RogueRose - 15-2-2018 at 07:03
I've looked for the ways that Zn and Pb are usually separated and it seems that an electrolysis/electroplating process is used to get pure lead
leaving behind an acidic zinc solution (or precipitate). This seems pretty energy intensive and also kind of complex (I'm not skilled in electro
chemistry). So I looked at the different solubilities of Zn & Pb salts and found many of them have opposite solubilities in alcohols. I listed
the different salts and am wondering if there is any drawback to doing seperations this way. I have a good bit of Pb/Zn mix that is probably anywhere
from 95/5 to 80/20 Pb/Zn and would like to separate them out.
PbOAc - anhydrous - 215g/100g Methanol at BP
ZnOAc - 1.5g/100ml methanol
PbCl2 - insoluble in alcohols
ZnCl2 - 430g/100ml in alcohol
PbSO4 - insoluble in alcohol - .0032g/100ml in H2O
ZnSO4 - 58g/100ml H2O, soluble in alcohols - unknown amounts
Pb(NO3)2 -.4g/L Ethanol, 13g/L methanol
Zn(NO3)2 - very soluble in alcohol
Chemi Pharma - 15-2-2018 at 07:30
I believe zinc don't form an alloy with lead. If you have a chunck cointaining a mixture of this metals, probably they are not intimately bonded. You
can simple put the chunck at a crucible and slight heat over a flame. The lead will be liquefied (327ºC), while the zinc don't (melting point
420ºC).
Other way is to put the chunck inside dilute HCl. The acid will react with the zinc, liberating hydrogen, affording zinc chloride and with the lead
don't, leaving the pure metal at the bottom of the vessel.
[Edited on 15-2-2018 by Chemi Pharma]
Bert - 15-2-2018 at 07:33
Wet chemistry, good practice.
You could just melt them, though.
As in the Parkes process-
It's a different route, but still a solubility based separation...
(Edit)
(Yay! Someone else likes history of metalurgy. Got Agricola?)
[Edited on 15-2-2018 by Bert]
RogueRose - 15-2-2018 at 10:00
Wow, I'm not sure what I have then with my Pb alloy. It was made from old wheel weights that I had made effort to separate diligently but had some
left overs that I melted together, they were semi-hard Pb weights (which was odd and why I set them aside) and weights I was pretty sure were Zn
though didn't have markings and seemed more powdery when broken. I guess the Pb weights could have had antimony in them but the end density was about
9.4g/cc and did't oxidize the same as the lead castings.
That is really interesting that Pb and Zn will separate. I'll have to melt them together and see this!
As the metal is in larger chunks, I don't believe that the HCl would penetrate to the middle being almost an inch thick, though I may be wrong. I
could remelt and pour into thin sheets then dissolve these. I'm in no rush so not melting would be fine but I'm unsure if the acid can reach the
middle of the metal, has anyone tried this or have experience?
Chemi Pharma - 15-2-2018 at 10:17
Melt the chunk with a crucible and run off the melted metal into a recipient with cold water slowly. You will get a great amount of solid irregular
droplets of the metal, easy digested by a dilute HCl solution.
I remember when I was young and melt lead to make videogames coins and play at lan houses for free
[Edited on 15-2-2018 by Chemi Pharma]
Bert - 15-2-2018 at 10:32
Did you make up a batch of bullet metal and now it doesn't cast well? If there is any chance you have Zn weights, you must control the heat while
smelting to below MP of Zn. Then you can just strain the Zn out along with the steel clips, rocks, bullet jackets and other trash-
Wheel weights made since about 1980 have 3% Antimony, .25-.5% Tin, and aroind .15% Arsenic. Not pure Lead. It is known that in an overheated melt,
wheel weight alloy WILL mix with Zn enough to mess it up, make it melt too high and have crappy fill out. So will linotype, babbit, "hardball", you
get the idea.
Find someone making fishing downrigger weights (or cannon balls, sailboat keels, something big and simple) and sell them the contaminated batch would
be my suggestion. Take the cash and go get clean alloy.
RogueRose - 15-2-2018 at 13:04
No, I just melted the stuff down into ingots to get rid of the dirty & irregular shaped wheel weights, and they make good for weighing things
down. I'd say about 20-40% of the wheel weights I got were Zn from my simple method of testing. I used a pair of wire cutters to see if they could
cut in or dent the weight and if they didn't I counted them as Zn - as they weren't marked at all. Most had a Pb or Zn marking on them and had a
definite difference in feel, by weight.
RogueRose - 23-2-2018 at 22:29
So I dug through the remaining scrap from melting down the wheel weights and found one that hadn't melted but was caked with metal oxides and some
unmelted metal on the outside. The weight was in original form and I found it was much harder than lead, had a silver look when using wire cutters to
cut in and very hard. It took much more heat from the blow torch and when it melted it didn't have the same amount of oxide forming on the outside.
After pouring into a small pool to cool my suspicions were confirmed that it was aluminium which I had never seen an aluminium wheel weight before!
The real shitter is that many of the weights only have the company name stamped (or raised printing) on them and the weight unlike others that say Pb
or Zn which really helps identify them!
I'm not sure if Al and Pb act the same as Pb and Zn, forming 2 different layers. I've found that Zn is a great solvent when hot and will dissolve Cu
and Al. I'm not sure if melted Pb will dissolve Al when it is in very hot liquid form (either hot enough to melt Al or just below the temp). The
lowered density of the Lead ingots I have now make a little more sense if the Al can be dissolved into it, as I think the density was just around
9g/cc or even lower in a few cases.
Using HCl would be a good choice to dissolve the Al that is in the ingots and maybe I'll melt them and pour them into thin sheets where the thickness
is a few mm allowing for less penetration. I should be left with fairly pure Pb after this but if there is Zn in the mix, I'll have a Al/Zn chloride
solution which may be a bugger to separate.
I'm trying to think of any other metal which many have been included in these weights and thought Antimony might be in there and am wondering what
procedure would be best toi remove it, it seems that the HCl may remove it from the metals, but that gives another metal salt to separate out!!