Sciencemadness Discussion Board - Seperating zinc, lead & iron in an economican and "easy" method?

Seperating zinc, lead & iron in an economican and "easy" method?

RogueRose - 29-10-2020 at 20:32

I've been trying to figure out the easiest way to separate a mix of lead and zinc (with some iron/steel mixed in with it as clips for the lead & zinc. I've tried doing a manual test where I would scrape or try to dent the metals to analyze softness and also look at how shiny the metal is but there are a sizeable amount that I just can't tell - IDK if it's an alloy or what. Also it's not really viable to do each piece by hand when processing many 5 gallon buckets, 20gal or 55 gallon drums of this stuff.

NOTE - I don't need help determining the iron or separate that. This will be the easiest part of the project - but most all pieces have some steel on/in them/

I have some old kitchen stoves (ready to be scrapped after they are "put to use") and I was thinking of using a stainless steel mesh screen with the metal sitting on top of it and having a cookie sheet below it and heat the oven to 680F or so - (60F above lead MP & 60F below Zinc) and these have a fan in the oven that can circulate the air. I can fit 4-5 shelves/racks in the stove & each rack can fit 2 9x13 cookie sheets. Stainless mesh on which the metals will sit can be anywhere from .1" square holes up to .25 or .3" holes.

I figure I could allow enough time for the metals to reach the set temp of 680 and then shake each tray or rack. I'm hoping the melted metals will fall through the wire mesh into the cookie tray (has 1/2" high walls). I'm just wondering if this is going to get the melted lead to fall through.

Now the only other option that I can think of is some kind of acid test - possible HCl and do small amounts at a time or just do a single drop on each one - but this would take a long time. I'm wondering if there is a better acid to try this, it would be ideal if I could submerge an entire tray just deep enough to cover everything and then pick out those that are fizzing.

If you can think of any better methods, PLEASE let me know. Or if you have suggestions on the melting process or comments on the acid application, I'd be very appreciative

I guess another option would be to use some metal salt solution where the zinc will dissolve or get a coating, while the lead won't. I'm thinking CuSO4 doesn't react with lead, though don't remember. I've been working on electronics heavily the last 2 years and chem isn't at the for front of my studies anymore.

AgCollector - 30-10-2020 at 05:17

I think this really depends on the size & composition of the mixture: is this a macroscopic mixture of, say, lead shavings and zinc shavings? Or, zinc wheel weights and lead wheel weights? Roughly how big are the pieces of metal?

Their densities are pretty different so if the pieces aren't too small you could measure specific gravity and go from there.

It sounds like you have actual tons of this stuff (55 gal drums) so the scale is something to consider too.

Bedlasky - 30-10-2020 at 06:32

Zinc and iron will dissolve in sulfuric acid, but lead not.

macckone - 30-10-2020 at 06:46

It sounds like these are clip weights with a lead/zinc alloy.
First I would melt the lead and zinc and filter off the iron/steel.
Next dissolve the lead/zinc alloy in glacial acetic acid with hydrogen peroxide (30%) (slow step).
Then precipitate lead by adding zinc chloride.
The lead chloride should be pretty pure.
That leaves zinc chloride and acetate in a mix.
That can be precipitated with sodium carbonate.

Trying to dissolve an alloy of lead and zinc in HCl will not work.
The lead chloride will passivate the surface.

If it isn't an alloy that is a different ball game.

phlogiston - 30-10-2020 at 07:03

Melting just for identification sounds rather energy inefficient and time consuming to me.

Quote:

Now the only other option that I can think of is some kind of acid test - possible HCl and do small amounts at a time or just do a single drop on each one - but this would take a long time. I'm wondering if there is a better acid to try this, it would be ideal if I could submerge an entire tray just deep enough to cover everything and then pick out those that are fizzing.

This seems like a pretty good method to me, and hydrochloric acid is a good choice.

Zinc will slowly dissolve in dilute hydrochloric acid with visible fizzing (the gas is hydrogen)
Lead does not dissolve in it.
Clean iron will dissolve very slowly, producing a faint green color. (Any rust on it will dissolve very quickly, producing an orange solution).

Im a little puzzled though that you are apparently not able to quickly distinguish them by density. Most people would normally be able to tell lead form zinc when they hold a piece in their hand, just by feeling the weight and eyeballing the size of the piece.
Are the pieces too small for this?

AgCollector - 30-10-2020 at 07:20

The problem with an acid test is most of the zinc wheel weights I've encountered are painted or plastic coated, and so would not show a reaction to HCl.

DraconicAcid - 30-10-2020 at 07:52

Quote: Originally posted by macckone

It sounds like these are clip weights with a lead/zinc alloy.
First I would melt the lead and zinc and filter off the iron/steel.
Next dissolve the lead/zinc alloy in glacial acetic acid with hydrogen peroxide (30%) (slow step).
Then precipitate lead by adding zinc chloride.
The lead chloride should be pretty pure.
That leaves zinc chloride and acetate in a mix.
That can be precipitated with sodium carbonate.

Trying to dissolve an alloy of lead and zinc in HCl will not work.
The lead chloride will passivate the surface.

If it isn't an alloy that is a different ball game.

I seem to recall reading that molten lead and molten zinc will not actually mix (this is used in liquid-liquid extraction of silver from lead, since the silver is more soluble in the zinc than the lead).

macckone - 30-10-2020 at 12:13

DraconicAcid,
There are lead/zinc alloys, so they obviously can mix.
It may happen if you were to pour molten zinc onto molten lead and not stir it as they would probably layer much like vodka and juice do, a little stirring and you have a mixture.

DraconicAcid - 30-10-2020 at 13:26

macckone, on the contrary- if you check the phase diagram here: https://www.researchgate.net/figure/Phase-diagram-of-the-sys...

You will see that under 800 oC, you will have two separate liquid phases. Under 600 oC, each of the two phases will have very little of the other metal dissolved in it. If you cool the system to under 418 oC, practically pure zinc will solidify, leaving a liquid layer of mostly lead with a few percent of zinc dissolved in it.

AgCollector - 30-10-2020 at 18:12

Quote: Originally posted by DraconicAcid

macckone, on the contrary- if you check the phase diagram here: https://www.researchgate.net/figure/Phase-diagram-of-the-sys...

You will see that under 800 oC, you will have two separate liquid phases. Under 600 oC, each of the two phases will have very little of the other metal dissolved in it. If you cool the system to under 418 oC, practically pure zinc will solidify, leaving a liquid layer of mostly lead with a few percent of zinc dissolved in it.

Yep, that's the basis of the Parkes process to remove silver from lead you mentioned earlier. I've been curious to try it at home but haven't gotten around to it yet.

[Edited on 31-10-2020 by AgCollector]

RogueRose - 30-10-2020 at 19:39

Quote: Originally posted by Bedlasky

Zinc and iron will dissolve in sulfuric acid, but lead not.

Good point. What do you think about adding a little H2O2 & a little heat to kick it off. I can tell the iron - that's no problem - but some of the lead & zinc have iron clips as a fair amount of this is wheel weights. Some of it is random size (1-8oz) weights that are used as ballast that is thrown in corners of some boats - it's really non-traditional but there's a few barrels of this stuff.

So I basically need to seperate wheel weights. I'm going to de-grease everything first as much as possible if I do the acid method.

I'm thinking that I could use a plastic rubbermade bin (about 20" x 36" x 12") and put about 1-3" of dilute acid with a little H2O2 in the bottom. remove any of the zinc that starts fizzing - or maybe remove the lead first b/c I think adding H2O2 to H2SO4 MIGHT start to dissolve lead - though I'm not sure..

The lead is the priority here, but I'm going to be seperating both and I have casting uses for each. The sources I mentioned are BY FAR the least expensive way to obtain this.

So this seems like an option. but I'm going to explore a little more.

RogueRose - 30-10-2020 at 19:47

Quote: Originally posted by AgCollector

I think this really depends on the size & composition of the mixture: is this a macroscopic mixture of, say, lead shavings and zinc shavings? Or, zinc wheel weights and lead wheel weights? Roughly how big are the pieces of metal?

Their densities are pretty different so if the pieces aren't too small you could measure specific gravity and go from there.

It sounds like you have actual tons of this stuff (55 gal drums) so the scale is something to consider too.

It's wheel weights and various ballasts (old sinkers) and some other oddly shaped chunks of the metals. The wheel weights - most have an iron clip on them.

I think the idea about density is a good idea. I'm thinking of melting say 20-30lbs of lead in an oven at 660-680F and then putting the wheel weights on top of that and as it heats up, the lead should melt into the melted lead, and the zinc shold remain solid and ffloat (along with the iron).

There's just too many pieecs to do individually with measurement. Some of these weight 1/8-1/4oz while others are up to 4-10oz for wheel weights. Some of the weights from semi trucks are over 1lb! But there's a lot of small ones that are a major PITA to sort. The first time I did a 5 gallon buckt I used wire cutters (good diagnol cutting wire cutters) to see if I could cut into the metal at all as only the lead was soft enough to make a REAL mark - but there were some that were about dead smack in the middle - I could make a mark, but only 1/2 as far as in the lead & the markings didn't make any sense when related to the elements. IDK if there are other metals they used like 15 years ago for wheel weights, but I was afraid to mix these with anything and these were about 15-20% of the bucket.

The MP of these odd ones was much higher than lead, but they floated in lead just barely. I'd say they were 90% of the weight of lead but just very hard. Maybe an alloy? But that just seened odd b/c I couldn't find anything stating anything but Pb, Zn and Fe was used for wheel weights.

RogueRose - 30-10-2020 at 20:11

Quote: Originally posted by macckone

Thanks. I think you hit the nail on the head for some of the weights I had from long ago (in the post above this). I couldn't figure out what the hell they were - harder than lead, softer than zinc and higher MP than lead I think.

I'm wondering if I could find some of these "oddities" and find therir MP and see if I can use the "melting pot" idea I had - use a 20-40lbs of molten lead - then put a layer of the weights on top & wait for the lead to melt (keeping oven at ~640-680 - it has a convection fan) - so any of the zinc should remain unmelted. IDK if the zinc will get soft, but if so, I'll just have to drop the temp until I find the sweet spot.

While I like the idea of dissolving both, I think that may be less economical than I'd prefer for what I'm planning. Ideally I'd just use old car/truck/tractor/forklift/UPS batteries - but if I've said it 10 times, I've said it 1000 - there's something fishy going on with dem der lead acid batteries when it comes to being 'pure lead" (even in their oxidized form). I've done well over 50-60 experiments with thsse trying to melt, or purify them in many different ways, taking them down to a pure salt & either decomposing, displacement or whatever - but they always come back to this unmeltable "sponge" lead that forms an oxide immediately upon heating - just as the pure lead plates do when initially removed from the battery.

I REALLY wish I could get some of you to work on this and co-oberate my findings. I'll send samples if anyone wants to try this for themselves. The internet is full of people sayiing "if you have a 60lb lead acid car battery you can easily get 30-50lbs of pure lead by jeating with a torch). Well, i've tried MANY diffeent fuels and gases, including acetylene and oxy-acetylene and all it does is turn it to a white powder -> orange powder -> yellow powder. The temps are MORE than sufficient to decompose any of the oxides but they just havent done so yet. I always end up with PbO for 95% of the pure lead from the battery plates (the PbO2 plates do the same, they just decompose to the PbO). I even made pure lead acetate - gorgeous, pure perfect white crystals and after doing displacement actions or decomposing them, they never produced a useable lead metal - it just made a VERY light (non-dense) light grey color metal that won't melt. It looked like "sponge lead" but IDK how it could have gone back to that form after dissolving into an acid and being displaced by another metal like magnesium or similar. ...

Anyone interested in trying to solve this conundrum? If you can figure it out and get a good method I'll pay you $100

Now I have tried adding PbO2 and PbO into a quartz tube, placed charcoal powder in front of it and heated the metal and the charcoal and blew air through it. This did reduce tje oxides but it's a cumbersome setup. I need to devise a method where I can provess 10-50lbs at a time, preferable the "sponge" form and the PbO2 as well. I think the hydrogen approach would work as well, so I'm considering revisiting a watergas setup or simply just using a wood gasifier to produce the CO to reduce the lead.

Hmmmm (exhale of being super tired of dealing with this).

If someone can come up with a reaction vessel where I can heat the lead/lead oxide while also getting the reducing gas to flow over it, I'd be happy to offer some kind of incentive (chems, paypal, etc). I just do't have time to mull over this for the 15th time and have 5-6 URGENT projects I need to finish - not this 'hobby" work.

PM me if you are interested.

Bedlasky - 31-10-2020 at 09:21

H2SO4 + H2O2 mixture definitely don't dissolve lead. Lead sulfate is insoluble in water and it passivate lead metal.

AgCollector - 31-10-2020 at 17:46

Quote: Originally posted by RogueRose

Quote: Originally posted by AgCollector

If your plan is to melt & cast the lead anyway, then I think heating is the way to go. You should be able to hold them at a temp where the lead will melt but not the zinc - then skim off the zinc, iron clips & other oxide / dirt, and cast the lead.

You could then either separate the zinc weights or heat still higher and melt the zinc, but the market for zinc is not as robust as it is for lead. Might be better to leave them as identifiably zinc weights in order to sell them, if that's your plan.

Heating this quantity of lead would produce quite a bit of fumes which you'd have to make sure to take into consideration; also, even with convection it might take a long time to provide enough energy to heat the mass of metal; the weight may also cause problems for the racks in the oven?

Why not get a large-ish cast iron pot, support on bricks and heat over a propane burner? You could use an IR temperature scanner (non-contact) made for grilling to keep an eye on temperature, then scoop out or ladle out things as needed.

unionised - 1-11-2020 at 05:39

If you put the whole lot in a metal drum (unsealed, of course) and heat it in a fire the zinc and the lead will melt.
The molten leard will sink to the bottom and the molten zinc will float on top (where it will also reduce any lead oxides).
The iron will float at the junction of the two liquids.

You can then let the drum cool down and rip it open.
That should give you a cylindrical block where one end is lead and the other is zinc, with a boundary marked by iron etc.
Saw it just above and just below the boundary and you have separated the metals.

The advantage to this is that you don't need to do anything with the molten metal. In principle you can light the fire and walk away until it burns out.
If anything goes wrong, you won't be there, so you can't get hurt.

macckone - 9-11-2020 at 08:56

Quote: Originally posted by DraconicAcid

That is great from a theoretical standpoint. In reality there is a good deal of dissolution of zinc and lead in both phases and getting good separation by cooling is not easy because you wind up with the endpoint solutions. 1-2% contamination is 'ideal'. But reality is messy.

DraconicAcid - 9-11-2020 at 11:25

So the phase diagram says that the two liquids don't dissolve in each other very much, but you're dismissing that as theory, and that in reality, they do dissolve a lot in each other? Sure, macckone, sure.