Zinc Removal with Steam and Flirting with Tinsel Fairy

[wimms]

Some time ago I had zinc in some of my melt. It came from range scrap, muriatic acid test was positive. I don't know how much but it was giving me hard time filling out my mold. So out of curiosity I got researching of ways to remove zinc at home relatively safely.

Sulfur doesn't sound nice, copper sulfide doesn't either. Besides it replaces zinc and Cu stays behind. It does dissolve in lead alloy to some degree and impacts mold fillout too. It also removes tin.

There is a process of lead desilverization with zinc where they intentionally add zinc to lead melt to extract the silver. Zinc preferentially alloys with silver and this alloy has higher melting point. This sounds promising as we could intentionally add silver by using silver containing solder in hopes to bring up both silver and zinc. But it has limit of applicability as zinc combines with silver only after zinc content in the melt is above 0.8%, meaning that this 0.8% of zinc needs to be removed later by other means.

Zinc vacuum vaporization that is industrially used for final zinc removal is out of reach for home setup.

I investigated molten salts on top of the melt hoping to find some salt compound that selectively reacts with zinc. There are some, but the temperatures needed go above 600C (1100F) and that seems too high for a steel pot that would be quickly corroded by molten salts. Besides there was chloride gas expected.

I investigated molten salt electrolysis at 400C (750F) where cathode would be solid zinc plate, anode would be the melt and molten salt would be the electrolyte. Seems promising but again some nasty gases are expected, and pot corrosion.

Caustics (Sodium hydroxide, NaOH) can be used to remove zinc, but it is not very active and leaves some sodium in the lead. I also don't fancy working with the most dangerous caustic when it is heated up to molten lead temps. Besides caustic also removes antimony.

I found that Zn reacts with phenols. C6H5OH + Zn → C6H6 + ZnO which is metane gas and zinc oxide. Where do you get phenols and how you introduce it into the melt? Well, I immediately thought that thermal pyrolysis of wood could be source of phenols, and it is. So what, cut a nugget off an aspen log, attach it to a steel paint stirrer, drown it into the melt and let it bubble while vigorously stirring with your power tool? Could be it, but there is lots of other **** in the products of pyrolysis that all tend to remain in the melt as impurities. Actually some of polymers like POM (plastic) are even cleaner than wood during pyrolysis, but I didn't really want to go there.

What really caught my eye was a process of solar hydrogen generation cycle that uses zinc oxide as a carrier of energy. It uses concentrated solar power to decompose ZnO at 1200C (2200F) into Zn and O2, after that Zn is delivered to reactor where it is mixed with superheated water steam to enable reaction Zn + H2O -> ZnO + H2.

https://en.wikipedia.org/wiki/Zinc%E...nc_oxide_cycle

I researched on steam reaction with metals and turns out that steam reacts with only metals higher than hydrogen on the reactivity series.
"Metals such as Mg, Al, Zn and Fe react with steam when red hot. Tin and lead react with superheated steam with great difficulty. Copper, Mercury, silver and gold do not react with water or steam at all.

Only metals which are above hydrogen in the reactivity series displace hydrogen from water or steam. The reactions of metals with water are redox reactions".

https://secondaryscience4all.files.w...-of-metals.png

By introducing steam into the melt we are doing redox reaction of water by using for that purpose the very catalysts we consider to be impurities of the melt. A redox reaction that acts as a flux. Brilliant! And it's selective.

Apparently this method of reacting zinc with steam is known in metallurgy already since at least 19th century, so its nothing new. Some industrial processes have even been that daring that they introduce liquid water into the bottom of the kettle in carefully controlled doses. It might be even possible at home, but only for the most daring.

So how could we introduce steam safely into the melt? It is very important that the steam is absolutely dry - which means superheated with a safe margin. Any water steam above 200C (400F) is dry. At 450C (842F) it is already suitable for reaction. Below that it reacts with zinc very slowly.

I had an idea that the simplest way to generate superheated steam at home is to take a pressure cooker, attach a small diameter copper tube (like brake line tubing) to the cooker (new entry, preserving safety and pressure control valve), bend it into a spiral heat exchanger and let the wet steam go through it. Then use gas burner to heat up the copper heat exchanger so that the steam temperature is raised to above 400C (750F). It becomes dry, pure H2O steam.

Now if the end of that copper tube is also bent into a spiral with a deadend and steam escape vents facing down, and this spiral is drowned into the melt, pressure cooker generated pressure is enough for this steam to displace inrushing lead and push the steam bubbles out into the melt. Stirring with plain steel paint stirrer above the bubbles creates enough reaction sites that over time all zinc should get reacted into ZnO and float on top of the melt as white powder. Hydrogen gas generated could be controllably burned without letting it escape into environment and causing potentially hazardous concentrations.

Steam seems to be the cleanest possible way to remove zinc and many other impurities. It removes Mg, Al, Fe, Ca, Carbon (char, soot), but does not react with tin, lead, antimony, copper.

The safety warning - we are intentionally introducing WATER into the bottom of the melt. If anything goes wrong with the steam superheater and wet vapor gets into the melt, the tinsel fairy might say hi in unforgettable manner. I think it is not hard to ensure water get superheated before entering the melt by having some of coil length submerged into the melt acting as heat exchanger before steam reaches the vents.

I haven't tried this process yet, but I'm really itching.
Thoughts? Has anyone here tried using steam before?

[OS OK]

So how could we introduce steam safely into the melt?

I haven't a clue, have worked around steam my whole career and it's always associated with condensation...whatever you do...be sure to make a video, this is going to be epic!

[DougGuy]

I think you be wise to do this in a closed vessel from a safe distance no?

[Smoke4320]

hey Ma watch this

[dragon813gt]

The copper method is the best one available for the home caster. While there are issues w/ it the alloy at the end has useful properties. Adding tin back in is very easy. W/ the cost of lead alloys I would just toss the contaminated lead and start w/ new alloy. But my time is more valuable than money.

[JimB..]

I suggest that if you run your copper tubing around the inside wall of your pot, maybe a couple layers, so that there is 3’ or so of tubing in the melt that your risk of condensation will be low. Maybe wrap the exposed copper tubing in nichrome wire as a heat source.

Would have to go find a reference to calculate how much pressure will be required to inject steam into the bottom of 10cm of lead.

Cameras must be running for this!

[wimms]

I haven't a clue, have worked around steam my whole career and it's always associated with condensation...whatever you do...be sure to make a video, this is going to be epic!

Tell me more. What kind of steam, at what temperatures, what causes the condensation in real life?

[wimms]

I suggest that if you run your copper tubing around the inside wall of your pot, maybe a couple layers, so that there is 3’ or so of tubing in the melt that your risk of condensation will be low. Maybe wrap the exposed copper tubing in nichrome wire as a heat source.

3 feet? Why do you think so much is necessary? I'd think 1-2 rings around the pot would suffice. Surely wet steam from cooker must be first preheated, then can be delivered to the pot with insulated tubing, perhaps it makes sense to have a thermometer to check the temp before submerging the pot coil, and if the tubing is small enough, heat exchange is fast. Some kind of steam delivery rate valve is necessary perhaps.

Would have to go find a reference to calculate how much pressure will be required to inject steam into the bottom of 10cm of lead.

This is simple. p = 0.0981 * h * SG where h is head(m) and SG is specific gravity. For lead, SG=11 thus
p = 0.0981 * 0.1 * 11 = 0.11 bar above atmospheric pressure. Pressure cookers work at 1-1.2 bar.

Cameras must be running for this!

Thats for sure

[vzerone]

Condensation, when speaking about steam, is when the steam returns to a low enough temperature to turn it back into water. When you boil water in a tea kettle and the whistle starts blowing on the spout you see, (what most peopel call steam) escaping from the spout. That's not steam, that's condensation as the air around the pot has cooled the steam enough to begin to turn into water. That invisible space you see (which is very short) from the tip of the spout to that condensation vapor is "steam".

Why not just shoot your zinc ladened alloy if it cast good? Many here do.

[dragon813gt]

at what temperatures, what causes the condensation in real life?

It's not just temperature. There's a pressure temperature relationship. Read this if you want to know more specifics: http://www.wermac.org/steam/steam_part3.html

[vzerone]

It's not just temperature. There's a pressure temperature relationship. Read this if you want to know more specifics: http://www.wermac.org/steam/steam_part3.html

As pressure goes up temperature goes up. Exact opposite happens as pressure goes down, to a vacuum even. This vacuum is why nuke subs have a steam bubble (and noise) problem with their screws (propellers). Yes it's hard to believe being deep in the ocean and steam is forming on the back side of their screw and the noise is a major concern for running silent.

[wimms]

Condensation, when speaking about steam, is when the steam returns to a low enough temperature to turn it back into water. When you boil water in a tea kettle and the whistle starts blowing on the spout you see, (what most peopel call steam) escaping from the spout. That's not steam, that's condensation as the air around the pot has cooled the steam enough to begin to turn into water. That invisible space you see (which is very short) from the tip of the spout to that condensation vapor is "steam".

That's trivial, I don't think that's what OS OK meant. I think he's been working with closed steam delivery systems where condensation is meant to be avoided, but still happens. Steam in closed systems is tricky, as its condensation point is dependent on pressure and temp, and condensation can cause drastic changes in pressure. So professional insight is welcome.

Why not just shoot your zinc ladened alloy if it cast good? Many here do.

I don't need it. I scrapped my batch. It's just interesting refining method that can go beyond just zinc.

[Boolit_Head]

Ahhh just after they turn on the video ask someone to hold your beer...

[OS OK]

Tell me more. What kind of steam, at what temperatures, what causes the condensation in real life?

When the steam, low pressure steam comes out of the boiler's interior it is pure vapor, heat and pressure but it has to be conveyed to the work point in the system...it is in the transfer of steam to that point where it starts to condense as it looses temperature. They place water traps in front of pressure vessels where the steam is used for heat transfer, say to a web of paper in making corrugated board (boxboard) but the steam looses temperature in the transfer and always makes condensate on both sides of the trap. You can't use steam without making condensate and in your application it's going to go right back into steam in the Pb pot...then blam!

Temps? If I remember correctly it was at 275*F.

EDIT: Something else that just occurred to me is that when you get hit by steam, it'll cook you before you can react to get away from it. Steam is explosive when it ruptures a pipe or vessel into the atmosphere and under pressure it will cut like a razor as it cooks you. I've always been wary about working around steam, I've seen couplings blow apart where the piping is connected to a rotating vessel...it's unnerving and sounds like a jet engine...makes me cringe!
I wouldn't mess with this idea...

[vzerone]

If you look at steam turbine engines the rotor are a series of small rotors going up to large rotors. High pressure steam ( preferrably super heated steam) acts upon the small rotor first because it's at fullest power. As it passes through that rotor it loses some of it's power (think heat and pressure) so the next rotor is larger so it captures more of weakened steam, and so forth till the last largest rotor and then through the exhaust.

You never want to check for a steam leak with you hand, not even on low pressure saturated steam. Heard of a fellow checking for a steam leak on a super heated steamline and he fell to the floor in anguish. The steam cut his hand off at the wrist and it was just a pin hole leak.

Another dangerous concern of even minute drops of condensate are vacuum towers used in all sort of indrustrial applications from chemical plants to oil refineriers. They blow up violently when they get a drop of water in them.

I concur with OS OK I wouldn't mess with that idea.

[vzerone]

[Silvercreek Farmer]

Dude, how much zinced lead do you have? My scrapyard will "trade" for a $.15/lb haircut.

[wimms]

When the steam, low pressure steam comes out of the boiler's interior it is pure vapor, heat and pressure but it has to be conveyed to the work point in the system...it is in the transfer of steam to that point where it starts to condense as it looses temperature. They place water traps in front of pressure vessels where the steam is used for heat transfer, say to a web of paper in making corrugated board (boxboard) but the steam looses temperature in the transfer and always makes condensate on both sides of the trap. You can't use steam without making condensate and in your application it's going to go right back into steam in the Pb pot...then blam!

Temps? If I remember correctly it was at 275*F.

I see. You probably work with steam that is used for heat transfer. It has to be wet or saturated steam for efficient heat transfer at destination through condensation. 275F seems to support that.

Pressure cooker provides wet steam and is not suitable for delivering directly into the melt, thats why I envision superheater, its purpose is to raise the temp of the steam to 400C (750F) at which point there is no chance that there is any condensate possible. Superheated steam has drastically lower heat transfer and we do not use very long piping, heat of the melt also only increases the temp of the steam, thus the conditions are rather different.

We won't use the steam for heat transfer. We'd want to make sure that superheated steam temp does not drop anywhere near hte saturation point before entering the melt and we are golden.

Just to make sure, superheated steam is abit different animal than saturated steam. I believe you know that and just missed my superheater on the way to the pot.

EDIT: Something else that just occurred to me is that when you get hit by steam, it'll cook you before you can react to get away from it. Steam is explosive when it ruptures a pipe or vessel into the atmosphere and under pressure it will cut like a razor as it cooks you. I've always been wary about working around steam, I've seen couplings blow apart where the piping is connected to a rotating vessel...it's unnerving and sounds like a jet engine...makes me cringe!
I wouldn't mess with this idea...

Fair warning. But we'd not need high pressures, we'd work with around 1 bar steam only as defined by pressure cooker's pressure regulating valve. This is rather tame. Though it's still a valid warning that steam leaks shouldn't be searched by naked hands, much like you shouldn't touch liquid lead to test if its warm enough. Pipes should have protective covers, insulation at least. That would dissipate any razor sharp steam jets.

[wimms]

If you look at steam turbine engines the rotor are a series of small rotors going up to large rotors. High pressure steam ( preferrably super heated steam) acts upon the small rotor first because it's at fullest power.

I concur with OS OK I wouldn't mess with that idea.

Guys, you are slightly overreacting. Please consider that proposed conditions are very different from typical industrial usage of steam.

Steam is hot. Right.
High pressure steam is dangerous. Right.
Wet steam says hello to tinsel fairy. Right.
Superheated steam at high pressure is extremely dangerous. Right.
Superheated steam at near atmospheric pressure is safe in the melt. It's just hot. But what's new in smelting?

We can arrange for rather safe application of steam for our usage.

[OS OK]

OK...sounds like you have yourself convinced that you can pull this off...just remember to video it...I wanna see what you look like 'before & after'...

"Hold my beer...watch this!"