Lead in hot dip galvanising

A. Hi Joyoti. We added your question to one of several threads we already had on lead in galvanizing (although I am not familiar with titanium additions to the bath). See thread 38207 for some input regarding spangle, or search the site for lots of threads related to lead and to spangle.

Luck & Regards,

A. Not all Hot dip galvanizers use lead in their zinc. You can contact ILZRO (the International Lead Zinc Research Organization) for reasons why some Galvanizers use lead. Type in the letters to search and it will come up.

A. In "Test for Lead in Hot-Dip Galvanizing Zinc", by Thomas H. Cook and Mohammed Arif, Metal Finishing (USA) October 1991, pages 29 to 31, Dr. Cook gives a test for lead in HDG and describes briefly the reasons for the use of lead in the bath.

A. Dear Mr. Ahmad;

Do you run a continuous Galvanizing line or Hot Dip one?

Why do you want to use Lead in the Kettle? Antimony is better.

Regards,

A. Sir:

In the USA lead is being eliminated from hot dip galvanizing, state by state due to the toxic nature of lead. There is technology available that enables lead-free zinc to work as well or better than leaded zinc for hot dip galvanizing. At this point I would NEVER recommend adding lead to a galvanizing bath.

It is true that antimony improves the results in hot dip galvanizing, however if one "strips" the zinc coating containing antimony the gas stibine (SbH3) is formed which is highly toxic and has caused deaths in hot dip galvanizing.

There are non-traditional ways to reduce the surface tension and the reactivity (of Sandlin Curve reactive steels), which enable excellent results in lead free zinc in hot dip galvanizing baths.

Regards,

A. Geoff,

I know of three cases in which the galvanizing employee who "worked" the dry ash on the kettle exceeded the limit on lead in his air sampling equipment. In these cases the lead in the zinc was about 1% and the lead in the dry ash was about 5%. I know this because I personally tested the lead in zinc and ash. Two of these companies now use MZR machines and two of the three use lead-free zinc.

In the USA, it is my understanding that the most strict state is California. I believe that anything that is toxic or can cause cancer must be labeled. I have seen many of these labels even here in South Dakota (a long way from California). Thus for a galvanizer to sell product in California containing 1% lead, each piece would have to be labeled. I believe that all the California galvanizers use lead-free zinc. There seems to be several other states with pending legislation regarding lead.

On the internet there is a story of a woman that ate wild pig and ingested one lead shot gun pellet, resulting in elevated lead in her blood. She nearly died. After an operation in which the pellet was removed she made a full recovery.

In North Dakota (USA) a hunting group gave wild game (deer) to food pantries for low income folks. The state tested and found elevated lead levels in folks eating this donated wild game. As a result, North Dakota condemned several hundred thousand pounds of deer. The source of the lead was found to be shattered lead bullets.

In my youth I thought nothing of putting slit lead shot on my fishing line by biting down using my teeth. I also once melted lead in my parents' basement to make fishing weights. I overheated the lead and became terribly ill.

Apparently shot gun pellets are now produced in steel and rifle bullets are now produced in copper. Indeed times are changing.

With proper technology, converting from leaded to lead-free galvanizing can be done seamlessly and with an excellent result.

Regards,

It's a long way from eating 100% lead, to touching/using galvanized steel where there was 1% Pb dissolved in the melt.

EU seems no different though in heading in the direction of reducing risk to the extent that prevents industry.

I'm sure that converting to lead-free galv is "seamless" as you said.

A. It's possible to galvanize with "lead free" (I have, but not here), but there doesn't seem to be any evidence that the typical levels of lead in galv melt have caused any health issues with users of galvanized products.

Hi, Geoff.

I'm not sure what standard of evidence we should apply to determine whether something like lead in galvanizing is or is not dangerous; with the Reach standards, I'm sure we'll be hearing more of that. But I do agree with the concept that we should not eliminate materials of construction based on fuzzy ideological grounds. Truthfully, every recent time there has been a plane crash my first impulse was to ask whether cadmium, chrome, or lead were omitted from critical parts on ideological grounds. I do not believe that inferior materials & processes with a protocol of more frequent inspection is really a proper substitute for more robust materials & processes.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 29, 2010

A. Geoff,

My experiences are that lead-free galvanizing is difficult, expensive, and gives a lower quality product. In the USA, due to its toxic nature and environmental restrictions, lead is being eliminated in hot dip galvanizing. Conventionally bismuth and nickel are being used in place of lead. Nickel is "on the environmental radar" in some states in the USA because it is known to cause cancer. To compound these problems, more and more steel in the USA is becoming more reactive toward zinc, causing grey, thick zinc coatings that may not adhere well to the steel. There are unconventional methods to galvanize without lead, nickel, or bismuth.

Ted,

Your point is well taken about safety versus environmental or economic considerations. Several years ago tin was used in hot dip galvanizing. The reason for its use was primarily economic. Increasing the tin content in the zinc caused a lowing of zinc consumption per ton galvanized. During this time, I received many telephone calls from galvanizers asking why their steel was cracking and why their hanging steel wires were breaking. Over time it was determined that above about 0.3% tin was causing the cracking of stressed steel products. Several lawsuits were successful on galvanizers and on at least one zinc company promoting the use of tin. I was concerned about safety issues and sent two letters to ASTM requesting they consider a maximum on tin in hot dip galvanizing. I received no response from ASTM.

Items affected by this tin cracking included: A stressed steel bridge, an overhead highway sign, large diameter steel pilings to support a building in a wet area, a soccer stadium roof support structure, steel scaffolding, large diameter pipe that peeled like a banana and other unreported structural products. It was a difficult time for hot dip galvanizers.

Regards,

Hi, Dr. Cook. Thanks for the calculation but I don't quite know the moral. . . Is it that California was not long ago the nation's wealthiest and best-positioned state but drove themselves to bankruptcy through lunacy?

You melted lead in the confines of a basement as a child, and did it wrong, but are still here to talk about it decades later. And I collected mercury from the trash behind the drugstore to play with it numerous times, played with asbestos, lit paper bags of magnesium shavings, and used carbon tetrachloride regularly for everything from reading watermarks as a stamp collector to cleaning the the white vinyl in my convertible.

It's good that we've reduced the permitted exposures to these things, but I'm mortified by extremism, not grateful for it.

Our present course is so laughably penny-wise & pound-foolish that I'm astounded at our blindness. We know exactly how to finish things like lawn furniture so they will easily last 15-20 years or more. But we harass the finishers who use the necessary ounce of phosphate, instead of the ones who don't! With the result that everywhere I look now I see garbage metal that lasts 2-3 seasons or less before rusting to uselessness ... so we have to mine ore to replace it; ship the ore to a smelter; smelt it and roll the steel; ship it to the fabricator; fabricate it, finish it, package it; ship it to a retailer -- only to ship it all to a landfill a half dozen times in the 20 year period instead of once! Countless tons of wasted metal, transportation, energy, packaging ... wasted chances and wrecked economy ... and we have the hubris to be proud that we saved the earth from an ounce of phosphate -- at the cost of tons of unsustainable waste :-)

Regards,

? What is the real reason that some people do not like lead in galvanizing?

A. Lead is very toxic and has poisoned humans since ancient times.

Regards,

opinion! That lead is toxic is an oversimplification.
Oxygen can be toxic, so can water. In fact most compounds can be toxic, but not at all concentrations, all exposures.
Concentration and exposure are all important.

People don't normally eat galvanizing.
The concentration of Pb in Zn is very low (typically <1%)

So where is the risk located in galvanizing? In the process or the product? At what stages, uses? And to who?

opinion! Geoff,

You are industrialist. Your position seems to be-- "Nothing is toxic so why should anyone worry."

For the actual workers in the plant, who work 8 to 12 hours/day for 250 days/year the toxic nature of these heavy metals can express health problems. Check the Health and Safety section of finishing.com.

Just as lead in the bones of ancient Romans show significant lead poisoning, which may well have led to the fall of the Roman Empire, we should learn from the past.

The "safe harbor" dose as defined in California is a few tenths micrograms/day for lead. Thus a one-ounce fishing sinker is sufficient for daily doses for an individual for 130,000 years. Although California "guidelines" according to Proposition 65 seem harsh, there are real reasons for these guidelines. Irrespective, these guidelines are what they are.

Regards,

opinion! Hi, Dr. Cook.

I don't think it's fair to characterize or attempt to assign motives to other people's statements, but I am interested to hear the evidence for the possibility that lead poisoning led to the fall of the Roman Empire. The evidence would have to be fairly convincing before I'd offer it much credence, since the Roman Empire is only one of hundreds of powerful empires throughout history, and every single one fell.

All galvanized and zinc plated hardware seems to labeled with Prop. 65 warnings, whether it contains lead or not -- which seems to achieve exactly the opposite of what you would like to see. We should reduce the use of and our exposure to toxic substances; but in teaching safety classes and in other instances, I've personally seen, time and again, the danger that over-aggressive warnings have placed people in. We seem to have totally forgotten today the story of "The Boy Who Cried Wolf".

Regards,

opinion! I don't deny being an industrialist, but the health and safety of those that enable industry (and I too spend a lot of time inside galvanizing plants), is very important.

But that needs to be based on good information. Information is presented in many ways these days, some of them not helpful to those that need it, and not helpful to those that rely on good decisions being taken, based on that information.

To just state that lead is toxic with no qualifiers about dose, concentration, exposure etc isn't very helpful, and could, without qualification be misleading.

I'm still searching for good information that shows that Pb in Zn for galvanizing, at the levels often used (<1%, >0.5%) is a hazard for either those exposed daily to the kettle, or to the consumers of galvanized products.

A. Geoff,

In the USA, the NIOSH Pocket Guide to Chemical Hazards September 2007 lists the LEAD Exposure Limits for NIOSH REL as: TWA 0.050 mg/M3 and the OSHA PEL TWA as: 0.050 mg/M3.

This pocket guide also lists several symptoms of lead poisoning.

About 35 years ago a galvanizer "working" the dry ash had an air sampler attached to his belt and a tube near his mouth. The lead result of the test was 0.058 mg/m3. Blood testing showed elevated lead levels. Lead in the zinc was about 1% and lead in the flux was 374 ppm. The galvanizing plant stopped working dry ash at an annual loss of $400,000/year. They now have a machine to recover zinc from the dry ash.

In my own testing of baghouse dust, out of seven samples, the three highest readings for lead were: 0.72%, 1.03%, and 1.26% (All of these were for "dry" kettle operations.) In contrast, the lead for "wet" kettle operations were all below 0.01%.

The aluminum levels in these baghouse samples were all about 100 times greater than the aluminum in the zinc bath. Thus aluminum oxidizes on the zinc surface and is trapped out as aluminum oxide. Thus, of all the aluminum added, 95% shows up in the skimmings and only 5% is in the zinc coating on the steel. This shows why aluminum must be added to the kettle zinc on a daily basis.

In separate testing of dry ash the lead percentages are commonly between 2% and 5% in zinc baths with around 1% lead. Thus lead likely oxidizes on the zinc surface and is trapped out as lead oxide powder. The fact that high lead levels are found in the baghouse dust shows that the lead must be airborne to be trapped in the baghouse.

At one time I was a lead advocate for galvanizing. Indeed the increased fluidity, and decreased surface tension of the zinc melt is quite improved. In addition there is some evidence that drossing is easier.

Nowadays I have changed my position about lead because I now know that some nasty ash sticks to the steel in leaded kettles. This surprised me very much. Testing of this nasty ash showed it to be about 50% zinc chloride, 0.25% iron and 0.50% manganese (likely from manganese in the flux, coming from the steel). In kettles without lead this nasty sticking ash does not form. Since OSHA is regulatory in the USA it is important to find alternatives for lead in hot dip galvanizing. Indeed there are excellent methods to galvanize without lead.

I do not have data showing that any end user of galvanizing has been harmed by lead in the zinc. There was a lawsuit in California regarding a watering can galvanized by an out of state galvanizer who had lead in his zinc. There were no proposition 65 labels on the cans. According to my source, the lawsuit was settled out of court for a few thousand dollars.

Regards,

Thomas,

That's good useful information, thanks.
I have some other sources also coming, and can assess the risk more quantitatively now.
I think that the sources of exposure are well controlled, so there doesn't seem a panic to make sudden changes, but the whole risk needs to be evaluated properly.

A. There is a variety of information about lead in galv zinc. Some good, some a bit misleading (in both directions).

1% Pb dissolved seems a very common level to run in much of Europe.
Many running Pb free experience problems with fluidity, and colour. Some have experienced dross issues on kettle floors. (Pb is often used to float the dross off the kettle floor)

A. Sir:

By using this SHG zinc as you receive it, I would expect great difficulty in skimming the molten zinc surface and having the zinc stay liquid long enough to withdraw the steel. I would also expect dull grey coatings (a bit brighter if aluminum is a added). The zinc surface is also likely to have both dross pimples and numerous smaller pimples on the product. Zinc usage is likely to be 25% higher than it could easily be.

Regards,

A. Sir,

If you wish to use lead in your zinc then add between 1% to 1.5% lead by weight of the zinc in your kettle.

I do not like lead in the zinc for a number of reasons, one of which is that leaded zinc attacks cast iron excessively and some of the zinc coating falls off into the molten zinc.

I now have 28 kettles using my process with excellent results all using no lead.

Regards,

A. Hi Mina. Your question is the subject of this thread, as well as letters 38207, "Minimize/maximize spangle in hot dip galvanizing", 24568, and "Lead (Pb) in Hot Dip Galvanizing". The topic is not easily dispatched in a paragraph or two, and invariably you don't simply remove the lead, you do some other things as well. But we'll see if any knowledgeable galvanizers can respond to you. Good luck.

Regards,

A. Dear Mina,
We use lead in our coil galvanising continuous line in Iran; we add lead just for increasing the size of spangles on sheets and coils.

A. Sir: In the USA lead is now almost never used in the zinc anymore. Bismuth at 0.03% in the zinc has replaced the lead. There are other ways to make up for not having lead.

Regards,