One for the chemists

[WotEver]

I’m cleaning some rusty parts in 45% Phosphoric Acid. When I remove them I’ll have a brown sludge at the bottom of the container. If I decant the more-or-less clear liquid and chuck the sludge will I have ‘active’ phosphoric acid, something somewhat less active, or something else entirely?

 

Thanks in advance. 

 

Oh... and do I have to neutralise the steel/iron or can I just rinse it thoroughly?

[Machpoint005]

Phosphoric acid works by converting iron oxide into iron phosphate. The brown sludge will contain phosphates, which can only have come from the phosphoric acid. The acid will therefore now be in a lower concentration but I can't tell you how low. It might well contain other substances to0.

[Boater Sam]

The effective strength will go down with use, the acid converts rust, ferrous oxide to iron phosphate, sludge. The solution will effectively be diluted.

Thorough rinsing should be fine, the instructions for rust cures containing phosphoric acid, Jenolite, etc. just say wash well. The rusty parts will be black.

 

Beaten to the post, that's why I don't back horses.

Edited May 9, 2019 by Boater Sam

[WotEver]

Okay, thanks both, as I suspected

 

[tree monkey]

1 hour ago, WotEver said:

Okay, thanks both, as I suspected

 

Now the technical question is answered

 

I tend to brush any waste onto bits of less vital metal work, for example I have a few Jerry cans that had small rust spots, brushed out the vactan, followed by primer etc from the same paint job

[bizzard]

1 minute ago, tree monkey said:

Now the technical question is answered

 

I tend to brush any waste onto bits of less vital metal work, for example I have a few Jerry cans that had small rust spots, brushed out the vactan, followed by primer etc from the same paint job

Chinese jelly can no prenty lust. 

[WotEver]

2 hours ago, tree monkey said:

Now the technical question is answered

 

I tend to brush any waste onto bits of less vital metal work, for example I have a few Jerry cans that had small rust spots, brushed out the vactan, followed by primer etc from the same paint job

Well, I’ll have plenty of waste... using 10 litres at present and it’s only just enough to cover all the items. 

[Cheshire cat]

Wow. It's pretty nasty stuff. It discolours paint

 

If anyone is wondering there is a place in Lymm that does it on ebay through the post

[Dr Bob]

12 hours ago, WotEver said:

Well, I’ll have plenty of waste... using 10 litres at present and it’s only just enough to cover all the items. 

I would guess the actual weight of rust you are converting is not that high so the depletion in phosphate ions will not be that great even when considering the larger phosphate ion.

I would doubt you are weakening the acid strength that much. I could calculate it but my head might hurt and it would only be useful if we knew the weight of rust removed.

[WotEver]

4 minutes ago, Dr Bob said:

I would guess the actual weight of rust you are converting is not that high so the depletion in phosphate ions will not be that great even when considering the larger phosphate ion.

I would doubt you are weakening the acid strength that much. I could calculate it but my head might hurt and it would only be useful if we knew the weight of rust removed.

Thanks. I have a scummy froth on the top at present. I’ll scrub the items later and see the best way to recover the acid. Would I be ok filtering it through a strong paper towel?

[Dr Bob]

1 hour ago, WotEver said:

Thanks. I have a scummy froth on the top at present. I’ll scrub the items later and see the best way to recover the acid. Would I be ok filtering it through a strong paper towel?

Probably.....if you need to? Maybe just scoop off the frothy top and decant the clear liquid. The Iron III oxide that is formed in the reaction should settle to the bottom of the liquid. If you are using the liquid just to remove rust then it wont matter if there is still some rust contamination in it. I dont think it is an equilibrium reaction so the presence of any iron III oxide or Iron phosphate will not slow it down.

If you want to filter through paper then yes that will work ......but just be a bit messy.

Messy didnt have a good game on Wednesday ...did he?

Co'mon you Reds.

[WotEver]

25 minutes ago, Dr Bob said:

Probably.....if you need to? Maybe just scoop off the frothy top and decant the clear liquid. The Iron III oxide that is formed in the reaction should settle to the bottom of the liquid. If you are using the liquid just to remove rust then it wont matter if there is still some rust contamination in it. I dont think it is an equilibrium reaction so the presence of any iron III oxide or Iron phosphate will not slow it down.

If you want to filter through paper then yes that will work ......but just be a bit messy.

Messy didnt have a good game on Wednesday ...did he?

Co'mon you Reds.

Thanks again. I’ll just decant it as is then, leaving behind as much sludge as I can and use that to spread around next-door’s huge tree... (did I just say that out loud?)

[Dr Bob]

27 minutes ago, WotEver said:

Thanks again. I’ll just decant it as is then, leaving behind as much sludge as I can and use that to spread around next-door’s huge tree... (did I just say that out loud?)

Flush it down the loo.

Phosphoric acid is good for cleaning toilets. We used to do it all the time on our lumpy water boat.......putting Coke down the toilet (the one you can buy in bottles, not the stuff you buy in the little bags) as Coke is essentially dilute phosphoric acid.

 

[WotEver]

5 minutes ago, Dr Bob said:

Flush it down the loo.

Does it dissolve limescale?

[tree monkey]

35 minutes ago, WotEver said:

Thanks again. I’ll just decant it as is then, leaving behind as much sludge as I can and use that to spread around next-door’s huge tree... (did I just say that out loud?)

Oy

[Sapphal]

14 minutes ago, WotEver said:

Does it dissolve limescale?

Yes

[cuthound]

2 hours ago, WotEver said:

Thanks again. I’ll just decant it as is then, leaving behind as much sludge as I can and use that to spread around next-door’s huge tree... (did I just say that out loud?)

 

I had a friend whose hedge was dying off. He thought the neighbour was poisoning it, but soil analysis didn't show anything.

 

He then set up a surveilance camera which captured his neighbor pouring boiling water on the roots! ?

[LadyG]

2 hours ago, tree monkey said:

Oy

copper nails

[tree monkey]

12 minutes ago, LadyG said:

copper nails

Just blunts saws when the tree does need felling