The Home Machinist!

Hi to all, I am looking for some advice on how to recover silver that is plated on a steel surface.The heavier deposits I sweat off with a torch but I have alot of material where the plating is only a thickness of .001 or .002 but there is alot of square inches. Some surfaces approx. 5''x10''.I have access to nitric acid and have tried a experiment with a small piece but dont see how this could turn a profit.Thanks in advance for any feed back

I spent years of my life refining precious metals for gain. What you propose is not going to be easy, and most likely will not be profitable. The problem you'll have is nitric dissolving steel along with the silver, then the remaining steel cementing silver (and copper) that's already in solution when the acid level drops.

Are you familiar with a sulfuric acid stripping cell? That may be a viable choice. The system was developed to strip parts that are plated with precious metals, but the plating is defective. It is reputed to not attack base metals so long as the temperature of the stripping cell remains cool.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Hi Harold, I have not heard of the stripping cell and would like to get more info on it if possible.I read of your past job on older posts and hoped you would have an idea for me.Thanks

Hi Harold, It looks to me like the cell has to do with a type of reverse electoplating? I am a mechanic on ww2 radial aircraft engines(thus the access to silver) and currently do some plating. I would not consider myself a professional plater I just know enough to get by. I currently operate a lead tank and Indium tank for bearings and a tin tank. This gives me access to a few diffrent size rectifiers if it helps.

pwa,
The method in question is a concentrated sulfuric acid stripping cell. It can be make quite simply, even with a steel housing, so long as you keep the acid chilled, and it does not contain water. Concentrated sulfuric can be created by buying battery acid from an auto parts store, and evaporated to expel the water. If you have any chemical connections, you may be able to buy it already concentrated. Your plating experience will certainly be beneficial, plus you would need a DC power supply, so you have a leg up.

I am somewhat familiar with the process, but never put my own system in operation. I specialized in high grade waste materials, so I avoided the vast majority of plated materials. As a result, I can't speak from the position of one that has experience.

Here's a patent number that will help explain the process to you. 2,185,858. click here

If, after you've explored the patent, you'd like to discuss this process, I co-moderate a forum that revolves around refining precious metals. There, we have many who have applied the stripping cell in a most basic manner. They are all willing to share knowledge, so if you're interested, please let me know and I'll provide a link. The board is open registration, so there's no hurdles to cross in making contact.

I'm able to help you with the purification of your recovered silver if you'd like. I processed silver when I refined. That, too, is a relatively simple procedure, one that requires nitric acid and distilled water. Let me know if I can help.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

WOW!!!, That sounds like exactly the set-up I need.Kinda funny the patent is from 1940 which is the time period all my material was manufactured.As far as the purification of my material I sent it to a refiner that it may get certified for sale.The last lot of 310 troy oz. had 4 oz. contaminates. This was just sweated of with oxy/acetylene torch and sent in, so I am quite happy with that.Its the material I toss out as scrap steel that has the thinner silver plating I cant get too thats killing me. It would appear I have access to everything in the article accept the tank which I will have no problem constucting.Something I have been wondering which I quess would ultimatley determine if there is a profit to be had(heck I would settle for breaking even) is how silver can be reclaimed before the chemicals have been depleted? Please introduce me to the forum you mentioned.Thank You very much Harold this sounds really,really, exciting. pwa(pratt whittney aircraft)

Once in solution (dissolved in nitric acid), recovery is quite simple. A piece of scrap copper is all that is required, assuming you don't have excessive free nitric acid present. The copper is introduced to the solution, where there's an electron exchange between the copper and silver in solution. Silver comes out as what is commonly termed cement silver, and copper goes in to solution. This recovery method is the fastest and easiest approach, and has the potential to yield respectable quality, as good as 99% silver.

The second option is to recover the silver as silver chloride---where HCl, or common table salt is introduced to the silver nitrate solution. There's an instant precipitation of silver chloride. It can be converted to elemental silver by several methods, but none of them are as convenient as the method of recovery that uses copper.

Scrap steel can be used to make a recovery, but it is not selective. If copper is in the silver nitrate solution, it, too, will be recovered. It is not a recommended procedure if purity is a concern.

Here's a link to the gold forum:

http://goldrefiningforum.com/phpBB3/index.php

Silver that is recovered from the sulfuric stripping cell may not be in solution. Gold so recovered reports as black slimes. The method of stripping was developed to recover the base pieces without damage, with no concern for the recovery of platings that were applied. Rarely has anyone used this method for recovery of silver, so you may have to do some experimenting to affect a recovery once stripped.

A reader recently posted on stripping silver plated flatware using an uncommon method. Indications are he is enjoying success. Check all of the posts in regards to silver for a good understanding of functional methods.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Hi Harold, This is funny,While searching for information I kept coming across your link and thought thats the site to get on but my trend micro tells me thats a dangerous page.Do you know why that is? The other day as my first experement I used a copper wire in the process and there must have been to much free acid,It would just eat the wire until I stopped feeding it in.Anyway I can tell this is going to be fun!!!

Don't be too concerned about the dangerous page warning. There has been a time or two that the site owner has had to remove some malicious code, but the forum is basically safe. I've been on it since its inception, running a typical virus program and have never had a problem.

The condition you reported, the copper wire being dissolved, is characteristic of excess nitric acid. You're between a rock and a hard spot with steel that has silver on its surface. When there's too little nitric present, the steel will cement both copper and silver. If there's too much, as you experienced, it dissolves the copper. Then, when the acid level is low enough and there's any steel present, both silver and copper will come down. That's the reason I suggested the sulfuric stripping cell, which you can explore without getting too deeply involved. A simple Pyrex dish can serve as a container, where you can try a piece to see how it behaves. If you can strip the silver without issues, recovering from the sulfuric solution won't be nearly as difficult as dealing with excess nitric.

To be perfectly honest, silver plated items are generally just sold as scrap, often for the value of the base metals upon which they are plated. You may find that you're doing as well with the material as you can hope, although I don't know that. Were I in that position, and I was still refining, I'd be inclined to use the scrap steel in what is known as a stock pot, where traces of greater values are recovered by the cementation process. That would gradually consume the steel, liberating anything of value, which would then report in the residues, along with other value and copper.

There's a lot to know when it comes to precious metals. Don't expect for it to make sense without a little effort.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Great, I will check out the site and I dont think for a second there is anything simple about metals recovery.How much fun would it be if it were easy? Thanks Harold