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airhuff
airhuff
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Long, long time ago I was employed to formulate rust removers for iron.We We needed to be concerned with toxicity, corrosivity, cost, waste disposal, effectiveness, speed, damage to the (uncorroded) metal, and flash rusting (rapid rusting once cleaner is rinsed off). 

Rust isn't just one chemical compound. It is generally hydrates of FeO$\ce{FeO}$ and Fe2)3$\ce{Fe2O3}$ (and there are a bunch of them, even if you exclude hydroxides). 

So, since different acids will have different effects with different chemicals, you won't necessarily be able to find the one magic bullet for any and all types of rust. The stronger the acid, the more metal will be attacked, unless passivation is used (there's two types chemical and electrical). Amines are also often used...). Strong acids Hydrochloric, sulfuric, nitric, are all more aggressive than the weaker organic acids. Naval Jelly (which I was involved with) uses phosphoric acid, but as you noted, it coats the steel/iron. These mineral acids can be dangerous and can't just be thrown out when finished. 

There are alternatives. One trick is to get the chloride, sulfate, or nitrate into solution by using a compound other than the acid. For instance, adding sodium chloride to a solution of citric acid should make the citric acid more aggressive, and yet, won't change the pH. (One reason for this is that FeCl3$\ce{FeCl3}$ is more soluble than the Iron Citrateiron citrate.) 

Some de-icers use nitrate or calcium chloride which may also be effective, and of course some fertilizers use nitrates, too (even some for indoor plants). So, if you'd rather not work with the strong acids (unless you're a careful person, you shouldn't work with them), you could try that approach. 

As far as I know, the only other acid commonly used for rust removal is oxalic acid. Hmmm, I think Zud cleanser usesuses it, if you can find it. It's a poison, so don't be licking your fingers until you've washed them (yes, even assuming you DID wear gloves!). I don't think it is much better than citric, in acid. In fact, I'd guess it's worse in terms of rust removal. 

Nitric acid will probably be difficult to find/buy. Hydrochloric acid is available (last I looked) at Home Depot ect. (Look in cleaning products, drain cleaners, and cement cleaners). Sulfuric acid, too. That is also used as battery acid, but I'm not sure if you can buy that at an auto parts store without the lead in it. Do not buy anything with lead in it! Do not use anything (like old battery acid) with lead (Pb) in it. Do not touch...you get the idea, right? Finally let me, look at a table of pKa values for the acids ... Yeah, the

The only other ions I might fool around with would be iodide and bromide, and maybe fluoride, just for grins and snickers. I've no idea where you'd get them from. (some aluminum cleaners (Aluminum Jelly?) have fluorides). Hint: one reason citric acid works pretty well is because the salt it forms is more soluble than something like iron phosphate, so it leaves the surface allowing further attack. 

So, effectiveness will depend not only on acid strength, but on iron salt solubility. Ideally, you want to avoid any oxidizing acid (since that will dissolve (oxidize) the metal) but in reality, a bit of metal loss helps get rid of that stubbornly clinging rust.

Long, long time ago I was employed to formulate rust removers for iron.We needed to be concerned with toxicity, corrosivity, cost, waste disposal, effectiveness, speed, damage to the (uncorroded) metal, and flash rusting (rapid rusting once cleaner is rinsed off). Rust isn't just one chemical compound. It is generally hydrates of FeO and Fe2)3 (and there are a bunch of them, even if you exclude hydroxides). So, since different acids will have different effects with different chemicals, you won't necessarily be able to find the one magic bullet for any and all types of rust. The stronger the acid, the more metal will be attacked, unless passivation is used (there's two types chemical and electrical. Amines are often used...). Strong acids Hydrochloric, sulfuric, nitric, are all more aggressive than the weaker organic acids. Naval Jelly (which I was involved with) uses phosphoric acid, but as you noted, it coats the steel/iron. These mineral acids can be dangerous and can't just be thrown out when finished. There are alternatives. One trick is to get the chloride, sulfate, or nitrate into solution by using a compound other than the acid. For instance adding sodium chloride to a solution of citric acid should make the citric acid more aggressive, and yet, won't change the pH. (One reason for this is that FeCl3 is more soluble than the Iron Citrate.) Some de-icers use nitrate or calcium chloride which may also be effective, and of course some fertilizers use nitrates, too (even some for indoor plants). So, if you'd rather not work with the strong acids (unless you're a careful person, you shouldn't work with them), you could try that approach. As far as I know, the only other acid commonly used for rust removal is oxalic acid. Hmmm, I think Zud cleanser uses it, if you can find it. It's a poison, so don't be licking your fingers until you've washed them (yes, even assuming you DID wear gloves!). I don't think it is much better than citric, in fact, I'd guess it's worse in terms of rust removal. Nitric acid will probably be difficult to find/buy. Hydrochloric is available (last I looked) at Home Depot ect. (Look in cleaning products, drain cleaners, and cement cleaners). Sulfuric acid, too. That is also used as battery acid, but I'm not sure if you can buy that at an auto parts store without the lead in it. Do not buy anything with lead in it! Do not use anything (like old battery acid) with lead (Pb) in it. Do not touch...you get the idea, right? Finally let me look at a table of pKa values for the acids ... Yeah, the only other ions I might fool around with would be iodide and bromide, and maybe fluoride, just for grins and snickers. I've no idea where you'd get them from. (some aluminum cleaners (Aluminum Jelly?) have fluorides). Hint: one reason citric works pretty well is because the salt it forms is more soluble than something like iron phosphate, so it leaves the surface allowing further attack. So, effectiveness will depend not only on acid strength, but on iron salt solubility. Ideally, you want to avoid any oxidizing acid (since that will dissolve (oxidize) the metal) but in reality a bit of metal loss helps get rid of that stubbornly clinging rust.

Long, long time ago I was employed to formulate rust removers for iron. We needed to be concerned with toxicity, corrosivity, cost, waste disposal, effectiveness, speed, damage to the (uncorroded) metal, and flash rusting (rapid rusting once cleaner is rinsed off). 

Rust isn't just one chemical compound. It is generally hydrates of $\ce{FeO}$ and $\ce{Fe2O3}$ (and there are a bunch of them, even if you exclude hydroxides). 

So, since different acids will have different effects with different chemicals, you won't necessarily be able to find the one magic bullet for any and all types of rust. The stronger the acid, the more metal will be attacked, unless passivation is used (there's two types chemical and electrical). Amines are also often used. Strong acids Hydrochloric, sulfuric, nitric, are all more aggressive than the weaker organic acids. Naval Jelly (which I was involved with) uses phosphoric acid, but as you noted, it coats the steel/iron. These mineral acids can be dangerous and can't just be thrown out when finished. 

There are alternatives. One trick is to get the chloride, sulfate, or nitrate into solution by using a compound other than the acid. For instance, adding sodium chloride to a solution of citric acid should make the citric acid more aggressive, and yet, won't change the pH. (One reason for this is that $\ce{FeCl3}$ is more soluble than the iron citrate.) 

Some de-icers use nitrate or calcium chloride which may also be effective, and of course some fertilizers use nitrates, too (even some for indoor plants). So, if you'd rather not work with the strong acids (unless you're a careful person, you shouldn't work with them), you could try that approach. 

As far as I know, the only other acid commonly used for rust removal is oxalic acid. I think Zud cleanser uses it, if you can find it. It's a poison, so don't be licking your fingers until you've washed them (yes, even assuming you DID wear gloves!). I don't think it is much better than citric acid. In fact, I'd guess it's worse in terms of rust removal. 

Nitric acid will probably be difficult to find/buy. Hydrochloric acid is available (last I looked) at Home Depot ect. (Look in cleaning products, drain cleaners, and cement cleaners). Sulfuric acid, too. That is also used as battery acid, but I'm not sure if you can buy that at an auto parts store without the lead in it. Do not buy anything with lead in it! Do not use anything (like old battery acid) with lead (Pb) in it. Do not touch...you get the idea, right? Finally, look at a table of pKa values for the acids.

The only other ions I might fool around with would be iodide and bromide, and maybe fluoride, just for grins and snickers. I've no idea where you'd get them. (some aluminum cleaners (Aluminum Jelly?) have fluorides). Hint: one reason citric acid works pretty well is because the salt it forms is more soluble than something like iron phosphate, so it leaves the surface allowing further attack. 

So, effectiveness will depend not only on acid strength, but on iron salt solubility. Ideally, you want to avoid any oxidizing acid (since that will dissolve (oxidize) the metal) but in reality, a bit of metal loss helps get rid of that stubbornly clinging rust.

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Li Zhi
Li Zhi
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Long, long time ago I was employed to formulate rust removers for iron.We needed to be concerned with toxicity, corrosivity, cost, waste disposal, effectiveness, speed, damage to the (uncorroded) metal, and flash rusting (rapid rusting once cleaner is rinsed off). Rust isn't just one chemical compound. It is generally hydrates of FeO and Fe2)3 (and there are a bunch of them, even if you exclude hydroxides). So, since different acids will have different effects with different chemicals, you won't necessarily be able to find the one magic bullet for any and all types of rust. The stronger the acid, the more metal will be attacked, unless passivation is used (there's two types chemical and electrical. Amines are often used...). Strong acids Hydrochloric, sulfuric, nitric, are all more aggressive than the weaker organic acids. Naval Jelly (which I was involved with) uses phosphoric acid, but as you noted, it coats the steel/iron. These mineral acids can be dangerous and can't just be thrown out when finished. There are alternatives. One trick is to get the chloride, sulfate, or nitrate into solution by using a compound other than the acid. For instance adding sodium chloride to a solution of citric acid should make the citric acid more aggressive, and yet, won't change the pH. (One reason for this is that FeCl3 is more soluble than the Iron Citrate.) Some de-icers use nitrate or calcium chloride which may also be effective, and of course some fertilizers use nitrates, too (even some for indoor plants). So, if you'd rather not work with the strong acids (unless you're a careful person, you shouldn't work with them), you could try that approach. As far as I know, the only other acid commonly used for rust removal is oxalic acid. Hmmm, I think Zud cleanser uses it, if you can find it. It's a poison, so don't be licking your fingers until you've washed them (yes, even assuming you DID wear gloves!). I don't think it is much better than citric, in fact, I'd guess it's worse in terms of rust removal. Nitric acid will probably be difficult to find/buy. Hydrochloric is available (last I looked) at Home Depot ect. (Look in cleaning products, drain cleaners, and cement cleaners). Sulfuric acid, too. That is also used as battery acid, but I'm not sure if you can buy that at an auto parts store without the lead in it. Do not buy anything with lead in it! Do not use anything (like old battery acid) with lead (Pb) in it. Do not touch...you get the idea, right? Finally let me look at a table of pKa values for the acids ... Yeah, the only other ions I might fool around with would be iodide and bromide, and maybe fluoride, just for grins and snickers. I've no idea where you'd get them from. (some aluminum cleaners (Aluminum Jelly?) have fluorides). Hint: one reason citric works pretty well is because the salt it forms is more soluble than something like iron phosphate, so it leaves the surface allowing further attack. So, effectiveness will depend not only on acid strength, but on iron salt solubility. Ideally, you want to avoid any oxidizing acid (since that will dissolve (oxidize) the metal) but in reality a bit of metal loss helps get rid of that stubbornly clinging rust.