Sciencemadness Discussion Board

Lead impurities

CHRIS25 - 14-11-2014 at 09:50

While there is info on the web about impurities in lead I am unable to find any leads (no pun intended) as to the following question:

Needing to make lead nitrate: I am using lab grade nitric acid, but using a lead bullet from 1830 that has been in the ocean for probably same amount of time. At the moment the lead nitrate solution is milk white, not what I expected, I expected dirty brown, or dirty yellow before filtering . Has anyone any ideas as to what significant impurity might be causing this?

gdflp - 14-11-2014 at 09:59

Most likely, it is tin content in the bullet. Tin doesn't dissolve in nitric acid, it simply oxidizes to insoluble tin oxides. Filtering should remove this just fine.

CHRIS25 - 14-11-2014 at 12:42

Quote: Originally posted by gdflp  
Most likely, it is tin content in the bullet. Tin doesn't dissolve in nitric acid, it simply oxidizes to insoluble tin oxides. Filtering should remove this just fine.

Ok I never knew that they added Tin to lead when casting the civil war type bullets, (that's what these are), I will do some testing.

MrHomeScientist - 14-11-2014 at 13:38

Seems a shame to destroy bits of history for chemistry! I think wheel weights are the usual go-to source for lead. I bought an ingot of 99.9% Pb on eBay.
I think gdflp is correct for the identity of the impurity. Antimony is another common additive, and I believe that also will oxidize to insoluble oxides. Filter and you should be good to go.

Edit: You should try the golden rain demo with your lead nitrate! It's one of the most beautiful experiments I've ever done.

[Edited on 11-14-2014 by MrHomeScientist]

CHRIS25 - 14-11-2014 at 16:14

Well I found about 300 of these bullets and just used two that were crushed, so no tears there. Yes, I will to do that golden rain experiment. Thanks for the pointer.

diddi - 14-11-2014 at 19:22

also consider antimony and bismuth in your list of impurities.

CHRIS25 - 15-11-2014 at 01:03

Filtering achieved nothing, there was is a fair amount of Tin Oxide layered on the filter paper, but solution is still milk. Plan "B" Take one of my lead ingots from the beach and re-smelt, and ladle off smaller portions, this stuff has to be better, I already skimmed off much of the impurities first time round. I don't need pure lead, so 0.5% impurities won't matter for end use.
Ps, don't you guys mean Tin Dioxide, not the SnO?

[Edited on 15-11-2014 by CHRIS25]

blogfast25 - 15-11-2014 at 07:10

Quote: Originally posted by CHRIS25  
Filtering achieved nothing, there was is a fair amount of Tin Oxide layered on the filter paper, but solution is still milk. Plan "B" Take one of my lead ingots from the beach and re-smelt, and ladle off smaller portions, this stuff has to be better, I already skimmed off much of the impurities first time round. I don't need pure lead, so 0.5% impurities won't matter for end use.
Ps, don't you guys mean Tin Dioxide, not the SnO?

[Edited on 15-11-2014 by CHRIS25]


That is a clear indication that it is indeed SnO2 (or at least in part). SnO2 has a tendency to peptise, in plain English: to run through a filter, especially when freshly prepared. So your tin dioxide is only partly retained on the filter.

You could just let that decant for several days of course: SnO2 is a dense material and will eventually sink to the bottom.

All kinds of impurities in lead artefacts are a common problem for preparing relatively pure lead compounds from them, as others correctly pointed out. Tin and antimony form their insoluble oxide on treatment with nitric acid, so these have been eliminated mostly. Bismuth does dissolve in nitric acid, so if there's any there it will be in your solution. Very old lead objects may also contain small amounts of silver, because the two often accompany each other in ores. If any, it will be in solution.


[Edited on 15-11-2014 by blogfast25]

CHRIS25 - 15-11-2014 at 07:53

Hallo, good, so I have begun a new reaction with some purified lead (by double refinement). this is not from the bullets, more modern scrap stuff found on beaches. The tin dioxide is an unexpected pleasure since I have a use for this. Though I am surprised at the amount. 15.6g from 26g of Lead? So I did three tests:
It is Insoluble in Alcohol
Insoluble in NaOH
InSoluble in water.
Tin Dioxide should have dissolved in the sodium hydroxide but did not.

[Edited on 15-11-2014 by CHRIS25]

blogfast25 - 15-11-2014 at 09:37

Quote: Originally posted by CHRIS25  
Tin Dioxide should have dissolved in the sodium hydroxide but did not.



I presume that by 'sodium hydroxide' you mean sodium hydroxide solution?

Whether or not a tin dioxide will dissolve in such a solution is not as straightforward a question as you make out. It depends on:

* age of the Sn(OH)4/SnO2. It ages very quickly and then becomes insoluble in even the strongest NaOH solutions (or strong acids, for that matter).

* How it was prepared (related to the point above). Freshly prepared Sn(OH)4 from acidic SnCl4 solution and ammonia will be reasonably soluble in NaOH solutions (as well as strong acid solutions).

* SnO2 prepared from treating tin metal with nitric acid is quite inert (insoluble in alkali/acids) in my experience.

So solubility in NaOH solutions is a very, very poor identifier for Sn(OH)4/SnO2.

All SnO2 can be 'dissolved' in molten NaOH, forming sodium stannate. From very alkaline solutions this can be crystallised as Na<sub>2</sub>Sn(OH)<sub>6</sub> (sodium stannate).

The quantity you're finding seems too high though. But maybe it was effectively a tin/lead alloy?

[Edited on 15-11-2014 by blogfast25]

CHRIS25 - 15-11-2014 at 11:50

The new batch, (not complete yet), has a crystal clear layer of solution on top of the precipitate, which is brilliant white, still with plenty of undissolved lead. So this is a good indication of my original refining of the raw lead. Great, at least I am assured of lead nitrate. Since Lead nitrate is soluble in water but insoluble in nitric acid I think that too much nitric acid evaporated as nitrous oxide and left me with not enough nitric acid to dissolve the lead even though I added 1 mole of acid to 0.4 moles of lead all in a 7M concentration.

I did some research on an american civil war site but could only find vague references to them casting lead bullets with tin, no percentages given. But I would, out of sheer curiosity, like to be able to discover the amount of tin/lead ratio that has been used. I could find no references to what might have been used back in 1860. Although these bullets actually date from 1835 Liverpool England, (long story here).

Working backwards from knowing 15g of tin dioxide, is it possible to calculate amount of tin in this? If tin is 118g/mol and the dioxide is 151g/mol:
15g = 0.1 mol ; therefore 0.1 mol of 118g = 11g tin? but I anticipate my logic to be wrong. This kind of calculating is something I am unfamiliar with.

blogfast25 - 15-11-2014 at 12:18

Quote: Originally posted by CHRIS25  

Working backwards from knowing 15g of tin dioxide, is it possible to calculate amount of tin in this? If tin is 118g/mol and the dioxide is 151g/mol:
15g = 0.1 mol ; therefore 0.1 mol of 118g = 11g tin? but I anticipate my logic to be wrong. This kind of calculating is something I am unfamiliar with.


No, the reasoning is correct and would indicate approx. 11/26 x 100 w% = 42 w% tin in your bullet.

Bear in mind that what you did wasn't a precise chemical analysis, so that number is approximate at best. Oxides in analytical chemistry usually require high temperature glowing to drive off the last bits of moisture for instance.

You seem rather pleased with the SnO2, are you planning to use it for something?

CHRIS25 - 15-11-2014 at 14:13

Ah, a bit of a relief there then, I recognise that it is approximate - but nevertheless a good guide, thanks for the feedback. I am interested in creating something new involving combining cyanotype and watercolour, but I want to create the pigments myself, I can't let go of the chemistry and buy them, this would ruin my self imposed insanity; besides this would upset the creative ideas that are brewing. So the tin dioxide and the lead nitrate are both ingredients in different yellows.