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Suggestions for deplating spool of silver plated wire

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chemguy

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Post November 23rd, 2012, 8:56 am

Suggestions for deplating spool of silver plated wire

Hello Everyone

I am required to recover silver from a spool of silver plated wire in large quantities. I believe the wire is silver over copper/Brass. I've dissolved some of it in nitric acid but ended up in vain dissolving silver along with the base metal. Moreover nitric acid did not dissolve the spool of wire completely. It finally ended up in a incomplete process with small bits of base metal undissolved. As nitric acid dissolves both silver and copper and the silver content being extremely low as compared to copper in the solution thus prepared. I was not able to cement out silver using copper.

I have read the posts for suggestion for deplating gold plated wire. But the solution provided in it to use nitric acid doesn't work out in my case and i also expect shielding because of the wires being closely spaced and touching each other.

Can anyone suggest me whether i should go with Sulfuric stripping cell or should i fuse the entire thing and separate it via copper sulfate cell.

Any suggestion/help will be greatly appreciated

Regards
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goldenchild

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Post November 23rd, 2012, 9:25 am

Re: Suggestions for deplating spool of silver plated wire

Just wondering why you are required to remove the silver from the wire. Trying to recover silver plating for the most part is worthless. The cost in trying to do so negates the value of silver. Usually by a large margin. The wire is probably worth more in its intended form than silver and copper.
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chemguy

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Post November 23rd, 2012, 9:31 am

Re: Suggestions for deplating spool of silver plated wire

Thank you for your reply.
But the wire is in the form of a spool and i cannot use it for any other purpose. It is sold as a scrap and i wish to extract silver from it and sell the copper too.
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chemguy

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Post November 23rd, 2012, 9:33 am

Re: Suggestions for deplating spool of silver plated wire

Moreover silver plating varies from 0.5% to 1%.
Acids are not costly at our place. They cost approximately 0.5-1 USD per liter
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goldenchild

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Post November 23rd, 2012, 9:37 am

Re: Suggestions for deplating spool of silver plated wire

I see. Maybe put it on Ebay and see if anyone else can use it in its current state. You may even end up making more money there then you would retail. But again, as far as recovering it I would be surprised if anyone could help you in a way that you would make a profit. Even the smallest one. Everything you need is here on the forum. If you can't find something it's usually for a reason...
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chemguy

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Post November 23rd, 2012, 9:39 am

Re: Suggestions for deplating spool of silver plated wire

The material i have is a waste from the wire drawing process and it is completely entangled.
So neither i can draw a wire from it nor i can make into a useful spool.
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chemguy

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Post November 23rd, 2012, 9:41 am

Re: Suggestions for deplating spool of silver plated wire

If i can extract silver from it. I can make a good fortune. As i can get about 300-400 kgs of such scrap daily.
Moreover there is 1 industry doing it near our vicinity.
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nickvc

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Post November 23rd, 2012, 11:39 am

Re: Suggestions for deplating spool of silver plated wire

Well if you can get big volumes I would suggest setting up a copper cell if the silver is of a low percentage,it has to be below 5% silver or the cell won't work well, and the silver will be recovered as slimes from the anode bags. The advantage is that the copper should also be saleable as it should be fine if you operate the cell correctly. There is loads of information on copper refining its one of the oldest and best known technologies around just google it.
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chemguy

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Post November 24th, 2012, 1:59 am

Re: Suggestions for deplating spool of silver plated wire

This is how the material will look like or it can be even more compact.
There is an industry over here which process it into ingots and then it extracts the metals from it.
I suppose they use the copper sulfate cell.
According to me electrolysis is the best way out. But with a somewhat different composition of electrolyte or difference in the shape of the anodic material.
As it is in the wire form it is going to have high surface area. Can anyone suggest me what will be its effect in the process in terms of current density or electric field that will be set up.
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nickvc

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Post November 24th, 2012, 2:44 am

Re: Suggestions for deplating spool of silver plated wire

Only my opinion but it needs melting into anodes and bagging to collect the slimes so big crucibles will be needed and the necessary safety gear to protect you in case of spillages or splashes of molten metals, good lifting tongs are a must. The cell is very widely discussed on the internet and in books so setting it up should be easy enough as should running and maintaining it.
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chemguy

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Post November 26th, 2012, 1:37 am

Re: Suggestions for deplating spool of silver plated wire

is it possible for me to use the sulfuric stripping cell if i change the form of by raw material by shredding it?
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butcher

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Post November 26th, 2012, 3:47 am

Re: Suggestions for deplating spool of silver plated wire

If using the concentrated H2SO4 stripping cell (5% HNO3), I would leave the wire as it is, the silver should strip from the copper. You will need good contact with the anode connection, and it may help to put the silver bundle of wire in a square box smashing the ball into a loose entangled bundle of square flat anode wire, clip one end to the anode connector and strip half the bundle, flip it over to strip the other half, Have not tried it but I cannot see why it would not work, I also believe silver would begin to accumulate after a while in the cell, (it may form silver sulfate and some silver remain in electrolyte), stripping the silver I think would be the easy part, and recovering the silver probably would not be that bad, but getting it converted back to silver metal may be a lot more difficult to deal with later to get back it converted to silver.

The wire looks to be thin and has a lot of surface area; I think for this material I would just use nitric acid (even if I had to distill a batch of home made nitric from sulfuric acid and fertilizer).

Another option I would just save the wire and use it next time I wanted to cement silver from a batch of silver nitrate solution, or use it for a collector in a melt.
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chemguy

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Post November 26th, 2012, 5:21 am

Re: Suggestions for deplating spool of silver plated wire

I tried with nitric acid, but as the silver content was too less, even after dissolving the entire quantity silver did not cement out properly when i used copper for cementing. Still i will give it a try again.
On this forum i read that there will be wire shielding effect and i will not be able to extract silver from the portion where the two wires are touching each other. So according to you will there be no trouble if i used the sulfuric acid cell.
I am going to take its trial in a day or two.
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chemguy

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Post November 26th, 2012, 5:26 am

Re: Suggestions for deplating spool of silver plated wire

GOLDSILVERPRO
can you please help me out.
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nickvc

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Post November 26th, 2012, 5:46 am

Re: Suggestions for deplating spool of silver plated wire

In the quantities your looking at 1.5-2 tons a week I really don't think a sulphuric cell will cope with the volume. The big refiners I'm pretty sure would pass this material onto a copper refiner for recovery especially if it's low grade as it would fit into their production very easily, the problem been would be the payment time as its usually 3 months plus for settlement if I remember correctly. The only choice for you in my opinion if you want a faster turnround is to run your own copper cells but your going to have to calculate the size your going to need to cope with the volume or to broker the material through a copper refiner, the latter may well be the better option as the set up costs for the cells would be considerable. Silver recovery is not cheap or easy and despite the rise in prices it's not cost effective unless it's high grade and I don't believe there is an easy option on this material, if you dissolve it in nitric the acid costs and volumes of solution would be large and disposal would be a big problem as would fume control, if you use a sulphuric cell or probably multiple cells the acid is very dangerous especially if hot and I'm not to sure how much the solution will hold and I'm fairly sure it will not strip all the silver without taking some copper into solution decreasing the amount of silver it can hold, I'm sure someone will correct this statement if I'm wrong.
GSP may be able to give you some insights into possible ways to recover this material as he has processed many tons of silver bearing scrap but in honesty I can't see a simple cheap method to handle this much material continuously.
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goldsilverpro

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Post November 26th, 2012, 12:17 pm

Re: Suggestions for deplating spool of silver plated wire

Electrolytic Stripping

I don't think that any electrolytic stripper will work on a mass of wire because I don't think that the current will "throw" into the center of that mass. In my experience, it will only strip the wire on the outside surface of the mass.

If you did shred it (good idea, by the way), you would need (in my estimation) to tumble it in the stripper in a barrel plating machine. They make polypropylene barrel platers with "herringbone" panels that would prevent the small pieces of wire from falling out. Here's one for sale on eBay. It doesn't say what it's made of or whether herringbone panels are used or not. It also doesn't say what type of contacts are in the barrel. There are 3 types of contacts available - center bar, button contacts, or danglers. In sulfuric, they would have to be made of lead or some harder lead alloy. All might work, but I would probably use danglers or buttons. I'm not saying to buy this one - I only wanted to show you what they looked like. When new, they're much higher priced. I used a Poly pro one in the sulfuric stripper. The plastic surface did degrade over time (became powdery) but I still was able to use it for several years
http://www.ebay.com/itm/SINGLETON-BARRE ... 3f1a034a66

If you did shred it and used a barrel plater, I would consider using an electrolytic cyanide solution instead of the sulfuric stripper. It would contain about 50g/l sodium cyanide and about 150g/l of sodium hydroxide and run at room temperature at about 4 volts - you'd have to experiment with the voltage and/or current density, though, for best results. The barrel construction is not as critical with the cyanide solution and it's much easier to get the silver out then with the strong sulfuric stripper. The high sodium hydroxide prevents attack on the copper and the silver plates out on 2 (one on each side of the barrel) fairly large 300 series stainless sheet cathodes about 3mm thick. The solution can be used over and over by periodically analyzing the cyanide and the hydroxide and making needed additions. I really haven't worked with this much. I proved it in beakers in the lab. We then set up a 50 gallon solution of it but we didn't have a barrel plater. We just put a bunch of silver plated flatware in a steel basket. It worked, but only on the outside of the mass. The stuff in the middle wasn't touched. A tumbling barrel plater would solve this problem.

A note on the "herringbone" plastic barrel panel. The plastic is quite thick. On one side of the panel, they drill angled holes half way through. They repeat this on the other side and the drilled holes meet in the middle of the plastic. The result is that the holes are v-shaped (like this > but with a much less severe angle). Therefore, small wires won't fall through the holes.

A note on "dangler" contacts. These are 2 flexible insulated cables with a heavy metal slug mounted on the ends. They enter the barrel from holes in the ends of the barrel. When the barrel turns, they flop around and make electrical contact to whatever is in the barrel.

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Immersion Stripping

It would be nice to use a solution the would strip the silver by simple immersion. That would allow you to retain all of the copper in a simple manner. From the figures you gave, from 0.5-1% silver, the copper is worth about the same as the silver.

I don't know how this would work but I did find a very interesting 2007 patent application for an immersion stripper. See the attachment. (Note: the rolled gold one is also interesting because they melt rollled gold or, gold-filled, and run it through a copper cell). It uses sodium persulfate as an oxidizer, sodium hydroxide to raise the pH, and ammonia to complex the silver. The problem I see with this is that, under normal circumstances, when you combine an ammoniacal silver solution with NaOH, you can create an explosive compound. Maybe the persulfate eliminates this possibility but I'm not enough of a chemist to know. It would be appreciated if one of the chemists would answer this question. If it's safe, it could be an answer for a lot of people on the forum. To precipitate the silver as AgCl, I would think one could simply acidify with HCl.

You might be able to use the common 95/5, H2SO4/HNO3, by volume, to strip the silver. If you think about it, it is similar to the electrolytic sulfuric stripper, except it uses the nitric as an oxidizer instead of providing oxidation from an anode. It is dangerous, especially when hot, but, since the silver is thin, it might work well at room temperature. As it slows down, you can add a little more nitric. When it is saturated, you could dilute it and drop out the silver as AgCl. Read this thread, especially the posts by henos. He runs it hot (80C+) and then lets it cool. Most of the silver crystallizes out as silver sulfate. He separates out the crystals and then reuses the solution, with some nitric additions, I assume. A good thing about running it hot is that no moisture from the air would be absorbed and dilute the solution, as would happen at room temperature. A problem with running it hot is, what sort of vessel do you heat it in? In the old days, they used white, fine grained cast iron, I believe. Heavy stainless might work but I'm not so sure about that. Titanium might work. Glass would work but you would be severely limited as to size, in order to keep things safe.
viewtopic.php?f=50&t=16166&hilit=sulfuric+nitric+silver

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Copper Cell

First of all, it was indicated that some of the wire might be brass. If the wire is used for electrical purposes, I can't see how this is possible due to the reduced electrical conductivity of brass as compared to pure copper. If there is brass, this could cause cathode deposition problems due to the zinc. I did find a patent and and article that seemed to somewhat solve the zinc problem. See attachments (note that the rolled gold one is also interesting for melting gold-filled and running it through a copper cell). In general, since the copper preferentially plates out first, before the zinc, the copper content must be analyzed and kept at a high level in order to prevent the zinc from co-depositing. Also, the zinc content in the solution must be controlled

Small copper wire is notoriously difficult to melt due to the formation of copper oxides on its large surface area. However, since this wire is coated with silver, this problem would seemingly be reduced. Most references I found packed the wire into the crucible and some first compacted the wire into blocks. One shredded the wire first into small pieces so it would better fill the voids. In all cases, they covered the copper with about an inch layer of charcoal chunks. This reduced any copper oxides that formed.

To avoid melting, I thought about packing the wire tightly into bagged titanium anode baskets. An alternative would be to somehow compress the wire into small blocks that would slip into the baskets. This would only work if the silver were thin enough so than the acid would penetrate through the porosity. I think this is worth a try. First, ball some up any try it in a beaker to see in the solution will penetrate and dissolve the copper.
http://www.ebay.com/sch/?_nkw=titanium% ... 6134127402

I just thought of this, but, with shredded wire, a barrel plater might work in the copper cell. Here again, though, the solution would have to be able to get to the copper through the porosity in the silver. I would probably get a barrel with button contacts or danglers and they would probably have to be made of hardened lead to prevent being dissolved or cut up.

Here are some threads on the copper sulfate/sulfuric cell. If you do go this route, I would suggest setting up to analyze the solution constituents so they can be adjusted when needed.
viewtopic.php?f=45&t=5396&p=46132&hilit=anaconda#p46132
viewtopic.php?f=37&t=6652&p=59443&hilit=copper+sulfate+sulfuric+acid+formula#p59443

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Hope this helps. Unless I think of something else, that's about it for ideas. It took more than 3 hours to write this and I'm worn to a frazzle. Whatever you do will require experimentation. What you're trying to do isn't easy.
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chemguy

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Post November 27th, 2012, 3:13 am

Re: Suggestions for deplating spool of silver plated wire

GOLDSILVERPRO
thank you for your valuable suggestion.
I will try out the things and report it over here.
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chemguy

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Post November 27th, 2012, 3:19 am

Re: Suggestions for deplating spool of silver plated wire

GOLDSILVERPRO
I highly appreciate your effort.
i am highly obliged to you and will not let your effort go in vain. I will do come out with fruitful results.
Cyanide is darn risky but i will give it a try, moreover cyanide is damn expensive, so its recovery will be an important issue. Here we get potassium cyanide.
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chemguy

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Post November 27th, 2012, 3:45 am

Re: Suggestions for deplating spool of silver plated wire

@GOLDSILVERPRO
do you think with this type of tumbler design using lead bars as interior or baffles and polypropylene cloth. i will be able to reach the center of all the mass with appropriate current.
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chemguy

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Post December 1st, 2012, 1:26 am

Re: Suggestions for deplating spool of silver plated wire

@ goldsilverpro

If i use the cyanide bath for deplating silver, then how can i extract the dissolved silver from it?
by electrolysis at 5v and 15 amperes using carbon anode and cathode and rotating disc type stainless steel at their center
or should i use zinc turnings/metal for cementing out silver?
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