Technical
Report
Advances
in
Encapsulation
Technologies
for
the
Management
of
Mercury­
Contaminated
Hazardous
Wastes
Contract
GS­
10F­
0275K
Task
Order
No.
0001
Submitted
to
U.
S.
Environmental
Protection
Agency
National
Risk
Management
Research
Laboratory
26
W.
Martin
Luther
King
Drive
Cincinnati,
OH
45268
Paul
M.
Randall
Task
Order
Project
Officer
Prepared
by
Sandip
Chattopadhyay
Wendy
E.
Condit
Battelle
505
King
Avenue
Columbus,
OH
43201­
2693
August
30,
2002
Contents
Figures............................................................................................................................................
iii
Tables.............................................................................................................................................
iv
Abbreviations
and
Acronyms..........................................................................................................
v
Abstract.........................................................................................................................................
vii
1.0
Introduction..............................................................................................................................
1
2.0
Encapsulation
Materials...........................................................................................................
3
2.1
Sulfur
Polymer
Cement
Encapsulation.........................................................................
4
2.2
Chemically
Bonded
Phosphate
Ceramic
Encapsulation.............................................
10
2.3
Polyethylene
Encapsulation........................................................................................
17
2.4
Other
Encapsulation
Materials....................................................................................
22
2.4.1
Asphalt............................................................................................................
22
2.4.2
Polyester
and
Epoxy
Resins............................................................................
23
2.4.3
Synthetic
Elastomers.......................................................................................
23
2.4.4
Polysiloxane....................................................................................................
23
2.4.5
Sol­
Gels...........................................................................................................
25
2.4.6
DolocreteTM.....................................................................................................
25
2.4.7
Materials
Used
With
Other
Metals..................................................................
25
3.0
Cost
and
Vendor
Information.................................................................................................
28
4.0
Future
Development
and
Research
Needs.............................................................................
30
5.0
References..............................................................................................................................
32
ii
Figures
Figure
2­
1.
Sulfur
Polymer
Cement
Encapsulation.......................................................................
5
Figure
2­
2.
Chemically
Bonded
Phosphate
Ceramic
Process......................................................
12
Figure
2­
3.
Polyethylene
Macroencapsulation.............................................................................
18
Figure
2­
4.
Materials
and
Additives
for
Solidification/
Stabilization
of
Other
Metals.................
26
iii
Tables
Table
2­
1.
Key
Performance
Data
for
Sulfur
Polymer
Cement
Encapsulation.............................
7
Table
2­
2.
Key
Performance
Data
for
Chemically
Bonded
Phosphate
Ceramic
Encapsulation..
13
Table
2­
3.
Key
Performance
Data
for
Polyethylene
Encapsulation.............................................
19
Table
2­
4.
Key
Performance
Data
for
Various
Encapsulation
Materials.....................................
24
Table
3­
1.
Summary
of
Cost
and
Vendor
Information
for
Encapsulation
and
Other
Treatment
Technologies...........................................................................................................................
29
iv
Abbreviations
and
Acronyms
ANL
Argonne
National
Laboratory
ANS
American
Nuclear
Society
ANSI
American
National
Standard
Institute
ARD
acid
rock
drainage
AS2O3
arsenic
trioxide
ASTM
American
Society
for
Testing
and
Materials
BDAT
best
demonstrated
available
technology
BNL
Brookhaven
National
Laboratory
BP
bench­
scale/
pilot­
scale
CBPC
chemically
bonded
phosphate
ceramics
CFR
Code
of
Federal
Register
CSF
ceramic
silicon
foam
DOE
United
States
Department
of
Energy
DOT
United
States
Department
of
Transportation
F
full­
scale
Fe2O3
haematite
H2S
hydrogen
sulfide
HDPE
high­
density
polyethylene
Hg2SO4
mercurous
sulfate
HgCl2
mercuric
chloride
HgS
mercuric
sulfide
INEL
Idaho
National
Engineering
Laboratory
KH2PO4
monopotassium
phosphate
LDPE
low­
density
polyethylene
LDR
Land
Disposal
Restrictions
MA
macroencapsulation
MgO
magnesium
oxide
v
MI
microencapsulation
NA
not
applicable
Na2S
sodium
sulfide
Na2S.
9H2O
sodium
sulfide
nonahydrate
Na2SO
sodium
sulfite
NR
not
reported
NRC
Nuclear
Regulatory
Commission
ORNL
Oak
Ridge
National
Laboratory
ppm
parts
per
million
psi
pounds
per
square
inch
RCRA
Resource
Conservation
and
Recovery
Act
SAIC
Science
Application
International
Corporation
SEM
scanning­
electron
microscope
SITE
Superfund
Innovative
Technology
Evaluation
SPC
sulfur
polymer
cement
STC
Silicate
Technology
Co.

TCE
trichloroethylene
TCLP
Toxicity
Characteristic
Leaching
Procedure
U.
S.
EPA
United
States
Environmental
Protection
Agency
VOC
volatile
organic
compound
vol%
volume
percent
wt%
weight
percent
WPI
Waste
Policy
Institute
vi
Abstract
Although
industrial
and
commercial
uses
of
mercury
have
been
curtailed
in
recent
times,
there
is
a
demonstrated
need
for
the
development
of
reliable
hazardous
waste
management
techniques
because
of
ongoing
hazardous
waste
generation
and
historic
operations
that
have
led
to
significant
contamination.
The
focus
of
this
article
is
on
the
current
state
of
encapsulation
technologies
and
materials
being
used
to
immobilize
elemental
mercury,
mercury­
containing
debris,
and
other
mercury­
contaminated
wastes,
soils,
or
sludges.
The
range
of
encapsulation
materials
used
in
bench­
scale,
pilot­
scale,
and
full­
scale
applications
for
mercury­
containing
wastes
are
summarized
in
this
report.
Several
studies
have
been
completed
regarding
the
application
of
sulfur
polymer
stabilization/
solidification,
chemically
bonded
phosphate
ceramic
encapsulation,
and
polyethylene
encapsulation.
Other
technologies
or
materials
reported
in
the
literature
or
under
development
for
encapsulation
include
asphalt,
polyester
resins,
synthetic
elastomers,
polysiloxane,
sol­
gels
(
e.
g.,
polycerams),
and
DolocreteTM.
The
objective
of
these
encapsulation
methods
is
primarily
to
physically
immobilize
hazardous
wastes
to
prevent
contact
with
leaching
agents
such
as
water.
These
methods
may
also
include
a
stabilization
step
to
chemically
fix
mercury
into
a
highly
insoluble
form.
Economic
information
relating
to
the
use
of
these
materials
is
provided,
along
with
available
vendor
information.
Future
technology
development
and
research
needs
are
also
discussed.

vii
1.0
Introduction
The
development
of
effective
treatment
options
for
mercury­
contaminated
wastes
is
a
significant
technical
and
practical
challenge
due
to
several
factors,
including
the
limited
economic
benefit
derived
from
mercury
recovery/
recycling,
the
high
toxicity,
volatility,
and
environmental
mobility
of
mercury,
and
the
varied
nature
and
composition
of
industrial
waste
products.
Principal
sources
of
mercury­
contaminated
industrial
wastes
include
chloralkali
manufacturing,
weapons
production,
copper
and
zinc
smelting,
gold
mining,
paint
applications,
and
other
processes
(
United
States
Environmental
Protection
Agency
[
U.
S.
EPA],
1997).
Although
industrial
and
commercial
uses
of
mercury
have
been
curtailed
in
recent
times,
there
is
a
demonstrated
need
for
the
development
of
reliable
hazardous
waste
management
techniques
because
of
ongoing
hazardous
waste
generation
and
historic
operations
that
have
led
to
significant
contamination.
This
document
focuses
on
the
current
state
of
encapsulation
technologies
and
materials
being
used
to
immobilize
elemental
mercury,
mercury­
containing
debris,
and
mercury­
contaminated
wastes,
soils,
and
sludges.

As
an
inorganic
element,
mercury
cannot
be
destroyed,
but
it
can
be
converted
into
less
soluble
or
leachable
forms
to
inhibit
migration
into
the
environment
after
disposal.
The
management
and
ultimate
disposal
of
mercury­
contaminated
hazardous
waste
is
controlled
by
U.
S.
EPA
regulations
known
as
the
Land
Disposal
Restrictions
(
LDRs)
(
40
Code
of
Federal
Register
[
CFR]
Part
268).
Under
the
current
LDR
program,
the
U.
S.
EPA
has
established
thermal
recovery
(
e.
g.,
roasting/
retorting)
as
the
best
demonstrated
available
technology
(
BDAT)
for
treatment
of
wastes
containing
greater
than
260
mg/
kg
of
mercury.
For
treatment
of
wastes
with
less
than
260
mg/
kg
of
mercury,
other
extraction
technologies
(
e.
g.,
acid
leaching)
or
immobilization
technologies
(
e.
g.,
stabilization/
solidification)
may
be
considered
(
U.
S.
EPA,
1999).
Because
mercury
contained
in
radioactive
or
mixed
waste
is
not
suitable
for
thermal
recovery
and
recycling,
the
U.
S.
EPA
also
recognizes
that
stabilization/
solidification
may
be
an
appropriate
treatment
option
for
heavily
contaminated
mercury
mixed
wastes
or
debris
(
Waste
Policy
Institute
[
WPI],
1999).

Stabilization/
solidification
relies
upon
mobility
reduction
resulting
from
a
combination
of
chemical
reaction
(
e.
g.,
precipitation)
and
physical
entrapment
(
e.
g.,
porosity
reduction).
Encapsulation
technologies
are
based
primarily
on
solidification,
and
act
to
prevent
hazardous
waste
from
coming
into
contact
with
potential
leaching
agents,
such
as
water.
Hazardous
waste
materials
can
be
encapsulated
in
two
ways:
microencapsulation
or
macroencapsulation.
Microencapsulation
involves
mixing
the
waste
together
with
the
encasing
material
before
solidification
occurs.
Macroencapsulation
involves
pouring
the
encasing
material
over
and
1
around
a
larger
mass
of
waste,
thereby
enclosing
it
in
a
solidified
block.
Sometimes
these
processes
are
combined.

The
U.
S.
EPA
is
considering
changes
to
the
LDR
program
to
require
a
macroencapsulation
step
prior
to
the
land
disposal
of
stabilized
mercury
wastes.
Mercury
wastes
may
be
stabilized
using
sulfide
or
other
chemical
fixation
processes,
but
the
stabilization
process
is
pH
dependent
and
may
not
permanently
immobilize
mercury
for
disposal.
The
optimal
pH
range
is
4
to
8
for
chemical
fixation
of
mercury
compounds
to
the
highly
insoluble
solid
form,
mercuric
sulfide
(
HgS).
At
high
pH,
the
more
soluble
solids
mercurous
sulfate
(
Hg2SO4),
mercuric
sulfate
(
HgSO4),
and
mercury
sulfide
hydrogen
sulfide
complex
(
HgS[
H2S]
2)
are
formed
depending
on
oxidizing
or
reducing
conditions;
while
at
low
pH,
hydrogen
sulfide
gas
escapes
from
the
waste
(
Wagh
et
al.,
2000;
Clever
et
al.,
1985).
Combining
stabilization
with
macroencapsulation
to
prevent
pH­
related
degradation
of
the
treated
waste
may
improve
its
long­
term
stability
and
therefore
minimize
any
potential
threats
to
human
health
and
the
environment.

The
range
of
encapsulation
materials
used
in
bench­
scale,
pilot­
scale,
and
full­
scale
applications
are
summarized
in
the
following
sections.
Economic
information
for
several
different
encapsulation
materials
is
provided,
along
with
available
vendor
information.
Future
technology
development
and
research
needs
are
also
discussed.

2
2.0
Encapsulation
Materials
Materials
used
for
encapsulation
of
mercury
must
be
both
chemically
compatible
with
the
hazardous
waste
and
inert
to
common
environmental
conditions
that
may
be
encountered
in
a
disposal
facility,
such
as
rain
infiltration,
groundwater
flow,
and
freeze/
thaw
cycles.
Sulfur
polymer
stabilization/
solidification
(
SPSS),
chemically
bonded
phosphate
ceramic
(
CBPC)
encapsulation,
and
polyethylene
encapsulation
are
just
three
of
the
techniques
that
are
currently
being
tested
and
used
to
improve
the
long­
term
stability
of
hazardous
wastes.
Studies
that
focus
on
the
management
of
elemental
mercury,
mercury­
contaminated
debris,
and
other
mercury­
contaminated
wastes
will
be
discussed.
Each
encapsulation
material
will
be
reviewed
in
terms
of
the
key
features
of
the
encapsulation
process,
current
applications
and
technology
status,
and
available
performance
data.
The
advantages
and
disadvantages
associated
with
each
material
will
also
be
discussed.

Performance
data
for
encapsulated
wastes
typically
include
both
physical
data
(
e.
g.,
strength,
density,
and
permeability)
and/
or
chemical
data
(
e.
g.,
leachability).
For
macroencapsulated
waste,
the
most
important
evaluation
criteria
are
the
compressive
strength,
the
waste
form
density,
the
presence
of
void
spaces,
and
the
barrier
thickness.
The
primary
concern
during
macroencapsulation
is
that
an
inert
surface
coating
or
jacket
is
created
which
substantially
reduces
the
potential
for
exposure
of
the
waste
to
leaching
media
(
Mattus,
1998).
For
microencapsulated
waste,
the
toxicity
characteristic
leaching
procedure
(
TCLP)
plays
an
important
role
in
determining
whether
or
not
the
material
can
be
accepted
by
a
landfill.
Macroencapsulated
materials
are
typically
not
tested
with
the
TCLP.
According
to
the
Resource
Conservation
and
Recovery
Act
(
RCRA)
LDR
rules,
mercury
hazardous
waste
is
defined
as
any
waste
that
has
a
TCLP
value
greater
than
0.2
mg/
L.
Mercury­
contaminated
wastes
that
exceed
this
value
must
be
treated
to
meet
the
Universal
Treatment
Standard
(
UTS)
of
0.025
mg/
L
or
less
prior
to
disposal
in
a
landfill.
The
TCLP
test
methodology,
Method
1311,
is
described
in
detail
in
the
U.
S.
EPA
guidance
document
SW­
846
Test
Methods
for
Evaluating
Solid
Waste,
Physical/
Chemical
Methods.
TCLP
tests
on
microencapsulated
material
may
require
size
reduction
to
meet
the
particle
size
specifications
in
Method
1311.
Instead
of
crushing,
cutting,
or
grinding
the
microencapsulated
material,
the
particle
size
requirements
are
typically
met
through
subsampling
the
waste
and
binder
formulation
and
casting
small
pellets
in
the
appropriate
size.
This
methodology
helps
to
meet
TCLP
test
requirements,
while
maintaining
the
barrier
surface
and
integrity
of
the
waste
form.
The
U.
S.
Nuclear
Regulatory
Commission
(
NRC)
has
also
developed
its
own
waste
form
testing
protocols
for
mixed
wastes.
In
general,
NRC
waste
form
testing
examines
the
influence
of
environmental
factors
on
the
final
waste
form
stability
including
the
effect
of
thermal
cycling
and
immersion
on
compressive
strength
and
the
impact
of
3
biodegradation
and
irradiation.
However,
a
detailed
discussion
of
these
waste
evaluation
criteria
are
beyond
the
scope
of
this
report.

2.1
Sulfur
Polymer
Stabilization/
Solidification
Conventional
stabilization/
solidification
methods
typically
include
the
fixation
of
metals
using
Portland
cement
and
fly
ash,
which
produces
an
impermeable,
solid
waste
form
and
creates
a
high
pH
environment
that
limits
the
solubility
and
leachability
of
most
metals.
However,
it
is
very
difficult
to
stabilize
mercury
with
cement­
based
processes
because
it
does
not
form
a
low­
solubility
hydroxide
solid
(
U.
S.
EPA,
1999).
For
this
reason,
a
significant
amount
of
research
has
gone
into
the
development
of
alternative
binding
materials
for
the
stabilization/
solidification
of
mercury­
contaminated
wastes.
As
discussed
below,
the
SPSS
process
can
be
used
to
both
convert
mercury
compounds
into
the
highly
insoluble
HgS
form
and
to
simultaneously
encapsulate
the
waste.

The
SPSS
process
relies
upon
the
use
of
a
thermoplastic
material
which
contains
95
wt%
elemental
sulfur
and
5
wt%
of
the
organic
modifiers,
dicyclopentadiene
and
oligomers
of
cyclopentadiene.
This
material
is
referred
to
in
the
literature
as
sulfur
polymer
cement
(
SPC),
although
it
is
not
a
cementitious
material.
SPC
melts
at
approximately
115oC
(
235oF)
and
sets
rapidly
upon
cooling.
It
is
relatively
impermeable
to
water
compared
to
conventional
concrete
and
has
a
high
mechanical
strength
at
approximately
double
that
of
conventional
concrete.
SPC
is
also
well
suited
to
harsh
environments
with
high
levels
of
mineral
acids,
corrosive
electrolytes,
or
salt
solutions,
according
to
research
completed
by
van
Dalen
and
Rijpkema
(
1989),
McBee
and
Donahue
(
1985)
and
others
as
quoted
in
Darnell
(
1996).

Figure
2­
1
provides
a
simplified
block­
diagram
for
the
SPSS
encapsulation
process
(
United
States
Department
of
Energy
[
DOE],
1994).
For
macroencapsulation,
molten
SPC
is
poured
over
and
around
large
debris
such
as
metal
scrap
and
is
then
allowed
to
set
into
a
monolithic
waste
form.
The
recommended
mixing
temperature
for
SPC
is
between
127­
138
oC
(
260­
280
oF).
Operating
in
this
range
will
minimize
gaseous
emissions
and
provide
optimum
viscosity
(
Darnell,
1996).

For
microencapsulation
of
liquid,
elemental
mercury,
a
two­
stage
process
referred
to
as
SPSS
has
been
patented
by
Kalb
et
al.
of
Brookhaven
National
Laboratory
(
BNL)
under
U.
S.
Patent
No.
6,399,849.
First,
the
elemental
mercury
is
mixed
in
a
heated
reaction
vessel
at
40
oC
with
powdered
SPC.
Other
chemical
stabilization
agents
such
as
sodium
sulfide
and
triisobutyl
phosphine
sulfide
can
also
be
added
during
this
initial
step.
The
heated
reaction
vessel
helps
to
accelerate
the
reaction
between
mercury,
SPC,
and
the
additives
to
form
HgS
and
an
inert
gas
atmosphere
helps
to
prevent
the
formation
of
mercuric
oxide.
Next,
additional
SPC
is
added
and
the
mixture
is
heated
to
130
oC
(
266
oF)
to
form
a
homogenous
molten
liquid,
which
is
then
poured
into
a
mold
and
allowed
to
set
into
a
monolithic
waste
form.
This
two­
step
process
minimizes
both
the
oxidation
of
mercury
to
mercuric
oxide
and
the
amount
of
unreacted
mercury.
In
addition,
the
researchers
have
confirmed
the
formation
of
two
forms
of
mercuric
sulfide
as
a
result
of
the
treatment
process.
Both
meta­
cinnabar
and
cinnabar
phases
were
identified
using
x­
ray
powder
diffraction
scans
(
Fuhrmann
et
al.,
2002).
BNL
has
two
patents
related
to
sulfur
polymer
encapsulation
(
U.
S.
Patents
No.
6,399,849
and
5,678,234).
BNL
recently
has
licensed
the
SPSS
technology
to
Newmont
Mining
Corporation
for
the
4
encapsulation
of
liquid
elemental
mercury
generated
as
a
byproduct
of
gold
mining
operations.
Newmont
and
BNL
are
currently
working
on
scaling­
up
the
technology
for
industrial
use
(
BNL,
2002).

Several
studies
have
been
completed
regarding
the
use
of
SPC
for
metal­
contaminated
wastes
including
Fuhrmann
et
al.
(
2002),
Mattus
(
1998),
and
Darnell
(
1996).
The
results
and
observations
from
these
studies
are
discussed
below,
along
with
a
summary
of
the
advantages
and
limitations
associated
with
the
SPC
encapsulation
method.
Table
2­
1
summarizes
key
performance
data
from
these
studies.

Figure
2­
1.
Sulfur
Polymer
Stabilization/
Solidification
Note:
Figure
modified
from
DOE
(
1994).
Additives
can
be
used
to
decrease
the
leachability
of
mercury.
Additives
reported
in
the
literature
include
sodium
sulfide
and
tri­
isobutyl
phosphine
sulfide
(
Fuhrmann
et
al.,
2002).

Fuhrmann
et
al.
(
2002)
presents
the
results
from
a
bench­
scale
study
for
the
treatment
of
radioactive
elemental
mercury
with
the
patented
SPSS
process
described
above.
Elemental
mercury
and
radioactive
elemental
mercury
were
obtained
from
waste
stocks
at
Brookhaven
National
Laboratory.
The
study
explored
three
issues
including
the
leachability
of
the
treated
waste,
the
formation
of
mercuric
sulfide,
and
mercury
vaporization
during
processing.
Several
treatability
tests
were
conducted
on
the
mercury
wastes
including
microencapsulation
with
SPC
alone,
with
3
wt%
triisobutyl
phosphine
sulfide,
3
wt%
sodium
sulfide
nonahydrate,
and
a
1.5
wt%
combination
of
these
two
additives.
Microencapsulation
of
the
elemental
mercury
with
5
SPC
alone
resulted
in
TCLPs
ranging
from
20
ug/
L
to
>
400
ug/
L.
The
final
formulation
that
was
chosen
was
the
3
wt%
sodium
sulfide
treatment
which
resulted
in
an
average
leachate
concentration
for
mercury
of
25.8
ug/
L
and
a
range
from
1.3
to
50
ug/
L.
Long­
term
leaching
studies
were
also
conducted
according
to
the
American
Society
for
Testing
and
Materials
(
ASTM)
Method
C­
1308.
This
test
demonstrated
a
very
low
release
rate
with
a
diffusion
coefficient
for
mercury
in
the
final
waste
form
on
the
order
of
10­
17
cm2/
s.
The
authors
also
explored
the
formation
of
mercuric
sulfide
through
x­
ray
diffraction
studies
and
determined
that
elemental
mercury
and
SPC
reacted
to
form
primarily
meta­
cinnabar.
However,
elemental
mercury
and
sodium
sulfide
nonahydrate
formed
primarily
cinnabar,
which
explains
the
improved
leaching
behavior
in
those
tests
with
3
wt%
sodium
sulfide
as
an
additive.
The
results
of
mercury
volatilization
studies
also
demonstrated
that
mercury
volatilization
was
reduced
through
the
treatment
with
sodium
sulfide.
Headspace
measurements
for
elemental
mercury
ranged
from
9.2
to
12.7
mg/
m3
in
vapor,
ranged
from
0.41
to
4.5
mg/
m3
with
just
SPC,
and
0.20
to
1.3
mg/
m3
with
the
addition
of
sodium
sulfide.
These
results
suggest
that,
for
adequate
retention
of
the
mercury
during
processing,
the
use
of
additives
such
as
sodium
sulfide
may
be
necessary
(
Fuhrmann
et
al.,
2002).

Oak
Ridge
National
Laboratory
(
ORNL)
completed
a
treatability
test
to
scale­
up
the
SPC
process
for
the
macroencapsulation
of
mixed
waste
debris,
contaminated
with
mercury
and
other
metals
(
Mattus,
1998
and
ORNL,
1997).
The
ORNL
treatability
study
objectives
included
scaled­
up
equipment
selection,
determination
of
the
size
and
shape
of
the
final
waste
form,
and
process
parameter
monitoring
and
optimization.
The
treatability
study
was
performed
using
two
mixed
waste
streams
generated
at
ORNL:


208
kg
(
457
lb)
of
cadmium
sheets
(
Resources
Conservation
and
Recovery
Act
[
RCRA]
waste
code
D006),
and

204
kg
(
448
lb)
of
lead
pipes
contaminated
with
mercury
(
RCRA
waste
codes
D008
and
D009).

The
cadmium
sheets
were
classified
as
debris
under
the
alternative
debris
standards
found
in
40
CFR
268.45.
Macroencapsulation
is
an
option
for
treatment
of
this
waste
code
under
the
alternative
debris
treatment
standards.
Macroencapsulation
with
SPC
also
satisfied
the
LDR
treatment
standards
for
radioactive
lead
solids
(
D008)
and
for
mercury
(
D009)
through
amalgamation,
as
sulfur
is
one
of
the
elements
that
is
able
to
form
a
non­
liquid,
semisolid
when
combined
with
mercury.

6
Table
2­
1.
Key
Performance
Data
for
Sulfur
Polymer
Stabilization/
Solidification
7
Author/

Vendor
Type
Scale
Waste
Type
Waste
Form
Size
Waste
Loading
(
wt%)
Compressive
Strength
(
psi)
Density
(
g/
cm3)
Before
Hg
TCLP
(
mg/
L)
After
Hg
TCLP
(
mg/
L)

Mattus
(
1998)
MA
BP
Mixed
waste
cadmium
sheets
5
gal
15.8
to
28.6
NR
NR
NA
NA
Mattus
(
1998)
MA
BP
Mixed
waste
lead
pipes/
gloves
contaminated
with
Hg
5
gal
31.3
t0
38.8
NR
NR
NA
NA
Fuhrmann
et
al.
(
2002)
MI
BP
Radioactive
Hgo
5
gal
33.3
NR
NR
2.64
0.020
to
>
0.40
Fuhrmann
et
al.
(
2002)
MI
BP
Radioactive
Hgo
with
3
wt%
triisobutyl
phosphine
sulfide
additive
to
SPC
5
gal
33.3
NR
NR
2.64
>
0.40
Fuhrmann
et
al.
(
2002)
MI
BP
Radioactive
Hgo
with
3
wt%
Na2S.
9H2O
additive
to
SPC
5
gal
33.3
NR
NR
2.64
0.0013
to
0.050
Darnell
(
1996)(
b)
MI
BP/
F
Metal
oxides
including
Hg,

Pb,
Ag,
As,
Ba,
and
Cr
at
5
wt%
each
NR
40
4,000
NR
250(
a)
<
0.2
Kalb
et
al.,

(
1996)
MI
BP
Mixed
waste
off­
gas
scrub
solution
NR
25
to
45
3,850
to
8,160
1.86
to
1.94
0.14
<
0.009
BP=
Bench­
Scale/
Pilot­
Scale.

F=
Full­
Scale.

MA=
macroencapsulation
MI=
microencapsulation,

NA=
not
applicable.

NR=
not
reported.

TCLP
=
Toxicity
Characteristic
Leaching
Procedure.

(
a)
Untreated
waste
TCLP
not
reported,
so
estimated
based
on
total
Hg
level
in
waste
divided
by
20.

(
b)
Sodium
sulfide
nonahydrate
was
added
to
reduce
metal
leachability.
The
equipment
used
in
the
study
included
primarily
a
5­
gallon
steel
container,
a
rigid
wire
basket,
a
handle
spacer
to
hold
the
debris
in
place,
a
vibrating
table,
external
heater
tapes,
and
a
melting
pot
and
pour
pipe
for
the
molten
SPC.
The
size
and
shape
of
the
final
waste
form
was
developed
based
upon
criteria
from
the
United
States
Department
of
Transportation
(
DOT)
hazardous
material
shipping
regulations
(
49
CFR
173.12),
the
hazardous
waste
disposal
facility
(
Envirocare),
and
general
safety
and
handling
considerations.
The
DOT
requirements
included
the
use
of
an
approved
container
with
a
total
waste
form
weight
limit
of
205
kg.
The
Envirocare
facility
specified
that
the
following
process
requirements
would
have
to
be
met
for
waste
acceptance:


The
barrier
had
to
be
in
intimate
contact
with
the
waste,


The
barrier
should
be
at
least
2
inches
thick
around
the
waste
material,
and

The
waste
had
to
be
encapsulated
using
a
continuous
pour.

Because
of
the
small
size
of
the
waste
form
mold,
some
preparation
and
size
reduction
of
the
cadmium
sheet
debris
and
lead
pipe
wastes
was
required.
In
a
radiological
fume
hood,
sheet
metal
scissors
were
used
to
reduce
the
size
of
the
cadmium
sheets,
which
ranged
in
length
from
4
inches
to
more
than
40
inches.
For
the
lead
pipe
wastes,
pieces
of
debris
were
bent
or
cut
to
the
target
size
(
e.
g.,
<
4
inches).
The
SPC
process
was
first
tested
with
non­
contaminated
materials,
so
the
waste
form
could
be
cut
transversely
and
observed
to
optimize
process
parameters.
Following
two
practice
trials,
the
radioactive
mixed
waste
streams
were
encapsulated
in
a
series
of
20
batches.
The
major
steps
involved
in
the
SPC
macroencapsulation
process
included
the
following:

1)
The
debris
was
placed
into
a
secured
wire
basket,
which
was
centered
in
the
drum
to
maintain
a
2­
inch
surrounding
layer
of
SPC,

2)
Molten
SPC
was
poured
into
the
drum
to
provide
both
the
outer
layer
of
SPC
and
to
fill
the
voids
between
the
debris,

3)
The
pour
was
continued
until
SPC
reached
2
inches
from
the
top
of
the
drum,

4)
Once
the
bottom
portion
of
the
waste
form
had
hardened,
the
spacer
holding
the
wire
basket
was
removed
and
a
cap
of
molten
SPC
was
added
to
fill
the
drum,
and
5)
Once
the
cap
layer
was
set,
the
drum
was
sent
for
land
disposal.

It
was
found
that
heating
the
debris
to
140
to
150
oC
(
284
to
302
oF)
for
six
hours
prior
to
the
pour
helped
to
ensure
that
fast
cooling
of
the
SPC
did
not
occur
at
the
waste­
binder
interface
and
helped
to
reduce
the
formation
of
air
pockets.
Vibrating
the
container
throughout
the
pouring
sequence
and
for
up
to
five
minutes
after
the
pour
also
improved
setting
of
the
waste
form.
Heating
tapes
were
used
to
maintain
a
target
temperature
of
190
oC
(
374
oF)
at
the
top
portion
of
the
container.
This
allowed
air
bubbles
from
the
setting
SPC
to
escape.
The
optimal
additional
heating
time
was
determined
to
be
10
hours
after
the
pour
had
ended.
During
the
surrogate
waste
test,
examination
of
the
waste
form
cross
section
revealed
good
contact
between
the
debris
pieces
and
SPC
and
no
identifiable
interface
between
the
two
pour
layers
(
i.
e.,
the
top
portion
of
8
the
drum
and
the
cap).
No
H2S
or
SO2
off­
gasses
were
detected
during
the
tests.
For
macroencapsulation
of
the
mixed
wastes,
waste
loadings
for
the
cadmium
sheets
ranged
from
15.8
to
28.6
wt%
and
for
the
lead
pipes
ranged
from
31.3
to
38.8
wt%.
Key
performance
data
from
this
study
is
summarized
in
Table
2­
1.

Darnell
(
1996)
demonstrated
the
use
of
SPC
for
the
microencapsulation
of
up
to
5
wt%
of
metal
oxides
including
mercury,
lead,
silver,
arsenic,
barium,
and
chromium.
Darnell
microencapsulated
a
variety
of
metal­
contaminated
wastes
including
dehydrated
boric
acid
salts,
incinerator
hearth
ash,
mixed
waste
fly
ash,
and
dehydrated
sodium
sulfate
salts.
These
treated
wastes
were
then
subjected
to
the
U.
S.
EPA
TCLP,
the
Nuclear
Regulatory
Commission
(
NRC)
waste
form
qualification
testing,
and
the
American
Nuclear
Society
(
ANS
16.1)
leaching
index
test.
Darnell
also
found
that
an
additional
chemical
stabilization
step
was
needed
to
treat
mercury
to
meet
TCLP
limits.
A
7
wt%
sodium
sulfide
nonahydrate
(
Na2S.
9H2O)
was
added
to
the
SPC
mixture
to
convert
metal
oxides
to
more
leach­
resistant
metal
sulfides.
The
U.
S.
EPA
TCLP
limits
were
achieved
for
all
metals.
Key
performance
data
from
this
study
is
summarized
in
Table
2­
1.

Darnell
(
1996)
also
discussed
the
issues
considered
during
scale­
up
of
the
SPC
encapsulation
process
for
mixed
waste
incinerator
fly
ash.
The
full­
scale
system
proposed
consisted
of
a
large
disposal
box
(
1
m
on
each
side)
that
would
be
stacked
in
an
above­
grade,
earth­
mounded,
concrete
disposal
vault.
The
box
would
be
surrounded
by
a
heated
mold­
form
to
prevent
swelling
due
to
the
approximately
3,000
lb
of
waste
and
SPC
to
be
placed
inside.
Both
the
box
and
the
waste
would
be
preheated
to
the
melt
temperature
to
prevent
the
SPC
from
freezing
upon
contact.
Automated
steam
or
oil­
heated
mixers
were
planned
to
provide
temperature
control
and
to
allow
the
mixer
to
be
shut
down
or
restarted
during
a
pour.
Temperature
controls
for
mixing
and
cooling
would
be
computer
controlled
with
the
appropriate
alarms
for
safety
(
e.
g.,
gas
detection
alarms).

The
following
is
a
list
of
advantages
and
limitations
associated
with
the
use
of
SPC
for
the
encapsulation
of
hazardous
wastes:

Advantages

SPSS
results
in
the
formation
of
a
very
insoluble
sulfide
compound
with
mercury
(
HgS).


SPSS
is
well­
suited
to
the
treatment
of
elemental
Hg.


No
chemical
reaction
is
required
for
SPC
to
set
and
cure;
therefore
greater
waste­
to­
binder
ratios
are
allowed
than
with
Portland
cement.


Relatively
low
temperature
process
(
127­
138
oC
or
260­
280
oF).


Superior
water
tightness
(
e.
g.,
low
permeability
and
porosity)
compared
to
Portland
cement.


High
resistance
to
corrosive
environments
(
e.
g.,
acids
and
salts).


SPC
has
a
high
mechanical
strength.

9

SPC
is
resistant
to
freeze­
thaw
cycling
and
has
coefficients
of
expansion
compatible
with
other
construction
materials.


Simple
to
implement
because
mixing
and
pouring
equipment
is
readily
available.


SPC
is
easier
to
use
than
other
thermoplastics,
like
polyethylene,
because
of
its
low
viscosity
and
low­
melt
temperature.


It
is
possible
to
remelt
and
reformulate
SPC.

Limitations

Although
SPC
encapsulation
occurs
at
relatively
low
temperatures,
volatile
losses
of
mercury
may
occur
and
engineering
controls
are
needed.
BNL's
patented
SPSS
process
was
designed
to
minimize
Hg
volatilization
and
99.7%
of
the
Hg
treated
remains
in
the
waste
form,
while
only
0.3%
of
the
Hg
is
volatilized
and
captured
in
an
off­
gas
system.


Aqueous
wastes
must
be
dewatered
prior
to
processing.


If
cooled
too
quickly,
SPC
will
develop
an
excess
of
voids
or
air
pockets,
which
could
allow
water
or
gas
to
penetrate
the
waste
form.


Metal
debris
or
pieces
with
large
thermal
mass
may
require
debris
preheating
above
the
SPC
melting
point
to
prevent
the
formation
of
air
pockets
around
the
debris­
binder
interface.


Not
compatible
with
strong
alkaline
solutions
(>
10%),
strong
oxidizing
agents,
or
aromatic
or
chlorinated
solvents.


Expanding
clays
cannot
be
used
in
SPC.


SPC
handling
requires
the
use
of
engineering
controls
to
mitigate
possible
ignition
and
explosion
hazards.


If
excessive
temperatures
are
created,
SPC
will
emit
hydrogen
sulfide
gas
and
sulfur
vapor.

2.2
Chemically
Bonded
Phosphate
Ceramic
Encapsulation
Chemically
bonded
phosphate
ceramics
(
CBPCs)
are
well
suited
for
encapsulation
because
the
solidification
of
this
material
occurs
at
low
temperatures
and
within
a
wide
pH
range.
The
DOE
Argonne
National
Laboratory
(
ANL)
has
six
patents
covering
the
use
of
this
material
for
the
encapsulation
of
hazardous
wastes.
The
technology
has
been
licensed
to
Wangtec,
Inc.,
for
the
treatment
of
incinerator
ashes
from
power
plants
in
Taiwan
(
DOE,
1999a).
Similar
to
the
SPC
technology,
successful
treatment
with
CBPC
is
due
to
both
chemical
stabilization
and
physical
encapsulation.
Although
mercury
will
form
low
solubility
phosphate
solids,
stabilization
with
a
small
amount
of
sodium
sulfide
(
Na2S)
or
potassium
sulfide
(
K2S)
to
form
HgS
greatly
improves
the
performance
of
the
final
CBPC
waste
form.
Hg3(
PO4)
2
has
a
solubility
product
of
7.9
×
10­
46,

compared
to
HgS
with
a
solubility
product
of
2.0
×
10­
49
(
Wagh
et
al.,
2000).

10
CBPCs
are
fabricated
through
an
acid­
base
reaction
between
calcined
magnesium
oxide
(
MgO)
and
monopotassium
phosphate
(
KH2PO4)
in
solution
to
from
a
hard,
dense
ceramic
of
magnesium
potassium
phosphate
hydrate
as
shown
in
the
reaction
below:

MgO
+
KH2PO4
+
5
H2O
 
MgKPO4.6
H2O
(
MKP)

Iron
oxide
phosphates
can
also
be
used
to
form
a
low­
temperature
ceramic,
but
research
into
the
use
of
this
material
is
limited
(
Seidel
et
al.,
1998).
CBPC
waste
forms
typically
have
a
density
of
1.8
g/
cm3
and
high
compressive
strengths
(>
2,000
psi).
They
also
have
an
open
porosity
that
is
up
to
50%
less
than
conventional
fabricated
cement.
Waste
loadings
up
to
78%
have
been
demonstrated
with
this
technology.
Figure
2­
2
provides
a
simplified
block­
diagram
for
the
CBPC
encapsulation
process.
First,
enough
water
is
added
to
the
waste
in
the
disposal
drum
to
reach
a
target
or
stoichiometric
water
content.
(
One
advantage
of
the
CBPC
process
is
that
it
can
be
carried
out
on
dry
solids,
wet
sludges,
or
liquid
wastes.)
Next,
calcined
magnesium
oxide
and
monopotassium
phosphate
binders
are
ground
to
a
powder
and
blended
in
a
one­
to­
one
ratio.
Additional
ingredients
(
e.
g.,
fly
ash
or
K2S
for
mercury
fixation)
also
are
added
to
the
binders.
The
water,
binders,
additional
ingredients,
and
waste
are
mixed
for
about
30
minutes.
Under
most
conditions,
heat
from
the
reaction
causes
the
waste
matrix
to
reach
a
maximum
temperature
of
approximately
80
oC
(
176
oF).
After
mixing
is
stopped,
the
waste
form
typically
sets
in
about
2
hours
and
cures
in
about
two
weeks.
Mixing
can
be
completed
in
a
55­
gallon
disposal
drum
with
a
planetary
type
mixer.
The
waste,
water,
binder,
and
additives
can
be
charged
to
the
drum
using
hoppers,
feeding
chutes,
and
piping
as
needed
(
DOE,
1999a).

Several
detailed
studies
have
been
completed
to
demonstrate
the
use
of
CBPCs
for
both
macroencapsulation
and
microencapsulation
of
hazardous
wastes
including
Singh
et
al.
(
1998),
DOE
(
1999a),
Wagh
et
al.
(
2000),
and
Wagh
and
Jeong
(
2001).
These
papers
describe
the
steps
involved
in
fabricating
the
CBPC
waste
forms
and
also
discuss
the
results
of
various
performance
tests
including
compressive
strength
measurements,
U.
S.
EPA
TCLP
tests,
and
leaching
index
tests.
Visual
observations
of
the
structural
integrity
of
the
waste
forms
were
also
made.
The
CBPC
encapsulation
process
has
been
tested
on
a
wide
variety
of
hazardous
wastes
including
low­
level,
mixed
waste
ash,
transuranics,
fission
products,
radon­
emanating
wastes,
salt
solutions,
and
heterogeneous
mercury­
containing
debris
(
Wagh
and
Jeong,
2001).
Table
2­
2
summarizes
key
performance
data
from
these
studies.

11
Dry
Solids
Sludge/
Other
Liquid
Waste
Resize/
Shred
Dual
Planetary
Orbital
Mixer
Waste
Form
Container
Water
MgO
KH2PO4
Additives
(
Fly
Ash/
K2S)

Figure
2­
2.
Chemically
Bonded
Phosphate
Ceramic
Process
12
Table
2­
2.
Key
Performance
Data
for
Chemically
Bonded
Phosphate
Ceramic
Encapsulation
13
Author/

Vendor
Type
Scale
Waste
Type
Waste
Form
Size
Waste
Loading
(
wt%)
Compressive
Strength
(
psi)
Density
(
g/
cm3)
Before
Hg
TCLP,

(
mg/
L)
After
Hg
TCLP
(
mg/
L)

Singh
et
al.

(
1998)(
b)
MA
BP
Cryofractured
debris
1.2
to
3
gal
35
5,000to
7,000
1.81
NA
NA
Singh
et
al.

(
1998)(
b)
MA
BP
Lead
bricks
NR
NR
5,000
to
7,000
1.8
NA
NA
Sing
et
al.

(
1998)(
b)
MA
BP
Lead­
lined
gloves
5
gal
NR
5,000
to
7,000
1.8
NA
NA
Singh
et
al.

(
1998)(
b)
MI
BP
Hg­
contaminated
crushed
light
bulbs
5
gal
40
5,000
to
7,000
1.8
0.200
to
0.202
<
0.00004
to
0.00005
DOE
(
1999a)
MI
BP
DOE
Surrogate
Wastes
of
nitrate
salts
and
off­
gas
scrub
solution
NR
58
to
70
1,400
to
1,900
1.7
to
2.0
540
to
650
<
0.00004
to
<
0.00005
Wagh
et
al.

(
2000)(
b)
MI
BP
DOE
Ash
(
HgCl2
at
0.5
wt%)
(
100
g)
NR
NR
NR
40
<
0.00085
Wagh
et
al.

(
2000)(
b)
MI
BP
Delphi
DETOX
(
with
0.5
wt%
each
HgCl2,

Ce2O3,
Pb(
NO3)
2)
(
100
g)
NR
NR
NR
138
to
189
<
0.00002
to
0.01
Wagh
et
al.

(
2000)(
b)
MI
BP
Soil
(
HgCl2
at
0.5
wt%)
(
100
g)
NR
NR
NR
2.27
<
0.00015
Wagh
and
Jeong
(
2001)(
c)
MI
BP
Detox
Wastestream
(
HgCl2
at
0.5
wt%)
(
162
to
500
g)
60
to
78
NR
NR
250(
a)
4.7
to
15.1
Wagh
and
Jeong
(
2001)(
c)
MI
BP
Detox
Wastestream
(
Hg
at
0.5
wt%)
(
162
to
500
g)
60
to
78
NR
NR
250(
a)
7.19
to
7.64
(
a)
Untreated
waste
TCLP
not
reported,
so
estimated
based
on
total
Hg
level
in
waste
divided
by
20.

(
b)
Potassium
sulfide
was
added
to
reduce
metal
leachability.

(
c)
Sodium
sulfide
nonahydrate
was
added
to
reduce
metal
leachability.
Singh
et
al.
(
1998)
demonstrated
the
macroencapsulation
of
four
waste
streams
with
CBPC
including
cyrofractured
debris,
lead
bricks,
lead­
lined
plastic
gloves,
and
mercury­
contaminated
crushed
light
bulbs.
The
cyrofractured
debris
consisted
of
metals,
wood,
bricks,
rocks,
and
plastics.
Some
material
handling
and
size
reduction
(
e.
g.,
shredding)
was
needed
to
fit
the
wastes
into
the
waste
disposal
drum.
The
study
was
a
bench­
scale
project
with
waste
form
sizes
ranging
from
1.2
to
5
gallons.
In
general,
debris
fragments
were
sized
to
be
less
than
one
third
the
diameter
of
the
drum.
The
CBPC
fabrication
process
was
approximately
the
same
for
each
waste
with
the
exception
of
minor
formula
changes
in
the
wt%
of
water,
ash,
or
binders
and
the
addition
of
K2S
in
the
mixture
for
the
mercury­
contaminated
crushed
light
bulbs.

Cryofractured
Debris
For
the
cryofractured
debris,
the
phosphate
ceramic
slurry
was
created
with
a
premixed
powder
of
calcined
magnesium
oxide
and
fly
ash
added
to
an
acid
phosphate
solution
in
a
Hobart
mixer.
The
CBPC
formula
consisted
of
a
ratio
of
40
wt%
ash,
40
wt%
binder
(
MgO
and
KH2PO4
powders
mixed
in
1:
1
molar
ratio)
and
20
wt%
water.
The
slurry
was
mixed
at
low
speed
until
it
reached
the
desired
consistency.
The
slurry
then
was
poured
into
the
drum
containing
the
waste
and
was
stirred
continuously
to
assure
homogeneity
of
the
mixture.
The
temperature
was
monitored
and
peaked
at
approximately
72
oC
(
162
oF)
and
the
CBPC
set
at
around
55
oC
(
131
oF).
The
final
waste
forms
had
a
waste
loading
of
35
wt%
and
a
density
of
1.81
g/
cm3.

Lead
Brick
and
Lead­
Lined
Gloves
The
low­
level
radioactive
lead
brick
and
lead­
lined
plastic
gloves
were
encapsulated
in
CBPC
formulated
from
60
wt%
ash,
25
wt%
binder,
and
15
wt%
water.
Macroencapsulation
of
the
lead
brick
involved
pouring
a
2­
inch
lower
base
and
allowing
it
to
set
for
one
hour
until
it
could
bear
the
weight
of
the
lead
brick.
The
macroencapsulation
of
the
glove
wastes
was
accomplished
with
the
use
of
a
plastic
cage
suspended
in
a
5­
gallon
pail.

Mercury
Contaminated
Light
Bulbs
The
mercury­
contaminated
crushed
light
bulbs
were
pre­
treated
by
mixing
with
a
potassium
sulfide
solution
for
approximately
1
hour.
The
glass
was
then
set
in
CBPC
with
a
similar
formulation
to
the
cryofractured
debris.
Mercury
levels
in
the
glass
waste
were
around
200
parts
per
million
(
ppm).
The
crushed
glass
ranged
in
size
from
2
to
3
cm
long
by
1
to
2
cm
wide.
During
the
mixing
of
the
waste
with
the
binder,
the
glass
was
crushed
down
to
sizes
less
than
60
mm
and
a
waste
loading
of
approximately
40
wt%
was
achieved.

Each
waste
form
was
allowed
to
cure
for
about
two
weeks
prior
to
performance
testing.
The
density
of
the
final
waste
forms
was
approximately
1.8
g/
cm3,
the
open
porosity
less
than
4%,
and
the
compression
strengths
between
5,000
and
7,000
psi.
The
cross
sections
of
the
final
waste
forms
were
observed
to
be
very
homogenous,
dense,
and
free
of
air
pockets.
A
complete,
intact
coating
with
continuous
adhesion
was
observed
around
the
lead
brick
and
other
wastes
and
no
gaps
were
present
at
waste­
binder
interfaces.
TCLP
tests
on
the
mercury­
contaminated
wastes
showed
200
to
202
µ
g/
L
in
the
untreated
wastes
compared
to
<
0.04
to
0.05
µ
g/
L
for
the
treated
wastes.
Key
performance
data
from
this
study
is
summarized
in
Table
2­
2.

14
A
DOE
study
(
1999a)
was
completed
to
test
the
effectiveness
of
CBPCs
in
the
treatment
of
salt­
containing,
mercury­
contaminated
mixed
wastes.
A
significant
proportion
of
DOE
mixed
wastes
contain
greater
than
15
wt%
salts
and
these
wastes
are
very
difficult
to
treat
with
conventional
methods.
Salts
adversely
impact
conventional
cement
matrices
by
causing
a
decrease
in
compressive
strength
and
an
increase
in
metal
leachability.
There
is
a
demonstrated
need
to
find
encapsulation
materials
that
can
allow
higher
waste
loadings
to
be
achieved
compared
to
conventional
cement
stabilization/
solidification.
The
waste
streams
used
in
this
study
included
saturated
salt
solutions
(
NaNO3
and
NaCl),
activated
carbon,
ion
exchange
resins,
spent
incinerator
off­
gas
scrub
solution,
and
Na2CO3.
These
surrogate
wastes
were
spiked
with
hazardous
constituents
including
lead,
chromium,
mercury,
cadmium,
nickel,
and
trichloroethylene
(
TCE)
at
levels
up
to
1,000
ppm.

Waste
loadings
in
CBPC
of
up
to
70
wt%
(
40
wt%
salt)
were
achieved
during
the
study.
Several
performance
tests
were
completed
on
the
CBPC­
encapsulated
wastes,
including
compressive
strength,
U.
S.
EPA
TCLP
tests,
and
salt
anion
leaching
tests
per
American
National
Standards
Institute
(
ANSI)
Method
16.1.
The
final
CBPC
waste
forms
fabricated
with
the
saturated
salt
solutions
had
densities
ranging
from
1.72
to
1.8
g/
cm3
and
compressive
strengths
ranging
from
1,800
to
3,500
psi.
The
binder
was
amended
with
K2S,
which
successfully
stabilized
mercury
to
meet
the
TCLP
limit
in
these
wastes.
Anion
leaching
indexes
of
6.9
and
6.7
were
measured
for
chloride
and
nitrate,
respectively,
which
barely
passed
the
demonstration's
criteria
level
(
6.0).
These
results
indicate
that
salt
leaching
may
deteriorate
the
waste
over
time
and
that
an
additional
binder
or
coating
technique
for
the
surface
may
be
needed.
Subsequently,
some
CBPC
waste
forms
were
coated
in
a
commercial
polymer
to
plug
the
surface
pores
and
the
combined
leaching
index
of
NO3
and
Cl
was
changed
to
12.6,
which
indicated
a
reduction
in
leaching
behavior.
Key
performance
data
from
this
study
is
summarized
in
Table
2­
2.

Wagh
et
al.
(
2000)
discusses
the
results
of
bench­
scale
studies
for
the
encapsulation
of
mercury­
contaminated
surrogate
wastes
including
DOE
ash
waste,
secondary
waste
streams
from
the
DETOXSM
wet
oxidation
process,
and
contaminated
topsoil.
The
surrogate
waste
streams
were
dosed
with
mercuric
chloride
(
HgCl2)
at
0.1
wt%
to
0.5
wt%
and
also
with
other
metals
including
lead
and
cesium.
Initial
tests
showed
that
encapsulation
with
CBPC
alone
caused
mercury
leaching
to
decrease
by
a
factor
of
three
to
five
times.
However,
for
adequate
mercury
stabilization,
Wagh
et
al.
determined
that
a
small
amount
of
Na2S
or
K2S
should
be
used
in
the
binder.
For
use
with
CBPC,
the
K2S
formulation
was
initially
deemed
to
be
the
most
appropriate
because
the
CBPC
binder
is
a
potassium­
based
material.
Other
potential
additives
for
mercury
stabilization
referenced
by
the
author
include
H2S
or
NaHS.
In
this
study,
K2S
was
mixed
directly
with
MgO
and
KH2PO4
powders
to
form
one
binder
powder.
The
optimal
range
of
K2S
in
the
binder
powder
was
found
to
be
0.5
wt%
and
it
was
also
established
that
levels
significantly
above
this
dose
resulted
in
the
formation
of
Hg2SO4,
which
has
a
much
higher
solubility
than
HgS
(
Hg2SO4
has
a
solubility
product
of
7.99
x
10­
7
versus
HgS
with
a
solubility
product
of
2.0
×
10­
49).
All
of
the
surrogate
wastes
were
successfully
treated
to
levels
below
the
U.
S.
EPA
TCLP
criteria
for
mercury
from
initial,
untreated
TCLP
levels
ranging
from
2.27
mg/
L
in
the
soil
to
189
mg/
L
for
the
iron
phosphate
wastes.
Long­
term
(
90­
day)
leaching
tests
were
also
performed
on
the
waste
forms.
It
was
determined
that
the
diffusion
of
mercury
through
the
CBPC
matrix
is
10
orders
of
magnitude
lower
than
in
cement
systems.
Key
performance
data
from
this
study
is
summarized
in
Table
2­
2.

15
Wagh
and
Jeong
(
2001)
continued
work
related
to
the
encapsulation
of
DETOXSM
wastes.
The
study
was
concerned
with
the
effect
of
haematite
(
Fe2O3)
on
the
fabrication
and
setting
of
the
CBPC
waste
form.
The
DETOXSM
wastes
contained
approximately
95
wt%
Fe2O3,
which
was
found
to
be
highly
reactive
and
caused
the
CBPC
slurry
to
set
too
quickly
before
mercury
could
be
effectively
fixed
into
HgS.
Additional
tests
were
conducted
in
order
to
modify
the
CBPC
fabrication
process
to
account
for
the
reactive
nature
of
these
wastes.
Two
surrogate
wastes
were
created
including
a
waste
stream
with
0.5
wt%
HgCl2
and
94.32
wt%
Fe2O3
and
a
waste
stream
with
0.5
wt%
HgO
and
95
wt%
Fe2O3.
Two
samples
of
each
surrogate
waste
were
pretreated
with
sodium
sulfide
nonahydrate
(
Na2S.
9H2O)
for
two
hours,
which
allowed
sufficient
time
for
the
mercury
to
form
HgS.
The
binder
was
then
added
and
the
slurry
was
mixed
until
it
set.
The
CBPC
samples
were
cured
for
three
weeks
and
subjected
to
the
U.
S.
EPA
TCLP
test.
Final
TCLP
results
for
the
treated
HgCl2
waste
ranged
from
4.7
to
15.1
µ
g/
L
and
the
HgO
wastes
ranged
from
7.19
to
7.64
µ
g/
L.
Waste
loadings
ranged
from
60
to
78
wt%.
Setting
times
were
rapid
(
10
to
18
minutes)
and
the
authors
suggested
that
it
may
be
possible
in
large­
scale
systems
to
slow
down
the
reaction
by
adding
boric
acid
(
at
<
1
wt%).
Key
performance
data
from
this
study
is
summarized
in
Table
2­
2.

The
following
is
a
list
of
advantages
and
limitations
associated
with
the
use
of
CBPC
for
the
encapsulation
of
hazardous
wastes:

Advantages

Waste
stabilization
is
due
to
both
chemical
stabilization
and
physical
encapsulation.


Low
temperature
process
(<
80
oC
or
176
oF).


CBPC
can
be
used
to
treat
dry
solids,
sludges,
and
liquids.


Unlike
SPC,
CBPC
requires
no
additional
heat
input.


High
waste
loading
(
up
to
78
wt%)
minimizes
disposal
volumes.


Superior
water
tightness
and
chemical
resistance
compared
to
Portland
cement.


Simple
to
implement
since
mixing
and
pouring
equipment
is
readily
available.


Nonflammable
and
stable
and
safe
with
oxidizing
salts.


No
secondary
wastes
are
generated.


The
process
does
not
generate
potentially
hazardous
off­
gasses.

Limitations

Pretreatment
with
K2S
or
other
compounds
is
needed
for
chemical
stabilization
of
mercury;
CBPC
alone
is
not
enough.


Excess
sulfide
will
increase
the
leachability
of
mercury,
so
careful
processing
is
needed.


Some
waste
constituents
(
e.
g.,
haematite)
may
accelerate
setting
times
and
decrease
workability
of
the
CBPC
slurry.


Only
limited
data
is
available
to
support
the
long­
term
effectives
and
durability
of
CBPC
waste
forms.


For
high
salt
wastes,
the
leaching
of
salt
anions
over
time
could
deteriorate
the
integrity
of
the
waste.
A
polymer
coating
of
the
waste
form
may
be
needed
to
decrease
the
leaching
of
salt
anions.

16
2.3
Polyethylene
Encapsulation
Polyethylene
is
a
thermoplastic
material
or
a
noncross­
linked
linear
polymer
that
melts
and
liquefies
at
a
specific
transition
temperature
(
120
oC
or
248
oF).
Polyethylene
physically
encapsulates
the
waste
and
does
not
interact
with
or
chemically
alter
the
waste
materials.
Polyethylene
is
readily
available
as
a
post­
consumer
recycled
material
(
e.
g.,
low­
density
polyethylene
[
LDPE]
and
high­
density
polyethylene
[
HDPE]
used
in
commercial
packaging/
containers).
It
also
has
good
chemical
resistance
and
is
water
insoluble.
According
to
Kalb
et
al.
(
1997)
the
physical
properties
of
LDPE
are
better
suited
to
encapsulation
because
HDPE
requires
greater
temperatures
and
pressures
during
processing
and
mixing
with
wastes.
LDPE
with
a
high
melt
index
from
50
to
55
g/
10
minutes
is
reported
to
provide
the
optimal
melt
viscosity
for
mixing
with
wastes
(
Kalb
et
al.
under
U.
S.
Patent
No.
5,649,323).

Figure
2­
3
provides
a
simplified
block
diagram
for
the
polyethylene
macroencapsulation
process.
The
key
equipment
used
in
this
process
typically
includes
a
polymer
extruder
and
feed
hoppers.
There
are
three
types
of
extruder
units
including
a
single
screw
extruder,
an
intermeshing
counter­
rotating
twin­
screw
extruder,
and
an
intermeshing
co­
rotating
twin­
screw
extruder.
These
extruders
melt
the
polyethylene
feed
through
both
heat
generated
by
friction
from
the
rotating
screw
and
supplemental
barrel
heaters.
Single
screw
extruders
are
well­
suited
to
both
macroencapsulation
and
microencapsulation
and
have
been
used
in
the
plastics
industry
for
over
50
years
(
Kalb
et
al.,
1992).
Kinetic
mixers
have
also
been
used
for
polyethylene
encapsulation
(
Jackson,
2000).
Polyethylene
macroencapsulation
typically
involves
the
use
of
a
basket
placed
inside
a
drum
to
allow
at
least
a
1­
inch
barrier
around
the
waste
material.
Molten
polyethylene
is
then
poured
from
an
extruder
over
and
around
the
waste
in
the
drum.
The
drum
can
be
rotated
to
ensure
a
more
uniform
distribution
of
the
molten
plastic.
(
An
alternative
to
on­
site
pouring
is
the
use
of
pre­
manufactured
containers.)
Polyethylene
microencapsulation
typically
involves
directly
mixing
the
waste
material
and
polyethylene
at
an
elevated
temperature
(
typically
120
to
150
°
C
or
248
to
302
°
F)
in
an
extruder.
The
mixture
of
waste
material
and
polyethylene
is
then
poured
into
a
drum
and
allowed
to
set.
Microencapsulation
may
require
several
pretreatment
steps,
including
drying
of
wet
wastes
and
physical
separation
to
resize
or
improve
the
particle
distribution
of
the
waste
(
Faucette,
1994).
At
the
Envirocare
facility
in
Utah,
the
optimal
processing
parameters
for
microencapsulation
in
a
single
screw
extruder
were
determined
to
be
a
maximum
of
2%
moisture
content
and
a
3­
mm
particle
size
limit
(
Jackson,
2000).
In
addition,
off­
gas
treatment
is
needed
for
any
water
vapor,
volatile
organic
compounds
(
VOCs),
or
volatile
metals
(
e.
g.,
arsenic
and
mercury)
in
the
waste
(
Faucette,
1994).
Polyethylene
microencapsulation
and
macroencapsulation
services
are
commercially
available.
In
1998,
the
Envirocare
facility
in
Utah
installed
and
permitted
a
single
screw
extruder
system
that
can
process
up
to
5
tons
of
waste
per
day.
The
final
waste
forms
are
typically
set
in
30­
to
55­
gallon
drums
and
have
a
minimum
exterior
surface
coating
of
LDPE
of
1
to
2
inches
(
Jackson,
2000).

Several
studies
have
been
carried
out
using
polyethylene
for
both
macroencapsulation
and
microencapsulation
of
hazardous
wastes,
including
Faucette
et
al.
(
1994),
Burbank
and
Weingardt
(
1996),
and
Carter
et
al.
(
1995).
In
addition,
several
commercial
vendors
(
e.
g.,
Chemical
Waste
Management,
Boh
Environmental,
and
Ultra­
Tech,
International)
provide
macroencapsulation
services
with
pre­
manufactured
HDPE
containers.
Encapsulation
with
polyethylene
has
been
demonstrated
with
numerous
waste
streams
including
mixed
waste
salts,

17
sludges,
and
ash.
Because
macroencapsulation
is
BDAT
for
radioactive
lead
solids,
several
studies
deal
with
macroencapsulation
of
lead
brick
and
shielding
waste
materials
including
Faucette
et
al.
(
1994)
and
DOE
(
1998).
One
study
was
found
which
dealt
with
the
encapsulation
of
radioactive,
concentrated
salts
and
basin
sludges
with
low
levels
of
mercury
ranging
from
1.3
to
9.2
ppm
(
Burbank
and
Weingardt,
1996).
Carter
et
al.
discusses
the
difficulties
encountered
with
the
microencapsulation
of
high­
level
arsenic
wastes
due
to
the
high
volatility
of
arsenic
trioxide.
In
general,
there
is
little
performance
data
available
on
the
effectiveness
of
polyethylene
encapsulation
of
mercury­
containing
wastes.
Key
performance
data
from
these
studies
is
summarized
in
Table
2­
3.

Faucette
et
al.
used
polyethylene
for
macroencapsulation
and
microencapsulation
of
a
variety
of
mixed
waste
streams
from
the
DOE
Rocky
Flats
Plant
in
Colorado.
The
purpose
of
the
macroencapsulation
demonstration
was
to
compare
two
containment
methods
including
physical
contact
(
e.
g.,
on­
site
pouring
of
the
waste
form)
versus
pre­
manufactured
inserts.
The
objectives
of
the
microencapsulation
demonstration
were
to
identify
optimal
processing
equipment,
test
various
additives
to
reduce
the
leachability
of
metals
in
surrogate
wastes,
and
complete
a
treatability
study
for
actual
salt
wastes.
Key
performance
data
from
this
study
are
included
in
Table
2­
3.

Dry
SolidsResize
Sludge/
OtherDryer
Pretreatment
Polyethylene
Feed
Single
Screw
Extruder
Off­
Gas
Treatment
(
Bag
House)

Supplemental
Heating
Tapes
Waste
Form
Container
Figure
2­
3.
Polyethylene
Macroencapsulation
Faucette
et
al.
demonstrated
the
macroencapsulation
of
low­
level,
mixed
wastestreams
identified
as
combustibles
(
e.
g.,
paper,
cloth,
plastics),
laboratory
glassware,
scrap
metals
(
e.
g.,
pipe,
valves,
hand
tools),
and
lead
(
e.
g.,
sheet,
bricks,
tape).
Two
different
approaches
were
used
to
create
a
1­
inch­
thick
polyethylene
barrier
around
the
wastes
including
physical
contact
and
18
Table
2­
3.
Key
Performance
Data
for
Polyethylene
Encapsulation
19
Author/

Vendor
Type
Material
Scale
Waste
Type
Waste
Form
Size
Waste
Loading
(
wt%)
Compressive
Strength
(
psi)
Density
(
g/
cm3)
Before
Hg
TCLP
(
mg/
L)
After
Hg
TCLP
(
mg/
L)

Faucette
et
al.

(
1994)
MA
LDPE
BP/
F
Combustibles,

laboratory
glassware,

scrap
metals,

and
lead
(
e.
g.,

sheet,
bricks,

tape).
5
to
10
gal
NR
NR
NR
NA
NA
Faucette
et
al.

(
1994)
MI
LDPE
BP/
F
F006
Waste
Code:
Nitrate
Salts
with
Cd,

Cr,
Pb,
Ni,
and
Ag
NR
50
NR
NR
NA
NA
Burbank
and
Weingardt
(
1996)
MI
LDPE
BP
Ammonium
sulfate/
solar
basin
sludge
1.25
gal
40
to
50
1,088
to
2,465
NR
0.46
[
9.2
ppm](
a)
0.442
to
1.07
Burbank
and
Weingardt
(
1996)
MI
LDPE
BP
Solar
basin
sludge
1.25
gal
40
to
50
1,088
to
2,465
NR
0.065
[
1.3
ppm](
a)
0.107
to
0.122
Carter
et
al.

(
1995)
MI
HDPE
BP
As2O3
NR
(
20
vol%)
NR
NR
NA
NA
Kalb
et
al.

(
1996)
MI
LDPE
BP
Off­
gas
scrub
solution
NR
50
to
70
1,950
to
2,180
1.21
to
1.45
0.14
<
0.009
(
a)
Untreated
waste
TCLP
not
reported,
estimated
by
total
Hg
level
in
waste
divided
by
20.
pre­
manufactured
inserts.
Polyethylene
was
used
with
a
melt
index
of
50
to
200
grams/
10
minutes
per
American
Society
for
Testing
and
Materials
(
ASTM)
D1238­
90b.
It
was
determined
that
LDPE
experienced
less
cratering
and
cracking
than
HDPE
and
had
a
lower
expansion
coefficient
(
e.
g.,
shrank
less
upon
cooling).
The
basket
holding
the
waste
material
in
place
also
had
to
be
flexible
and
yield
as
the
polymer
cooled
and
contracted.
During
scale­
up
to
a
5­
gallon
container,
Faucette
et
al.
found
that
it
was
necessary
to
modify
the
process
by
using
a
"
crock
pot"
to
heat
the
waste
form
to
control
the
temperature
and
viscosity
of
the
polyethylene
during
the
pour.
Faucette
et
al.
also
stated
that
the
basket
required
to
hold
the
waste
could
cause
potential
leak
paths.
Macroencapsulation
with
a
pre­
manufactured
polyethylene
insert
also
was
demonstrated.

The
insert
consisted
of
an
open
top,
thick­
walled
polyethylene
liner,
which
was
placed
into
a
5­
gallon
metal
container.
The
insert
then
was
filled
with
waste
and
capped
with
molten
polyethylene.
The
pre­
manufactured
insert
resulted
in
a
waste
form
of
known
thickness
and
only
the
cap
needed
to
be
poured
on
site.

One
limitation
of
polyethylene
encapsulation
is
that
wastes
must
be
dewatered
prior
to
processing.
Faucette
et
al.
tested
four
different
types
of
drying
units
for
pretreatment
of
waste
materials
including
a
spray
dryer,
a
horizontal
thin
film
evaporator,
a
vertical
thin
film
evaporator,
and
a
horizontal
rotary/
blender
dryer.
The
drying
units
were
tested
for
their
ability
to
concentrate
a
nitrate
salt
aqueous
waste
stream
contaminated
with
various
metals
and
high
chlorides
and
sulfates.
The
horizontal
thin
film
unit
was
chosen
because
it
produced
salts
with
the
largest
particle
size
and
the
highest
bulk
density.
Several
additives
to
the
polyethylene
were
tested
for
their
ability
to
reduce
the
leachability
of
cadmium,
chromium,
lead,
nickel,
and
silver.
The
addition
of
surfactant
(
0.5
wt%
sodium
stearate)
was
found
to
improve
the
wetting
of
the
salts
by
the
polyethylene
and
reduce
the
leachability
of
cadmium
and
chromium.
Calcium
oxide
and
magnesium
oxide
also
significantly
reduced
the
TCLP
results
for
cadmium
and
chromium.
Carbon,
alumina,
diatomite,
and
class
C
fly
ash
were
found
to
reduce
chromium
leachability
by
93
to
98%,
but
cadmium
was
unaffected.
It
also
was
determined
that
excess
water
(
e.
g.,
>
2
wt%)
caused
the
salts
to
clump
together,
resulting
in
highly
variable
feed
characteristics
and
a
heterogeneous
product.

Burbank
and
Weingardt
explored
the
use
of
polyethylene
for
the
microencapsulation
of
mixed
wastestreams
at
the
DOE
site
in
Hanford,
WA.
Two
wastes
contained
detectable
levels
of
mercury
along
with
other
metals,
including
ammonium
sulfate
cake
wastes
with
9.2
ppm
of
mercury
and
solar
evaporation
basin
sludge
with
1.3
ppm
of
mercury.
These
wastes
were
incorporated
into
polyethylene
at
a
40
to
50
wt%
loading.
Prior
to
encapsulation,
calcium
oxide
was
added
to
the
wastes
to
help
reduce
the
leachability
of
metals.
Based
on
TCLP
results,
the
amendment
of
the
wastes
with
calcium
oxide
did
not
reduce
mercury
leachability.
Microencapsulation
of
the
ammonium
sulfate
cake
waste
with
polyethylene
resulted
in
a
mercury
TCLP
of
0.442
mg/
L.
With
the
addition
of
calcium
oxide,
this
same
wastestream
had
a
mercury
TCLP
of
1.07
mg/
L.
It
is
clear
from
these
results
that,
even
at
relatively
low
levels
in
waste,
polyethylene
encapsulation
alone
cannot
adequately
reduce
the
availability
of
mercury,
and
chemical
stabilization
(
e.
g.,
transformation
to
HgS)
is
necessary
prior
to
the
encapsulation
of
such
wastes
with
polyethylene.
Also,
due
to
the
high
processing
temperatures
of
polyethylene
encapsulation,
it
is
likely
that
a
large
fraction
of
mercury
in
these
wastes
will
be
volatilized
20
unless
it
has
been
chemically
fixed.
Key
performance
data
from
this
study
are
included
in
Table
2­
3.

Carter
et
al.
used
HDPE
with
a
melting
point
of
130
oC
(
266
oF)
and
an
operating
temperature
of
180
 
210
oC
to
microencapsulate
powdered
arsenic
trioxide
(
As2O3).
It
was
found
that
at
a
20
volume
percent
(
vol%)
loading
of
this
compound,
the
viscosity
of
the
HDPE
increased
dramatically
and
the
mixture
became
unworkable.
Scanning
electron
microscope
(
SEM)
micrographs
showed
that
the
arsenic
trioxide
had
sublimed
and
recrystallized.
When
arsenic
trioxide
was
stabilized
to
calcium
oxide,
the
volatility
decreased,
but
achievable
waste
loadings
in
HDPE
remained
low.
Mercury
and
its
compounds
are
also
highly
volatile
compared
to
other
metals
(
e.
g.,
mercuric
chloride
sublimes
at
300
oC
or
572
oF),
so
the
results
of
this
study
could
provide
some
insight
into
the
challenge
of
using
polyethylene
to
process
wastes
containing
high
levels
of
arsenic
and
mercury.
Key
performance
data
from
this
study
are
summarized
in
Table
2­
3.

There
are
several
vendors
that
provide
macroencapsulation
services
with
pre­
manufactured
HDPE
containers
including
Chemical
Waste
Management,
Boh
Environmental,
and
Ultra­
Tech,
International.
These
macroencapsulation
methods
are
allowed
under
the
alternative
debris
standards
(
40
CFR
268.45)
because
the
definition
of
macroencapsulation
for
debris
does
not
preclude
the
use
of
materials
that
meet
the
definition
of
tank
or
container
(
40
CFR
260.10).
Chemical
Waste
Management
provides
½
­
inch­
thick
HDPE
vaults
measuring
21
feet
by
7
feet
for
the
disposal
of
hazardous
waste
debris.
A
3­
inch­
thick
soil
liner
is
used
in
the
vault
to
provide
a
physical
cushion
between
the
bottom
of
the
vault
and
the
debris.
Soil
or
sand
is
typically
used
to
fill
any
void
spaces
around
the
debris.
Once
the
vault
is
full,
the
lid
is
secured
to
the
vault
with
adhesives
and
screws.
The
vault
then
is
placed
in
a
subtitle
C
landfill.
Chemical
Waste
Management
also
provides
225­
millimeter
HDPE­
lined
roll­
off
boxes
for
hazardous
waste
debris
disposal.
Boh
Environmental's
Arrow­
PakTM
technology
consists
of
compacting
55­
gallon
drums
filled
with
mixed/
hazardous
waste
debris
into
12­
inch­
thick
pucks.
The
compacted
drums
are
loaded
into
an
85­
gallon
metal
overpack
drum
and
then
into
a
1­
inch­
thick
HDPE
tube
about
21
feet
in
length
and
30
inches
in
diameter.
Each
tube
fits
the
equivalent
of
21
55­
gallon
drums.
Both
ORNL
and
DOE's
Hanford
have
used
this
technology
for
the
macroencapsulation
of
mixed
waste
debris.
This
technology
achieves
a
mixed
waste
debris
volume
that
is
typically
one­
fourth
that
of
on­
site
macroencapsulation
with
polyethylene
(
INEL,
2002).
Ultra­
Tech,
International
offers
a
series
of
pre­
manufactured,
medium­
density
polyethylene
containers
for
macroencapsulation.
The
containers
can
be
custom­
made
in
any
size,
but
have
been
manufactured
to
over­
pack
one
55­
gallon
drum
to
containers
52
inches
in
diameter
and
20
feet
in
length.
A
resistance
wire
system
is
embedded
in
the
lid
of
each
container.
Once
the
debris
waste
is
in
place,
an
electrical
current
is
applied
to
the
wires,
heating
them
up
to
melt
the
polyethylene,
and
creating
an
effective
seal
around
the
top
of
the
container.
This
technology
is
currently
being
tested
by
DOE's
Mixed
Waste
Focus
Area
Program
(
Ultra­
Tech,
International,
2002).

The
following
is
a
list
of
advantages
and
limitations
associated
with
the
use
of
polyethylene
for
the
encapsulation
of
hazardous
wastes:

21
Advantages

Polyethylene
has
a
high
mechanical
strength,
flexibility,
and
chemical
resistance.


Polyethylene
is
highly
resistant
to
biological
degradation.


Polyethylene
allows
higher
waste
loadings
(
up
to
70
wt%)
compared
to
conventional
Portland
cement.


Polyethylene
is
readily
available
in
postconsumer
recycled
forms.


Equipment
is
commercially
available
and
the
process
can
be
automated,
so
the
operator
input
requires
only
drum
placement.


Pre­
manufactured
vaults
and
containers
can
be
used,
which
provide
a
final
waste
form
of
known
barrier
thickness
and
integrity.


Because
HDPE
is
used
in
landfill
liners,
extensive
studies
have
been
performed
to
document
the
chemical
resistance
and
long­
term
durability
of
HDPE.

Limitations

External
heating
is
required
and
the
process
occurs
at
a
higher
temperature
than
the
SPC
and
CBPC
methods.


Polyethylene
does
not
chemically
incorporate
the
waste,
and
with
mercury­
containing
wastes
volatilization
may
be
a
significant
concern.


Chemical
stabilization
of
mercury­
contaminated
wastes
prior
to
encapsulation
may
be
necessary
to
meet
TCLP
requirements.


The
encapsulation
of
high­
level
arsenic
wastes
with
polyethylene
is
problematic
due
to
the
sublimation
of
arsenic
compounds
at
high
temperature
(>
200
oC).


Small
quantities
of
secondary
waste
are
generated.


For
large­
scale
or
on­
site
pouring,
LDPE
is
preferred
because
HDPE
is
prone
to
cratering,
cracking,
and
excessive
shrinking.


LDPE
is
intolerant
of
the
presence
of
free
liquids
and
organics.


Wastes
must
be
pretreated
to
remove
moisture.


Molten
polyethylene
can
cause
severe
burns,
so
extra
safety
precautions
are
necessary.


Small
quantities
of
secondary
waste
are
generated.

2.4
Other
Encapsulation
Materials
Several
other
materials
have
been
developed
and
demonstrated
for
the
encapsulation
of
mercury­
containing
hazardous
wastes
including
asphalt,
polyester
and
epoxy
resins,
synthetic
elastomers,
polysiloxane,
sol­
gels
(
e.
g.,
polycerams),
and
DolocreteTM.
Key
performance
data
are
summarized
in
Table
2­
4.
In
addition,
a
variety
of
materials
currently
available
for
the
encapsulation
of
other
metal­
containing
wastes
are
discussed.

2.4.1
Asphalt
Asphalt
or
bitumen
has
been
used
to
microencapsulate
soil
contaminated
with
low­
levels
of
heavy
metals
(
Smith
et
al.,
1995
and
Hubbard
et
al.,
1990).
Radian
corporation
reported
using
cold­
mix
asphalt
to
microencapsulate
soil
contaminated
with
mercury
(
78
mg/
kg).
The
material
had
a
compressive
strength
of
176
psi.
Hot­
mix
asphalt
was
deemed
to
be
inappropriate
because
the
elevated
temperatures
could
promote
the
volatilization
of
mercury
(
SAIC,
1998).
Kalb
et
al.

22
(
1996)
discusses
the
microencapsulation
of
up
to
60
wt%
of
a
mixed
waste
incinerator
off­
gas
scrub
solution
with
asphalt.
The
mercury
TCLP
in
the
untreated
wastes
was
0.14
mg/
L
versus
<
0.009
mg/
L
in
the
asphalt
microencapsulated
waste.
Compressive
strengths
averaged
570
psi
in
the
final
waste
forms.

2.4.2
Polyester
and
Epoxy
Resins
Polyester
is
an
example
of
a
thermosetting
resin
or
a
cross­
linked
polymer
that
undergoes
a
chemical
reaction
to
solidify.
Several
thermosetting
resins
have
been
tested
for
the
encapsulation
of
salt­
containing
mixed
wastes
including
orthophthalic
polyester,
isophthalic
polyester,
vinyl
ester,
and
a
water­
extendible
polyester.
These
wastes
contained
metals,
including
mercury,
at
the
1,000
ppm
level.
With
polyester
resins,
waste
loadings
of
50
wt%
were
achieved
for
unconcentrated
spent
off­
gas
scrub
solutions
and
70
wt%
for
nitrate/
chloride
salts.
In
addition,
compressive
strengths
ranged
from
5,100
to
6,200
psi.
Mixed
waste,
salt
surrogate
TCLP
tests
for
mercury
ranged
from
<
0.01
to
0.2
mg/
L
(
DOE,
1999b).
Orebaugh
(
1993)
reported
using
several
epoxy
resins
(
e.
g.,
Stycast
2651
and
Thermoset
300)
to
macroencapsulate
mixed
waste,
lead
billets.
The
waste
forms
were
subjected
to
6­
foot
drop
tests
to
gauge
their
stability
and
mechanical
strength.

2.4.3
Synthetic
Elastomers
Synthetic
elastomers
are
materials
having
properties
similar
to
natural
rubber
and
have
been
used
in
the
microencapsulation
and
stabilization
of
metal­
contaminated
wastes.
Carter
et
al.
explored
the
use
of
styrene­
butadiene
rubber
(
Solprene
1204)
for
the
encapsulation
of
powdered
arsenic
trioxide
(
As2O3).
Up
to
64
wt%
of
arsenic
trioxide
was
incorporated
into
the
rubber,
but
beyond
this
level
the
rubber
became
unworkable.
Meng
et
al.
(
1998)
reports
using
tire
rubber
for
the
immobilization
of
mercury­
contaminated
soils.
A
clay­
loam
soil
was
spiked
with
mercuric
oxide
and
mercuric
chloride
at
300
mg/
kg.
Acetic
acid
leachate
tests
showed
a
reduction
from
3.5
mg/
L
in
the
untreated
soil
to
0.034
mg/
L
in
the
soil
mixed
with
tire
rubber.
The
used
tire
rubber
contained
approximately
2
to
4%
sulfur
and
less
than
32%
carbon
black.

2.4.4
Polysiloxane
Polysiloxane
or
ceramic
silicon
foam
(
CSF)
consists
of
50
wt%
vinyl­
polydimethyl­
siloxane,
20
wt%
quartz,
25
wt%
proprietary
ingredients,
and
less
than
5
wt%
water.
The
use
of
this
material
for
encapsulation
is
patented
by
Orbit
Technologies.
The
material
sets
at
room
temperatures
(
30
oC
or
86
oF)
and
is
resistant
to
extreme
temperatures,
pressures,
and
chemical
exposure.
The
polysiloxane
technology
was
demonstrated
on
salt
waste
surrogates,
which
were
spiked
with
lead,
mercury,
cadmium,
and
chromium
at
1,000
ppm
levels.
Up
to
50
wt%
waste
loading
was
demonstrated.
The
final
waste
form
had
a
compressive
strength
of
600
psi
at
40
wt%
loading.
For
high
chloride
salt
wastes,
the
mercury
TCLP
was
0.01
mg/
L
and
for
high
nitrate
salt
wastes
the
mercury
TCLP
was
0.06
mg/
L.
The
final
waste
forms
for
both
waste
types
did
not
pass
for
chromium.
The
authors
recommend
pretreatment
for
the
chemical
stabilization
of
wastes
with
metals
at
levels
greater
than
500
ppm
(
DOE,
1999c).
In
addition,
Miller
et
al.
(
2000)
reports
on
the
use
of
silicone
foam
to
encapsulate
a
DOE
surrogate
waste
containing
high
levels
of
chromium.
Salt
waste
loadings
of
up
to
48
wt%
were
achieved
in
this
study.

23
Table
2­
4.
Key
Performance
Data
for
Various
Encapsulation
Materials
24
Author/

Vendor
T
ype
Material
Scale
BP
Waste
Type
Waste
Form
Size
Waste
Loading
(
wt%)
Compressive
Strength
(
psi)
Density
(
g/
cm3)
Before
Hg
TCLP
(
mg/
L)
After
Hg
TCLP
(
mg/
L)

Kalb
et
al.

(
1996)
MI
Asphalt
Off­
gas
scrub
solution
NR
30
to
60
540­
610
1.08
to
1.42
0.14
<
0.009
Radian(
b)
MI
Asphalt
F
176
NR
NR
NR
Soil
(
Hg
78
mg/
kg)
NA
NR
DOE
(
1999b)
MI
Polyester
BP
Salt­
containing
mixed
wastes
NR
50
to
NR
50
5,100
6,200
(
a)
<
0.01
to
0.2
Orebaugh
(
1993)
MA
Epoxy
BP
Mixed
waste,

lead
billets
5
gal
NR
NR
1.43
to
1.5
(
Resin
Only)
NA
NA
Carter
et
al.

(
1995)
MI
Styrene­
butadiene
rubber
BP
As64
NR
2O3
NR
1.7
(
Rubber
Only)
NA
NA
Meng
et
al.

(
1998)
MI
Tire
Rubber
BP
(
3.5
Soil
(
Hg
300
mg/
kg)
(
100
g)
(
4
g
rubber
/
100
g
soil)
NR
NR
acetic
acid)
(
0.034
acetic
acid)

DOE
(
1999c)
MI
Poly­
siloxane
BP
Salt­
containing
mixed
wastes
NR
50
420
to
637
NR
50(
a)
0.01
0.06
to
DOE
(
1999d)
MI
Sol­
Gels
BP
Salt­
containing
mixed
wastes
NR
60
to
70
1,050
to
1,513
NR
50
(
a)
0.044
to
0.23
Dolomatrix
(
2001)
MI
Dolocat
NR
NR
145
NR
rete
 
F
Hg­
waste
15,300
mg/
kg
765(
a)
<
0.1
(
a)
Untreated
waste
TCLP
not
reported,
estimated
by
total
Hg
level
in
waste
divided
by
20.

(
b)
SAIC
(
1998).
25
2.4.5
Sol­
Gels
Sol­
gels
or
polycerams
are
a
hybrid
material
derived
from
the
chemical
combination
of
organic
polymers
and
inorganic
ceramics.
A
DOE
study
(
DOE,
1999d)
explored
the
use
of
a
polyceram
consisting
of
a
polybutadiene­
based
polymer
combined
with
silicon
dioxide
for
the
stabilization
of
high
salt
wastes.
The
salt
waste
surrogates
contained
lead,
chromium,
mercury,
cadmium,
and
nickel
at
1,000
ppm
levels.
The
polymer
and
silicon
dioxide
are
combined
first
and
then
mixed
with
the
waste
and
then
solidified
to
encapsulate
the
waste.
The
setting
of
the
waste
form
takes
place
at
temperatures
ranging
from
66
to
70
oC
(
151
to
158
oF).
Waste
loadings
from
30
to
70
wt%
were
demonstrated.
Compressive
strengths
of
the
final
waste
forms
ranged
from
137
to
1,513
psi.
The
initial
waste
forms
in
the
demonstration
had
a
high
open
porosity
and
did
not
pass
the
TCLP
test
for
mercury.
Another
set
of
waste
forms
were
fabricated
and
subjected
to
a
secondary
infiltration
of
polyceram
solution
after
initial
drying.
The
second
set
of
tests
was
able
to
demonstrate
a
decrease
in
the
mercury
TCLP
to
0.044
mg/
L.

2.4.6
DolocreteTM
DolocreteTM
is
a
proprietary
calcined
dolomitic
binder
material
that
can
be
used
for
the
microencapsulation
of
inorganic,
organic,
and
low­
level
radioactive
waste.
DolocreteTM
is
reported
to
successfully
encapsulate
wastes
containing
aluminum,
antimony,
arsenic,
bismuth,
cadmium,
chromium,
copper,
iron,
lead,
mercury,
nickel,
tin,
and
zinc.
The
encapsulation
of
mining
waste
with
up
to
590,000
mg/
kg
of
arsenic
resulted
in
a
TCLP
of
3.9
mg/
L,
which
meets
the
current
arsenic
TCLP
limit
of
5
mg/
L.
Mercury­
contaminated
wastes
with
up
to
15,200
mg/
kg
were
treated
to
reach
a
TCLP
level
of
<
0.1
mg/
L.
Compressive
strengths
of
the
final
waste
forms
often
exceed
145
psi
(
Dolomatrix,
2001).

2.4.7
Materials
Used
With
Other
Metals
For
the
stabilization/
solidification
of
other
hazardous
metal
wastes,
cement,
Pozzolan,
and
lime
are
the
most
commonly
used
encapsulation
materials;
however,
research
continues
into
the
use
of
other
binders
and
additives
to
enhance
performance
of
the
final
waste
form
and
to
reduce
project
costs
(
Conner
and
Hoeffner,
1998).
Figure
2­
4
lists
binders
and
additives
that
have
been
found
to
decrease
metal
leachability
including
fly
ash,
clays,
slags,
iron
compounds,
activated
carbon,
and
other
materials.
In
addition
to
conventional
cement,
Pozzolan,
and
lime­
based
binders,
another
encapsulation
material
reported
in
the
literature
is
proprietary
silicate
binders.
Several
vendors
and
authors
report
using
silicate­
based
materials
for
the
encapsulation
of
metal­
contaminated
wastes
including
Chemfix
Technologies,
Inc.;
Silicate
Technology
Co.
(
STC),
Mitchell
et
al.
(
2001);
and
Evangelou
(
2000).
Other
°
Type
I,
II,
V
Portland
cements
°
Class
F
fly
ash
°
Cement
kiln
dust
°
Lime
kiln
dust
°
Slag
°
Sodium
silicate
and
proprietarypolysilicatemixtures
°
Dolocrete
TM
°
Calcium
carbonate
(
limestone)
°
Calcium
sulfate
(
gypsum)
°
Iron
oxide
(
hematite)
°
Calcium
phosphate
(
apatite
)
°
Organophillic
clay
with
additives
pH
Control
°
Sulfuric
acid
°
Phosphoric
acid
°
Buffer
solution
Other
Pretreatment
Additives
°
Potassium
permanganate
(
oxidation)
°
Hydrogen
peroxide
(
oxidation)
°
Calcium
hypochlorite
(
oxidation)
°
Potassium
or
sodiumpersulfate
(
oxidation)
°
Ferric
or
calcium
chloride
(
precipitation)
°
Ferric
or
ferrous
sulfate
(
precipitation)
°
Magnesium
oxide
(
adsorbent)
°
Activated
carbon
(
adsorbent)

Note:
Based
on
information
from
Wickramanayake
et
al.,
2001;
Conner
and
Hoeffner,
1998;
Sun
et
al.,
2001;
Dutre
and
Vandecasteele,
1995;
and
Rha
et
al.,
2000.

Figure
2­
4.
Materials
and
Additives
for
Stabilization/
Solidification
of
Other
Metals
Chemfix
Technologies,
Inc.,
has
developed
a
stabilization/
solidification
process
using
proprietary
additives
of
soluble
silicates
and
calcium­
containing
reagents.
This
process
was
tested
under
the
U.
S.
EPA's
Superfund
Innovative
Technology
Evaluation
(
SITE)
program
in
March
of
1989.
The
ChemfixTM
process
was
most
successful
in
reducing
the
leachability
of
cadmium,
copper,
chromium,
lead,
nickel,
and
zinc.
However,
some
difficulty
was
experienced
in
the
treatment
of
arsenic
and
mercury­
containing
wastes.
Before
treatment,
lead
TCLP
levels
ranged
from
390
to
890
mg/
L
in
contaminated
soil.
After
treatment,
lead
TCLP
levels
ranged
from
<
0.5
to
47.0
mg/
L
or
a
94%
to
>
99%
reduction
in
lead
leachability.
Initial
copper
TCLP
26
levels
in
contaminated
soil
ranged
from
12
to
120
mg/
L,
whereas
after
treatment
levels
were
reduced
to
0.54
to
0.60
mg/
L
or
a
96%
to
>
99%
reduction.
The
compressive
strength
of
the
final
waste
form
was
90
psi
(
U.
S.
EPA,
1991).

STC
developed
a
stabilization/
solidification
process,
which
relies
upon
the
use
of
a
proprietary
silicate­
mineral
reagent
that
binds
the
metals
into
a
layered
alumino­
silicate
structure.
The
STC
process
was
tested
in
the
U.
S.
EPA
SITE
program
in
November
of
1990.
The
SITE
program
involved
the
testing
of
the
STC
process
on
soils
contaminated
with
both
inorganic
constituents
(
e.
g.,
arsenic,
chromium,
and
copper)
and
organic
constituents
(
e.
g.,
pentachlorophenol).
Before
treatment,
arsenic
TCLP
levels
ranged
from
1.1
to
3.3
mg/
L.
After
treatment,
arsenic
TCLP
levels
ranged
from
0.09
to
0.88
mg/
L
or
a
35%
to
92%
reduction.
Chromium
TCLP
levels
actually
increased
as
a
result
of
treatment
from
<
0.05
to
0.27
mg/
L
before
treatment
to
0.19
to
0.32
mg/
L
after
treatment.
Initial
copper
TCLP
levels
ranged
from
1.4
to
9.4
mg/
L
and
were
reduced
by
90%
to
99%
to
0.06
to
0.10
mg/
L.
The
compressive
strength
of
the
final
waste
forms
ranged
from
760
to
1,400
psi
(
U.
S.
EPA,
1992).

Mitchell
et
al.
reports
using
silica
microencapsulation
for
the
treatment
of
aqueous
acid
rock
drainage
(
ARD),
which
contained
elevated
levels
of
aluminum,
arsenic,
copper,
iron,
nickel,
and
sulfate.
The
process
employs
a
proprietary
mixture
of
chemicals
referred
to
as
KB­
1TM,
which
includes
a
silica­
based
reagent
to
chemisorb
the
metals
from
the
aqueous
phase
into
a
solid
matrix.
The
sludge
generated
from
this
water
treatment
process
was
able
to
meet
TCLP
limits,
which
eliminated
the
need
to
dispose
of
the
material
as
a
hazardous
waste.
Evangelou
(
2000)
also
discusses
the
treatment
of
ARD
through
the
microencapsulation
of
pyrite
with
iron
phospate
or
silicate
binders.
Silicate
materials
were
found
to
reduce
the
leaching
of
sulfate
from
pyrite
wastes
relative
to
the
control
treatments
with
limestone
and
phosphate.

27
3.0
Cost
and
Vendor
Information
Table
3­
1
includes
a
summary
of
typical
cost
data,
along
with
vendor
information,
for
several
materials
used
for
the
macroencapsulation/
microencapsulation
of
hazardous
wastes.
Table
3­
1
also
includes
typical
costs
for
competing
technologies
for
mercury­
contaminated
hazardous
wastes
including
thermal
recovery,
acid
leaching,
and
vitrification.
However,
it
should
be
noted
that
both
thermal
recovery
and
acid
leaching
will
generate
highly
concentrated,
secondary
waste
streams
that
will
ultimately
have
to
be
immobilized
prior
to
disposal.
In
general,
vitrification
is
best
suited
to
low
volatility
metals
as
opposed
to
mercury
and
arsenic.
The
cost
data
presented
in
Table
3­
1
are
meant
to
provide
an
order­
of­
magnitude
cost
range
for
each
technology.
True
technology
costs
will
be
specific
to
the
waste
type,
waste
chemical
and
physical
properties,
and
the
levels
of
contaminants
in
the
waste.

28
Table
3­
1.
Summary
of
Cost
and
Vendor
Information
for
Encapsulation
and
Other
Treatment
Technologies
29
Technology
Developer/
Vendor
Estimated
Full­
Scale
Costs
Reference
SPSS
Brookhaven
National
Laboratory,
NY
$
2.88/
kg
or
$
1.31
per
lbs
Morris
et
al.
(
2002)

CBPC
Argonne
National
Laboratory,
IL
$
15.45
per
kg
or
$
7.00
per
lbs
DOE
(
1999a)

Polyethylene
(
on­
site
pour)
Envirocare,
UT
$
90
to
$
100
per
ft3
DOE
(
1998)

Arrow­
Pak
(
HDPE)
Boh
Environmental,
New
Orleans,
LA
880
drums
for
$
1,100,000
(
Hanford,
2002)

Ultra­
Macroencapsulation
System
Ultra­
Tech,
International,
FL
30"
dia,
40"
height
$
480
to
$
700
6'
x
6'
x
20'
$
20,000
(
Ultra­
Tech,
2002)

Polyester
Resin
SGN
Eurisys
Services
Co.,
Richland,

WA
$
11.52
per
kg
or
$
5.22
per
lbs
(
DOE,
1999b)

Synthetic
Elastomer
No
vendor
information
available
$
25
per
ton
of
used
tire
rubber,
4
wt%
in
treated
soil
Meng
et
al.
(
1998)

Polysiloxane
Orbit
Technologies,
Carlsbad,
CA
$
1,900
per
ft3
(
DOE,
1999c)

Sol­
Gels
Pacific
Northwest
National
Laboratory,

Richland,
WA
NA
(
DOE,
1999d)

Other
Technologies
Acid
Extraction
Environmental
Technologies
International,
Wyomissing,
PA
$
100
to
$
250
per
ton
Mulligan
et
al.
(
2001)

Cement­
Based
Stabilization/
Solidification
Various
$
16.37
per
kg
or
$
7.42
per
lbs
$
5,000
per
ft3
DOE
(
1999a)

DOE
(
1999c)

DeHg
®
Nuclear
Fuel
Services,
TN
$
8.48
per
kg
or
$
3.85
per
lbs
Morris
et
al.
(
2002)

Thermal
Recovery
Mercury
Recovery
Services,
New
Brighton,
PA
$
650
to
$
1,000
per
ton
Mulligan
et
al.
(
2001)

X­
TraxTM
Thermal
Desorption
Remediation
Technologies,
Tuscon,
AZ
$
100
to
$
600
per
ton
Mulligan
et
al.
(
2001)

Vitrification
Westinghouse
Science
and
Technology
Center,
Pittsburgh,
PA
$
400
to
$
870
per
ton
Mulligan
et
al.
(
2001),

(
U.
S.
EPA,
1997)

Note:
The
cost
data
presented
above
are
meant
to
provide
an
order­
of­
magnitude
cost
range
for
each
technology.
True
technology
costs
will
be
specific
to
the
waste
type,
waste
chemical
and
physical
properties,
and
the
levels
of
contaminants
in
the
waste.
30
4.0
Future
Development
and
Research
Needs
A
large
body
of
literature
exists
regarding
the
research
and
development
of
alternative
materials
to
conventional
Portland
cement
for
the
encapsulation
of
hazardous
metal­
containing
wastes.
SPC,
CBPC,
and
polyethylene
are
the
most
established
materials,
and
each
has
its
advantages
and
disadvantages
for
use
in
the
macroencapsulation
or
microencapsulation
of
mercury­
containing
hazardous
wastes.

Although
several
studies
were
noted
which
demonstrated
the
successful
encapsulation
of
high­
level,
mercury­
containing
wastes
with
SPC
and
CBPC,
the
body
of
evidence
for
competent
polyethylene
encapsulation
is
limited.
The
higher
temperatures
of
the
polyethylene
process
may
pose
some
difficulty
in
effective
encapsulation
of
these
wastes
due
to
the
volatile
nature
of
mercury
compounds.
A
better
understanding
of
the
long­
term
stability
of
final
waste
forms
may
be
needed
for
some
binder
materials.
In
general,
the
long­
term
stability
of
materials
encapsulated
with
SPC
or
CBPC
have
not
been
addressed,
except
for
encapsulated
mixed
wastes,
which
are
extensively
tested
under
NRC
protocols.
Improving
the
understanding
of
the
kinetics
of
low­
temperature
processes
such
as
SPC
or
CBPC
could
help
in
scale­
up
and
process
optimization.
Also,
a
better
understanding
is
needed
regarding
the
role
of
excess
sulfides
in
increasing
mercury
leachability.
In
addition,
the
performance
objectives
or
acceptance
criteria
for
macroencapsulated
wastes
could
be
standardized
to
provide
guidance
regarding
the
minimum
layer
thickness
of
the
barrier,
the
expected
long­
term
leaching
performance
of
the
final
waste
form,
the
target
compressive
strength,
and
the
tolerance
for
void
spaces
in
the
final
waste
form.

Currently,
few
full­
scale
commercial
applications
of
encapsulation
technologies
are
available;
however,
further
commercialization
and
technology
transfer
may
occur
if
the
demand
for
macroencapsulation
increases
as
a
result
of
changes
in
regulatory
requirements.
Both
SPC
and
CBPC
processes
have
been
patented,
but
licensing
of
the
technologies
has
generally
been
limited
to
one
or
two
companies
and
application
of
these
processes
at
the
industrial­
scale
is
limited.
The
Envirocare
facility
in
Utah
does
have
a
full­
scale
system
in
place
for
polyethylene
encapsulation.
In
addition,
the
use
of
pre­
manufactured
HDPE
containers
for
macroencapsulation,
as
allowed
under
the
U.
S.
EPA
alternative
debris
standards,
appears
to
offer
a
cost­
effective
solution
to
the
disposal
of
hazardous
waste
debris.
The
use
of
other
materials
such
as
synthetic
elastomers,
polyester
resins,
polysiloxane,
or
sol­
gels
appears
somewhat
promising,
but
relatively
few
studies
have
been
completed
to
date.
With
several
of
these
materials,
including
polysiloxane
and
sol­
gels,
it
appears
that
an
additional
chemical
stabilization
step
may
be
needed
when
elevated
levels
of
metals
are
present,
since
the
TCLP
criteria
for
mercury
and
chromium
were
not
met
in
initial
trails.
In
addition,
the
use
of
asphalt
for
encapsulation
is
most
likely
limited
to
contaminated
soils
with
only
low
levels
of
mercury
or
other
metals.
Because
of
the
varied
nature
of
industrial
wastes,
site­
specific
treatability
tests
will
most
likely
be
required
for
the
selection
of
the
most
appropriate
encapsulation
material.
The
selection
criteria
should
include
chemical
compatibility
of
the
waste
and
binder
materials,
final
waste
form
performance,
technology
implementability
(
e.
g.,
the
availability
of
processing
equipment
and
vendor
experience),
safety
and
health
issues,
and
project­
specific
estimated
costs.

31
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