Sciencemadness Discussion Board - Reducing lead oxides with carbon/charcoal

Reducing lead oxides with carbon/charcoal

RogueRose - 27-4-2019 at 05:06

I was thinking of trying to reduce some "red lead" (PbO2) plates from an old battery to get a little experience with carbothermic reduction. On the Wiki page for PbO2 it says that it decomposes upon heating in air in the following order:

Decomp in air:

Code:


PbO2  →  Pb12O19  →  Pb12O17  →  Pb3O4  →  PbO          
     290C       350C        375C       600C
     554F       662F        707F      1112F

I tried the above and heated the PbO2 (~20-25g) with a propane blow torch in a ceramic crucible at red heat for 4-5 minutes (total of about 7-8 mins w/ pre-heat) and once it cooled only a thin layer of PbO (yellow/orange lead) had formed. I thought I would get more PbO/Pb3O4 for that amount of heating, so I'm wondering about taking it to the next step - complete reduction.

I've seen some people heat lead oxide in a drilled out piece of wood and then heated with a torch from above but the video was heavily edited so IDK if it took 20-30 mins to make 10g of lead or if it took 3-4 mins once heated. I'm wondering if it might be better to use crushed charcoal, powdered charcoal or even saw dust mixed with the oxide. Also should the oxide be powdered or would crumbled pieces from the plates be adequate (2-5mm size pieces).

Finally does this process need a supply of O2 to work or can it be heated in a kiln or forge using some non-combustible source (induction, electric resistance or arc heating) or would propane/kerosene/oil be a better source?

Sulaiman - 27-4-2019 at 06:30

I've recently been playing at casting lead to make a bob for a pendulum.
I tried just melting lead and quite a lot of oxide (dross) was produced.
On my second and third attempts, after doing a little research, I added wood shavings.
What a difference ... nice shiny lead with only a little oxide,
so using a drilled-out lump of wood should also be good I guess.

Obvious but I'll say it anyway
- be sure that any mold you pour molten lead into has NO traces of water,
- if working outside due to the fumes, check your weather forecast before starting
- lead is difficult to saw through or drill into and screws quickly loosen

RogueRose - 27-4-2019 at 06:41

Quote: Originally posted by Sulaiman

I've recently been playing at casting lead to make a bob for a pendulum.
I tried just melting lead and quite a lot of oxide (dross) was produced.
On my second and third attempts, after doing a little research, I added wood shavings.
What a difference ... nice shiny lead with only a little oxide,
so using a drilled-out lump of wood should also be good I guess.

Obvious but I'll say it anyway
- be sure that any mold you pour molten lead into has NO traces of water,
- if working outside due to the fumes, check your weather forecast before starting
- lead is difficult to saw through or drill into and screws quickly loosen

I'm thinking that I might try baking the saw dust first to make sure there is no water in it and that should hopefully give better results. If it is as simple as adding sawdust to the oxide then that will be nice.

I do remember seeing a video some time ago with someone melting lead for casting bullets or pouring shot and they put sawdust on top and they never had to skim off the dross. I'm guessing that a similar process might work with aluminum as well when melting it as it seems that Al forms the oxide much faster than most other metals - maybe it would work with Zn too! This will be an interesting experiment.

Sulaiman - 27-4-2019 at 06:52

No need to dry the wood first - it will be more than dry within seconds of going onto the lead

You need to stirr the molten lead to get it clean ... I used a wood stick !

RogueRose - 27-4-2019 at 07:18

Quote: Originally posted by Sulaiman

No need to dry the wood first - it will be more than dry within seconds of going onto the lead

You need to stirr the molten lead to get it clean ... I used a wood stick !

I was a little worried that if there was much moisture in the sawdust that it might create steam and explode if mixed in. I am excited to try this with Al though. Now I just need to make a good burner for a forge.

fusso - 27-4-2019 at 07:29

I'd tried this a few years ago. I used carbon made from pyrolysing sugar. A huge excess as I don't know much about stoich at that time. I used a small food can as a crucible. Grind the carbon and mix with the PbO. Heat with blowtorch from above. Another attempt used a hairdryer to blow hot air onto the mixture after the blowtorch initiation. Tada! Both attemts gave pool of liquid lead formed at the bottom.

Sulaiman - 27-4-2019 at 07:52

Quote: Originally posted by RogueRose

... I was a little worried that if there was much moisture in the sawdust that it might create steam and explode if mixed in. I am excited to try this with Al though. Now I just need to make a good burner for a forge.

Guess what I want to do soon

fusso - 27-4-2019 at 08:07

@sulaiman
Wait, aren't you going back to Malaysia soon?

Sulaiman - 27-4-2019 at 09:26

Yes, hopefully in early June, contracts for house sale almost signed, most small household items wrapped, non-transportable chemicals passed on to a member,
but I still have six weeks to play

vmelkon - 3-5-2019 at 11:53

If you want to go from PbO2 to Pb, then just make powdered charcoal. Mix with the PbO2 powder.
Then apply heat.

I used a propane torch. I placed the power in a iron can.
Small beads of lead form. You need to mix the powder as you heat it and they will coalesce into bigger droplets of lead.

You can let it cool and collect the large solid drops of Pb and melt them together. I think I made about 15 g.