Chrome plating mist /fume control: PFOS, fume suppressants, surface tension reducers

A. I have previously discussed this and other issues with Mr. Phil Mulrine of EPA's RTP. At that time a fume suppressant that met 30 dynes /cm3 was proposed to be RACT (reasonable available control technology). This information is not current so you should check for updates. You might find more current information from : http://members.aol.com/ryoung7547/elenvnav.html  Also, if you get flagged for "steel pickling" MACT due to electroplating you can suggest that this was not intent of CAA amendments. This has been successfully achieved with EPA previously.

A. What they are using and referring to is a fume suppressant and/or a surface tension reducer. The fume suppressant forms an oily foam blanket on the surface and is usually a fluorocarbon. Reducing the surface tension of the chrome plating bath offers the evolving hydrogen bubbles less capacity to form bubbles to carry plating solution out.

You can talk to DuPont or to any local distributor of plating supplies.

Please don't read this response as an affirmation that the use of a fume suppressant and/or surface tension reducer without an exhaust scrubber is always adequate because:

1). First you have to determine if you are a 'decorative' chrome shop or a 'hard chrome' shop; they may use different suppressants.
2). You not only need to use the suppressant, but follow the rules for testing and recording your results.
3). Rules are in a state of flux, and local codes may override federal rules anyway.

A. Personally, I don't feel that fume suppressant is always an adequate substitute for an exhaust ventilation system, but your main problem may be that need to also control the surface tension. But try dropping the solution level in the chrome tank to whatever extent is possible as well -- it can make a very big difference. I once visited a plant that had been built with very deep tanks for vertically chrome plating navel gun barrels. When they no longer processed parts that long, they decided to drop the solution level to at least 36 inches below the tank rim. Without fume suppressants or a ventilation system, they had no detectable chrome emissions! Apparently, in the absence of drafts, the chrome mists fell back into the tank before rising this 36 inches or so. That much freeboard is impractical for most shops, but I think it indicates that every inch of freeboard makes a big difference in emissions.

A. Hi Christos,

What Ted said about ventilation hit the nail on the head ... and yes, the lip of the tank should be min. 6" (sorry, I forgot ... 15 cm!) from the liquid level.

I have seen very poorly designed fume hoods inefficiently exhausting a chrome tank but with the addition of some surfactants, they became 'efficient' !

If this Atotech material works that efficiently, doesn't cause any side effects, is reasonably priced, then it will prove a huge benefit to platers.

But as a typical Doubting Thomas, me thinks it ain't so.

A. Fume suppressants (foam blankets) are not very effective and are short lived however, surface tension reducers are very effective in eliminating chrome mist and spray (as has been proven in several tests by U.S. EPA et.al.) If you are using one of the modern fume suppressants/surface tension reducers check to see if your surface tension is below 45 dynes (I prefer 35). This may be done with some accuracy using a relatively inexpensive piece of glassware called a stalagmometer.

A. We have used a fume suppressant for ten years, and it works very well. There are no fumes you can see or smell, and there are no chrome stains on or near the tanks. The one we use is available from Atotech USA.

Thanks, Jeffrey. To be clear, you do hard chrome plating with no local exhaust on the tank, and do not have an unusually low solution level in the tank, and need nothing but fume suppressant for control? I worked for M&T Chemicals and Harshaw Chemical Co., the two components of Atotech decades ago, and am happy but a bit surprised that the development efforts were that successful! If you are at liberty to say, do you use conventional sulfuric catalyzed, fluoride, or high efficiency etch free chrome?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Ted: Our chrome bath is sulfuric/boric acid catalyzed, no fluoride. approx. 32 oz/gal, solution level 4" from top. No ventilation of any kind. We have done 8-hour employee air monitoring with no Cr+6 detected. Also installed a temporary exhaust system, no scrubber, just a blower and ductwork, and passed the Cr emission test by a factor of 10. You can lay a white paper on the anode/cathode bars, and no yellow stain @ 2000 amps. The product is Fumetrol 140. Worth it's weight in gold, which is almost what it costs.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

Thanks Jeff!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. I have had the same results as Jeffrey in our shop.

The problem is companies want to keep on selling scrubbers, regulators want more regulations, and a plating society was willing to go along for the ride. Scrubbers were embraced, surface tension reducing agents were shunned. It was an excellent job as people to this day will denounce surface tension reducing agents.

Todd Osmolski
- Charlotte, North Carolina, USA

Dear friends,

Thank you all for responding. In fact, one of the two products I mentioned is Fumetrol 140!

We do use an exhaust system and the space above the solution level is about 30 to 40 cm.

Well, the problem probably seems to be that the filters of the exhaust system, which is situated at the basement of the shop (under the bath), have to be changed more often because they were blocked.

Anyway, thanks again, pretty interesting discussion.

A. Jamie,

If memory serves me correct Fumetrol 208 is a cost engineered product that contains less of the surface tension reducer and more surfactant. Switch to a product which is mostly surface tension reducer. These are relatively quite expensive ($85-160 U.S. depending upon vendor/manufacturer) but are based on fluorocarbon technology.

A. If it is possible, what I would do is plan for a large amount of freeboard plus the exhaust system. Chromium mist droplets are heavy, and with extravagant freeboard much of the chrome will fall back into the tank and not need to be exhausted.

We're going through the same issue in the USA. With only a little exaggeration, EPA no sooner claimed that chrome MACT standards were achievable and affordable through the use of fume suppressants than it began banning them. But PFOS and related chemicals are getting scary as we see them directly causing androgyny in fish :-(

A. Hi Bert,

What Ted said about banning suppressants is news to me ... but his remarks about 'freeboard' are interesting ... I used to think that a 6" (sorry! 15 cm) freeboard was OK.

On the subject of, you say, an expensive exhaust system ...
why expensive?

Welded mild steel ducting and hoods. Anyhow, go into the fin.com library for more data on that.

POLLUTION ... Back in the early 80's, the allowable specs for chrome in B.C. were ll grains/l000 cfm of chrome sulfuric acid. Using a well designed (and made) ordinary 2 stage PVC mist eliminator, horizontal design with sine curved blades, tests indicated that these were 30 times LOWER than the then acceptable limits.This is a l2 micron eliminator...but in your terminology that is 0.7 mg/M3

My 1974 design followed that route but was a good 3 micron inertial scrubber.

A. Activated carbon might work. But, frequently, charged ions like the salts of anionic surfactants have a higher affinity for anionic ion exchange resins. These compounds are going to be even more acidic than non-fluorinated surfactants of this type and will only be present as the free acid at very low pH values.

A. Hi Mohsin,

The U.S. specs for chromic emissions are very tough, i.e., 0.05 mg/cu M....maybe too tough.

The specs back in l978 in B.C. were ll grains of sulfuric/chrome per 1,000 CFM (or was it per single CFM, I forget).

Using an ordinary but very well built CT-120/2 blade type eliminator, we achieved 0,34 grains .... that's equivalent to 30 times lower than those specifications BUT translated into metric, it's only O.7OO mg/cu.M Yes, I have that in writing.

You definitely need some exhaust.

Does this help?

A. Based on the usage of the fluorinated products, I can't figure out how so much got to the POTW that the POTW was high!

A. Since this product is getting into the effluent via drag out from the plating solution, the most effective way to limit this is to reduce the drag out in the plating facility by implementing waste reduction methodology.

A. Nope, chrome solutions would destroy that in no time. If you use surface tension reducers in your chrome bath, you need the ones that are specifically designed for chrome plating. The chemical suppliers that offer these additives have spent big bucks on R&D to solve this particular issue for you, so the additives are expensive. Until recently most suppliers offered PFOS or similar compounds, but those chemicals are becoming banned, so they are now offering brand new proprietary additives.

A. We were just asked by the Air Quality folks to lower the emissions of our chromic acid anodizing tank. We are looking into some of the Fumetrol products. I see that they have a new product that is PFOS-free.

A. Hi, Dave.
Evaporation, per se, from a chrome plating tank is almost always considered good rather than bad as it allows the return of some chrome-contaminated dragout.

The normal problem is chrome fumes or mists evolving from the tank which should not be confused with evaporation. These can be addressed with a lowered solution level in the tank, wetting agents, and fume suppressants. Some people use "chroffles" (polypropylene ping pong balls), but I am not convinced they are worth the effort.

You might also see www.pfonline.com/articles/reducing-hexavalent-chromium-emissions about a special membrane cover which purportedly allows hydrogen and oxygen to escape from chrome plating tanks while containing the chrome fumes. Good luck.

A. You might have better luck using a stalagmometer. There are several companies that sell this instrument and I'm sure they could provide you with a procedure that would work for you. Tensiometers are a big pain to use because there are many sources for error. And as for a literature source, I would check the International Critical Tables for a value, it might be in there.

". . . try dropping the solution level in the chrome tank to whatever extent is possible as well -- it can make a very big difference. I once visited a plant that had been built with very deep tanks for vertically chrome plating naval gun barrels. When they no longer processed parts that long, they decided to drop the solution level to at least 36 inches. Without fume suppressants or a ventilation system, they had no detectable chrome emissions! Apparently, in the absence of drafts, the chrome mists fell back into the tank before rising ha 36 inches or so. This much freeboard is impractical for most shops, but I think it indicates that every inch of freeboard makes a big difference in emissions."

A. Hi Bob. It was a very long time ago, mid 1970s, and I was not involved in the chrome fume control. I was visiting on a different matter but inquired when I noted the very low solution level. One of the plant's engineers explained the situation and demonstrated it by holding a white handkerchief over the tank. But I have no data or history on it. I sent you the name of the shop in private.

Regards,

A. Good day Ram.
Have you checked for surface tension with a stalagmometer?

Regards,

A. The most common and reliable alternative to any fume or mist suppressant is a well designed Local Exhaust Ventilation system integrated with smart tank covers that completely capture and control the mist/fumes, reduce heat loss, reduce evaporation, and most importantly reduce your electrical bill! With the banning of PFAS>PFOS>PFOA based fume suppressants, many forward thinking operations already rely on these systems, which can completely pay for their initial investment over a period of only a few years through proven energy savings. Over a 25 year life-cycle of the equipment, smart tank covers will have save hundreds of thousands of dollars in medium to large process line operational costs.

A. Hi Rajkamal. We attached your inquiry to a fairly long thread on the topic because there aren't easy answers, there are only balancing acts :-)
1. Re-use might be possible by replacing evaporation losses in the chrome tank with recirc water from the fume scrubber ... but more efficient fume scrubbing results from including sodium metabisulfite in the recirculating water to convert the hex chrome to tri chrome, and that would render it non-reuseable.
2. More freeboard, tank covers, and use of fume suppressants and surface tension reducers minimizes the waste, but fume suppressant can be an environmental problem itself. If 'impurity level is high' what are the impurities? Sorry, I don't know what you mean by "like slurry base"."

Regards,

A. Typically, metallic impurities in the washdown solution are very high, and the chromic acid concentration is also very high. Provided that there is enough evaporation from the chromium plating tank, the washdown solution can be returned to the plating tank, but purification to first remove metallic impurities is recommended. Ion exchange is one method, but the life of the resin is short.

One-time use of the resin is a possibility. One liter of resin will remove about 2 equivalents of metal impurities. Unfortunately, trivalent chromium is also removed and it would be better to oxidize the trivalent chromium back to hexavalent before purification, or to use a membrane cell to re-oxidize and also remove impurities.

A. Hi Bill. While I don't claim that other plating solutions are mother's milk, the extreme environmental issues we talk about in chrome plating are pretty much restricted to chrome plating for a number of reasons.

• Hard chrome plating / engineering chrome plating tends to be orders of magnitude thicker than other platings -- often being used for such purposes as rebuilding worn components, and requiring far higher currents.
• Chrome plating is horribly inefficient. Only somewhere between 10 and 25% of the applied electricity deposits chromium, and all the rest generates hydrogen gas. Other plating solutions are usually 75-99.9% efficient, generating way less hydrogen gas. If you reduce the plating current in other solutions they just plate proportionally slower, but chrome plating simply stops below a threshold current.
• Strong chromic acid is an extremely powerful oxidizing agent which precludes the use of most surfactants, whereas the surfactants used in most other plating solutions are sodium lauryl sulphate or similar compounds -- essentially baby shampoo.

To my knowledge PFOS/PFAS is not and was not used for any solutions other than chromic acid.

Luck & Regards,

A. Hi Bhoopendra. Please search the site for threads about topics 2, 3, and 4. We have roughly 100 threads on those chrome plating topics. Obviously you are doing one or more things wrong, but unless you tell us what you are doing via a pretty complete data dump, it's hard to answer. Chrome plating books wouldn't be hundreds of pages if it were possible to explain how to do it right in a couple of paragraphs :-)

Topic 5 is a very serious problem, to which Topic 1 is an answer. Other vendors can offer their equivalents, but Atotech and their "Fumetrol" products have been mentioned.

Luck & Regards,

A. Hi Jiyaul
There are four ways that I can quickly think of to reduce airborne chrome emissions:

1). Use a fume suppressant -- an oily skin on the surface of the tank, which captures much of that mist.
2). Use a surface tension reducer, which limits the ability of the little droplets to form around the hydrogen gas and be carried out as bubbles.
3). Reduce the solution level in the plating tank so a greater percentage of the mists simply fall back in rather than escape to the ambient air or an exhaust system. I once visited a plating shop with exceptionally deep plating tanks designed for plating older very long battleship cannons. For the newer, shorter, barrels, they lowered the solution level in the tanks to about 36- 42" inches below the tank rim, and the reduction in emissions was incredible.
4). Employ an exhaust system with dry mesh pads or fume scrubber to capture the escaping mists.

Focusing first on the first point: fume suppressants have been very successful but Fumetrol 140 is PFOS-based. PFOS is a 'forever chemical' which environmental regulators have been focused on for a while, and which the public around the world is now extremely concerned about. Although I don't know the regulations in Chennai, I do not think you should use it anywhere in the world here in 2023.

Non-PFOS fume suppressants are, to my limited understanding, available but not as effective ... which brings us to the second point: a combination of surface tension reducer plus non-PFOS fume suppressant may do the job. This graphic from the California Air Resources Board gives a quick flavor for the issue ⇨

If you are able to employ even a relatively small measure of point three, along with one and two, that would be great. Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey