1
CuO
As2O5
CrO3
Copper(
II)
oxide
Arsenic(
V)
oxide
Chromium(
VI)
oxide
Product
Chemistry
1.
Chemical
Overview
Chromated
Copper
Arsenate
(
CCA)
is
a
unique
wood
preservative
pesticide
in
many
ways:
First,
it
is
one
of
the
few
inorganic
wood
preservatives
and
second,
it
is
a
mixture
of
three
metals
which
are
the
actives
in
the
this
wood
preservative
and
the
metals
are
used
as:
chromic
acid,
copper
oxide
and
arsenic
acid.
The
Agency
has
decided
that
the
REREGISTRATION
ELIGIBILITY
DOCUMENT
(
RED)
for
CCA
will
cover
the
two
ingredients:
chromic
acid
and
arsenic
acid
but
in
addition,
the
following
compounds
will
also
be
part
of
the
product
chemistry
of
the
RED
document:
potassium
dichromate,
sodium
chromate,
sodium
dichromate,
arsenic
pentoxide,
arsenic
trioxide,
ammonium
arsenate,
sodium
arsenate
and
sodium
pyroarsenate.
Copper
oxide
is
not
part
of
the
RED
and
it
will
be
considered
in
a
later
science
chapter
and
RED.

There
are
a
number
of
CCA
formulations
in
the
market;
however,
it
was
agreed
that
this
RED
will
consider
only
CCA­
C,
which
has
a
specific
percent
of
three
metals
and
the
formulation
is
based
on
the
percent
oxides
of
these
metals.
Since
CCA
is
a
mixture
of
three
inorganics,
it
does
not
have
a
unique
chemical
name,
it
is
recognized
as
chromated
copper
arsenate.

Chemical
Name:
Chromated
Copper
Arsenate
Common/
Trade
Name:
CCA­
C
Chemical
Family:
Inorganics
CAS
Registry
No:
N/
A
Manufacturers:
Osmose
Wood
Preserving,
Inc.,
Hickson
Corporation,
Chemical
Specialities,
Inc,
2
2.
Manufacturing
Processes:

I
Chromated
copper
arsenate
(
CCA­
type
C)

This
mixture
is
prepared
by
the
standard
set
by
American
Wood
Preservatives
Association
(
AWPA).
The
active
ingredients
in
CCA­
type
C
are
required
to
have
the
following
composition:
CrO
3
(
chromium
in
+
6
oxidation
state):
47.5%
CuO
(
copper
in
+
2
oxidation
state)
18.5%
As
2
O
5
(
arsenic
in
+
5
oxidation
state)
34.0%

Starting
reagents
for
these
ingredients
are
selected
from:
Arsenic(
V)
as
arsenic
acid
or
sodium
arsenate,
Chromium(
VI)
as
potassium
or
sodium
dichromate,
Copper(
II)
as
copper
sulfate
or
basic
copper
carbonate
or
copper
hydroxide.
Prior
to
the
manufacture
of
CCA­
C,
the
third
ingredient
arsenic
acid
in
itself
is
manufactured
by
a
batch
process
1
CCA­
C
is
manufactured
by
a
batch
process.
Typically,
in
a
mixing
tank
chromic
acid
and
arsenic
acid
are
added
and
slowly
copper
oxide
is
added
as
the
addtion
of
copper
oxide
is
an
exothermic
process.
Batch
temperature
is
maintained
around
75
o
C.
The
duration
of
each
step
in
the
batch
process
depends
on
the
size
of
a
batch.
Each
batch
is
allowed
is
allowed
to
settle
in
a
settling
tank
for
12
hours
to
eliminate
the
insoluble
impurities.
The
product
is
filtered
and
transfered
to
delivery
vehicles.
Each
batch
is
analytically
analyzed
for
individual
as
well
as
combined
total.
2
Chromic
acid
is
made
by
reacting
sodium
bichromate
liquor
and
sulfuric
acid
at
elevated
temperatures.
A
crude
crystal
is
filtered
off
which
contains
chromic
acid/
sodium
bisulfate,
sulfuric
acid
and
water.
The
crude
crystal
is
melted
and
chromic
acid
and
sodium
bichromate
layers
separate
out.
Chromic
acid
is
sent
to
a
series
of
rolls
to
convert
the
product
into
flakes
and
these
flakes
(
99.9%)
are
packaged.
3,4
Chemical
reactions:

2Cr2O3
+
2Na2CO3
+
3O2

2Na2CrO4
+
CO2

2Na2CrO4
+
H2SO4

Na2Cr2O7
+
Na2SO4

+
H2O
Na2Cr2O7
+
2H2SO4

2CrO3
+
2
NaHSO4
+
H2O
3
A.
Arsenic
Acid:

Arsenic
acid
is
prepared
by
a
batch
Process:
99%
pure
Arsenic
(
III)
oxide
(
As
2
O
3
)
is
fed
through
a
variable
speed
rotary
valve
from
a
weigh
tank
into
a
stainless
steel,
jacketed
reactor.
This
reactor
is
also
fitted
with
S.
S.
ducts
for
collector
of
noxious
gases
(
like
NO
x)
.
A
known
volume
of
preheated
(
about
55
o
C
)
nitric
acid
(
46%)
is
then
charged
into
the
reactor.
The
reaction
is
carried
out
in
the
presence
of
a
catalyst
KI
(
0.402
g
of
KI/
ton
of
arsenic(
III)
oxide
diluted
to
5
gallons).
No
x
gases
(
NO
and
NO
2
)
are
collected
and
used
to
generate
nitric
acid.
Arsenic
acid
obtained
is
76­
77%
pure.
1
Chemical
reaction:

As2O3
+
2HNO3
+
2H2O

2H3AsO4
+
NO
+
NO2
B.
Sodium
arsenate:

The
manufacturing
process
for
sodium
arsenate
is
similar
to
arsenic
acid:
In
a
typical
batch
process
,
112.3
lbs.
of
arsenic
acid
are
added
to
41
lbs.
of
sodium
hydroxide
in
the
presence
1782
lbs.
of
water.
The
neutralization
reaction
is
complete
in
about
twenty
minutes.
5
Chemical
reactions:

H3AsO4
+
2NaOH
+
H2O

Na2HAsO4
Na2HAsO4
+
NaOH

Na3AsO4
+
H2O
C.
Arsenic(
III)
oxide:

Arsenic
(
III)
oxide
is
not
manufactured
by
the
registrants
and
is
available
from
various
manufacturers.

D.
Sodium
and
potassium
bichromate
(
dichromate):

Either
one
of
these
chemicals
can
be
the
starting
material
for
making
chromic
acid
which
is
one
of
the
ingredients
for
the
manufacture
of
CCA
(
type
C).

Sodium
bichromate
is
manufactured
by
feeding
a
mixture
of
dry,
pulverized
chrome
ore,
soda
ash,
lime
and
dried
recycle
residue
into
a
kiln
at
elevated
temperatures.
The
resultant
roast
is
treated
with
water
and
water
soluble
sodium
chromate
is
removed
from
the
mixture
solution.

Sodium
chromate
liquor
is
filtered
and
polished
to
remove
the
impurities
and
used
as
feed
along
with
sulfuric
acid
to
the
evaporators
where
sodium
bichromate
liquor
is
made.
Crystals
of
sodium
bichromate
are
obtained
by
cooling
the
hot
concentrated
liquid.
3
4
E.
Arsenic(
V)
oxide
(
Arsenic
pentoxide).

Obtained
from
other
manufacturers.

Product
Chemistry
Assessment:

Arsenic
Acid:
5
The
physico­
chemical
characteristics
are
described
as
follows:

Chemical
Name:
Arsenic
acid
Chemical
Formula:
H
3
AsO
4
CAS
#:
7778­
39­
4
Formula
Wt.:
142.0
g
Color
Colorless
Odor:
None
Physical
state:
Liquid
Melting
Point:
n/
a
Boiling
Point:
104
o
C
Specific
gravity:
1.9
Vapor
pressure:
n/
a
Dissociation
constant
K
a:
n/
a
pH:
1.8­
1.9
(
1%
solution)
Stability:
Stable*

*
Arsenic
acid
is
incompatible
to
zinc,
any
galvanized
metal,
aluminum,
magnesium
and
hydrogen
gas.
It
reacts
with
all
these
metals
and
produces
arsine
(
AsH
3)
which
is
highly
toxic.

K
OC:
n/
a
Solubility:
slightly
soluble
5
Arsenic(
III)
oxide:
5
Physico­
chemical
characteristics:

Chemical
Name:
Arsenic(
III)
oxide
Chemical
Formula:
As
2
O
3
Formula
Wt.:
197.84
g
CAS#:
137­
53­
3
Color:
White
Physical
state:
Solid
Specific
gravity:
3.74
Solubility:
3.7
g/
100
cc
water
,
20
o
C
Melting
Point:
312
o
C,
sublimes
at
193
o
C
Vapor
pressure
8.5
x
10­
10
mm
Hg
Stability:
Stable
Cr(
VI)
oxide:
4
Physico­
chemical
characteristics:

Chemical
Name:
Chromium(
VI)
oxide
Chemical
Formula:
CrO
3
Chemical
Family:
Metal
oxide
Formula
Wt.:
100.0
g
CAS#:
1333­
82­
0
Color:
Dark
red
crystals
Physical
State
Solid
Specific
gravity:
2.70
Solubility:
62.5%,
20
o
C
Melting
Point:
196
0C
Vapor
Pressure;
n/
a
Stability:
Stable.
K
OC:
n/
a
6
Sodium
dichromate:
3
Physico­
chemical
characteristics:

Chemical
Name:
Sodium
dichromate
dihydrate
Common/
Trade
Name
Sodium
bichromate
dihydrate
Chemical
Formula:
Na
2
Cr
2
O
7
.
2H
2
O
CAS#:
7789­
12­
0
Color:
Bright
orange
crystals.
Ruby
red
liquor
Formula
Wt.
298.00
g
Melting
Point
(
anhydrous)
356
o
C,
and
decomposes
at
400
o
C
Note:
Hydrated
salt
loses
water
of
hydration
at
84.6
O
C
Density:
2.35
g/
cc
at
25
o
C
Bulk
Density:
Loose:
77.0
lb/
ft3
Tapped:
90.0
lb/
ft3
Solubility:
74%
at
25
o
C
Note:
The
process
of
dissolution
is
endothermic.

Stability
(
in
air):
At
25
o
C,
it
deliquesces
pH:
3.0­
4.6
(
conc.
dependent),
25
o
C
Boiling
Point:
n/
a
Vapor
Pressure:
n/
a
Note:
Aqueous
solution
of
sodium
bichromate
(
dichromate)
is
dark
red
and
a
pH
of
4.00;
its
boiling
point
varies
with
the
concentration
of
solution
as
69%
solution
boils
at
119
o
C
and
85%
solution
boils
at
127
o
C.
Similarly,
specific
gravity
of
69%
solution
is
1.72
while
that
of
85%
is
1.95.
7
Arsenic
pentoxide:
4
Physico­
chemical
characteristics:

Chemical
Name:
Arsenic
pentoxide
or
Arsenic(
V)
oxide
Trade
name/
common
Name:
Arsenic
acid
anhydride
Chemical
Formula:
As
2
O
5
Formula
Wt.
:
229.84
g
CAS#:
1303­
28­
2
Appearance:
Amorphous
lump
or
powder,
deliquescent
Solubility:
Very
soluble
in
water
and
slowly
produces
arsenic
acid.
Specific
Gravity:
4.32
Melting
Point:
315
o
C,
decomposes
Boiling
Point:
n/
a
Vapor
pressure:
n/
a
The
registrants
submitted
data
on
pH
measurements
of
various
formulations
of
CCA­
C:

Product
Measured
pHa,
b
*
1.
CCA­
C:
50%
1.0056
*
2.
CCA­
C­
60%
0.677
*
3.
CCA­
C:
70%
0.5558
*
4.
CCA­
C:
72%
0.4109
*
5.
Special
K­
33
1.91010
(
Preservative)
*
6.
CCA­
B:
K­
33­
B
0.98011
(
40%)

Note:
a.
The
pH
meter
readings
were
obtained
usually
with
1:
5
dilution
of
the
concentrates
with
water.

b.
The
pH
meter
readings
are
the
average
of
the
duplicates.

*
Represents
a
concentrate
8
Bibliography
for
Product
Chemistry
Science
Chapter
MRID
CITATION
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Muchow,
Terry.
1989.
Arsenic
Acid
Product
Chemistry
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Guideline
Reference
No.
61­
1.
Guideline
Reference
No.
61­
2.
Guideline
Reference
No.
61­
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Division,
Osmose
Wood
Preserving,
Inc.
January
25,
1989.

40992002
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Terry.
1989.
Sodium
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Product
Chemistry
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Reference
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61­
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Guideline
Reference
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61­
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Guideline
Reference
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61­
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Osmose
Wood
Preserving,
Inc.
January
25,
1989.

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Terry.
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K­
33­
C
(
50
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Wood
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EPA
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Wood
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January
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1989.

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61­
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pH
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63­
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70
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72
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prepared
by
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1991.
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63­
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prepared
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for
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Wood
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Inc.
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1991.

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60
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