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topic 29208

The effect of citric acid on steel

A discussion started in 2001 but continuing through 2019


Q. I was just wondering if ordinary (household) citric acid has a corrosive effect on steel, aluminium, iron and copper. This is for a school assignment.


Brendan M [last name deleted for privacy by Editor]
- Sydney, N.S.W, Australia


A. I recommend trying the experiment yourself. Go get some lemon juice and put it on the various metals and record the results. Your testing may take anywhere from a few minutes to a few days, and you will have the satisfaction of discovering the answer on your own.

Good luck.

Dan Brewer
chemical process supplier - Gurnee, Illinois



Dan Brewer sure beat me to the punch! Yes, try things out yourself ... but to get some faster results, what about heating up the citric juice, this increases the molecular activity (so someone once said to me) and being lazy and as a teenager (well, I was one once, long, long ago) I'd want a fast answer.

Others follies teach us not
Nor much their wisdom preaches
But most of sterling worth is what
Our own experience teaches. (by ANON, not by me!)

You might remember those lines. Very true, too. And by doing something like this YOURSELF, you'll always, always remember it which you won't if you are given a simple answer.


freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Science Fair Projects for Elementary Schools
from Abe Books


Science Fair Projects
from Abe Books


Does lemon juice rust steel?


Q. I am doing a science fair project on the corrosion effect of different substances on steel. One of the substances I chose was lemon juice (citric acid). I have to say what is in the citric acid that's causing the steel to rust. I have no idea. Can you tell me?

Thanks heaps,

Emma R. [last name deleted for privacy by Editor]
Student - Wellington, New Zealand


A. Hello,

Citric acid reacts very quickly with iron, but does not in itself rust the iron. The water in the lemon juice will help to rust the iron, however, in the presence of air. A steel nail dropped into a citric acid solution will dissolve in a matter of hours. The same thing happens if you drop it in a bottle of "Coke", which has citric acid, phosphoric acid, carbonic acid and other things in it for flavor.

If you need help with your project, let us know. We work with citric acid products every day and have a lot of data.

lee kremer
kremer signature
Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner


thumbs up signThanks Lee. "Dissolve" in Coke is probably too strong a word though; let's say "begin to dissolve".

There's a lot of urban legend about Coke, and I've found that a 12-ounce bottle of Coke will not completely dissolve even the innards of a copper plated zinc penny in a month, let alone a nail in a couple of hours :-)

Part of the discrepancy probably arises from the fact that acids are consumed by the dissolution of the metals. Hollywood shows us a test tube of acid poured on a 2-foot thick block of metal eating it's way through at an inch a second, but in fact all of that acid, even the strongest acid, would be totally consumed by the first 1/32" of metal or so. Perhaps if you put a steel nail under a small waterfall or jet of fresh Coke it could dissolve in relatively short order, but probably not in a single can in a lifetime.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Why does juice clean copper?


Q. I work with pure lime, orange, lemon and grapefruit juice (which I understand contains citric acid) for a science project in school. I tested the pH value of the respective fruit juices and placed separate pieces of copper strips in each fruit juice. After a while I saw that the copper strips turned shinier than before. Is there an explanation for this?

Nas W [last name deleted for privacy by Editor]
- Singapore


A. Pure citric acid does not corrode iron. In fact, it is a very effective rust remover and used widely for that purpose! As you have noticed, it will remove corrosion and leave clean, bare metal. Corrosion will set in due to the contact with air and humidity afterwards. I have myself cleaned rusted, chalked up cast iron cylinder heads by dumping them in citric acid solution and they came out like new.

Holger Kneisner
- Braunschweig, Germany


Q. To whom it may concern,

I am doing an experiment regards on citric acid and rust in school. As I was doing my experiment, I was curious of what is the chemical equation of the citric acid and rust or either the product of the citric acid and rust when its being reacted together. It would be appreciated if you know any of references or websites that would help me to get more information about my experiment.

Thank You.

Ramona P [last name deleted for privacy by Editor]
student - Pago Pago, AS, American Samoa

A. Hi Ramona. The thing is, acids will attack ("begin to dissolve") metals, with variable success depending on the particular acid and the particular metal ... but they will dissolve the "tarnish" or "rust" (metal oxides) easier and faster than they dissolve raw metal. So the first thing you usually will see is tarnish removal or rust removal. That is because the metal oxide that was on the surface is now dissolved in the acid. But if you let the acid evaporate so the metal that was dissolved in it cannot stay dissolved, you'll see a rusty mess :-)


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Does citric acid dissolve copper?

2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi I'm wondering for a school project will citric acid rust away a strip of copper and if so how long would it take?

Jessica J. [last name deleted for privacy by Editor]
student - Port Stephens NSW AUST

March 2014

A. Hi Jessica. In science class we have to use words more carefully than around the house. Copper doesn't "rust" because "rust" is defined as the corrosion product of iron; and copper is not iron and doesn't contain iron -- but copper can dissolve or corrode or tarnish.

As Lee says above, the citric acid itself doesn't cause rust, it's a bit complicated. The acid can dissolve copper, but it's oxygen in the water that combines with the dissolved copper to form copper oxide tarnishes. A large bowl of citric acid might completely dissolve a very thin and very small piece of copper foil in a reasonable number of days.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


Q. In a book called "400 Hints for Homes" the following sequence sequences is given for the removal of a rust stain: "Moisten with lemon juice, add salt and dry in the sun. Rinse off and repeat if necessary". Can I know the chemistry and physics of this operation

Michelle [last name deleted for privacy by Editor]
student - Batu Caves, Selangor, Malaysia


A. Hi,

I believe all depends on concentrations. The nail in citric acid may be true at 100% concentration, but we actually demonstrate the OPPOSITE. At around 0.2% (2000 ppm) of citric acid in water, a nail actually coat itself gray and ABSOLUTELY NO rust appears. Pure tap water results in comparison in ugly corrosion.

I did no detail study on concentrations and their impact.

Does anyone know at what concentrations citric acid acts corrosive, and at what concentrations it acts inhibitive on corrosion? Citric acid is actually termed to be an ANTI-OXIDANT. Go figure.

Looking for any clarifications.


Hans J.Krause
- Montreal, Quebec, Canada

thumbs up signHi Hans, I'm not claiming that your facts are wrong -- I don't know. But most or all acids remove/deter rust while the object is immersed in them because they dissolve rust faster than they dissolve pure metal.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

February 25, 2012

Q. I'm working on a project to find out why lemon juice can remove rust on a paper clip. Can anyone give me a help? I'll really appreciate that. Thanks.

Ruth Y [last name deleted for privacy by Editor]
- Hong Kong, China

February 27, 2012

A. Hi Ruth.

Acids like citric acid dissolve metals but they dissolve rust (metal oxide) faster. Your chemistry book may tell you that an acid plus metal will yield hydrogen plus a salt of that metal, so the rust dissolves as a metal salt. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

February 28, 2012

Q. Chinese old folks believe cooking lime juice or vinegar in a steel pot is bad for health.
So is this a myth or it is true? As there is a chemical action between citric acid and steel when heat is added, we are consuming the rust and whatever deposit in the food that are harmful of our body.

Q Susan [last name deleted for privacy by Editor]
- Singapore

March 2014

A. Hi Susan. Surely, yes, the acid in lime juice or vinegar will dissolve some amount of iron, but iron is an essential nutrient, not a poison. But does it dissolve so much that it could make for a harmful overdose, or is it such a minimal amount that it has no effect on health? Sounds like a great topic for a research paper: you'd have to experiment to figure out how much iron it dissolves, then compare that to what a normal daily intake of iron should be. Sounds very interesting! Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Metal Samples

January 5, 2013

Q. What happens when you put copper, steel, aluminum, and brass in pure lemon juice? And why does it happen.

Jonah [last name deleted for privacy by Editor]
- New York, New York, USA

January 6, 2013

A. Hi Jonah. Let us know what happens when you put samples of those metals in lemon juice, and we'll try to help you explain your project results. Best of luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

November 3, 2013

Q. What liquid will make a steel nail rust faster: orange juice, vinegar, salt water, or tap water? Please help. : )

Anna [last name deleted for privacy by Editor]
- Weehawken, New Jersey, U.S.A.

November 4, 2013

A. Hi Anna. Get four non-metal bowls, put those four liquids in the bowls, put a nail in each (fully submerged) and start recording what you did and what you saw in your lab book (a notebook where you've pre-numbered the pages, so you are not tempted to rip a page out). If you think you recorded something incorrectly, strike it through once but leave it legible.

Then come back in a week with your observations and we'll be happy to comment on them. But please don't make the mistake of trying to figure out which of the four liquids should cause the most rust until you've actually done the experiment. Because if you do, you will be tempted to discount contrary observations and give too much weight to observations which agree with your expectations. You would then be learning a lesson in "junk science" instead of real science; junk science should be avoided until you are a hungry climatologist looking for a grant :-)
Best of luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

May 4, 2015

Hi, my question regarding citric acid is whether this citric acid is helpful in obtaining No. 8 stainless steel finish?

Please solve my query.

DHARANI moorthy
- banglore karnataka india

May 2015

thumbs up signHi cousin Dharani. Yes, I do think it can be helpful.

Please detail your situation and why this question has come up and I'm confident we can very quickly offer a more helpful answer. Thanks!


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

August 24, 2015

Q. In cleaning pennies with lemon, does other amount of salt make a difference in the chemistry of the experiment.

continue okorie
- Houston Texas,USA

A. Hi Continue. You already recognize that the cleaning is better with some salt, than with "no" salt, but you probably also recognize that there is no such thing as "no" when it comes to chemical concentrations. Surely there are one or more molecules of salt in your quintillions of molecules of lemon juice even if it is ultrapure. So you already know the answer, that at least within some possible limits, increasing the salt concentration improves the cleaning. Exactly how much salt you must add to reach maximum efficiency without wasting any salt probably depends on the size of the lemon and it's ripeness.


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

Black residue on steel from citric acid?

August 8, 2016

Q. I am trying to use citric acid to remove some rust from old tilling disc blades. They have been sandblasted, and when immersed in a solution of citric acid they quickly develop a black film that smells like petrochemicals. In the same bath I placed some rusty horseshoes which came out just fine, with the rust removed. The black residue and smell on the disc blades is very confusing. I am concerned because I am trying to make cooking pans out of these disc blades. Any help or suggestions are greatly appreciated!

Bland Hoke
- Jackson Wyoming USA

August 9, 2016

A. Horseshoes are soft iron with a low carbon content.
Tilling discs will be high strength steel with a relatively high carbon content. Acid removes the rust and dissolves some iron exposing the black carbon. Another pass through the sand blaster will remove the carbon.

geoff smith
Geoff Smith
Hampshire, England

September 21, 2016

Q. Hi, we are doing a lab in chemistry. One of the application questions asks why kool aid should not be put in a metal container (the citric acid in the kool aid will eventually give the kool aid a metallic taste if put in a metal container). What happens here and why does this happen?

Rebecca Thomson
- London, ON, Canada

September 2016

A. Hi Rebecca. The assertion is that the Kool Aid will dissolves some of the metal into it -- enough to taste. It is probably a combination of chelation and metal dissolution by acid as previously explained on this page.

But what are you testing for and how?


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

September 29, 2016

A. It depends on the metal!

I expect most metal containers meant for holding beverages will be stainless steel, which ought to be fine. I would see nothing wrong with using titanium, either. Aluminum would be okay in the short term, though there is a reason that aluminum beverage cans are coated on the inside.

But a whole discussion on what acids at what strengths will dissolve which metals is probably more than the class assignment is looking for. ;)

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

November 5, 2016

A. Using hydrochloric (muriatic acid) to de-rust steel is asking for trouble down the road. Sure, it's very effective at dissolving surface rust, but no matter how you neutralize it with lye or sodium bicarbonate (baking soda), or wash with water, it leaves behind chloride salts trapped in the surface. Unless you immediately follow up with another form of surface treatment, the highly electronegative chloride will attract oxygen from the air, causing rust to develop. Once started, that form of rust is like a cancer, and slowly eats away the base metal.

3% citric acid in hot water is my preferred solution to dissolve rust off of steel. This dilute weak acid WILL NOT attack the base metal, unlike muriatic acid. I've used it many times. It's cheap, it's relatively green, and it's safe.

Alternatively, phosphoric acid, at about 3% in hot water is much safer to work with than is muriatic acid, and will remove rust very quickly, but you must keep it warm. If left in too long, black iron phosphate will deposit on the surface, which might not be what you want. Nevertheless, that coating is very rust resistant, and forms an excellent bond with metal primers if the piece is to be painted. I keep an old ceramic electric crock pot in my shop for derusting small parts. I mix either 3% citric acid, or 3% phosphoric acid in the pot, drop in the parts and turn the pot on low. A few hours later the parts are clean. A few times, I've left the pot running overnight for very heavily rusted parts.

And that's all I have to say about that!

Tom Nelson
- Tustin, California, USA

September 13, 2017

Q. Citric acid: can it be mixed with naphtha to remove scales like iron sulfide?

Adel Zubedi
N/A - Hadhramaut, Seyun, Yemen

May 18, 2019

Q. Are we talking about the citric acid that can be used in cooking?

Rody j Hayes
- newport uk

May 2019

A. Hi Rody. When we use citric acid for industrial purposes there may be additives or specific concentrations for specific applications. But for the student science projects on this page, yes, food grade citric acid [linked by editor to product info at Amazon] should be fine. Good luck with it.


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

Citric acid for cleaning phosphate buildup from spray tips, etc.

June 17, 2019

Q. I am looking for an industrial application to dissolve zinc phosphate buildup from plastic parts, spray tips, etc., that are used as a pretreatment in a powder coat paint application.
My first idea was to use muriatic acid at an approximate 3:1 ratio with water. However, I have not been able to find data on possible secondary chemical reactions (read somewhere about the formation of chlorides, possibly chlorine gasses).
With that being said, I am now considering testing a small sample of parts in citric acid at full strength and a 2:1 ratio.
Any ideas if this will dissolve the zinc and any possible negative chemical reactions I need to consider?

Stuart Bland
Powder coating paint industry - Jacksonville, Texas USA

June 17, 2019

A. Normally hydrochloric acid is used, same as muriatic acid.
The concern is what is called white nubbing caused by the chlorides, a good rinsing before use will prevent this. The reputable suppliers also add fluorides in small amounts to the make up and replenisher to prevent this.

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada

June 18, 2019

Q. Thank you very much for the reply. Muriatic acid was my first thought for use, I am considering a less invasive chemical to use, primarily due to safe handling for my employees, that was the rationale for considering a concentration of citric acid. Long term exposure to high concentrations of citric acid in fruit juices and soft drinks has proven to be detrimental to tooth enamel, though I may try to dissolve zinc phosphate from plastic parts, see if it will work. If so, considerably safer to use and waste will be more environmentally friendly at disposal.

Stuart Bland [returning]
powder paint application - Tyler, Texas USA

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