Sciencemadness Discussion Board

Removing lead stuck to Stainless Steel

UnintentionalChaos - 4-6-2007 at 20:21

Just throwing a bit of handy advice out there, but if I'm working with lead as electrodes, for example, they usually come out of solution with all sorts of oxides and junk on them. To clean the lead up, I melt it in a stainless crucible and pour new electrodes, the molten lead pouring out easily from under the oxide slag. The issue is that while the lead doesn't stick to the crucible, the oxides tend to stick and often attach small chunks of lead metal to the walls with them. I find these very frustrating to get off since HCl and H2SO4 are useless at removing lead (the HCl actually doing damage to the stainless by complexing the chromium oxide protective layer). Nitric is a bit too precious for cleaning a crucible and scrubbing proves useless. I have recently found that even fairly dilute mixtures of hydrogen peroxide and acetic acid readily attack lead metal while doing absolutely nothing to stainless steel. I used regular 5% vinegar and some 7.5% peroxide, but the mix worked when diluted to half that strength.This is not news for most of you, I am sure, but it must be useful to someone out there. I also noticed that the sediment produced by dropping some lead into this mixture is significantly gray in color. Is this some lead dioxide forming, or just unreacted lead dispersed in regular white lead oxide? This sediment seems to be quite resistant to dissolving in excess vinegar.

Pyridinium - 4-6-2007 at 20:26

Sounds like you're converting the stuck Pb and its oxides to Pb(OAc)2.

Another method that might get the oxides / Pb off is cathodic reduction, to make some hydrogen bubbles to scrub off the oxide coating? Not sure if it would work, it's just a thought. I'm too lazy at the moment to check the reduction potentials for the relevant species... :-P

UnintentionalChaos - 4-6-2007 at 20:41

Its not so much a coating as a lot of small globs. I broke down and used HCl at one point which probably removed the lead by dissolving the steel out from under it, but it didn't finish the job. The strange thing is that even tiny quantities of lead cloud the acetic acid solution, quantities that should have no issue being dissolved to form acetate.

Eclectic - 5-6-2007 at 07:16

Vinegar has some of everything that was in the original apple juice,
distilled white vinegar would have anything volatile produced from the same, so expect some traces of volatile organic and inorganic acids along with the acetic. You don't get the cloudy precipitate with photo grade glacial acetic acid.

Mr. Wizard - 5-6-2007 at 08:33

This is a problem with gun barrels too. Years ago mercury was often used to dissolve the lead. Now it's not practical for safety and other reasons. Common vinegar and hydrogen peroxide are now used to accomplish the job. Searching under cleaning gun bores might reveal more details. Many gun barrel cleaning solutions also include ammonia to dissolve the copper left behind from copper clad bullets.

Pyridinium - 5-6-2007 at 14:44

Quote:
Originally posted by Eclectic
Vinegar has some of everything that was in the original apple juice,
distilled white vinegar would have anything volatile produced from the same, so expect some traces of volatile organic and inorganic acids along with the acetic. You don't get the cloudy precipitate with photo grade glacial acetic acid.


It might be interesting to run some simple tests on a couple batches of dist. white vinegar to see what comes down from Ag+, Ba++, and a couple others.

12AX7 - 5-6-2007 at 15:08

I've never had lead stick to steel, stainless or otherwise. It should chip right off...

Tim

Pyridinium - 5-6-2007 at 18:59

Quote:
Originally posted by 12AX7
I've never had lead stick to steel, stainless or otherwise. It should chip right off...

Tim


I actually cast some molten lead tonight, well more properly I de-cast it (melted down some scrap and granulated it by pouring into cold water). I noticed two things:

1. Some lead and oxides stuck to the inside of the steel crucible (now it's happening to me!!!)

2. The quenching-water from the lead retained a white, cloudy precipitate hanging in it after I poured some off into a jar. I looked closer and found it to be blue-gray, metallic, iridescent. Really neat looking. It was actually tiny lead particles that were so small they hung in the water. Now, we all know lead has a high density, but if the particle size and shape is just right you can get almost anything to make a suspension in water.

The molten lead droplets had exploded into mossy lead when they hit the water. Now they are rapidly oxidizing just from sitting in the air.

unionised - 6-6-2007 at 11:45

"Vinegar has some of everything that was in the original apple juice"
Sure about that?

Eclectic - 6-6-2007 at 11:52

Well, since apple vinegar is apple juice fermented with acetobacter, yes!