EPA/540/2-89/012
SUPERFUNDTREATABILITY
CLEARINGHOUSE
Document Reference:
Assink, J.W. "Extractive Methods for Soil Decontamination, A General Survey and
Review of Operational Treatment Installations." Apeldoorn, Netherlands. Technical
Report. 13pp. November 1985.
EPA LIBRARY NUMBER:
Super-fund Treatability Clearinghouse - EUTT
-------
SUPERFUND TREATABILITY CLEARINGHOUSE ABSTRACT
Treatment Process: Physical/Chemical - Soil Washing/Chemical Extraction
Media: Soil/Silty
Document Reference: Assink, J.W. "Extractive Methods for Soil Decon-
tamination, A General Survey and Review of
Operational Treatment Installations." Apeldoorn,
Netherlands. Technical Report. 13 pp. November
1985.
Document Type: Contractor/Vendor Treatability Study
Contact: U.S. EPA, ORD
HWERL
Woodbridge Avenue
Edison, NJ 08837-3579
212-264-2525
Site Name: Ecotechniek BV (Non-NPL)
Location of Test: Netherlands
BACKGROUND; The treatability study report provides a general overview of
soil decontamination by extraction and reports on the field application of
three specific different soil washing/solvent extraction systems. Each
system is similar in design and removed contaminants from soil including
crude oil and metals.
OPERATIONAL INFORMATION; The soil to be cleaned is mechanically pretreated
to remove large objects such as pieces of wood, vegetation remains,
concrete, stones, and drums, while hard clods of soil are reduced in size.
The sieve residue may be cleaned separately. The pretreated soil is then
mixed with an extracting agent such as acids, bases, surface active agents,
etc. The primary purpose of this step is to transfer the contaminants to
the extraction fluid, either as particles or as a solute.
The soil and the extracting agent are separated. The contaminants, the
smaller soil particles (clay and silt particles) and the soluble components
in the soil are generally carried off with the extraction agent. The soil
undergoes subsequent washing with clean extracting agents and/or water to
remove as much of the remaining extraction fluid as possible. The larger
particles carried off with the extraction phase are separated as best as
possible and, if required, undergo a subsequent washing with clean
extracting agent. The contaminated extraction fluid is cleaned and can be
re-used after the addition of chemicals.
PERFORMANCE; All types of contaminants may be removed from the soil by
extraction if they can be dissolved in the extracting agent or dispersed in
the extraction phase. Extraction is especially suitable for sandy soil,
low in humus and clay content, because of the sand particles' (50-80 urn)
relatively high settling velocity. Sludge residue from this process
generally has to be disposed of. Currently, four installations for
extractive cleaning of excavated soil are operational in the Netherlands.
3/89-10 Document Number: EUTT
NOTE: Quality assurance of data aay not be appropriate for all uses.
-------
The operational soil washing installations have proven successful for
removing cyanides; PNAs (polynuclear aromatics) and mineral oil; heavy
metals; halogenated hydrocarbons and other contaminants with efficiencies
exceeding 80% (see Table 1).
CONTAMINANTS:
Analytical data is provided in the treatability study report. The
breakdown of the contaminants by treatability group is:
Treatability Group
W07-Heterocyclics & Simple
Aromatics
W08-Polynuclear Aromatics
Wll-Volatile Metals
W12-0ther Inorganics
V13-0ther Organics
CAS Number
TOT-AR
TOT-PAH
7439-92-1
7440-66-6
57-12-5
TOX
CRUDE
Contaminants
Aromatic Hydrocarbons
Total Polycyclic
Aromatic Hydrocarbons
Lead
Zinc
Cyanide
Total organic halogens
Crude Oil
TABLE 1
CONTAMINANT REMOVAL EFFICIENCY
Initial Concentration
Contaminant
CN (galvanic)
Zn
Cd
Ni
Pb
Aromatics
PNAs
Crude Oil
450
1600-3000
66-125
250-890
100
240
295
79
Final Concentration
After Treatment
15
300-500
5-10
85-95
25
41
15
2.3
Removal
Efficiency
%
(approximate)
94
83
92
66-89
75
81
95
97
NOTE: This is a partial listing of data. Refer to the document for more
information.
3/89-10 Document Number: EUTT
NOTE: Quality assurance of data Bay not be appropriate for all uses.
-------
Contaminated Soil
First International TNO Conference on Contaminated Soil
11-15 November, 1985, Utrecht, The Netherlands
edited by
J.W. ASSINK
TNO Division of Technology for Society, Apeldoorn, The Netherlands
W.J. VAN DEN BRINK
TNO Corporate Communication Depanment, The Hague, The Netherlands
1986 MARTINUS NIJHOFF PUBLISHERS
a member of the KLUWER ACADEMIC PUBLISHERS GROUP
DORDRECHT / BOSTON / LANCASTER
-------
655
EXTRACTIVE METHODS FOR SOIL DECONTAMINATION; A GENERAL SURVEY AND
REVIEW OF OPERATIONAL TREATMENT INSTALLATIONS
J.W. ASSINK
TNO, P.O. box 342, 7300 AH APELDOORN, NETHERLANDS
1. ABSTRACT
In a general introduction to extractive methods attention is given to the
basic principles, the potential fields of application and the costs of
methods for treating contaminated soil.
The operational installations for extractive treatment in the Netherlands
(Heijnans Milieutechniek BV, HWZ Bodemsanering BV, Bodeasanering Nederland
BV and Ecotechniek BV) are described in the second part of the paper.
2. INTRODUCTION
The remedial methods used to. Jreat contaminated soil may be broadly
divided into two main categories ' ' :
- Methods aimed at preventing or restricting the dispersion of the conta-
mination to the immediate surroundings
- Methods aimed at removing or destroying the contamination, also referred
to as "cleaning"
The last category nay be further divided into two sub-groups:
- Excavation of the soil and subsequent cleaning, on-site or elsewhere.
The most important techniques to be considered are:
. thermal treatment
. extraction, including methods based on wet-classification
. flotation
. steam and air stripping1
. microbiological treatment
. miscellaneous, e.g. chemical treatment for the purpose of detoxifi-
cation
. combinations of the above-mentioned techniques
- Cleaning of the soil without prior excavation. These methods are usually
referred to as in-situ cleaning. The most important techniques are:
. extraction
. steam and air stripping
. microbiological treatment.
This paper deals only with the cleaning of excavated soil by means of
extraction. The extractive methods for this purpose comprise every
cleaning method by which contaminants are transferred to and carried off
by a liquid phase; only flotation is being excluded. The following topics
will be discussed:
- A general description of the extraction process
- Field of application
- Available installations and state of the art in the Netherlands
- Costs of the cleaning method.
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656
3. GENERAL DESCRIPTION OF THE EXTRACTION PROCESS
3.1. Principal cleaning mechanisms
Two principal removal mechanisms may be distinguished in extractive
cleaning:
- The contaminants are dissolved in the extracting agent, with or without
the assistance of a chemical reaction preceding or acting simultaneously
with the extraction
- The contaminants are dispersed in the extraction phase in the form of
particles (suspended or colloidal), with or without the assistance of
prior mechanical treatment. The subsequent separation between the
contaminated particles and the relatively clean soil particles in the
slurry is to be based on differences in:
. particle size (sieving or classification)
. settling velocity (wet classification)
. surface properties (selective coagulation or flotation)
. combinations of these properties.
Since contaminants are often for the greater part adsorbed to clay
particles and humus, moderate to fair cleaning may result whenever these
clay fractions and humus are separated from the soil by classification.
3.2. Process scheme
A general diagram of the extraction process which includes prior and
subsequent treatments is given in figure 1. In this figure, the following
successive steps are indicated (numbers correspond to those in figure 1):
1. The soil to be cleaned is pretreated to remove large objects such as
pieces of wood, vegetation remains, concrete, stones, drums, etc., while
hard clods of soil are reduced in size. The sieve residue may be cleaned
separately.
2. The pretreated soil is nixed intensively with an extracting agent. The
primary purpose of this step is to transfer the contaminants to the
extraction fluid, either as particles or as a solute.
3. The soil and the extracting agent are separated. The contaminants, the
smaller soil particles (clay and silt particles) and the soluble compo-
nents in the soil are generally carried off with the extraction agent.
4. The soil undergoes subsequent washing with clean extracting agent and/or
water to remove as much of the remaining extraction fluid as possible.
5. The larger particles carried off with the extraction phase are separated
as best as possible and, if required, undergo a subsequent washing with
clean extracting agent.
6. The contaminated extraction fluid is cleaned, whereupon part of it is
re-used after the addition of chemicals, if required.
It is not always necessary to separate the soil particles and the extrac-
ting agent before going on to the actual cleaning step for the extraction
fluid. In the case of certain types of contamination, the purification
step (this is usually a chemical detoxification or flotation) may be
applied directly to the suspension of soil particles and extraction
fluid. In such cases, the separation of the soil particles fro« the extrac-
tion phase takes place after the actual purification step.
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657
roMVII \A1EP
SOIL
P«£lRtA1.1£.Vl
OF SOIL
1 '
FIXING i
EX.RAC. ION
SIEVING RESIDUE
EXIRACUSC
— -*.
SOLIDS OK SLLKRY
I1AISLY) L10LIO
.LHAR.-LMN UF 3O.L
i N ) \ i -vV t
>,)«„
• -.-. •
E\l f^U\ ,\C
ACEW
.^ ,i^CN.
FOSl-lttAHlVI
. J
[ON OF
»l 1C '.!
POSI-I«LA1 1LM
M'1. L U ISE OF SOIL
fAnliCl.Es)
,
IHEAI'XM JF
L^IKAL
:M. A^.I
SlUFLl'S El!-
isc ACEM
Figure 1: extraction of contaminated soil (general process scheme)
3.3. Extractive methods and extracting agents
For the purpose of this paper the following extractive nethods are
distinguished:
a) Methods, based on classification; the contaminants are generally not
dissolved but mainly dispersed in the extraction liquid and are
separated fro* the soil on the basis of differences in settling
velocity. Hot or cold water, without any additives, may be used.
b) Methods, based on extraction with an aqueous liquid; to be subdivided
into:
- acids
- bases
- solution of surface active agents (detergents)
- solution of complexing agents.
Solutions of detergents and bases are preferably combined with classifi-
cation (see a.) in order to yield a satisfactory cleaning result (see
next paragraph)
c) Methods, based on organic solvents.
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658
Aqueous extracting agents are usually preferred. Therefore methods a
and b are preferred to method c, a preference based on a large number of
considerations, such as:
- Safety of the extracting agent for man and environment
- Prevention of additional groundwater- and air pollution
- Natural presence of water in the soil
- Purification possibilities of contaminated extracting agents
- User friendliness
- Costs of the extracting agent.
As has been mentioned before, a number of aqueous extracting agents may
be distinguished. Besides plain water, the addition of chemicals aimed at
improving the extraction efficiency Bay be considered.
Among the chemicals which nay be added are:
- Acids, such as HC1, H.SO^ and HNO-; the primary purpose of these acids is
to dissolve contaminants such as Keavy metals
- Bases, such as Na.CO. and NaOH; the purpose of these substances is either
to dissolve or disperse contaminants in the extraction phase. Especially
clay and humus, which contain a large quantity of contaminants, will be
easily dispersed.
- Surface active agents; addition of these agents facilitates dispersion,
for example of oil
- Sequestering agents (complex formers) such as citric acid, ammonium
acetate, NTA and EDTA; these substances will mainly remove the
"available" fraction of inorganic contaminants and will therefore abate
the adverse effects of the soil to the ecosystem.
In addition to the separate use of the above-mentioned chemicals,
combinations thereof may be considered. The extraction process may also be
favourably influenced by elevating the extraction temperature, or by prior
oxidation of the contaminants with the assistance of an oxidizer (e.g.,
hydrogen peroxide or ozone).
It is also possible in principle to employ org-nic solvents as extract-
ing agents, an especially valuable factor if the contaminants to be removed
are not, or scarcely soluble in an aqueous extracting agent, and will not
disperse in it either.
The organic solvents suitable for this purpose must preferably be
water-soluble, e.g. acetone, ethyl acetate, ethanol and isopropyl alcohol.
In the case that water-insoluble solvents are used, the soil should be
dried prior to the extraction.
If organic extracting agents are used, the treated soil should undergo
subsequent treatment to ensure that any remaining extracting liquid is
completely - or virtually completely - removed.
3.4. Cleaning the Extraction Fluid
A large number of physical, chemical and biological purification methods
are available to clean the contaminated aqueous extracting agents that
have resulted. In practice, coagulation, flocculation followed by sedimen-
tation or flotation are often used. However, other techniques such as
aerobic and anaerobic biological purification, ion exchange, electrolysis,
membraae filtration equally may be considered. These methods are exten-
sively used in industry and are described in detail in the literature. For
more information on this subject, the general literature is referred to.
4. POTENTIAL FIELD OF APPLICATION
4.1. Types of Soil
The extraction process is best suited for the cleaning of sandy soils
low in humus and clay content; it is fairly easy to separate sand particles
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659
larger than 50-80 \M from the extraction fluid because of their relatively
high settling velocity. Separation nay be achieved by using relatively
simple separation equipment, such as settlers. A second reason why the
extraction process is highly suitable for the cleaning of sandy soil is
that sand particles have a relatively small specific surface area; thus,
the amount of contaminants adsorbed to the sand particles after cleaning
is relatively low.
The presence of a small quantity of clay particles and/or humus-like
substances in the soil imposes no restrictions on the extraction process.
However, it is to be expected that most of the clay particles and humus
will remain in the extraction phase when the soil particles are separated
from it by simple separation techniques such as sedimentation. They will
ultimately end up in the residual sludge.
Other types of soil (e.g. loamy soil, clay, peat and former waste dumping
sites) are for three reasons generally much more difficult to clean by
extraction than sandy soil is. Firstly, humus-like components, silt and
clay particles readily form a relatively stable suspension with the extrac-
tion liquid. This is especially true for aqueous extracting agents with a
high pH. If the contaminants are present in the extraction liquid as sepa-
rate small particles, it is often impossible to separate relatively clean
soil particles from the contaminated particles.
The second reason for difficult extractive cleaning is that many types of
contaminant are readily adsorbed by humus and clay particles. In such situ-
ations the amount of extracting agent required for a sufficient cleaning
may be prohibitive to a feasible process.
The last reason is that former waste dumping sites (but sometimes also
"normdl" sites) are very heterogeneous, and may therefore give rise to
important practical problems in treating these sites.
Furthermore, it should be stressed that the amount of residual sludge
resulting from these types of soil may be prohibitive for an economically
feasible extraction process.
4.2. Contaminants
Table 1 gives a survey of the potential applicability of extractive
methods concerning the different kinds of contaminant in sandy soils. Not
every given indication of applicability has yet been proven, therefore
the table should be considered to be provisional. The symbols used in the
table are:
+ generally applicable
+/- occasionally applicable, depending on the actual contaminant(s) and
the form in which they are present in soil
-/+ seldom applicable, or only a minor amount of the contaminant(s) will
be removed
generally not applicable.
"Applicable" does not always imply that a contaminated site will be
cleaned to a satisfactory extent. Table 1 refers only to the technical
applicability; the actual applicability also depends on factors such as
mentioned further on.
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660
TABLE 1. Potential applicability of extractive methods for sandy soils.
Classifica
tion with
water
Aqueous liquid .
Contaminant
Complex- Deter-
Acid Base ing gent
l) agent M
Organic
liquid
Aliphatic volatile
and
aromatic non-vo-
hydrocarbons latile
Polynuclear aroraatics
Halogenated hydrocarbons
(volatile)
Organic pesticides
Heavy
metals
and
metalloids
kationic
anionic
free
Cyanides
complexes
Miscellaneous
(inorganic compounds)
*/-
-/* */- -/*
-/*
1) this method comprises a separation of humus and fine mineral particles
(approx. < SO (Jm) from the soil; these compounds will end up in the
residual sludge
2) in the case of a water immiscible liquid, extraction must be preceded
by the drying of the soil
3) these will evaporate to some extent during drying and/or extraction
As may be concluded from table 1, extractive methods are applicable to
virtually every type of contaminant, if only the appropriate method and
process conditions are chosen and can be realized.
ft. 3. Overall evaluation
As has been stated before, the actual applicabilities of the extractive
methods do not solely depend on their technical ability to remove conta-
minants. Other factors influencing the selection of a certain method are
for instance:
- costs of cleaning up
- safety of the method (health risks, explosion risks etc.)
- environmental impacts (especially in the case of organic extracting
agents)
- waste streams e.g. (possibilities for 'the final disposal of residual
sludge)
- possibilities of reuse of the cleaned soil.
- desired degree of contaminant removal
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661
The costs of cleaning a given quantity of soil depend on many factors;
the principal ones are:
- depreciation of, and interest on the investment in the treatment
- installation
g - costs of labour
q - costs of analyses for the purpose of process control
- disposal of residual sludge (amount and type of sludge)
- the standards which cleaned soil and waste water have to satisfy
- demand for chemicals and energy
•f
Table 2 gives a qualitative indication of the amount of residual sludge,
* the demand for chemicals and the estimated range of the costs involved in
the various extractive methods. The symbols used in this table are:
+ favourable or unproblematic
•* 0 moderate
- strongly limiting, or negative.
The given costs of cleaning are exclusive of costs involving the excava-
tion and transport of soil. In view of the lack of sufficient practical
data, the estimated costs should be regarded as approximations.
TABLE 2. Survey of some relevant factors for the selection of extractive
methods to treat excavated sandy soil.
Amount of Demand Estimated
Extractive method residual for costs 2)
sludge chemicals (Dfl/tonne)
Classification with water *) + 80-150
Aqueous liquid
- acid
- base l)
- complex ing agent
- detergent l)
Organic liquid
Vo
-/o
Vo
-/o
+/0
of-
o
-
o
-
150-300
150-200
> 200
150-250
> 200
1) humus and fine mineral particles are separated fron the soil and will
end up in the residual sludge
2) Dfl 1,- = approx US$ 0.3 (June 1985)
5. OPERATIONAL INSTAILATIONS FOR EXTRACTIVE TREATMENT
5.1. Heijmans Hilieutechniek B.V. 4
5.1.1. General. Heijaans installation for extractive cleaning has been
in operation since the spring of 1985. Its capacity cones to 10-15 tonnes
of soil per hour. The whole installation has been constructed in containers
and is therefore transportable.
5.1.2. Process description. A simplified process scheme is given in
figure 2. The following steps may be distinguished:
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662
DRY AND W£l
SIEVING
DEVICES
'« . • . \ - ) 4
••'"_, M 1 -. J\
J
J ' ,
i 1
i i
i
-OR
O.CLi
J-
0«ib
)
:.--„. -?iV,
CLl
SOLIDS. SLL'RRV
I1A1XLY) LliJLID
Figure 2: process scheme of the installation of Heijmans Milieutechniek
B.V.
HAkl -LI' WAlf K
GRASS. CUU.5. EIC.
tMI kl,U ^
COMAMISAICD ID »M,
SOIL ,u m»
—— S*)LtOb. ^H'HR^
(MAIM.I) l.l';Lll>
IH'I IOKAL
Figure 3: process scheme of the installation of HUZ Bodemsanering B.V.
-------
663
1) Separation of coarse materials (> 10 mm)
2) Intensive mixing of soil and water in prder to disperse all soil
particles and to scour off the contaminants (scrubbing), in combination
with a chemical oxidation (only in the case of cyanides, for detoxifi-
cation)
3) Separation of coarse sand (> 60 pm) by hydrocyclones
4) Dewatering of the treated sand
Separation of coarse, low-density materials, e.g. cokes and grass
in a tiltable plate separator. Any free floating oil
5)
6) Separation of silt
is skimmed off.
7) Coagulation and flocculation of the polluted extracting agent; followed
by flotation of the formed floes.
The cleaned extracting agents is generally recirculated to a great extent.
It is possible to control the pH between approx. 3 and 12 in almost every
apparatus of the plant.
5.1.3. Fields of application. The firm claims the following potential
fields of application:
- Cyanides
- Water immiscible and low-density (< 1000 kg/m3) hydrocarbons
- Heavy metals,
or combinations of these types of contaminant (see also table 1). The soil
should preferably contain less than 30% of fine solids (< 63 pm) and humus-
like compounds.
At this moment, the results of a number of test runs are available. Table 3
gives some examples.
TABLE 3. Some results of test runs executed with the extractive installat-
ion of HeijMns.
Contaminant
Mineral oil
Galvanic CN
Zn
Cd
Ni
Initial
concentration
(mg/kg)
3.000-8.000
450
1.600-3.200
66-125
250-890
Concentration
after treatment
(mg/kg)
90-120
15
300-500
5-10
85-95
Removal
efficiency
(%)
approx. 98
approx. 94
approx. 83
approx. 92
66-89
5.2. HVZ Bodemsanering BV
5.2.1. General. HWZ has developed an extractive cleaning plant for sandy
soil in co-operation with TNO. The plant has a capacity of 20 tonnes of
soil per hour and has been in operation since the autumn of 1984. The
installation itself is containerized, which allows for dismantling and
setting-up elswhere.
5.2.2. Process description. A simplified process scheme is given in
figure 3. The following steps may be distinguished:
1) Separation of coarse materials (> 10 mm)
2) Intensive mixing of soil and water in order to disperse all soil
particles and to scour off the contaminants (scrubbing)
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664
3) Washing of the soil with a suitable extracting agent in up-flow column
(jet-sizing). The bottom stream consists of sand particles larger than
approx. 100 pm
4) Dewatering of the cleaned soil
5) Separation of coarse, low-density materials, e.g. cokes
6) Separation of silt (approx 50-100 pm) by hydrocyclones. This fraction is
normally fed to the dewatering sieve (4), but may also be handled
separately
7) The spent extracting agent is cleaned in a number of steps. Cleaning is
carried out by pH-adjustment, coagulation, flocculation, sludge
separation in a tiltable plate separator, removal of the surplus of
added iron by aeration and flotation and finally a last pH-adjustment.
The cleaned extracting agent is recirculated to a great extent.
5.2.3. Field of application. The plant was initially developed for the
cleaning of soil contaminated with cyanides. Besides cyanides, the poten-
tial applicability of the installation is conformable to table 1. Thus,
the installation may be considered for the purpose of cleaning soil conta-
minated with mineral oils, aromatics, PNA's, some chlorinated hydrocarbons,
cyanides and/or heavy metals. Some of the results obtained thus far are
given in table 4.
iM
Contaminant
CN (gaswork)
PNA (gaswork)
EOC1
Zn
Pb
Initial
concentration
(mg/kg)
100-200
36
20-24
81
approx. 100
Concentration
after treatment
(mg/kg)
approx. 10
0,7
0,3-0,5
27
approx. 25
Removal
efficiency
(I)
approx. 95
98
98-99
67
approx. 75
5.3. Bodemsanenng Nederland BV
5.3.1. General. The installation of Bodemsanering Nederland (BSN) has been
in operation since 1983 and was originally developed to separate oil froa
sandy soil. Its capacity is approximately 20 t/h, and the installation is
easy to transport to a contaminated site.
5.3.2. Process description. The oil separation is based on a high pressure
water jet curtain spouting loose the contaminants from the sand particles.
A simplified process scheme is given in figure 4. The process comprises the
following steps:
1) Separation of coarse materials (£ 100 mm)
2) High pressure washing
3) Separation of coarse sand by sieves and hydrocyclones (> 63 pm)
4) Separation of silt by sedimentation (30-63 pm)
5) Separation of process water, oil and fine mineral fraction {< 30 pro)
6) Dewatering of the treated soil.
Step 4 and 5 may be enhanced by coagulants and flocculants. The process
usually uses water without any additives. This fact offers the option of
an additional microbiological treatment of the spent process water and/or
the treated sand, as has been indicated in the process scheme. The process
water will be often - for the greater part or completely - recirculated to
the high pressure separator.
-------
66S
' (DIM UJSALl*
, MICKHttK)|ji(,ILAL I
sinmnris *• IHFU^M '
1 (iM'l h'VAl ) t
">! I WAI I H
M-.I'AKAIHH
M U'CL f 1 J. (.(it1 )
Figure 4: process scheme of Che installation of Bodemsanering Neder-
land B.V.
Figure 5: process scheme of the hot-water washing plant of Ecotechniek
B.V.
-------
666
5.3.3. Fields of application. BSN claims the following fields of applica-
tion:
- all aliphatics and aromatics with low densities (floating on water)
- contaminants that are largely adsorped to those soil pjrucles that will
end up in the residual sludge (process step 5)
- volatile contaminants, e.g. per- and trichloro ethylene (these are strip-
ped to the air when the soil is led through the high pressure washer)
- some water-soluble and biodegradable hydrocarbons, provided the micro-
biological option is being chosen
- all types of soil with a maximum amount of residual sludge (< 63 M™) of
approx. 20% or approx. 2.5 t/h.
Some results obtained with this installation are given in table 5.
TABLE 5. Some practical experiences with the treatment installation of BSN.
Contaminant
Aromatics
PNA's
Crude oil
Concentration
before treatment
(mg/kg)
240
295
79.000
Concentration
after treatment
(mg/kg)
45*
15
2.300
Removal
efficiency
(%)
81
95
97
••'•' the concentration of aromatics was reduced to 10 mg/kg on account of
microbiological activity 6 months after treatment
5.4. Ecotechniek BV
5.4.1. General. Ecotechniek BV has had a so-called thermal washing instal-
lation available for several years. The installation's capacity comes to
approximately 20 tonnes of soil per hour. ^
5.4.2. Process description. A simplified process scheme is given in figure
5. The process roughly comprises the following steps:
1) The contaminated sand is slurried up with recycle water and
(indirectly) heated with steam up to a max. of 90°C. Oil is dis-
persed in the water; any floating oil is skimmed off
2) Separation of sand particles
3) Dewatering of sand by natural draining
4*5) Oil containing process water is cleaned in two steps; separation of
particles and oil thicker than water, and subsequently what may
be skimmed off.
The temperature of the system is dependent on the type of oil to be
separated.
5.4.3. Fields of application. The installation is especially suitable for
sand heavily contaminated with (crude) oil, preferably less dense than
water.
Thus far, experience has been gained in treating 5000 tonnes of beach
sand contaminated by an oil spill. Sand containing 200,000 ag/kg of oil i
could be cleaned to a final concentration of 20,000 f»g/kg, which resulted
therefore in a removal efficiency of 90%. The treated sand is used in the
preparation of asphalt.
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»,. CONCLUSIONS
- Extractive methods comprise a number of techniques, with the common
feature that the contaminants in the soil are transfered to a suitable
liquid.
- In principal, all types of contaminant may be removed from the soil
by extraction, if only the right process and process conditions are
chosen.
- Extraction is especially suitable for sandy soil, because the slov,
and non-settling particles (< 30....60 |jm, humus) will generally er.d
up in a contaminated, residual sludge. This sludge generally has to be
disposed of. Moreover, clay particles and humus .n e much more difficult
to clean than sand particles.
- Up to now, four installations for extractive cleaning of excavated
soil are operational in the Netherlands. The specific applicabilities of
these installations overlap only partly, although they are all based on
aqueous extraction agents.
- The operational installations have proven applicable for cyanides,
PNA's (poly nuclear aromatics) and mineral oil; heavy metals, haloge-
nated hydrocarbons and other contaminants are often also removed to a
great extent (> 80%).
7. ACKNOWLEDGEMENT
The author wishes to express his gratitude for the contributions of
Mr C.J. Muntinga (HWZ Bodemsanering B.V.), Mr M.J.J. Heijmans,
Mr B. Hilberts (both Heijmans Milieutechniek B.V.), Mr G.H.J. Ruiters
(Bodemsanering Nederland B.V.) and Mr R.C. Reintjes (Ecotechniek B.V.).
8. LITERATURE
1. W.H. Rulkens, J.W. Assink: Extraction as a method for cleaning contami-
nated soil: possibilities, problems and research; Proc. Conf. Management
Uncontrolled Hazardous Waste Sites, Washington DC 1984 (Hazardous Materi-
als Control Research Institute, Silver Spring, Maryland, 1984) pp 576-583.
2. M.A. Smith (edit.): Contaminated Land: Reclamation and Treatment. Plenum
Press, New York and London, 1985.
3. Handboek Bodemsaneringstechnieken (Handbook Techniques for Remedial
Action), Staatsuitgeverij, The Hague, 1983.
4. Personal communication with B. Hilberts (Heijmans Milieutechniek B V.,
P.O. box 2, 5240 BB Rosmalen, Netherlands).
5. Personal communication with C.J. Muntinga (HWZ Bodemsanering B.V.,
Vanadiumweg 5, 3812 PX Amersfoort, Netherlands).
6. Personal communication with G.H.J. Ruiters (Bodemsanering Nederland B V.,
P.O. box 22002, 6360 AA Nuth, Netherlands).
7. Personal communication with R.C. Reintjes (Ecotechniek B.V., Benelux-
laan 9, 3527 HS Utrecht, Netherlands).
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