Refining pewter through electrolysis

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marethyu

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Jun 9, 2018
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I was going to build an electrolytic cell to refine a bunch of pewter that I have laying around and was wondering if anyone had built a proper cell like this before or had any insights. I haven't really seen anyone refine large amounts before just very inefficient small-scale cells. I'm looking to refine about 50kg of what I believe to be lead free pewter. I think I want to build a cell with hydrochloric acid electrolyte and maintain a current density on the cathode of 0.2 - 0.4 Amps per square inch according to a study I read studying ideal current densities. I was wondering if anyone knows what I ideal voltage to hold the cell would be as I haven't seen any clear numbers and have seen voltages from 3-6v used. Also was wondering what an ideal cathode material would be. I have heard of people using stainless steel, titanium, and even seen people use paper clips in lab demos. All of these materials dissolve in hydrochloric acid though so I was wondering if it makes a big difference as to what I use or if being used as a cathode is just able to protect them from oxidation. Also, are there any issues with electrolyte fouling? I've read pewter mainly contains Bi, Sb, Cu as contaminates but also can contain Pb, Ag, and other trace metals. I will probably add a little sulfuric acid to the electrolyte to make sure if there is any lead it stays insoluble. Any other suggestions?
 

marethyu

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Jun 9, 2018
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Is there any benefit to using KOH instead of HCl to prepare the electrolyte? I haven't seen any literature using Potassium stannate as a means to refining tin just for electroplating as it seems to deposit tin on an electrode very uniformly. From what I can tell, using KOH would just be more expensive and hazardous otherwise unless I'm missing something. I've seen electrolytes with nitric and sulphuric acid used but chose HCl because it is very cheap, relatively safe, and will easily dissolve antimony which is important considering some pewter alloys contain a significant percentage of antimony.
 

jimdoc

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What is your goal in refining pewter?

I would just sell it as is to ammunition re-loaders. Or actually I would keep it for that purpose.
 

marethyu

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Jun 9, 2018
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If I refine it to 99%+ it just about doubles its resale value for me and It shouldn't take a lot of time or effort of effort once I know what my cell parameters and design choices are.
 

jimdoc

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I don't see how it could be worth doing. Rotometal's prices for tin and pewter are about the same.
 

galenrog

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Jan 16, 2010
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I believe you will find that your total costs, including proper waste treatment and disposal will far exceed the value of metals recovered, and then refined.

By the way, which metal in pewter is normally valuable enough to even consider this?

Time for more coffee.
 

marethyu

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Joined
Jun 9, 2018
Messages
16
I was going to go after the tin with it priced at $27 a kilo it would be profitable for me. I treat my own waste for the most part from silver refining so that isn't a big issue for me and already have all the chemicals and equipment needed just need to set it up for tin. Generally, I would agree between higher amperage power supplies, casting anodes, waste treatment, and the cost of buying the scrap it is difficult to be profitable without large amounts of material or running it parallel to more profitable processes like I'm doing.
 

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