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Old 20-06-2020, 15:10   #1
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Reconstituted zincs

I have a number of old, partially depleted, zinc anodes lying around. I'm wondering if I can melt them down and re cast. I have a small foundry set up in my workshop, and it would be a trivial task to form new teardrop anodes.
Any chemists on line?

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Old 20-06-2020, 15:21   #2
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Re: Reconstituted zincs

Watch out for the fumes from molten zinc - very toxic
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Old 21-06-2020, 05:03   #3
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Re: Reconstituted zincs

If you found a way to re-use all the zincs which are thrown away every year at our marina, you'd have a pretty good thing going. And they all come with SS bolts and nuts; those things get tossed out too. I assume there's no money in it, or someone would be going around collecting them.
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Old 21-06-2020, 05:04   #4
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Re: Reconstituted zincs

The zincs are not pure zinc.
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Old 21-06-2020, 06:01   #5
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Re: Reconstituted zincs

Another route is a wire brush on a grinder. In my case it's aluminum, but as long as you clean down to shiny stuff one that still has structure can be reused. I have two sets and rotate them each time I haul out.
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Old 21-06-2020, 09:50   #6
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Re: Reconstituted zincs

I suspect that anything which would alloy with zinc would probably have similar electrochemical properties and not deleterious to the zincs protective properties.

I'd recast the scraps and put them to a useful purpose.
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Old 21-06-2020, 10:23   #7
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Re: Reconstituted zincs

Quote:
Originally Posted by S/V Illusion View Post
The zincs are not pure zinc.

Besides the honestly deadly fumes etc, this is the problem, first new zincs are an alloy and not “pure” even extremely expensive gold is only .999 pure.
But as zincs get wasted the zinc is leached out leaving behind an alloy that is lower in zinc, melt it down for an anode and you have a less effective anode.

Besides, try aluminum anodes, I predict you’ll be happier with them, I know I am.
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Old 21-06-2020, 10:30   #8
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Re: Reconstituted zincs

There are old timers who melt lead tire weights to cast bullets.

That said what you are talking about sounds very toxic and dirty, doubt it would be worth it unless you just want to try it to try it
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Old 21-06-2020, 10:51   #9
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Re: Reconstituted zincs

Every professional shipyard that I know keeps expired zinc anodes in a box on a pallet ... this valuable box of anodes is kept inside , under lock and key

When you remove an anode from your hull, good manners dictates that you collect them and deliver the old anodes to the recycle boss at the shipyard

when this anode box is full, itís shipped back to the anode supplier and the shipyard receives substantial compensation

Recycling an anode is not simple

A zinc anode is a precise alloy

A pure zinc anode, or incorrect alloy would passivate and become inert

Google mil spec anode for a description of this alloy

Iím not familiar with the composition of an aluminum anodes ... you can be sure that this anode is also a precise alloy
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Old 21-06-2020, 14:39   #10
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Re: Reconstituted zincs

Quote:
When you remove an anode from your hull, good manners dictates that you collect them and deliver the old anodes to the recycle boss at the shipyard
What a bizarre notion of "good manners".

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Old 21-06-2020, 14:51   #11
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Re: Reconstituted zincs

Quote:
Originally Posted by slug View Post
Every professional shipyard that I know keeps expired zinc anodes in a box on a pallet ... this valuable box of anodes is kept inside , under lock and key

When you remove an anode from your hull, good manners dictates that you collect them and deliver the old anodes to the recycle boss at the shipyard

when this anode box is full, itís shipped back to the anode supplier and the shipyard receives substantial compensation

Recycling an anode is not simple

A zinc anode is a precise alloy

A pure zinc anode, or incorrect alloy would passivate and become inert

Google mil spec anode for a description of this alloy

Iím not familiar with the composition of an aluminum anodes ... you can be sure that this anode is also a precise alloy
So good manners say I give said object

Good economics says heís gets well paid for free donation.

Do I get a tax write off or compensation for my old zinc?
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Old 21-06-2020, 15:10   #12
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Re: Reconstituted zincs

Thanks for all the responses, I'll give away the idea. Seems too much trouble, dirty, dangerous, possibly ineffectual and bad manners.
Removing the anodes, polishing them back to solid metal would work, however I only slip annually and would not trust the remaining zinc for another year.
I already cast aluminium, so there's an idea. I just scavenge old window frames etc, however the end result is often a little honeycombed. May be an advantage as it increases the surface area.
Or maybe I just spend the $100 like always - teardrop, rudder halves and bow thruster.
Jon
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Old 21-06-2020, 15:12   #13
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Re: Reconstituted zincs

Can't get them to fit my prop nut so every 2 years the oxy acetylane torch comes out ! Collected enough used ones to last me the next 30 years
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Old 21-06-2020, 17:05   #14
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Re: Reconstituted zincs

Don't just cast a piece of aluminum and expect it to work as an anode. Aluminum anodes are really an alloy and have other metals in them.
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Old 21-06-2020, 17:16   #15
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Re: Reconstituted zincs

For the composition of zinc anodes...
https://www.aegion.com/-/media/Aegio...Anodes-UK.ashx
gives the US MIL A-18001K ASTM B Element Analysis (% by Weight) as
Aluminium 0.1 - 0.5
Cadmium 0.025 Ė 0.07
Iron 0.005 max
Lead 0.006 max
Copper 0.005 max
Others 0.10 max each
Zinc Remainder
so to me it looks like 99% zinc with the only intentional alloying elements being being tiny amounts of aluminum and cadmium.

I spent a few weeks training with the welding apprentices at work during a low sales and production period. From that quite limited experience, my understanding is that galvie flu is caused by welding or oxy acetylene cutting zinc plated or galvanized steel. The zinc metal is vaporized at the melting point of iron, the zinc gas reacts with the oxygen in the air to become a white zinc oxide smoke, and the zinc oxide when breathed injures membranes in the nose and lungs. Smeared with a little grease on your nose, zinc oxide makes a good sun block, but in your nose... not so good. We ground back the zinc and wore a respirator.

Looking at Wikipedia, the vapor pressure of zinc at its melting point of 420C is about 10Pa (0.10mbar). Zinc boils at 907C where its vapor pressure is 1013mbar, 10,000 times greater. A zinc coating would be completely vaporized well before iron would melt at 1538C. I'd expect the danger of galvie flu from casting zinc to be much less than the danger of welding on zinc plated or galvanized steel.

There are several youtube videos of people casting zinc seemingly without problems. I've melted broken zinc pencil anodes out of their brass bases with a propane torch before with no problem.

I'm a chemical engineer not an industrial hygienist and no expert in any of this. Does anyone know better?

Bill
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