Citric Acid - Is it Technically a Passivating Chemical or Just a Chelator?

I'm no expert either. Sounds like a cleaning process........not even that fancy. You could probably do it with vinegar. It'll be interesting to hear what the experts say.

Hey - what are you doing in this section - thought you were an electrical expert?

So far the experts here are saying about what you can find if you Google the question. Some say it is only a fancy cleaning process, and some say it does remove some metals from the surface matrix, thus making it a surface treatment and throwing us into a classification as a metal finishing process. So far no real hard numerical data. I thought that a process that has been used for 70 years would have a wealth of data by now to show how much surface removal is created by a set concentration for a set time period, but this is not showing up - just personal beliefs - no data. Actually have one bit below that shows etching for a year in 10 times the concentration used for the purpose of passivation, and the year time line is about 17000 times as long as a passivation bath.

I could set up this test myself, as I have done this with nitric acid, and had a lab tell me the final Cr and Ni concentraions. But I doubt that the sewer authority would hold my data as reliable, due to a bit of self interest here.

I'm not an expert at anything, (maybe close in coatings), just know enough to be dangerous.

One would think that the sewer "AUTHORITY", would have the data and the answer to you're question. Maybe they just know $hit.

A test for heavy metals in your ph adjusted rinse should solve it, the name for the process shouldn't matter. (Although, I would always call it cleaning in the future).

Dealing with the sewer authority does sound like a fun and productive way to spend your time though.

If the sewer authority in Pennsylvania is anything like the one here in Houston, it is populated by people who weren't smart enough to get a job in the real world. Had a guy in Houston's code enforcement ask me if nitrogen was flammable last year! And he was their chief engineer for crying out loud!

He probably got promoted to that job from the DMV.

Unfortunately, it is not really the sewer authority causing the fuss, it is their big city engineering firm. I am sure I could convince the locals that citric just cleans the metal very well, but not the engineering firm. They are requiring hard data to show no metal ions beyond the "free iron" contamination and loose molecules of ss are being removed, or it meets the EPA definition of chemical etchant. I can find several samples of an Auger analysis of nitric acid passivated ss on the web without much of a search. These are real impressive. We had it done ourselves for a customer back around the turn of the century (2000). The increase of Cr to Fe ratio in the first several nanometers is very impressive. This definitely removes metal from the surface and re-arranges things, thus making that process a chemical etchant. But can I find one for citirc passivation? No! The funny part of this is that the nitric is considered an etchant of ss, but we have stored 40% nitric in a tank for over 20 years now with no apparent loss of metal. Once the first few nanometers are re-arranged, the process stops. So how much Cr and Ni can there be in a rinse water? But, it is defined as an etchant. I seriously doubt that citric does the same thing, but can't find data to prove it, despite the use of citric as a passivation aid for over 70 years.

Temperature is a big factor in citric acid aggressiveness. If it is too cold, it won't do diddly squat.

I have been recommending citric acid as a non hazardous alternative. It has been approved by a couple of municipal authorities I am told. Dang, now you have me rethinking. But I guess it is a more passive passivator than the previous acids used.

I could be wrong but passivating removes the ferrous materials....maybe i'm thinking of electropolishing.

Nitric passivation actually improves the chromium content of the exposed surface a bit. The passivation is actually by the oxygen in the air and the enriched matrix with extra chromium creates a protective layer = passivation. This I have known for 20 years, but I need to know if citric does this also, because when this happens, chromium and nickel are both released along with the "free iron" and go into the waste stream. This makes the process a surface treatment, not cleaning, and would remove us from non-categorical permitting and makes us a "metal finishing" operation.

Thank you for your opinion. I can show you quite a few "experts" out there that would rebuke your beliefs and say it only cleans and removes "free iron". Do you have numerical data to prove this? That is what I need.

I can try them.

I am beginning to think we will have to resort to Auger analysis again, as we have done in the past for select customers, to prove that ambient temperature nitric passivation will work sufficiently well. Very expensive, and if we do the tests, there is always the question of altered samples to serve our purpose. I was hoping for outside data on this since it has existed as a process for 70 years plus. There is no doubt after an Auger test that nitric alters the surface matrix significantly, thus qualifying it as a surface treatment. But, does citric actually do this or just clean away free iron and dirt, thus being just a cleaning process.

You may find that a service company already has the data you need. They would use the data as a sales pitch. Check these guys out with an email or telephone call.

If it were merely a cleaning treatment, removing surface contamination but not altering the surface itself, it would not remove the heat tint from welding since that is a solid state change in the surface itself. So logically it is removing material from the substrate.

If the heavy metals present in the rinse solution are higher than allowable limits, could we precipitate these out with pH elevation before neutralizing the rinse back to 7pH?

The metals will not be mobile (ionized) so will be part of the SS. Raising the pH will help to precipitate metals but the company must have a means of collecting or filtering the suspended solids. Rorschart has mentioned that the cutting dust will have more metals than the citric wash and I believe that to be the case. Raising the pH will help precipitate these metals and thus send them into the SS from the dissolved phase (if they are in that state). Just collect and remove the SS will likely mean the company would have acceptable discharges to the sewer. Iron is generally not a problem with sewage plants as it can aid in phosphorous removal. Mention chrome and they will think it is hexavalent chrome and want it removed.

You can precipitate out a number of metals with pH. Adding a flocculant also helps. You can, but you may not without a license since it is considered waste treatment. We are licensed to treat our waste from our plating and passivatoin processes, but we find that treating the very low pH nitric passivation bath is more costly than sending it out as hazardous waste or shipping it to an acid recycler.

Thank you - some numerical data I can send to the sewer authority to support my contention. I will try this.

Unfortunately, I can also say that we have kept nitric at 40% in a ss tank for nearly 20 years now with little appreciable surface removal, and I know that nitric acid treatment definitely pushes us out of non-categorical permitting. This is considered a "surface treatment" by EPA and thus makes us a metal finishing operation.

We use citric acid it all of the time to clean any residual iron from our new stainless equipment. The chemical we make reacts with iron so the iron must be removed. We mix it to a 3 to 5% solution by weight and then we add ammonia to it to get the pH in a range of 3 to 3.5 and then heat the solution to 65 to 90 degrees. Below 65 degrees the acid has little effect and the effect increases as the temp rises, I assume the max temperature of 90 is to prevent boiling of the solution. The Citric does it best work at those temperatures and is an excellent chelator. The iron is held in solution with the acid so doesn't layer out inside the equipment making it hard to get out when the solutions is drained. I don't think what we are doing is passivating, just cleaning. I do not know of any heavy metals being removed from the stainless but am no expert. We have not had any problems with waste disposal in the past.

What I could understand from your post is that, whether citric acid and nitric acid rinsing of your electroplating baths are comparable.

Theoretically speaking . Yes.

It is all about the basis of Chelate complex formation.

The poly valent Heavy metals like Fe, Cr, Cu, Zn etc are starving for electrons electron deficient], whereas the the ligand group radicals like- COOH groups of Citric acid, Nitrate groups of NO3 of nitric acid being surplus of electrons are potential electron donors to form covalent or co ordination bond formation between metals and ligand groups of citric or nitric acids, thereby inactivating the deleterious effect metals.

The other ligands are OH, nitrites,amino acids etc. Most of the commercial chelating agents are rich of electro negative ligand group radicals, you may expect better sequestration of your heavy metals in wash effluent.

Among Citric and nitric acid, citric being a poly carboxylic acid,the probability of heavy chelate formation is better. just apart from being a larger complex organic molecule.

Hope I am closer to your question demand?

But, does the citric remove significant amounts of chromium and nickel from the ss matrix, thus becoming a "surface treatment", not just cleaning, as we are told the nitric does? As I understand the nitric process, it actually improves chromium content on the top surface layer thus allowing easier oxidation by air, which is really the passivation process. Does citric do this?

The sewer authority contends that a passivation bath is a "surface treatment" not just cleaning, since it alters the surface matrix by removing iron, nickel and chromium that are not"free" but bound in the matrix. We are allowed to clean ss, and removal of the "free iron" impurities is considered cleaning. Removal of metals from the matrix of the ss is surface treatment. What does the citric acid do to the top layer of ss?

What you can do is to compare both citrate treated and nitric treated wash water samples for unchelated residual metal using EDTA Titration. Lesser the EDTA consumption so is the effectiveness of heavy metal removal.

Thank you, but I can't do this - the sewer authority, and ultimately the EPA, would not hold any data I derived from a test as legitimate due to my personal involvement in the permitting process. What I need is data someone else has derived to show metal removal by a typical 5% citric acid bath. The food industry has used this process for 70 years for treating ss. Someone has to have done this test already and have the data available for presenting to the sewer authority.

Maybe these guys can help.

http://www.finishing.com/286/80.shtml

Hi Phys,

Just consult "Citric Acid/Wikipedia" and check note #12. It's reading will be good for your project.

Make sure everyone knowns how to handle chemicals, Gil.

Did a search here, lots of stuff. They would have the data to put this to rest.

http://www.epa.gov/

They are the cause of this problem - interpretation of their metal finishing and NPDES rules by the sewer authority and their engineering firm have led to the need to prove this isn't a "chemical etching" (as nitric passivation is) as listed in the guide for metal finishers. They want hard data to show what citric acid does to the metals surface. I have my own data and from other sources on what nitric does, as we have an Auger analysis done on nitric passivated surfaces as have others, but nothing on citric acid. Believe me, the nitric does a real number on the top several molecular layers of the ss, greatly enhancing the Cr to Fe ratio. Does citric do this too?

I can't find any specific listing on citric acid and whether it is a "metal etchant" or just a "cleaner" in a ten minute search, but a thorough search of this site would take years.

Phys-

Take a look at this site:

http://www.finishing.com/466/18.shtml it is a series of posting concerning the subject

Also try: http://www.howtobrew.com/appendices/appendixB-1.html it is also on the subject of passivating St Stl but at a less professional level. Sort of reminds of my "Iron City" days!

Good Luck, Old Salt

Phys,

I just spoke to this guy on the phone. He recently went through a case just like yours, up in Virginia, (he's local, near me in NC).

He explained that citric acid does not passivate, but it does remove trace amounts of iron, only. Long story short, the local idiot authorities up in Virginia accepted his letter explaining the process, and his credentials, and the permit was issued.

This is the guy and he said he'd try to help you out. Shoot him an email or give him a call.

http://www.finishing.com/Consultants/probert.shtml

That may be technically correct. Except, what the removal of the iron and some attached chrome and nickel does is to expose the steel now with surface enriched chrome and nickel to the air where it oxidizes to form a stable surface (passivated) in regard to the valance. The stabilization likely would not proceed without the removal of the excess iron from the surface so it is passivation. If you can prove only iron in the wash the sewage plant would likely be happy to accept it as it may be useful to help remove P. It is the problem with the removal of chrome (primarily) and nickel that raises the alarms with the approval authorities. Nomenclature aside, satisfing these concerns would lead to approval. If I were the inspector, I would likely approve with supporting data (as OP is looking for) or if the plant had suspended solids removal. The organic acid will chelate with the iron.

Yeah, that's exactly what the guy told me. He also told me that studies and data are hard to find, because for the experts in the field, it's just a known fact, like why is water wet.

At this point, I just gave this guy a call to see if he could help phys get his permit. Sounds like he can. He also concurred that local authorities on things like this are brain dead idiots for the most part. I seriously doubt, that the local guys would accept any data found on the internet anyway. An official looking letter from an accredited guy in the field seems to do the trick though.

Gotta run this by upper management and see if the cost of a consultant is in the budget. It is worth it to me, if he can help, to avoid a lot of paper work and sampling and testing as required under a metal finishing permit, but is it worth it to my company? Right now I am afraid they'll tell me to do my job and accept a different permit category.

I don't think he would have to fly up there. He was very familiar with what you're doing. He said only trace amounts of iron are released, less than draining canned vegetables in your sink.

He was a nice enough guy to talk to. Maybe run your scenario past him before talking to management, see what he says. Didn't seem like the type that would try to bill you for a phone/email conversation.

Not quite that cut and dried - most people do not realize that there is a whole lot of Cr and Ni allowed to go the the sewer. At another plant that is listed as a metal finishing plant, we pickle and then water rinse large products. The pickling bath is a nitric/hydro-fluoric mixture - quite nasty. We never come within 25% of exceeding allowable limits of Cr and Ni to the sewer. That process removes entire layers of the metal matrix at a rapid rate and relaeases a whole lot of Cr and Ni ions - a lot more than passivation by nitric acid does. The release of the metals should be, but is not the concern.

This silly flap is strictly over the definition of what the citric bath does. Does it alter the surface matrix by removing bound metal ions and is thus a surface treatment as defined by EPA metal finishing rukes concerning chemical etching or does it just remove the impurities such as the free iron contamination and thus is just a cleaner? Much Cr and Ni may go to the sewer, as long as we don't do surface treatment. We are allowed to polish and grind the ss, and therefore obviously send some to the sewer already as a dust. The EPA definition of polishing and grinding as a metal finisher involves oils, which being a sanitary product producer, we would never be allowed to do. Most of our polishing is dry. Therefore we are not a metal finisher despite grinding on the surface of stainless and obviously surface finishing. Crazy, isn't it?

Ya know, I've been waiting for Milo to stop in and offer an opinion. Of everybody here, HE would be probably THE expert I'd look to.

HOLY CRAP!!!!!!!!!!!

Don't worry, by the time you get them satisfied, your plant will probably be shut down and we'll be importing your stuff from China.

It is a bit crazy. I am in Canada and we would only have federal input if the sewage was discharging to a body of water and not meeting discharge guidelines. The feds are only involved in international boundary waters such as great Lakes or Oceans or in the territories. Primary inspection is from the provinces. The operating authority most likely the municipality would have sewer use bylaws and they would define at what levels things can be discharged to the sewer. Once at the plant, the responsibility for discharge to a stream, etc lies with the operating authority and they pay for the monitoring. Most metals would be removed at a plant with settling basins and digestion. The final disposal of digested sludge can be landfill or agriculture spreading. Disposal on agricultural land is beneficial to the farmer if the nutrients are high and the metals are low. Lots of calculations involved to determine this capability and is usually cheaper than landfilling or handling as a hazardous product. Sewage Sludge is generally OK for agricultural lands. I mention this only to make you aware of the final disposal issues. In a large sewage system, your metal discharge may be a moot point. The sewer use bylaws are meant to give a level playing field to all discharges from all plants to a sewer system. If you have to deal with a layer of inspection such as EPA, it could be a game changer. The EPA seems to control the sewer use bylaws.

I suspect if pickling can remove all concerns and is cost effective it may be an option. Most of the metals will be found in the SS so that's why I suggest using some form of SS removal.

By the way Kramarat is ice wet? or water when it is a gas? Or if you go for a swim does the water get Kramarated or do you get watered? Wet is another crazy term but describes how you feel if you fall in the drink. You won't fall in the drink if the water is ice (sufficiently thick) and thus you won't get wet.

On a personal level, I prefer pickling, sometimes it's a blended Canadian tincture, on the rocks, (that's where the ice comes in).

It makes problems like this much easier to digest, even laughable.

Unfortunately pickling does not remove the concerns. This is done at another plant which is permitted as a metal finishing operation and we are trying to avoid that here due to increased paper work and testing requirements. To be classified as that for a single process we might perform 2 or 3 times a year would be a bit tough to swallow. We might be talking about a few hundred gallons of rinse compared to our average discharge of 400,000 gallons a year, mostly rinse waters from a dish detergent cleaning and process waters from generating RO and DI water. Citric passivating is not that common yet in pharma work. We also can not move most products built in this building to the other without hiring a trucking line.

Also, pickling is for non-sanitary portions of equipment mounted in a utility space, such as the outside of a heat exchanger. It makes a beautiful "sand blast" finish. The passivated products are sanitary polished very low Ra finishes and the pickling quickly turns them to very high Ra, while passivating theoretically improves the finish.

Phys,

Check this out. Very pertinent. These people have done the study. Technically speaking it is passivating, but very safe.

http://www.controlelectropolishing.com/images/CEC_Pollution_Prevention.pdf

Yeah, it is a passivation aid (passivating is really the oxidation of the Cr on the ss surface matrix by oxygen in the air) which is what nitric is too, but is it an etchant as nitric is? (does it remove some of the matrix bound metal ions as nitric does?)

The article you sent me to conveniently skips over this saying they could not segregate heavy metals from the passivation process from those from other processes in the plant, and no where did they run an Auger test on the surface of the ss to see if chromium enrichment had occured.

Again we have a citric acid proponent who skips over the actual process of what the acid does to the surface matrix of the ss and whether or not the surface matrix is changed as it is with nitric. Yes the citric process allows the ss to self passivate, as the nitric does, but does it chromium enrich the matrix also, or just clean very well? It is well known that a very aggressive cleaning of the surface with other chemicals will allow a passivation to occur, but much slower than with nitric acid. All proponents of citric passivation avoid this subject, which I need an answer to, and I believe this is because the chromium enrichment by nitric is well known and recorded, but their citric acid won't do this part. If true, that is what I want, since then this is just a super cleaning process without etching and we still qualify as a non-categorical user for the sewer permit.

Won't some citric proponent fess up and say it just cleans real well to allow passivation, but does not chromium enrich the surface by selective metal ion removal?

Thinking out loud here, so bear with me.

Since you only do this once in a blue moon, suppose you were to capture the rinse water and truck it to the other facility that is already permitted? Would that solve the issue?

One other thought. Since the issue is probably "dose/time" dependent, could you not capture the contaminated runoff, and dilute it with your normal and allowed run-off such that the concentrations are much reduced?

Trucking it off to an already permitted facility sounds like a viable plan.

Dilution is not the solution however. In the past there have been companies operating under that philosophy that got slapped with major fines (in the US). I can't cite the court case that decided this, but it was emphasized in my courses in water treatment.

Dilution is legal if it is a designed part of a waste collection system We already use that at our other plant to help to neutralize acidic waste and lower heavy metal concentrations. We collect all of the waste streams in a large tank. Since we have a minor acidic flow with heavy metals and a major clean DI water flow (from hydro-pressure testing - no chemicals added) and a fairly healthy basic flow from a cleaning process, the end stream is often fit to go to sewer as is. Most people don't realize how much heavy metals can go legally to sewer, so the metal portion is always well below legal discharge limits before any neutralization occurs.

However, if you intentionally add water to drums of waste or a waste collection tank just to dilute a waste, then you get fried when caught. The dilution must be a legitimate part of the waste collection process as our clean water stream is. If we had someone turn on several faucets for ten minutes before each waste dump, then we would not be legal. Don't tell anyone, but I had an environmental inspector (name and organization with held to protect the guilty) tell me to make washing the floor a routine procedure when the tank was nearing full if we suspected that the waste would not be inside limits. We never have to do that fortunately. I suspect that is pushing the rules a bit far.

Perhaps you could repurpose the used citric acid water as a "degreaser" additive to the mop bucket and mop the floors? =b

Yes to first proposal. A bit time consuming and tedious, but it would work. I know upper management is not keen on this.

No to the second. The problem is not concentration as we will never reach allowed Cr and Ni limits with a passivation even if we dump the used acid itself. As I said before to someone, the whole thing is strictly a definition problem. If the process with citric acid removes bound metal ions, it is defined by EPA as a chemical etchant (and also a passivator) and makes us a metal finishing facility, not a non-categorical one. (there are advantages to remaining non-categorical) So, is citric acid an ss etchant? Looking at how many tanks of 304 and 316 ss there are in the food industry, I would certainly hope not, but I can not get by with just logic. I am still being required to present hard data that shows no metal removal (other than free iron) at 5% and 1/2 hour soak. And, yes, I checked - if we are involved in the sampling and testing to prove this, it is not acceptable. This has to come from an outside source.

I can not find a sample of an Auger test on a citric "passivated" ss sample anywhere, but can easily find samples of such for nitric passivation. This clearly shows me that the citric acid does not do any thing like what the nitric does to the surface matrix, or the proponents of it would be waving them around saying see here - just as good as nitric. But, again, this is just logic - not hard data.

I think part of your difficulty arises from the fact that the changeover to citric acid passivating from nitric acid is a relatively new thing and the industry is still coming to grips with it and the data may not be widespread like the Nitric data is.

Heck, what if you were to feed the runoff to one of your RO/DI filters? (again, thinking out loud)

The Germans were citric passivating in the 1930's - hardly new. I smell a cover up by the purveyors of citric acid passivating solutions. I think it doesn't re-arrange the surface matrix as nitric does, and they don't want potential customers to know this. There are very few pharmaceutical companies allowing citric passivating, and they have the bucks to get Auger testing done to prove if citric is the same as nitric. This whole mess is over a tank for a beverage manufacturer. They have used citric passivating for their tanks for decades.

I'm not saying it is a whole new process, just that most everybody followed QQ-P-35C which specified Nitric acid because it was more aggressive and the process time was much shorter and it was a Fed/MIL standard and EVERYTHING that the Feds bought specified it (and most everybody else did too.) but then the the feds cancelled the standard, handed it off to ASTM to handle, and EPA started really cracking down and everybody had to move out of their comfort zone and change to citric processing.

Pharma companies probably aren't allowing it because if they were to change their processes one iota, even something as simple as this, they'd have to go back to the FDA and wrestle with them so they'd just as soon continue the way they always did and pay the money to deal with the waste stream.

Ohhh - you know about FDA validation.

Bureaucracy and idiocy know no bounds.... but I repeat myself....

There must be a bureaucrat in the audience....

Ain't No Bureaucrat gonna talk back to anyone with a "Who is John Galt?" tagline, my friend...

Milo

Thanks to all for the interesting subject matter and postings. I just finished a large Industrial Water plant using Ozone to treat the water and we had the contractor use citric acid for all the Stainless steel to meet the Engineer's spec on passivating the SS line from Ozone generators to the contact Chambers. I now have a better understanding.

You might like to know that ASTM regard citric acid as a passivator - see ASTM A967.

Regards

EnmaxLtd

I would be hard pressed to convince anyone that citric acid was as powerful an oxidizer as nitric acid and was "oxidizing" the chrome in the stainless. I think the citric binds the free iron removing it from the surface and allows the chromium to self heal.

I think that your use of the term chelator is closer to what it is actually accomplishing, as it is binding up residual stray iron Fe from tool and process on the surface which would start corrosion cells.

It is likely that it is picking up some Nickel too.

My understanding is that the nitric is also providing oxidation which helps form the protective chromic oxide film. I haven't seen anything that claims that citric is doing that.

You should have an analysis of your spent citric acid run to see if you meet your POTW limits for metals.

But from my understanding, the citric is chemically reacting with the free iron left on the product from the tool and process and shop dirt.

Milo

So Citric Acid won't remove heat tint? I had understood it would. if it will remove that, it is definitely doing more than picking up "free iron".

What is Heat tint chemically? Iron oxide? (FeO Wustite, blue in color and soluble in acid.) Not Fe2O3 or Fe3O4.

Its a weak pickle.

Milo

I understood heat tint on stainlesses to be a combination of Chrome Carbide and Chrome Oxide caused by chrome diffusing toward the surface and depleting the layer immediately under the layer of chrome forming a corrosion cell as a result.

We pickle to remove heat tint - passivation only protects against corrosion.

Yes, that is what I believe also, but the sewer authority (hired consulting engineer) is insisting on hard numerical data to prove this. Otherwise, the after citric bath water rinse (we just want to send the rinse to sewer, not the acid bath) will be considered the same as a nitric rinse, and determined to be a product of a "chemical etching" process. Certainly the nitric does this, as the finished surface matrix is chromium enriched quite a bit higher than the basic metal, but I don't think the citric does. Once that determination is set, we lose our non-categorical manufacturing permit and become a much tougher to adhere to metal finishing manufacurer and are permitted as same. I still need data to show citric is basically a super cleaner, not a ss etchant.

None of the proponents or vendors of citric acid passivating solutions will touch that concept. No Auger analysis of the surface matrix contents - no after passivating heavy metal content analysis on the acid or rinses - nothing but literature saying this is as good as a nitric passivation.

I am absolutely amazed that this dilemma even exists. It ties right in with all of the blogs and threads regarding US competitiveness in the global marketplace.

What you're doing essentially, is washing some freaking stainless steel in lemon juice.

It's totally dumbfounding. This amounts to nothing more than red tape B.S., that's going to cost your company time and money. I just don't get it.

The government, whether local, state or federal, should be there to help you get your product to market, in a safe, environmentally friendly way, not setting up roadblocks designed to extort money from you. What a load of crap!

Sorry for the rant dude. I'll get out of here.

Thank you - this is what I was looking for - honest data on the effectiveness of citric acid and how much of an etchant it really is. All other sources I found had strong opinions but no data to prove it.

If I could vote 100 times for this answer I would do it, because this is what I was looking for.

You're welcome. Thanks for the feedback. Typically we deal in the results and the "how tos?" and not the "why fores?" So the "why fore" data can sometimes take a bit longer to find...

Milo "97 bottles of GA on the wall, 97 bottles of GA ..."

Good going Milo. I figured from the start it was going to be Milo to the rescue on this one.

I had totally missed the thread someohow and was pointed to it via private message from another member.

The link that was given was to the OP, and showed no other responses, then all of a sudden I'm post number (insert some huge double digit number here.)

Anyway, thats a big YAY Tam for the CR4 community on this one.

Milo

Thanks to all who responded. The data from Boeing was the clincher. Sent it off to the sewer authority's engineer today. Now we wait to see if it flies, because he will run it past EPA.

This is going to sound entirely off topic, but................I went through a similar situation last year regarding the definition of, "manufacturing".

I want to make a product in my basement, to be sold off site. The local zoning people told me no, I'm not zoned for manufacturing, period.

I ended up finding a person in the state dept of commerce, (an entity that wants to see companies and individuals producing), that listened to my story and made the calls necessary to help my local officials understand the definition that I was looking for..........I had the green light within 48 hours.

Sometimes you've got to find other ways to skin a cat. Especially when dealing with bureaucrats.

I wonder if these people could help.

My thinking here, is that if you could get your citric acid solution from a company that carries the greenseal certification, and that product is sold as a "cleaner" specifically, you may be able to get the, "definition" that you need to get your sewer approval, without reclassification..........maybe?

http://www.greenseal.org/AboutGreenSeal.aspx

I havent read all the replies so dont flame me if someone has already given the following information.

Citric acid is a weak organic acid. It will remove iron oxides slowly and is not very good at removal as an acid. At elevated temperatures it will give you an active iron surface. It has NO oxidative effects. there is a process called citrosolve - which uses a combinaiton of mono ammonium citrate which actually reacts faster that citric to remove the oxides. The resulting solution must then have the ph raised to 10 - 12 and an oxidizing agent added (such as oxygen, sodium nitrite or hydrogen peroxide) this will give you a good passive surface. The passivation results in the combination of removing the free iron and then oxydizing the surface.

Nitric acid does this in one step. As the acid both reacts with the oxides and forms them. Nitric acid is also incredibly corrosive and can only be used Carefully on stainless steel. (excess temperature and time can result in severe metal loss and deep pitting.)

Whatever you do the solutions will contain nickel and chrome. I have been told the solution containing citric acid are more difficult to treat for disposal as the citric tends to counter the precipitation steps often used to get rid of the metals in solution.

so to conclude the answer to your question. A cleaning process that uses citric alone isnt going to give a very good level of passivation, AND it doesnt matter which method you use the acid will contain some heavy metals.

Tom McCartney

Doesn't matter anymore - the engineer for the sewer authority had it all wrong. EPA has the last word on this and they say ANY PROCESS, if it is called a PASSIVATION process, regardless of actual physical and chemical reactions involved, is a COATING process, which is one of the big 6 processes in determining the metal finishing category, and thus requires an NPDES as a metal finisher, not non-categorical.

The sewer authority is the big loser here - we were not going to pickle or nitric passivate at this plant to avoid the metal finishing category, but now, we have no reason not to do those processes here.

Someday I would like someone at EPA to show me the "coating" we are doing when we run some citric through one of our tanks and rinse it. Better start classifying Minute Maid as a metal finisher too.

"regardless of actual physical and chemical reactions involved" Yes, Bureaucratic Science at its finest.

milo