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topic 20235

Lead in hot dip galvanising

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A discussion started in 2003 but continuing through 2019

2003

Q. Dear Sir,

As a consultant on environmental matters, I have been asked to address the question - "why is some lead added to hot dip galvanising baths?" So far I have received three answers

1) to protect the bottom of steel baths used to hold the molten zinc against corrosion through Zn/Fe alloy formation;
2) to give a "sparkle" to the finished galvanised work;
3) to "wet" the steel so that the final zinc coat is strongly adhering to the steel.

Could someone please enlighten me as to which of these is correct? Also, is it possible to perform hot dip galvanising without the necessity of adding lead to the bath?

Hope you can help,

Robert Angel
- Canberra, ACT, AUSTRALIA


2003

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.

M. Stroia
- Canton, Ohio


2003

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.

tom_rochester
Tom Rochester
Plating Systems & Technologies, Inc.  
supporting advertiser
Jackson, Michigan, USA
plating systems & technologies banner ad


April 26, 2012

Q. Dear Sir, Could you please help to share the information of the usage rate of EZDA and lead in hot dip galvanising production? Currently, our benchmarking is 0.50 kg per 1Mt production output for EZDA & also 0.50 kg per 1Mt production output for lead under normal production running. Is this correct? TQ, From SB Yeo, Malaysia

Yeo Seng Boon
Production - Malaysia


April 27, 2012

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

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



May 1, 2012

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

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA


May 4, 2012

A. 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 galvanzing? In the process or the product? At what stages, uses? And to who?

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



May 12, 2012

A. 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,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA


May 14, 2012

A. 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 overwhelming 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 hardware seems to labeled with Prop. 65 warnings, whether it contains lead or not -- which seems to achieve just exactly the opposite of what you would like to see. I can't agree with the state of California that the moral of "The Boy Who Cried Wolf" is that the boy would be right to cry wolf every time he sees a chipmunk or poodle, and I've personally seen the danger that these over-aggressive warnings have placed people in.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey



May 15, 2012

A. 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.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



May 17, 2012

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 percents 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.

Now days 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, Dr. Thomas H. Cook, Hot Springs, South Dakota,USA

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA


May 17, 2012

A. 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.

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland




September 21, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,

What is the best addition ratio for lead in galvanizing pot?
Based on what lead is add into kettle pot?either:

1)During drossing
2)Output(tonnage)

How percent of lead,should be maintain in kettle pot?

For flux solution-what is formula to maintain it?

Thanks/Regards

PJ SINGH
- Rawang, Selangor, Malaysia


First of two simultaneous responses -- September 25, 2012

A. Dear PJ;

There is no actual limit for lead in galvanizing pot. Lead can be dissolved up to 1.4% in galvanizing temperature range. Excess will be remain as molten lead at the bottom of the kettle. Also will be some protection for dross kettle contact, extending kettle life.

My personal advice would be adding a few hundred kilos to a few hundred tons after drossing (depending on your production rate and drossing frequency). Never be afraid of using excess lead as long as your environmental policies allow.

Ozge SARACOGLU
galvanizing - Ankara, TURKEY


Second of two simultaneous responses -- September 25, 2012

A. Sir:

The solubility of lead in zinc varies with zinc temperature. In deg F:

820 °F 1.2%Lead 840 °F 1.4%Lead 860 °F 1.6%Lead

It is true that about 1% lead in the zinc "improves" the galvanizing process and reduces zinc usage. However, in recent times I have found some negative aspects of using lead in the zinc including process, environmental, and health problems. About 0.4% to about 0.5% lead in the zinc MUST be avoided.

There are much better ways to get much better results, but I am not allowed to put them on Finishing.com., because it would constitute advertising. Ted Mooney has photos proving some of these ways, but it is unlikely that he can publish them.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA


No one faults you for not giving away your life's work for free, Dr. Cook, but it is you, not us, who declines to publicly share that information; you're welcome to post as much technical detail here as you wish. It is true that we must decline to print the hundreds of promotions for proprietaries that we receive each week.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey



October 4, 2012

A. There 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)

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



October 11, 2012

Q. Dear Sir,

Currently we are using Korea special high grade zinc jumbo block (Zn: 99.995% min)

The Chemical composition of these blocks are:

1)Zn 99.996
2)Al <0.0001
3)Cd <0.0001
4)Cu 0.0006
5)Fe 0.0003
6)Pb 0.002
7)Sn <0.0001


I have few questions:

1)Is there any proof show that-usage of zinc can cause "white rust " to the product.

2)What is the chemical composition for quality zinc block?

Thanks.

PJ SINGH
galvanizing - Rawang, Selangor, Malaysia


October 14, 2012

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,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA


December 24, 2013

I am going to start a new galvanizing plant. My kettle capacity is 150 MT of Zinc. How much lead must I put in the kettle before firing? And what grade of lead to use?

Shabbir Qureshi
- Jubail ,North Province, Saudi Arabia


December 26, 2013

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,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA



January 27, 2014

Q. Hi,
I want to know if we remove lead from the galvanizing dip, what will be the result on final product? How will it effect the surface quality of HDG?

Thanks

Mina Rad
- UAE, Dubai


January 28, 2014

A. Hi Mina. Your question is the subject of this thread, as well as letters 38207, "Lead free hot dip galvanizing", 24568, "Lead (Pb) in Hot Dip Galvanizing", and 55727, "How much lead needed to start up a new galvanizing kettle?". 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,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey



January 30, 2014

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.

Mohammad Reza Ourang
R&D Center - Qazvin, Iran



October 19, 2019

Q. Sir,
My kettle capacity is 181 MT. Zinc
How much lead in kettle?

Vinayak Retar
Tata Projects Ltd. - Nagpur.Maharastra ,INDIA.


October 29, 2019

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, Dr. Thomas H. Cook, Hot Springs, SD USA

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs SD USA



October 25, 2019

Q. Does anyone know of a published investigation/risk assessment for Lead emissions to air from hot dip galvanizing?

Peter Johns
Environmental Assessment - Perth Western Australia

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