Document ID: EPA-HQ-RCRA-2004-0009-0011
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2005-05-10T04:00Z

Heritage
Conference
Call
Thursday,
October
30,
2003
2:
30
PM
Conference
call
with
Dr.
Ralph
Roper:
Attendees:
Juan
Parra
Hugh
Davis
Q1:
How
does
pH
affects
the
solubility
in
raw
Guardian
EP
dust
Data:
shows
that
minimum
solubility
is
maintained
at
pH
11.5
The
calcium
content
of
the
EPA
dust
ranges
from
22
to
33%
due
to
lime
added
as
a
treatment
reagent
in
the
EP
gas
cleaning
process
at
Guardian.
The
solubility
data
is
the
above
chart
is
most
likely
governed
by
the
solubility
of
calcium
selenate
and/
or
calcium
selenite.

Chemistry:
Selenium
is
an
oxyanion­
forming
element.
Selenium
is
found
in
high
concentration
in
leachate
in
alkaline
media.
Under
oxidizing
conditions,
the
oxyanionic
species
selenite
(
Se
O32­)
and
selenate
SE042­
are
the
predominant
forms
of
Se.
The
Se
species
HSe­
and
H2Se
are
only
stable
under
strong
reducing
conditions.
Cement
additives
such
as
blast
furnace
slag
may
generate
reducing
conditions.
Selenite
is
considered
to
be
the
less
mobile
species.
It
forms
inner
sphere
complexes
with
surface
functional
groups
under
neutral
and
acidic
conditions.
.
In
cement
pore
water,
CA
occurs
in
millimolar
concentrations,
CA
Se03
limits
the
solubility
of
selenite.
Selenate
sorbs
via
weakly
bonded
outer
sphere
complexes
and
has
lower
affinity
with
for
oxide
surfaces.

Q2:
Why
use
Portland
cement
as
a
reagent
for
stabilization
of
Selenium?

The
mayor
hydration
products
in
cement,
calcium
silicate
hydrate
(
CSH)
and
calcium
(
sulfo)
aluminate
hydrate
is
important
for
sorption
and
substitution
for
contaminants.

High
pH:
At
high
pH
(
low
[
h+]),
cation
(+)
adsorption
is
favorable
and
anion
adsorption
is
limited
on
the
negatively
charged
surface
oxide
sites.
Substitution
for
SO42­
in
etringite
and
monosulfate
is
suggested
to
be
the
most
efficient
sorption
reaction
for
several
oxyanions,
including
SeO42­
and
H2O
located
in
the
interchannels,
while
monosulfate
in
the
intralayers.
Sulfate
substitution
in
ettringite
and
monosulfate
have
been
reported
for
selenate.

The
selenite
sorbtion
by
ettringite
was
around
25%
uptake
from
solution,
five
times
higher
than
the
sorbtion
of
selenate.
Selenate
had
up
to
80%
uptake
from
solution
by
sorption
on
monosulfate,
twice
as
well
as
selenite.

Q3:
What
alternative
management
methods
for
the
Guardian
waste
were
evaluated?

From
January
 
March
2003,
Heritage
explored
several
approaches
for
managing
the
selenium
bearing
waste
generated
by
Guardian.
Heritage
has
performed
nearly
200
TCLP
tests
on
this
particular
wastestream
using
a
wide
variety
of
stabilization
concepts
but
none
appeared
capable
of
achieving
the
5.7
mg/
L
TCLP
criterion
reliably.
Although
Heritage
continues
to
explore
and
test
alternative
stabilization
techniques
for
this
wastestream,
a
workable
method
is
not
available
at
the
current
time.

Selenium
recovery
by
hydrometallurgical
recovery
was
a
treatment
option
that
has
been
evaluated
by
Heritage
in
their
variance
petition.
Several
other
methods
for
extracting
selenium
out
of
waste
were
evaluated
and
various
methods
for
converting
the
extracted
selenium
to
a
useful
product
were
also
tested.
Previous
attempts
to
recover
materials
from
relatively
low
volume
wastes
suggest
that
financial
viability
was
a
concern."