Used sawdust flux

[cbrick]

In years past I always dumped the used sawdust flux in the trash when the coffee can I collected it in started to get full. It was much heavier than a can of burnt sawdust so I knew there was something in it but what?

About 2 1/2 years ago I decided to save it and re-melt it, I don't know how many fluxing's it took to get the can full but many, numerous actually, it took that long to get the can heaping full and yesterday I dumped it into the Dutch oven to melt out . . . well, whatever was in it.

Kind of interesting, the full can weighed 13.7 pounds (including the can), that's a lot for a coffee can full of burnt sawdust ash. I melted out a 4.0 pound ingot of what I assume is mostly tin (probably some Pb & Sb also) because it was at liquidus temp under 400 degrees.

I was left with 1/2 coffee can of a very fine, jet black powder that weighed 9 pounds 7 ounces (including the can) with no visible signs of any metal, just the fine powder but very heavy for it's quantity.

One half of a coffee can that weighs over 9 1/2 pounds? I put all of it back into the Dutch oven and cranked up the heat to full. A half hour later and nothing, no smoke, nothing at all melting. After an hour with the heat on high and nothing, an hour and a half and nothing.

I let it cool down and put it back in the coffee can, it still weighs 9 1/2 pounds for a half a can. There is obviously something in this fine powder that was fluxed out of my alloy over a 2 1/2 year period, no idea what but it's heavy and it doesn't smoke or melt.

Rick

[zxcvbob]

Mix in a little used motor oil (or cooking grease works even better) and cook the hell out of it in a tightly covered steel pot for about an hour. Be careful when you remove the lid because it might flare-up. You should get several pounds of lead if you can hold the temperature high enough (a hotplate will do it if it's the kind where the coils will glow orange)

It's probably not cost effective, but keeping the lead oxide out of the landfill's gotta be a good thing.

[Hardcast416taylor]

Don`t tell me you`ve been using ironwood sawdust???[smilie=1:Robert

[cbrick]

Ironwood is no problem . . . with a diamond blade. :shock:

Rick

[cbrick]

zxcvbob, no, not gonna try and salvage anything else from it. The whole thing was just an experiment to see "what if". I do all sorts of differrent such things just to see "what if". It's all got to do with the education of Rick and I thought others here may find this interesting as well.

I'll not be adding any oil to sawdust ever again. I did that once with olive oil and the resulting fireball caused the loss of the underwear, never could get the stains out.

Rick

[montana_charlie]

I'll not be adding any oil to sawdust ever again. I did that once with olive oil and the resulting fireball caused the loss of the underwear, never could get the stains out.
(...chuckle...)

[buck1]

Dirt?

[sagacious]

Your experience with reclaiming useable lead from 1st-run dross is the same as mine. The reclaimed alloy usually has a low melting point, and pours exceedingly well. The final dross is a fine black powder.

When lead ingots are exposed to water, minerals and metals will precipitate onto the lead, and most sources of lead also contain seemingly unlikley impurities in small quantity. Those compounds are later removed during fluxing, and accumulate over the years in the dross can. The powdery black dross probably contains a host of metals. If you mixed it generously with borax and brought the mess to a yellow heat for 15 minutes, and then let it cool undisturbed, you'd probably find a small disk of brittle metal composed of Fe, Cu, Zn, Al, and others.

[zxcvbob]

Not borax, charcoal or something equivalent. (I've done it before, several times.) About half of the black sand turns into lead, and the remaining half is much lighter than it was (but still kind of heavy) Dull barely-red heat is good enough.

[LeadThrower]

If the black powdery residue is truly a mixture of metal oxides and little else, the metal(s) could be recovered nicely in a thermite reaction. This is another "what if" experiment and not something that would be economical or particularly safe for the uninitiated. Powdered aluminum or magnesium would reduce the less active (and more valuable by casting standards) metals such as lead, antimony, and tin.

If anyone wants to ship me some of the fine black powder I'd give it a try (pm me). All in the name of science, ya know? We just need to be certain that the packaging won't leak nasty metal oxides on the mail carriers!

[cbrick]

LeadThrower,

Since I haven't yet tossed what's left I'll ship it off to you, just out of curiosity don't ya know. What is a thermite reaction? All of the alloy that was fluxed with this is from clip-on WW, no other lead or scrap alloy was used so if you can figure out what's in it this should help the members here (and me :coffee:) understand just what is in WW plus what sawdust appears to be so good at removing.

Will have to be after the holiday weekend, I have about an 18 hour day at work today and the next three days is the Extravaganza of Silhouette. Shooting first! :Fire:

I have a plastic container with a sealed lid I can put it in and ship it flat rate box, that should keep our civil servants safe.

I'll PM you next week when I have some time to deal with it.

Rick

[sagacious]

This is not intended to discourage, but attempting thermite reduction of unknown metallic compounds is neither safe nor likely to be effective. Stoichiometric ratios must be followed when mixing the known-composition reagents, and this becomes impossible with unknown compounds. Also, some thermite-type reactions, such as copper and zinc thermite, are well-known to proceed with such speed as to cause an explosion. Note that the unknown-composition dross is a black powder, and that CuO is also a black powder.

Not preaching, just sayin. Good luck, and stay safe.

[LeadThrower]

Some background: Thermite reactions are a general class of reactions where an active metal is used to reduce a less active metal. The typical thermite reaction is conducted with powdered aluminum and iron oxide. The reaction is incredibly exothermic. In layman's terms, the aluminum wants the oxygen in the iron oxide more than the iron does. The result is the production of aluminum oxide and molten iron. It's a dramatic reaction and a favorite of chemistry students everywhere.

The hazards of performing the reaction on unknown oxides are certainly on my mind (along with the fact that the powder might well contain sulfides and intermetallics which will behave in unknown ways). Safety is my primary concern, which is why I didn't suggest that anyone else actually try it. I'm a professional chemist and have performed the aluminum/iron oxide reaction several times.

Sagacious makes several good points: For the reaction to initiate and propagate, the ratio of reactants must be "correct" within a narrow range. This will be an experiment, since we don't know what the composition of the powder is. Sagacious is also correct in that the probability of success is quite low. As for explosions, tiny quantities and correct safety equipment (blast shield, etc.) will be employed.

Of course, it's very likely that even if the reaction works the recovered material won't be identifiable. Worth trying, tho'

Thanks for raising some important points, Sagacious!

I look forward to your PM, Rick.

[Bloodman14]

This should be interesting!

[cbrick]

I got really tied up at work for the past couple of weeks. I have a couple of days off now so . . . LeadThrower, still interested? I sure don't want to get anyone hurt, are you sure this will be safe?

Rick

[HORNET]

I think the correct phrase is "Hold my beer and watch this...." LOL

[btroj]

Yep Hornet, this calls for a video.

[zxcvbob]

Something else you really need to be careful about here. I assume you are going to use aluminum for the reducing agent. Aluminum may react with antimony to create aluminum antimonide AlSb in the residual ash and dross when you are done. If it gets wet, it will release stibine gas SbH3 which is a deadly poison.

(so if you go through with this, thoroughly wet the ash afterwards out in the open on a windy day)

Just use carbon or carbon monoxide for the reducing agent.