# Take it or leave it



## jislizard (Jan 13, 2010)

I should probably lurk more before posting but sometimes I get carried away, I promise to go back through the threads and give them all a good read but I thought I would post a quick question.

I have picked up 24Kg of Australian junk silver coins, (50% Ag, 40% Cu, 5%Zn, 5% Ni if memory serves me well)

I know the best advice is to wait for the spot price to go up and then dump them onto eBay which will be by far the easiest way of converting them back to cash.

However, in theory, would I be better served trying to get the silver out of the coin or would it be easier to remove the copper and then the other metals from the coin and leave the silver?

My wife is keen on jewellery making so 100% pure is not the target, anywhere around 92.5% would be acceptable.

I will now go back and read the rest of the forum, thanks

Mark


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## Harold_V (Jan 13, 2010)

jislizard said:


> However, in theory, would I be better served trying to get the silver out of the coin or would it be easier to remove the copper and then the other metals from the coin and leave the silver?


How would you propose to do that?

Alloys of metals are not readily separated. Considerable effort is required. In this case, assuming you had intentions of making a recovery, you'd be best served dissolving the coins in dilute nitric acid, then recovering the silver with copper. There are other approaches, but none of them to which I am privy would allow you to remove a specific metal without destroying the coin entirely. If that's what you had in mind, it won't work. 



> My wife is keen on jewellery making so 100% pure is not the target, anywhere around 92.5% would be acceptable.


I agree, but it's important that the balance be material that does NOT destroy the properties of the metal. Therefore, in a case like this, you are very best served by recovering the silver, then insuring its quality by parting in a silver cell. That way all traces of copper oxides will have been removed, along with other potential contaminants, then you can make fresh sterling that will have the desirable qualities that allow it to be worked properly. 

In this case, unless you wish to get involved in refining, you would be better served to sell the coins for the silver content. 

If, by chance, you have an interest in refining karat gold, the coins could be used to great advantage for inquartation. That way processing serves a dual purpose. 

Harold


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## jislizard (Jan 13, 2010)

Thanks for the quick reply.

I have been working my way through the old posts and Nitric Acid seems to be the way to go. I can get some from the lab, or order it in. The process looks fairly involved but there seems to be lots of advice on the forum so it is not too daunting.



> jislizard wrote:However, in theory, would I be better served trying to get the silver out of the coin or would it be easier to remove the copper and then the other metals from the coin and leave the silver?
> 
> 
> How would you propose to do that?



I was hoping you would propose it and I would do it!

I was actually hoping that there would be some way of using electricity to draw the copper out and then a few other chemicals to leach out the zinc leaving the silver behind, I figured that if it was possible someone may have tried it before. 50% silver coins are very common over here, all silver coins from 1946 to 1963 in Australia were 50% and there are plenty of hoards around similar to the one I just picked up.

I am a member of a coin club and one of the members was telling me a story about a colleague of his at the plating factory who ran all his pocket change through a plating bath to remove some of the silver from the coins, when they were a dull grey colour and pitted all over the surface he would wash them off and spend them. The remaining silver he kept. I have no idea how much he recovered in this way or how many contaminants there were in the recovered silver but it got me thinking.

I tried electrolysis to remove the copper from cupro nickel coins and although that ended in a ton of sludge and some pretty coloured water I am pretty sure I know where it went wrong. It was also quite interesting and an area I was keen to explore as the price of the copper came almost up to the face value of the coins for a while back in 2008-09

Anyway, back on topic, I have no karat gold to recover but I will be using the forums search function to look up "inquartation" and "silver cell".

I am keen on refining as I think that if the cost of silver keeps increasing it will soon be worth while separating and refining it, especially if I can also recover the copper content, at the moment I only value the coins for their 12 Kg of silver and haven't factored in the 10 Kg or so of Copper.

(I will also be browsing the forums looking for ways of separating out the copper from cupro nickel coins (75% copper, 25 % Nickel, nothing else added!) Australia has already done away with its copper coins due to the rising cost of copper and the amount in the lower denominations 5c and 10c is close to the face value so it won't be long until they are withdrawn and replaced or reduced in size)

Thanks again

Mark


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## goldsilverpro (Jan 13, 2010)

You're in between a rock and a hard place with 50% silver. A silver cell won't work well when the silver is too low - less than 90%. In the other direction, a copper cell won't work because the silver is too high. I know of no electrolytic system that will work for that alloy. Like Harold said, nitric acid is about the only way to go. Nitric will dissolve everything in the mix. After cementing the dissolved silver onto copper, the silver should be about 98-99% pure, with Cu, Zn, and Ni. You can add back a little copper to end up with sterling (92.5% silver). I doubt if the small traces of Zn and Ni impurities will affect the final product that much.

Here's the way I would do it. I've written this up about a dozen times, but each time it's probably a little different:

(1) For each gram of metal you want to dissolve, measure out 2.7 ml of concentrated nitric acid and 2.7 ml of distilled water, in separate containers. This is based on the approximate requirements of 1.22 ml of nitric per gram of silver and 4.17 ml of nitric per gram of the alloying metals. The water is there to make the dissolving go smoother and to prevent the formation of copper nitrate crystals when the solution cools.

(2) Under a fume hood, put the metal in a suitable container. I prefer using a plastic bucket. Cover the metal with the distilled water.

(3) Add about 1/4 of the nitric. You should see an immediate reaction with brown fumes coming off. The reaction will heat the solution. When the reaction slows to a crawl, give it a stir and another 1/4 of the nitric. Repeat until all the nitric has been added. Cover and let it work overnight. Note: This is assuming that the room temperature is about 70F (21C) or higher. If it is cold, you might leave it longer or put everything into a large beaker and heat it until there is no more reaction. The idea is to make sure most of the nitric has been consumed by the dissolving of the metal. Any residual nitric will dissolve copper in step (6).

(4) Carefully pour off the solution into another bucket. If there is any undissolved metal left, put it in a beaker and dissolve it heated with a small amount of 50/50, nitric acid/distilled water. Combine all solutions.

(5) Filter the solution. This isn't entirely necessary, but it will get rid of any dirt, etc., that was present and you will end up with a cleaner product.

(6) Under the hood, put several lengths of copper buss bars in the solution. Copper tubing will work but buss bars are better. The buss bars or tubing should be long enough to stick out of the solution 3 or 4 inches, for easier removal. You should immediately [if all the nitric was used up in steps (3) and (4) - if not, the excess nitric will dissolve copper at this point - the silver won't start cementing until most all of the excess nitric has been consumed] notice a gray material forming on the copper. This is the silver. Every so often, stir the solution with one of the lengths of copper. Let this work overnight.

(7) In the morning, give it a stir and test the solution for any remaining silver. Add one drop of dilute HCl or salt water solution to the surface of the solution. If a white cloud forms, there is still silver present and you must let it work awhile longer.

(8) When the solution tests zero silver, remove the bars. While removing them, scrape and rinse off any silver clinging to them, with a squirt bottle containing water, into the solution.

(9) Let the silver settle. Siphon or pour off the solution without disturbing the silver sludge. Filter the silver and rinse it well until the rinse water (tap water is OK at this point) comes though water clear with no trace of blue. This blue color can be seen more intensely by collecting some of the rinse water coming out the tip of the filter funnel, in a small beaker or test tube, and adding a little ammonia. You can see the blue better by holding the test tube or beaker in front of a piece of white paper

(10) Dry the silver. At this point you can weigh it and melt it with a little added copper (say, 6 to 6.5%), if you want an alloy of approximately 92.5%. Use reducing melting conditions, so the copper doesn't oxidize too much. You can also buy alloying copper that contains small amounts of materials that help prevent oxidation, from jewelry suppliers.

*OR*,

Just sell the coins intact on EBay or elsewhere and buy your wife some sterling to work with.


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## jislizard (Jan 13, 2010)

Selling the coins is always in the back of my mind and if I hadn't spend 13 years working in a laboratory I wouldn't even consider any of the techniques you have mentioned.

However, your instructions are so detailed it would be a disservice to us both if I didn't at least consider them.

A few questions arise from your procedure.

The coins are dirty, not just oxidised, they have come from circulation so there are all the oils and dirt from handling and the cardboard box they were stored in also rotted leaving its own peculiar taint.

I have considered throwing them in the dishwasher, leaving them in methylated spirits or soapy water to remove the dirt. I also considered melting them down and pouring them into shot (I originally thought of pouring them into a convenient shape for electro processing but it seems that is one thing less I have to consider.) Coins though seem to have a fairly decent surface area to volume ratio so they should dissolve fairly readily, not as well as a powder but we are talking 20+ Kilos and I don't want to file that down.

If filtering the coins disolved in the Nitric acid will remove the dirt then I am happy to leave them alone but I would hate to introduce yet more contaminants into the final product. If the risk is neglible I will leave them be.

The other question is, what is a decent amount to batch process? I suppose it depends on what size reaction vessels I can find but I don't want to end up with a big bucket of sludge that is too heavy to lift or is in danger of falling through the base of the fume cabinet. I would also like to complete the process in under a day so I don't have open buckets of reagents hanging around the place and a big to-do list for the next day. I would rather split the coins into managable sizes and process them over a period of time. The temp dependant aspect should not be too much of a factor as it is 30C at the moment and if i tun the Air Concitioner off it soon comes up to temperature.

I can't do anything until I get access to a fume cupboard anyway but I am working on that.

Thank you very much for the info, I will be printing it out and adding it to the hoard. If the forum hasn't already done so you should put together an eBook of FAQs and Standard Operating Procedures to offset the cost of running the forum. I have seen many selling on eBay along the lines of "recover Gold from household scraps" etc. If you already have one please point me in the right direction.

One last question on a slightly related note.

In 1966 Australia put out a 50c coin, in 80% silver. That year the price of the silver in the coin went above 50c and consequently very few of the 38 million made stayed in circulation. They currently contain around $6 of silver. Fortunately these coins are accepted by the silver refiners, even in small numbers (they won't accept any of the 50% coins unless you have around 100Kg so they tell me). This leads me to beleive that they either get so many of them that it is worth their while to refine them or that they are financially more viable to process than the 50% coins. As I have read, <90% will not work in a silver cell and these coins have even more silver so a copper cell won't work either. Is it just the increased return from the same weight of coin that makes this worthwhile or the less waste products they have to dispose of that makes 80% coins more attractive for refining than 50% coins? They don't exactly offer enough for me to bring all my 80% coins to them though.

Thanks again for all the great practical advice given and I am still bearing in mind that eBay will probably give me the same amount of profit at far less trouble.

Mark


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## goldsilverpro (Jan 14, 2010)

I wish you guys would tell me your background before I do these things. I sort of wrote that tongue-in-cheek. Like, if you had a choice to go through this long ass procedure or, just sell them, what would you do? Now, I see that you are knowledgeable and serious and a man after my own heart.

(1) You should have no problem dissolving them as is. I don't think you'll need to clean them. Everything should come out in the wash. As long as there's not too much garbage to inhibit the dissolving, it should go OK. Just remember that you're using a powerful acid that will cut through about anything. I wouldn't worry about the dirt. Anything that will cause problems will be as a solid and easily filtered (or settled and decanted) out.

(2) I like to do this sort of stuff in 5 gallon plastic buckets. Working in this size is easily handled. If you do 1 kilo (2.2 pound) batches, this should require about 2.7 liters of acid and 2.7 liters of distilled water, for a total of 5.4 liters. This isn't too much in a 20 liter (5 gallon) bucket. You might be able to run 1.5 kilo batches but, the problem with running too much is that, the deeper the solution, the slower the dissolving. I like to keep things shallow because the dissolving goes faster and, therefore, the solution stays hot. You could put 5 kilos in the bucket, work the acid in several batches, and pour each batch off when it stops working. Your situation is fairly easy, since you know exactly what you are dissolving and can therefore closely predict how much total acid and water it will take. The dissolving of metals in nitric is reasonably stoichiometric. Also, at 30C, you shouldn't have to heat the solutions. 

I usually worked in a 12 foot fume hood, so setting up 12-24 buckets wasn't a problem.

Really, for 50% material, there's not much choice on how to do it. No matter what, you have to dissolve it in nitric. For this reason, refiners don't like to run 50% silver and, if they do run it, they will charge a lot. I don't know what you can buy these junk coins for, but the refining costs should be reflected in the price and they should sell for quite a bit under spot. The same thing happens in the U.S. with junk 40% Kennedy halves.

In a book I wrote 20 years ago, as advertised in my signature below, I detail the processing of 80% silver contact points in much the same manner.

To get the silver to 99.95 to 99.99% pure. Once you go through the nitric process, the silver can be melted into bars and run through an electrolytic silver cell. This is the tried and true method of purification and it always works. A reason that the silver must be at least 90% is that, each ounce of copper entering the solution displaces 3.4 ounces of silver since the amount of nitrate ion is finite. Also, when the copper in solution reaches 10-12 oz/gal, it starts contaminating the silver crystal. Therefore, solution must be removed and replaced with fresh silver nitrate solution. Do the math and you'll see that 90% is about the practical break even point. Actually, anything below about 96-98% can be a pain in the butt. 

An interesting purification alternative would be to experiment with the formate method as detailed by 4 metals in the thread below. I haven't tried it but I trust 4metals' abilities. In his method, the silver is not cemented out with copper. He claims 99.99% purity.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=1275&hilit=silver+9999


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## jislizard (Jan 14, 2010)

Hi GoldSilverPro, My background is more Biomedical Science than chemistry and now-a-days all the tests are done with kits, most of the hospital chemical stores have been turned into offices and all the reagents taken away for recycling or disposal. We can still order things in and there are a few old timers who actually understand chemistry, even though there is no real need for them anymore, so Nitric acid won't be an issue, and we still have reaction vessels and fume hoods but that is because it costs more to remove them than to leave them in place. Distilled water on tap for the analysers is a bonus.

It was a very nice positive response and you should never assume any newbies on this forum know anything about this sort of thing, better safe than sorry when it comes to chemicals.

Even with my years in the lab we never never did anything even similar to this and it was never covered at school or uni. Fortunately the formulas look familiar enough to understand and although I never could quite grasp the concept of Moles I can follow a recipe!

Cheers

Mark


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## jislizard (Jan 14, 2010)

Having a bit of trouble finding the "Add to Cart" button on the website, I am using IE and Firefox and I can't seem to find it. Rest assured that when I do find it I will be getting a copy of your eBook.

Cheers

Mark


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## Palladium (Jan 14, 2010)

Another book you will find helpful is Hoke.
It's in my sig line below. 8)


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## jislizard (Jan 15, 2010)

Thanks, just took a look at Hoke, don't think I will print it out as it is though!.... I might have a chance to use Optical Character Recognition through Adobe Professional and convert it into a text document where I will be able to edit the line length manually, should be able to drop it down to about half the number of pages, might even be able to get the contents working but sorting out an index is beyond me and I doubt that it would get much use anyway.

Cheers

Mark


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## goldmelts (Jan 21, 2010)

I might be interested in your coins if you wish to sell. I'm in the land of oz also. Where are you located?


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## jislizard (Jan 22, 2010)

Redcliffe, near Brisbane in Queensland. Probably won't be selling them straight away as I have only just picked them up but never say never!
Cheers

Mark


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## goldmelts (Jan 23, 2010)

I'm in Syndey, let me know with you wish to sell. Thanks


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