DES-UNH POLLUTION PREVENTION PARTNERSHIP
INTERNSHIP PROGRAM FINAL REPORT
Project Title:
Intern:
Facility:
Contact Person:
Sulfates
Katherine Powers
Home: 46 County Rd
Amherst, NH 03031
(603) 673-7006
Work: Tel: (603) 883-2885 x4168
Fax: (603) 880-0561
Email: kpowers@hadco.com
HADCO Corporation
21 Flagstone Dr.
Hudson, NH 03051
Lee R. Wilmot
Corporate Safety
Health & Environmental Manager
Tel: (603) 898-8010 x2424
Fax: (603) 890-1298
Email: lwilmot@hadco.com
Executive Summary:
In order to reduce the sulfate loadings in HADCO-Hudson's
wastewater, the chemistries responsible for the elevated levels
(Ardrox PC-7076S and Cobra Etch) must be substituted, reduced or
treated.
Several technologies were considered to reuse the
chemistries, but reducing the amounts of chemicals used seems like
the best option.
By switching from Ardrox PC-7076S to PC-7077F
and PC-7077, the acceptable copper loading in the bath will
increase requiring fewer adds. New lines in the preclean process
will also decrease the amount of Ardrox chemistry used by
utilizing a feed and bleed system and reducing drag-out.
Regenerating the Ardrox through diffusion dialysis, acid
sorption, electrodialysis, filtration, or crystallization is not
possible. Either the sodium persulfate is reduced or the copper
is not removed from the solution.
IX resins are still being
tested, but the initial tests had poor results.
Producing a usable concentrated sulfuric acid from the spent
baths is another option.
Membrane electrodialysis is one
technology that is being tested. Filtration will produce a dilute
sulfuric acid; US Filter is looking into concentrating it.
In
order to use the sulfuric acid it should be about 70%
concentrated.
Most vendors are unsure if they can achieve this
high concentration.
Using calcium carbonate to precipitate calcium sulfate is
another option to reduce the sulfates. This method would create
thousands of pounds of sludge a year. Shipping the spent acid out
for treatment is also a possibility but a costly one.
Introduction:
HADCO is one of the largest printed circuit board
manufactures in the world.
In preparation of increasing
production and chemical usage, HADCO must make sure they comply
with their current air and water permits. The sulfate loadings in
the wastewater may exceed HADCO's water discharge permit if
chemical usage increases. My project this summer was to address
this problem and find a solution.
Two of the major sources of sulfates at HADCO-Hudson are the
preclean and oxide lines.
In preclean the raw material, copper
clad laminate, is cleaned to allow proper adhesion of the
photoresist material in the following process. The cleaning
process involves the application of an acid (Ardrox PC-7076S) to
remove a thin protective chromate layer and a thin layer of
copper.
The copper is removed to make the surface uniform and
rough for the adhesion of the photoresist.
The copper clad
laminate is then rinsed and dried.
To prevent corrosion of the copper traces, the exposed copper
is oxidized. The cores are first cleaned in soap and then rinsed.
An acid (Cobra Etch) removes a thin layer of copper from the
traces to eliminate corrosion, and the cores are rinsed.
After
being dipped into sodium hydroxide, the oxide is applied and the
cores are rinsed again.
Currently the spent Ardrox PC-7076S and Cobra Etch, which are
high in sulfates, are used to make reagent for the ROMAR (Recovery
of Metal and Recycle) wastewater treatment process.
Goals/objectives:
The objective of this project was to research HADCO's options
for reducing the sulfate loadings and perhaps implement one of
these methods. Ideally the sulfate loadings could be reduced by
chemical substitution or a reduction of chemical usage. Treatment
technologies for the spent chemistries were also investigated.
Approach/methodology:
The sulfate issue was approached in several different ways.
First the major sources of the sulfates, 50% preclean and 50%
oxide, were defined. Then the amount of sulfates due to decants
from the bath and drag-out in the rinsewater were determined.
Approximately 25% of the sulfates from the oxide line are from
drag-out in the rinsewater.
Since the sulfates were distributed 50/50 over the preclean
and oxide lines, we first looked into where HADCO could save the
most money; preclean.
Reducing drag-out and treating the
rinsewater and Cobra Etch on the oxide lines were also
investigated.
Chemical
substitution,
chemistry
reduction,
chemical regeneration, and sulfate removal were all approaches
that were researched.
Chemical usage/equipment needs:
The Ardrox PC-7076S solution is made up of 6% sulfuric acid,
9% sodium persulfate, and <1% fluoboric acid.
The fluoboric is
used to remove the protective zinc and chromate film layer, and
the sulfuric and sodium persulfate etch the copper away. When the
copper level in the bath reaches 3.5 oz/gal or the etch rate drops
below 7.25 microinches/minute, some of the solution is decanted
out and an add of fresh Ardrox is made. Approximately 600 gallons
of Ardrox is added each week.
In the oxide line, the Cobra Etch is made up of 17% sulfuric
acid and 2% hydrogen peroxide.
The Cobra Etch passes through a
chiller where some of the copper sulfate is crystallized out. The
copper loading in the bath is between 4 and 7 oz/gal. The etch
rate determines when solution is decanted out and an add is made.
Concentrated sulfuric acid (74%) is added to replenish the bath
and to reduce the amount decanted. 73 gallons of Cobra Etch are
decanted each week.
Releases/ Wastes generated at the facility:
The wastes generated from the preclean process are spent
Ardrox solution and rinsewater.
The spent Ardrox solution
contains copper sulfate, sodium persulfate, sulfuric acid and
sodium sulfate.
In the oxide line, copper sulfate, rinsewater,
and spent Cobra Etch containing sulfuric acid, copper sulfate and
peroxide are all wastes.
As stated above, these corrosive acid wastes are used to make
up the reagent for ROMAR the wastewater treatment process.
Hydrochloric acid could be used instead of sulfuric to make up
this reagent.
Work accomplished/project results:
Chemical Substitution:
Chemical substitution on the preclean line was attempted.
The best option is another Ardrox chemistry which separates the
fluoboric (PC-7077F) from the sulfuric and sodium persulfate (PC7077). Separating these would allow a higher copper loading to be
maintained in the sulfuric bath requiring it to be changed less
often.
This new chemistry has not been tested at HADCO, but a
trial will take place when the new lines are installed in Hudson.
Switching to PC-7077 could reduce the overall sulfate loadings in
the wastewater 15%.
Pumice, peroxide, ferric nitrate and peroxidi-sulfuric acid
were also looked into as possible substitutes for the Ardrox
chemistry. Pumice is hard to handle and creates a lot of waste.
Peroxide would require a rinse tank after the fluoboric acid to
eliminate contamination. Since HADCO's new lines do not have an
extra tank this is not a viable option, but it is still being
looked into. Ferric nitrate was the chemistry that Alpha Metals
used before sodium persulfate.
The sales rep from Alpha Metals
said they switched because the persulfate was easier to control.
Peroxidi-sulfuric acid is similar to sodium persulfate except it
has two hydrogens instead of sodiums. The chemist at Alpha Metals
is still researching this possibility.
Ardrox Regeneration:
Several technologies were investigated to reuse the spent
Ardrox solution.
Crystallization would have been the easiest
option, but the copper sulfate wouldn't crystallize out of the
Ardrox PC-7076S. It is unclear if the chemistry of the bath would
not allow the copper sulfate to form crystals or if the copper
loading was simply not high enough. Circuit Chemistry Equipment
and Swenson, both crystallizer vendors, have neither dealt with
nor heard of copper sulfate being crystallized out of sodium
persulfate.
The lowest copper level they'd ever achieved in
sulfuric peroxide was 1.5 oz/gal; slightly lower than the level
the Ardrox bath is maintained at.
Electrowinning, electrodialysis, and ion exchange (acid
retardation) would reduce the persulfate rendering the Ardrox
solution unusable.
Acid sorption and diffusion dialysis would
remove the copper sulfate and the sodium persulfate because they
are both metal salts.
These technologies would leave a very
dilute sulfuric acid. Neither ultra nor microfiltration will be
able to remove the copper sulfate from the sulfuric/persulfate
solution because the sodium persulfate molecule is larger than
copper sulfate. Reverse osmosis would remove the water and leave
a concentrated spent solution. Ardrox PC-7076S is too acidic to
use reverse osmosis.
Joe Landers from Compliance and Recycling Inc. (CARI) is
testing two resins for an ion exchange technology. These resins
should remove the copper from the spent Ardrox and leave the
solution active. Initial testing on these resins showed a 15-20%
removal of copper, but the etch rate of the treated solutions were
2.29 and 6.96. These etch rates are well below the minimum 7.25
leading me to believe the resin is oxidizing the sodium
persulfate.
Further testing needs to be done to confirm these
results. The etch rate of the initial spent solution is unknown.
Remove sulfates from spent Ardrox:
If the sulfates could be removed from the spent Ardrox bath
in the form of sulfuric acid, the sulfuric could be used on the
oxide line to replenish the Cobra Etch. Reusing the sulfates in
this way would reduce the amount sent to waste treatment.
Ion
exchange to remove sulfates would not work in the case of the
Ardrox or Cobra Etch because the sulfate loadings are so high the
resin would have to be regenerated too frequently.
Membrane electrodialysis is one possible option.
This
technology would reduce the persulfate into two sulfate and sodium
ions, plate out the copper, separate the sodium from the sulfates,
and concentrate the sulfuric acid stream.
The copper could be
sold for recycling ($0.70-$1/lb), the sulfuric acid reused, and
the caustic stream sent to waste treatment. Testing is currently
being
done at ELTECH Research Corporation in Ohio.
There has been a
problem with the material of the cathode.
Ardrox is not
compatible with titanium; 316 SS would be a material of choice
according to HADCO's engineers.
Another factor is how
concentrated the sulfuric acid can be. In order to use it at the
Hudson facility the sulfuric should be about 74% concentration.
Oxide line (Cobra Etch and rinse water):
Currently, the microetch on the oxide line is being chilled,
and the copper sulfate precipitates out of solution.
This
prolongs the life of the bath, but adds still need to be made
because the sulfuric concentration decreases.
When production
increases, HADCO may need to increase the crystallization rate so
that the copper loading stays at 4-7 oz/gal.
If the copper
loading increases, the etch rate will decrease and more adds will
need to be made.
Since the Cobra Etch is already being regenerated, treating
or decreasing the decants or reducing the amount of drag-out were
the main focus on this line.
Although an additional hoist is
being added to this line, it is not to allow a longer drip time
but to increase the through put. A longer drip time would cause
oxidation and decrease the quality of the boards.
The rinse water is being tested with membrane electrodialysis
at ELTECH.
The initial testing went well.
The peroxide was
destroyed,
copper
plated
out,
and
the
sulfuric
slightly
concentrated to 1.1%.
As stated above the concentration of the
sulfuric acid will need to drastically increase for this to be a
viable option.
Other Options:
Treating the Ardrox, Cobra Etch, or rinse water with lime
(calcium carbonate) to precipitate out calcium sulfate would
reduce the amount of sulfates in wastewater.
In an experiment
this method drastically reduced the sulfates; in one case 90%.
Unfortunately large amounts of calcium sulfate were produced that
would need to be shipped out with the F006 sludge. Using PC-7077
at 137K core square feet, the estimated sulfate loading will be
672 mg/L.
In order to decrease the loading to 500 mg/L with
calcium carbonate, 770 lbs lime would be required per week,
producing 954 lbs. of calcium sulfate per week or 24.8 tons/year.
This method would reduce the sulfates, but is not a pollution
prevention solution.
The cost of shipping the spent Ardrox and Cobra Etch out for
disposal/recycling is also being investigated.
Pollution prevention benefits:
The pollution prevention benefits depend on the method used
to reduce the sulfate loadings.
A reduction in the amount of
chemistry, regenerating the chemistry, or producing a usable
sulfuric acid would all be benefits.
New lines in the preclean
process may also be a benefit if they decrease the amount of dragout in the rinsewater.
References:
Compliance and Recycling Inc.
Joe Lander/ Bill Matheson (508) 670-1448
Alpha Metals
Jim Noble/ Jane Reed (603) 893-8700
Larson Technologies
Bob Larson (603) 895-6262
Crystallizers:
Swenson
Lou Laposa (708) 210-5069
Circuit Chemistry Equipment
Jim Cran (612) 476-2025
Diffusion Dialysis: Baker Brothers
Tim Howard (617) 344-1700
Pure Cycle Environmental Technology
Dan Bailey (413) 283-8939
3400
Acid Sorption/ IX ion retardation: Eco-Tec
Paul Paganin
(905)
831-
Membrane electrodialysis: Memtek
Dave Hill (508) 667-2828
ELTECH Research Corporation
Jeries Bishara (216) 357-4021
Filtration:
US Filter
Bert Stultz (412) 772-0044