohesiveness, stickiness). See the
effectiveness test procedure in the Selection Guide
for Oil Spill Applied Technologies.
Solidifier Products Need to Be Listed on the NCP
as Miscellaneous Oil Spill Control Agents
Because:
Solidifiers can vary in chemical composition,
including additives, although the actual composition
of each product is proprietary. Listing is necessary
so information on their chemical composition,
physical properties (e.g., density), and toxicity are
made available in a standard format.
Proceedings of the 1991 Oil Spill Conference. American
Petroleum Institute, Washington, D.C., pp. 411-414.
Ghalambor, A., 1996. The effectiveness of solidifiers for
combating oil spills. Louisiana Applied Oil Spill Research
and Development Program, OSRADP Technical Report
Series 96-006, 68 pp.
Walker, A.H., J. Michel, G. Canevari, J. Kucklick, D.
Scholz, C.A. Benson, E. Overton, and B. Shane, 1994.
Chemical oil spill treating agents: herding agents,
emulsion treating agents, solidifiers, elasticity modifiers,
shoreline cleaning agents, shoreline pre-treatment
agents, and oxidation agents. Marine Spill Response
Corporation, Wash., D.C., Tech. Report 93-015, 328pp.
References:
Dahl, W., Lessard, R.R, Cardello, E.A., Fritz, D.E.,
Norman, F.S., Twyman, J.D., Clayton, E.W., Knight, B.L.,
Crane, R.D., Johnson, S.J., and Martin, B.R., 1996.
Solidifiers for oil spill response. Proceedings of the
Society of Petroleum Engineers Conference on Health
Safety and Environment, SPE paper No. 35860, pp. 803-
810.
Fingas, M., R. Stoodley, N. Stone, R. Hollins, and I. Bier,
1991. Testing the effectiveness of spill-treating agents:
Laboratory test development and initial results.
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