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Letter 5040
Chemistry of nitric acid solutions -
formation of nitrates?
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Hello,
I am posting this letter for two reasons: 1) to ask a question and
2) to notify the readers of this issue. My company provides
environmental consulting services to several clients, a number of
which perform metal finishing operations including pickling, acidic
or alkaline pre-cleaning, etching, galvanizing, chromate coating,
manganate coating, painting, powder coating, etc. The bulk of our
services are in performing Toxic Release Inventory (TRI) Reporting
(aka SARA 313 or EPCRA reporting) under Community-Right-to-Know. TRI
reporting is based on a specific list of chemicals and chemical
compounds deemed to be toxic and which regulated facilities must
consider (and report) if thresholds are met.
For the 1995 reporting year, the chemical compound category Water
Dissociable Nitrates was added to the list of chemicals to be
considered (note: only reportable when in aqueous solution). In June
1999, the USEPA published guidance to assist with determining if
water dissociable nitrates must be reported. In March 2000, the USEPA
announced an enforcement action to ensure that water dissociable
nitrates are being reported as appropriate. The enforcement action is
initially predicated on any facility that reported treating nitric
acid on site in excess of 18,000 lbs/yr (In essence, the USEPA
believes such a facility "coincidentally manufactured" sufficient
water dissociable nitrates to meet or exceed the threshold for
reporting.) One of our clients actually received a letter under this
enforcement action asking them to "show cause" why they did not
report water dissociable nitrates and/or to admit that they should
have. This letter also states the USEPA believes that a facility
which submits a report for nitric acid showing minimal releases
(including on site treatment) may be in violation (should have
releases, treatment, or recycling).
The USEPA's guidance does provide some information on this issue,
however, we do not believe the examples adequately portray the
chemistry involved in nitric acid streams in metal finishing
operations, as the examples basically assume a nitric acid and water
only solution treated with sodium hydroxide (i.e., the examples do
not account for metal ions, other acids such as HF or sulfuric, or
the use of polymers as flocculants).
So much for the dissemination of information part...especially if
this issue seems familiar to your facility.
My question, probably pretty obvious by now, is whether there is
any solid information available concerning the chemistry of nitric
acid and/or nitrates in metal finishing operations and/or the
wastewater treatment thereof. What we have used in the past (prior to
the USEPA's publishing of this guidance) is a qualitative statement
from a wastewater treatment text that when a nitric acid stream which
contains metals is neutralized and subject to polymer addition, the
bulk of the nitrates will form metal complexes and precipitate out of
solution (water dissociable nitrates are only reportable in aqueous
solution).
Given the USEPA's decision to concentrate on this issue, we would
like to use something more substantial if possible. For some of our
clients, the application of the estimation calculations in the
USEPA's examples is sufficient to demonstrate that any nitrates
formed would not meet the applicable threshold (note: the USEPA's
guidance does not consider solubility, although in the case of sodium
nitrate it should be considered because it is only partially
soluble).
Another piece of information we have come across is that it is
possible that a significant portion of the nitric acid is consumed in
the metal finishing operation and forms NO, water and the appropriate
metal oxide (iron, zinc, chromium, etc. depending on the surface
chemistry of the metal being finished), thus reducing the amount of
nitric acid available to form nitrates.
Of course, if the available information suggests that nitrates are
in fact formed, then we will advise our clients to report them...but
the biggest mental stumbling block that I keep coming back to is that
none of our clients are required to monitor for nitrogen and/or
nitrates is their discharge streams (some are NPDES regulated and
some are POTW regulated). It would seem to me that if any of these
facilities are discharging 2,000 lb/month of nitrates, they would
already be required to monitor for and stay within certain limits of
nitrogen and/or nitrates?
Lastly (if you have read this far), I would like to say Kudos to
your organization for providing this forum. I scanned through quite a
bit of your site before deciding that my particular issue was not
previously addressed and found this site very informative. Some of
the material discussed I have previously picked up through
discussions with our clients and some information was new to me.
Thank you.
Patricia L. Steffan
- Pittsburgh, PA, USA
Most of the nitric acid would end up as water soluble nitrates,
so, yes, I would recommend that the plater admit that it should have
been reported.
You are opening a Pandora's box to ask why a plater might not be
reporting Nitrous oxides to other regulatory agencies. It is NOT
because no one else is concerned with Nitrous oxides. You are
supposed to report them, as I read in any air pollution permit I have
ever seen. We know that nitrous oxide is a major pollutant causing
smog and respiratory problems.
I wish I had a dollar for every plater who is discharging
unreported NOx from their general ventilation fans and fume hood
scrubbers, especially those who bright dip aluminum. How about the
plater or finisher who passivates stainless steel in chromic/nitric
solutions? Some NOx is being formed in that reaction.
Estimating the release of NOx: If someone is dipping metal into a
solution of nitric acid, especially when you can see the brown Nox
fumes leaving a tank, you know that some NOx is being formed. I
believe that NOx should then be estimated and reported to the
governing agency. The amount of nitrates converted to NOx is not
100%, it is probably not 10%; How about estimating the amount of NOx
by estimating the amount of metal being removed during a bright
dip,(measured in tenths of a mil), multiplying by an estimate of the
surface area of the part, and calculating the NOx from the reaction
occurring during the bright dip. The reaction is somewhere in the
plating literature.
I used this method when writing an air permit for a finishing
company, located in New Jersey, and the application was accepted as
written.
The key is to estimate the amount with a chemical equation, and
some production based unit. It is quite reasonable to an engineer if
you tell her that I process 1500 square feet of aluminum, I remove
0.00001" from every square foot, and the metal removed weighs so many
grams, and so many grams will react with so many grams of nitric
acid, and the volume from so many grams of NO, at STP, is so many
liters, etc.
To this very day, our electroplating community, with the blessings
of the American Electroplaters Society and their Government Relations
department (committee, Lobby, whatever), instead of trying to
estimate the Pollutant of the Month for the EPA, so the EPA can look
at it and forget it, starts a campaign to discredit the EPA for even
daring to look in our direction for that pollutant. Why do we platers
think that we know more about epidemiology than the people who are in
that business? If we are so good at it, we should quit our jobs and
go into it full time, and show everybody how to do it. It was said
best at a Garden State Electroplaters Society, when we complain that
the cost of pollution control is too much, we just become "The Greedy
Plater" who is not happy to add the cost of control to his product.
Why else would be so afraid to estimate the amount of the pollution
for the EPA?
Thank you, tom
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You should be aware that nitrates are only slightly consumed
during use (those nasty brown fumes coming off nitric strippers,
etc.). Nitrates are probably also the most soluble of all salts
encountered in finishing operations, and it is extremely unlikely
that they are removed during conventional precipitation treatment.
Given these facts, the nitric acid added to any process will most
likely show up in the effluent from that process with little net
loss.
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Bill Vins
microwave & cable assemblies
Mesa (what a place-a),
Arizona
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.
As for the technical elements of the question, I suspect that Bill
is right on target and your question is answered, Patricia.
Logic mode off, vent mode on . . .
Tom is not entirely wrong, but since he asks rhetorical questions,
I'll respond to them.
The main objective of a plater is to stay in business and make
money, which requires fighting to minimize unreasonable regulations
and reporting requirements. The main objective of the EPA is
self-perpetuation and enlargement. The main objective of the
Government Relations lobbying group is also self-perpetuation and
enlargement. Think about what makes a man or woman break into a cold
sweat: loss of their livelihood, and you'll have to agree about
everyone's "main objective".
So much for the "Common Sense Initiative" hot air.
I'll give Tom two reasons a plater "would be so afraid to estimate
the amount of the pollution for the EPA":
- the first is self-incrimination (I am sure that he doesn't
invite traffic cops to follow him around everywhere he drives);
- the second is the sure & certain knowledge that the moment
platers willingly supply this requested information, the
self-perpetuation aspect of the EPA will mean that they must start
right in on regulations and reporting requirements for the next
thing.
The problem is not that platers think that the experts they hire
"know more about epidemiology" than the experts that the EPA hires.
The problem the refusal of some people to see that the EPA is not all
goodness and light -- it too is staffed with humans whose principal
interest is regulation as a means to grow their empire.
In the end it may well be that reporting of water soluble nitrates
is useful and epidemiologically correct. Who knows, but I doubt it
because the EPA has been regulating platers element by element, one
after the other, since 1974 -- and is only now getting to nitrates
some 26 years later; it is completely appropriate to consider the
possibility that they may be regulating way beyond the point of
diminishing returns, and that their main incentive may be concern
about keeping themselves employed more than real concern about
environmental damage to POTWs from nitrates in plating shops.
Vent mode off, smiley mode on . . . . Cheers!
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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