Lead/zinc separation

[Reddot]

In a number of posts people have cautioned about smelting wheel weights at high temperatures in cast you mixed some zinc wheel weights in by accident. They state that if you get any zinc in the batch the whole batch is ruined. Lead starts to melt at 621 degrees and zinc starts to melt at 692. If one inadvertently smelts some zinc into their batch of lead why couldn't you let the bad batch solidify and then remelt and allow the zinc to float to the top and scoop it off?

[jforwel]

Being relatively new myself I'll take a stab at this. Some people will pick through the WWs and pull out the zinc ones before smelting. That's too time consuming for me. I melt the WWs down based on the advise of others here, by keeping the temperature below 700. That way the zinc floats to the top.

As for your re-melting question; I have learned through some books that some metals with high melting temps will re-melt at a lower temp once alloyed with other stuff. Therefore it is unlikely that you would be able to separate zinc once it's mixed with your lead. Antimony is an example of a high melt temp metal by itself but once alloyed with lead it's there to stay and melts when the lead melts.
There was a post here that said zinc will sometimes float to the top like oatmeal, but I don't have enough experience with that.

On a side note I just ran into a guy who casts with zinc. I think he shoots mini cannon balls. After smelting 300 pounds of WWs I told him I wish I had known sooner.

[oneokie]

Supposedly what you state is correct. Do a search for "contamination". Several posts say that by slowly raising the temp of the alloy to the liquid state will allow the zinc to seperate and float. When doing this, do not flux or stir. IIRC, the target temp is 600°, or less depending on the amount of Sn in the mix. More tin=lower liquidus temp.

[leadman]

I melted about 200 pounds of wheelweights this week. I stuck a thermometer in the pot and the lead would get slushy at just over 500'. It was liquid at 550'. The zinc weights would float at this temp.
Lead with some zinc is usable for casting but I had to raise the temp. to almost 800'. Worked best with pistol boolits. Very hard to cast 22 cal. boolits.

I was using one batch that I melted before reading the posts here on zinc. I watched for seperation while this batch was heating up but did not see any lead/zinc seperation.

[wiljen]

In a number of posts people have cautioned about smelting wheel weights at high temperatures in cast you mixed some zinc wheel weights in by accident. They state that if you get any zinc in the batch the whole batch is ruined. Lead starts to melt at 621 degrees and zinc starts to melt at 692. If one inadvertently smelts some zinc into their batch of lead why couldn't you let the bad batch solidify and then remelt and allow the zinc to float to the top and scoop it off?



You are using Kelvin temps for Zinc and Farenheit for Lead.

Zinc melts at 787F - Lead melts at 621F - plenty of range to separate the two by keeping temp below 780. Once alloyed, zinc will not come out of solution just by lowering the heat below 787 though.

[grumpy one]

Bear in mind that zinc may be capable of dissolving in molten lead at a temperature far below zinc's melting temperature. Try comparing the temperature at which sugar will first dissolve in water, with the temperature at which sugar melts. Some of my own past accidental contaminations of pots of WW have happened at temperatures in the high 600s F.

[docone31]

I have zinc in my melt. I just tossed in some roofing lead and blended it in.
works ok with me. Sizes well, I paper patch so it wraps and fires well. My ACP really likes it.
I just thinned it out some.
Yeah, high temp makes a good casting with my batch.

[Reddot]

"You are using Kelvin temps for Zinc and Farenheit for Lead."

Thanks for pointing that out. I thought that the two temperatures were a little close.