Muriatic acid?

[DieMonkeys]

Instead of using phosphoric acid, couldn't I use muriatic acid to remove the rust from my gas tank?

Ospho costs $20.99 for a gallon while muriatic acid is only $3.99 a gallon. I do get a 20% discount but there's still a big difference between the two.

[Billy Ricks]

Muriatic is more likely to damage sound metal. Phosporic acid acts only on the rust. You can pick up a gallon at Home Depot in the paint department for about $12.

[Boondocks]

The argument against muriatic acid (hydrocloric acid) is:
It's highly corrosive and is very toxic.
It will remove rust, but will also rapidly cause rust on good surfaces.
It leaves no protective coating and the surface(s) must be quickly treated with an antirust agent.

Phosphoric acid is less damaging to the treated surface, and the resulting black coating may be painted (or oiled if not painted). It is the active ingredient in products like Naval Jelly.

I would not use muriatic acid in a confined area like a gas tank to remove rust. It would likely cause more problems than it solved.

[themess]

Muriatic acid means, "industrial grade hydrochloric acid", which means that it isn't quite as chemically pure as the laboratory grades. It is a strong acid, but not as strong as sulfuric or nitric acid. It releases the gas HCl, which is extremely noxious and can be dangerous. I strongly discourage its use by people who haven't been trained in handling dangerous chemicals.

Phosphoric acid is a mild acid. It is an ingredient in many soft drinks, especially colas. Industrially, it is used to remove rust from lightly rusted metal. With the correct chemistry, it can leave a phosphate coating on steel, which both inhibits rust slightly, and provides a substrate that improves adhesion of paint and some other coatings. While phosphoric acid shouldn't be played with, it isn't nearly as dangerous as strong acids, and once eye protection is used and it is kept far away from children and animals, it can be used safely by most people.

[rustybronco]

It is a strong acid, but not as strong as sulfuric or nitric acid. It releases the gas HCl, which is extremely noxious and can be dangerous. I strongly discourage its use by people who haven't been trained in handling dangerous chemicals.

I once mixed sulfuric and nitric acid (dont remember how many moles) in water to dissolve iron nails, I did it outside it made gobs and gobs of yellow orange smoke, bubbled, popped and did all sorts of nasty things, NASTY NASTY STUFF!!!!!!!!!!!!!!!!!

[MissFabulous]

Phosphoric acid is a mild acid. It is an ingredient in many soft drinks, especially colas. Industrially, it is used to remove rust from lightly rusted metal. With the correct chemistry, it can leave a phosphate coating on steel, which both inhibits rust slightly, and provides a substrate that improves adhesion of paint and some other coatings. While phosphoric acid shouldn't be played with, it isn't nearly as dangerous as strong acids, and once eye protection is used and it is kept far away from children and animals, it can be used safely by most people.

This makes it very tempting to try cleaning out my gas tank with coca cola and marbles... I think I'll try old gas first though! The rust in mine isn't too bad... I've been told so many options for cleaning it... I want to try the most benign methods first.

Is phosphoric acid the stuff in POR-15? The cleaning portion of it anyway? What is the stuff in CLR and Lime Away? How bad are these to use on metal?

[waterman]

This thread brings back ugly memories. In organic chemistry, I had to clean a round bottom flask that we had burnt some organics to carbon in. After soaking a week with acetone to remove stain the professor suggested a mix of nitric and sulfuric acid for removal. I of course didn't think to rinse flask before adding the acids. After a quick pouring and swirl, I made three steps before I had a volcano of noxious orange stuff violently exitting flask all over my arms. With some presence of mind, I yelled to have someone turn on the chemical hoods and threw the flask in before I ran to sink. After the pain subsided, the chemical burns appeared on arms and hands. Good times...

Both muriatic and phosphoric acids are strong acids. Mixing acids makes them stronger. Always add acid to water not other way around. Both will remove rust, but phosphoric as stated, leaves behind a better surface for a coating.

I have used POR 15 products for a tank that was very rusty with good results. They used to have a kit with appropriate cleaners (mostly acids) for motorcycle tanks that was around $40.

Be sure that you rinse and drain tank well with water before hitting with acid since highly concentrated acids can do nasty things to organics like gasoline. If you are going to epoxy it (kreem or por) make sure tank is bone dry. A hair dryer (don't tell wife) stuffed in the gas cap will speed process.

Sorry about length. In my lab story, I was fine except for the pretty lab partner who thought I was screwing off in class and wouldn't talk to me for weeks.

[cberkeley]

I think you inadvertently got very close to making a very powerful explosive, if my chemistry class memory is in tact:shock:

[Boondocks]

This makes it very tempting to try cleaning out my gas tank with coca cola and marbles... I think I'll try old gas first though! The rust in mine isn't too bad... I've been told so many options for cleaning it... I want to try the most benign methods first.

Is phosphoric acid the stuff in POR-15? The cleaning portion of it anyway?

Yes.

What is the stuff in CLR and Lime Away? How bad are these to use on metal?

They both contain phosphoric acid. They should work to remove rust, but I would use POR-15 since it makes products specifically formulated for rust removal and prevention in fuel tanks.

[jpaul]

I think you inadvertently got very close to making a very powerful explosive, if my chemistry class memory is in tact:shock:

Sulfuric and nitric acids are two of the three components needed to make nitroglycerine or TNT.
The best way to remove rust from a tank or any surface is to buy something formulated to do the job. Otherwise you risk serious injury if you screw up, or get stuck with hazardous chemicals left around when the job is done. It ain't worth it to save a few bucks.

[rustybronco]

Sulfuric and nitric acids are two of the three components needed to make nitroglycerine or TNT.

i didn't question the gentleman whom i got them from when he asked, what was i going to do with them.. i knew what could be done in the wrong hands.
rust bluing a shotgun was my answer...and its intended use.

[waterman]

You are right about the nitro. In a somewhat different manner as you need different organics to do that. I did make some by accident once and will not tell that story publically. I will say very dangerous and unstable stuff. Not to be played with.
In my lab situation it was the cleaving of the acetone that rendered the noxious nitric gases (nitric oxides I believe). Thankfully, these experiences taught me to consider what may occur when mixing chemicals and maybe in a broader sense life. Not too much of a surprise, I work with dangerous chemicals daily.

[joeyplumley]

Use electrolysis - it costs next to nothing! Works great on our tanks w/ the level float inside - you should probably remove that if you're going to dump acid in there. I don't know if either acid would eat up the plastic, but electrolysis will have no effect on it. Heck, you COULD leave the petcock in, although I wouldn't since it'd get so much crud in it.

Electrolysis setup:
http://www.altelco.net/~jacil/clay/motorcycle/KElecSetup.html

Detailed explanation:
http://users.eastlink.ca/~pspencer/nsaeta/electrolysis.html



Phosphoric works good. Look for the Behr "Concrete Etcher" at HD or Lowe's. I think it was $15/gal last time I bought some. Stay away from muriatic - your tank will begin rusting instantly while you rinse the acid out.

[themess]

This makes it very tempting to try cleaning out my gas tank with coca cola and marbles... I think I'll try old gas first though! The rust in mine isn't too bad... I've been told so many options for cleaning it... I want to try the most benign methods first.

Is phosphoric acid the stuff in POR-15? The cleaning portion of it anyway? What is the stuff in CLR and Lime Away? How bad are these to use on metal?

Coca Cola just might work. It has a pH of about 2. The sugar in it would temporarily seal the surface. I don't know if there are sharp bends inside a gas tank, ones that marbles couldn't get to.

Phosphoric acid is likely in some of the products that you mentioned. I know that I see it listed on many strong cleaners. As the instructions say, try it out on a small area first. There are just too many kinds of metals to say in advance.

I once mixed sulfuric and nitric acid (dont remember how many moles) in water to dissolve iron nails, I did it outside it made gobs and gobs of yellow orange smoke, bubbled, popped and did all sorts of nasty things, NASTY NASTY STUFF!!!!!!!!!!!!!!!!!

"Your ass will be grass if you add water to acid!"

"Aqua Regia" is pretty close to the strongest aqueous acid available. It is made by adding a small amount of sulfuric acid to nitric acid, which shifts the dissociation equilibrium of the dissolved HNO3 to the right.

No professor should tell any undergraduate student to make it. Straight nitric acid should have cleaned out that flask pretty well, and it is especially good at attacking organics. Another one that is very good is hot perchloric acid. Either one is far safer than aqua regia. And even better would have been to put ammonia in it and let it sit for a week.

[Mike_H]

I agree, Coca-Cola will probably dissolve the rust. It is pretty nasty stuff. Don't believe me, spray it on your beautiful bike paint job, and come back after a week...No, don't. The coke will pit the paint anywhere there is a droplet of it. Mythbusters also used it to clean the rust from chrome. Worked better than they're storebought stuff...