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Stripping zinc with vinegar


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I am making a propane forge, and could only get some parts in galvanized. Small amounts of zinc being heated and burnt off I find reasonable (electroplated fasteners), but I want to avoid large exposure to zinc, even though it is a necessary nutrient and eliminated from the body reasonably well for a metal, it can quickly build up to toxic levels. I grind away zinc at least 1/2 inch back from any welds on galvanized sheet metal, avoid heating of hot-dip galvanized, solid zinc or die-cast parts, etc.

It was recommended by several people to use vinegar or muriatic acid to strip the zinc off. I decided to use white vinegar as I had some. I put my parts in a Ziploc bag with about a quart of vinegar. Overnight the bag inflated and split at the bottom, but the parts remained covered with vinegar. I removed and rinsed the parts, but was very surprised that half the zinc remained. This brings up the first question: How long and how much vinegar is needed to strip say a 2 inch diameter x 8 inch galvanized pipe? Yes, I know thickness of zinc varies from part to part, even in the same batch.

I cut up a rinsed out apple juice jug to make a bucket, put my parts in with fresh vinegar and put it in the corner, figuring I would not mess with them today. About 5 minutes later I had to get something out of the garage, and started coughing uncontrollably as soon as I walked in. I opened the garage door and moved the jug outside. It took about 10 minutes sitting outside to feel normal again.

My chemistry is very rusty, and the msds for distilled white vinegar (acetic acid 5%) and hydrogen gas seem to be not helpful. Vinegar vapor is listed as an irritant, but does not make me cough like that. I use it to clean with on a regular basis with little ventilation. Hydrogen gas is an odorless, tasteless, non-irritating, flammable, suffocation hazard. My second question is: Why is dissolving zinc with vinegar so vile? Is there a different, possibly toxic, gaseous product produced besides hydrogen?

Lastly, is muriatic acid significantly quicker at dissolving zinc? I mean minutes instead of hours or days. Will less be needed? Short soak time is very desirable when working outside without a roof available. Right now it is raining in my jug of vinegar and parts. Cost for a gallon of white vinegar is just a couple of dollars at the grocery store while a gallon of muriatic acid is $20-$30 last I checked. If volume of acid needed is similar, then I can wait a few days to remove the zinc, with my jug outside.

Thanks in advance for any insight
Phil

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Muriatic acid is only $5-$7 dollars per gal, alot of times it is sold in 4 gal cases which is probably what you saw at $25-$30. Most places will sell it by the gal though, hardware stores and pool supply stores will any way, I'ev seen it for as much as $10 a gal but have never personally paid over $6.
I have never used it to remove zinc but it is a lot more potent than vinegar so I would imagine it would work a lot faster.
I use to use it to clean seawater heat exchangers and if it is clean acid it would only take at most 10-15 min to clean and that is if it was really bad, but as the acid gets older and more used it gets weeker and takes longer to clean.

welder19

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Ok, I put my quart of vinegar into a larger container, added about a quart of water to cover, then added about a pint of muriatic acid. Remaining zinc was cleaned off with a fizz in about 20 min. When I dumped the remaining solution onto limestone gravel it ate about 2 inches deep, 2 ft circle. At least it is neutralized.

Conclusion:Muriatic acid is a fast, cost effective zinc removal agent that may remain effective after one use. It produces some serious fumes, and vigorously effervesces, almost like boiling water, so work outside, wear gloves, etc.

I guess I answered some of my own questions. Vinegar is definitely safer, I have a nice, chemical irritation on my knuckles from splashing while trying to pull the parts from the muriatic acid/vinegar solution before I decided to dump them. Using a dip wire and wearing rubber gloves would have solved that problem.

If I am ever needing to strip zinc off parts around non-adults, vinegar would be my choice, even though it takes much longer.

Original concentration of muriatic acid was 31.45%.

Thanks
Phil

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Tip; just use metals that are not galvanized, You just got a small taste of the hazards and by saying you have a skin irritation you were not following safety protocols at all for this. Trust an old fire captain that has seen a lot that there is just no reason you can relate that makes this a good idea. One side note is that if you had the right metal you could have gone on with your project and not had an exposure. This is a good hobby to learn and enjoy and has some inherent hazards try and limit them!

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Yup! you got it! Muriatic acid IS the nasty!!!:o Cuts through limestone and cement based materials like nobodies bidness.... I use if for carbon removal after anealing copper. I've been using the same sulution for about 6 months now and its STILL cutting strong. Watch out for rust... As I'm sure you've noticed. You will need to oil the steel or it will continue... Good luck on your forge:)

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Fe-wood:
Yep, noticed the rust in minutes between the vinegar and muriatic acid dips. I promptly sprayed them down after rinsing.
Rich:
Sometimes non-galvanized is difficult to source locally. I thought I would be better off using what I could get easily and stripping it. My knuckles are happily back to normal. I try to be safe, I have nitril gloves, just didn't put on a pair. I get complained at for making friends and family wear gloves, dust masks, ear plugs, etc., so I really should think more about it for myself. I thought the channel locks I used would have long enough handles, but the turbidity of the solution meant I could not see the edges to grab.

If there is a chemist here, let me know why the vinegar only dip set me coughing so badly. Obviously fumes were produced. Just post a nice (or not so nice) equation.

Someone should do a blueprint on chemical safety. I don't recall seeing one. If it exists, please point it out.

Phil

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Fe-wood:
Snip...
If there is a chemist here, let me know why the vinegar only dip set me coughing so badly. Obviously fumes were produced. Just post a nice (or not so nice) equation.

Someone should do a blueprint on chemical safety. I don't recall seeing one. If it exists, please point it out.

Phil


Phil, just a guess based on a lifetime of playing with chemicals, but very often when reacting acids with metal there exists a fine haze of very fine particles of acid above the container. It is created by the hydrogen bubbles bursting and projecting the liquid into the air. In still air and warm conditions the excess water will evaporate from the particles and they get to the point that convective currents carry them around.

Bottom line you end up sucking acetic acid into your nose.

Moral of the story: Chemical reactions are best done in open air with a fan behind you. Practical concideration. Do not store hydrocloric acid inside a dwelling structure or in a closed shed with metal tools near by. The plastic containers that hydrocloric acid is sold in have a nasty habit of gradually emitting hydrogen cloride gas which cause rusting and corrosion of nearly anything over time.
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Moral of the story: Chemical reactions are best done in open air with a fan behind you. Practical concideration. Do not store hydrocloric acid inside a dwelling structure or in a closed shed with metal tools near by. The plastic containers that hydrocloric acid is sold in have a nasty habit of gradually emitting hydrogen cloride gas which cause rusting and corrosion of nearly anything over time.


Boy, ain't that the truth!!! When I first started removing scale from the copper, I was doing it inside with the muriatic acid tank on the floor. over the weekend EVERYTHING within a 20 radius had a light haze of rust on it... even the hot rolled legs of a table! Now it lives outside (bad tank!).

I might add that having the fan behind you can cause an eddy effect and swirl the fumes into your breathing area. I have mine off to the side somewhat to avoid this. Just a thought-
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Muriatic acid is another name for hydrochloric acid (HCl) which is a strongly dissociating acid. This means that in solution there is a lot of hydrogen ions (protons) available to produce a strong acidic effect.

Stomach acid is HCl with a pH of approx 1.5. That is why I laugh when people say colas are bad for you because it will dissolve a nail in 2 weeks. You are putting cola into a much more acidic environment when you drink it so it's all relative.

When I worked in a chemistry lab, I used concentrated HCl or glacial acetic acid (think ultra-concentrated vinegar) to clean rust and mineral scale off of glassware when citric acid (a weaker organic acid) was taking too long, even when heated. Most of the work occurred in a fume hood but when you do get a whiff, your eyes water and you cough like crazy, especially with the glacial acetic acid.

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  • 2 months later...

I use the zinc that I remove to protect other tools. First I use phosphoric acid to remove the zinc. After that, I use the zinc laden phosphoric acid to parkerize steel.

Then I treat with oxpho blue to finish the process.

I originally got the method from Bob Smalser, a rather brilliant woodworker. Then I added zinc to the formula and have been happy with the results since.

The ferrule on the knife was a nut that I removed zinc from before heating it on the forge and then pounding it on a tapered punch.

Bob

17783.attach

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Hmm... I've been wondering about reblueing as I have a hunting rifle that suffered from cat pee before it came into my possession. Took at least 5 cleanings to stop smelling like a litter box. The urine stripped all coatings off the metal and caused some minor pitting. The weapon is currently heavily oiled and waiting for me to decide what to do.

Very interesting links. The repair of the shipyard gouge was nice and is appropriate for the woodworking chisel thread, even though it is not making the tool.

Phil

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  • 2 weeks later...
Muriatic acid is another name for hydrochloric acid (HCl) which is a strongly dissociating acid. This means that in solution there is a lot of hydrogen ions (protons) available to produce a strong acidic effect.

Stomach acid is HCl with a pH of approx 1.5. That is why I laugh when people say colas are bad for you because it will dissolve a nail in 2 weeks. You are putting cola into a much more acidic environment when you drink it so it's all relative.

When I worked in a chemistry lab, I used concentrated HCl or glacial acetic acid (think ultra-concentrated vinegar) to clean rust and mineral scale off of glassware when citric acid (a weaker organic acid) was taking too long, even when heated. Most of the work occurred in a fume hood but when you do get a whiff, your eyes water and you cough like crazy, especially with the glacial acetic acid.


Nice response full of facts. I just wanted to add that vinegar is only a 5% solution of acetic acid, which as SM pointed out, is a very weakly dissociating acid. To work a little more safely, instead of a 1:4 ratio (one cup acid, one quart water), it might be a good idea to use only one cup per gallon of water, which will give you a little bit under a 2% mixture of HCl.:)
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UF,
24 hours did not remove all the zinc, it removed about 50%, although I was not using a full gallon. I only had about a quart for the parts, originally a 2 inch diameter x 8 inch galvanized pipe cut in half, already drilled for the mounting bolts for my burners.

The zinc eroded away from the exposed edges faster than in the middle. Based on this I suggest filing, scraping, or grinding a small amount of zinc off to encourage electrochemistry.

As far as cat pee, the rifle sat under urine soaked boxes for an undetermined time not longer than 2 years. It was in the possession of my brother-in-law (the same person from the welder thread) until the government and his shrink said he can't have weapons anymore. He willingly surrendered it, but I am not allowed to sell it unless the rest of the family approves, which does not bother me. It was loaded when I received it, and the brass cartridges were pitted deeply. The cartridges were disposed of through the police dept.

Phil

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...24 hours did not remove all the zinc, it removed about 50%, although I was not using a full gallon. ......Phil


I appreciate the information. I have about 40 to 60 lag bolts that I removed from an old workbench. I figure it would be a shame to throw them away. Instead I would like to remove the zinc so that I can reforge the bolts into screw hooks. If I understand correctly, leaving the bolts in vinegar for a few days will remove the zinc?
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Yep, its that easy. When I need to next I am going to take a 5 gallon bucket and add 2-3 gallons of vinegar to it. Something to prevent aerosol vinegar from choking, such as a towel cover, is necessary. I would put the lid on top of the towel, but not lock it down the hydrogen gas needs an exit.

Vinegar also removes rust effectively, and that is likely my next use since I have a pile of small scrap sheet metal from barrel hoops I'm going to try cleaning and pile welding.

Phil

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  • 4 weeks later...

I think Charlotte has the right idea - an aerosol of chemicals is probably what got to you. But I doubt that was just the vinegar, as vinegar fumes and aerosol aren't that much different. I suspect what you got a snootful of was an aerosol of zinc acetate. That wouldn't be volatile, but you can make an aerosol of anything. And zinc fumes are a known hazard.

I've encountered such things myself. While cleaning iron in vinegar, I get a rather pungent "iron" smell from the mix. It takes a lot more iron to harm you than it does zinc, so this is only an annoyance. (BTW, an overdose of iron can be injurious. No need to panic, just be aware.) More to the point, when soapmaking one dissolves lye in water. The best approach is to work by weight and use ice for about half the water. Otherwise, (I surmise) an aerosol of lye forms above the hot mixture - very irritating to the nose.

For future reference, it sounds like you sidestepped a REAL hazard when that bag broke. Whenever you put zinc or other metals in acid, the gas that bubbles off is hydrogen. Hydrogen-air mixtures, like acetylene-air mixtures, explode (not just burn) over a very wide range of concentrations. Unlike acetylene, however, hydrogen diffuses very rapidly through air, so if not contained, you're not too likely to reach the lower explosive limit while pickling metal in acid. Do your pickling outside or in an actively ventilated room in the future.

Muriatic acid can be diluted a lot and still be much more effective than vinegar for the simple reason that it's a stronger acid. Vinegar is 5% acetic acid, so you could do a seven-fold dilution of your muriatic acid and have the same acid strength at a much lower pH - hence faster reaction.

And, as Charlotte mentioned, muriatic fumes will rust anything, quickly. Keep it away from fine tools. I doubt that HCl can actually penetrate the plastic container, but is surely can get by a poor seal.

Bruce
NJ

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  • 1 month later...

a few months ago i used a 1:1 ratio of water and muriatic acid to remove the zinc from a galvanized stove pipe 12 inches in diameter that i was using for my forge ventilation. i soaked it in a bucket for about 10 minuets and it was crystal clean. coated it in wax and that's that.

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I wont get into the bad stuff... seems pretty well covered... just one additional tid bit.... The fumes produced are caustic to bare steel... I have on many occasions set a plastic bucket out front of my shop to do just as you did.. and the fumes have greatly attacked the piles of metal several feet from the bucket.... Oh and one other thing... don't ever forget and leave anything you care about in the acid to long.... i turned a hard to find chain into a crumbled pile of bits by leaving it overnight on accident....

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  • 1 month later...

New easy container for smaller parts:
1 plastic coffee can with its snap on lid
1 piece of string
vinegar

Fill the can with vinegar,
add your part(s) up to about 6 inches long,
lay the string over the edge of the can (to vent the container)
snap lid on over the string

After soak is done, remove lid, remove string, remove parts. Put lid on properly and it is leak resistant on the shelf for next time.

I have not had vinegar corrode other metal in my workshop or garage.

Phil

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  • 5 years later...

Fe-wood:
Yep, noticed the rust in minutes between the vinegar and muriatic acid dips. I promptly sprayed them down after rinsing.
Rich:
Sometimes non-galvanized is difficult to source locally. I thought I would be better off using what I could get easily and stripping it. My knuckles are happily back to normal. I try to be safe, I have nitril gloves, just didn't put on a pair. I get complained at for making friends and family wear gloves, dust masks, ear plugs, etc., so I really should think more about it for myself. I thought the channel locks I used would have long enough handles, but the turbidity of the solution meant I could not see the edges to grab.

If there is a chemist here, let me know why the vinegar only dip set me coughing so badly. Obviously fumes were produced. Just post a nice (or not so nice) equation.

Someone should do a blueprint on chemical safety. I don't recall seeing one. If it exists, please point it out.

Phil

I'm not a chemist but..

the reaction produces hydrogen, I imagine you reacted because as it fizzed small vinigar  particles where carried with the hydrogen. Meaning you was breathing a vinigar vapour.

a chemist would tell you exactly but that's my theory.

andy

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