# Cementing Ag with Cu



## Oz (Nov 8, 2008)

I have seen several posts on cementing silver from nitric acid with copper describing a blue solution to be the indicator of all the silver being cemented out. Typically you would have a green solution after taking a sterling silver into solution, however if you have higher copper you can get a cobalt blue starting solution that has much dissolved silver. I recently cemented a batch of 60/40 silver/copper and thought some might like to see pictures for comparison to their own reactions.

I don’t know how often others may process high copper silver, but I wanted to point out that blue does not necessarily mean that the reaction is near complete. You can have a lot of Ag in a solution that is blue.


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## Platdigger (Nov 8, 2008)

Looks good Oz, so, your next steps are just to dry and melt?
Randy


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## Oz (Nov 8, 2008)

Thanks, there is nothing fancy about cementing silver but did not remember pictures of it on the forum showing a progression. Because most think of the blue as the end of the reaction when you can have significant silver in a copper/silver nitrate solution I thought it would be a good set of pics to put up.

The precipitate will be filtered and washed then cast into an anode for a silver cell. I figured it was time to reclaim some PGMs from the silver I use for inquartation of gold, and a silver cell is a gap in my refining education. I also had a good deal of high copper silver I put in with my inquartation silver in this case. I will also cast some bars for resale and want to be confident in the purity.


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## Platdigger (Nov 8, 2008)

Just "washed" with plain water?
Randy


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## lazersteve (Nov 8, 2008)

Oz,

Great post.

I'd like to add that sometimes the green color appears when there is Palladium in solution also.

Steve


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## Oz (Nov 8, 2008)

Platdigger,

I will do a hard boil in distilled water, distilled is not necessary in this case but the dehumidifier in the basement gives me more than I could ever use for free so I tend to use it for all my refining. I am only washing to remove dissolved copper and nitrates as this will be cast into an anode to be parted in a silver cell. It is that much less copper and it is preferable not having the nitrates off-gas when I melt it in a crucible.


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## Oz (Nov 8, 2008)

Thanks Steve,

I have never gone after palladium with nitric by itself and cemented with copper. Usually I have it in AR or HCl-Cl with other PGMs or hitching a ride from gold inquartations. Maybe that could be something to try with a bag of monolithic capacitors I have. I would be interested in hearing more about your experience with Pd in nitric by itself or combined with other elements.


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## Harold_V (Nov 8, 2008)

lazersteve said:


> I'd like to add that sometimes the green color appears when there is Palladium in solution also.


On the outside chance that traces of iron get dissolved, it, too, can yield a green solution. Color alone is not a good indicator of an absence of silver in a copper solution, although it can be a good way to know when to start testing. It's also a good idea to agitate the cemented silver to rinse the dragged down silver nitrate from the settled cement silver. A solution that tests barren will often still have a generous amount of silver nitrate trapped in the bottom, much the same way pollutants are dragged down when precipitating gold. 

Often the solution will remain green when all of the silver is down. A test with DMG or stannous often reveals the presence of palladium, or even platinum, as Steve has alluded. Each is slow to cement, and always the last to come down, after all of the silver is down. 

Smart people never assume anything about a solution-----they should all be tested before disposal. 

Harold


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## Oz (Nov 8, 2008)

Harold_V said:


> Often the solution will remain green when all of the silver is down.


That’s worth knowing, I have not had that happen. Possibly because I am seldom in a hurry and leave copper in the solution longer than needed that I have always ended blue.



> Smart people never assume anything about a solution-----they should all be tested before disposal.


As always Harold good advice, I test all solutions with stannous however it would be wise for me to test silver cementations with DMG more often than I do despite the length of time I leave copper in solution. The last picture shown was taken Friday and will have copper 2 copper rods in it over the weekend while I’m away.

I would love for one of the chemists on the forum to explain the chemistry behind the color changes. I would guess that it is oxidation state changes primarily with the copper. For the record, the material in the solution pictures is ACS grade nitric and the silver and copper do not have contaminates greater than 1/10th of 1 percent to help them in eliminating other variables. The silver I referenced that had PGM “contaminates” was run separately to make the recoveries of them simpler.


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## Lino1406 (Nov 14, 2008)

Silver concentration with DMG?


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## Harold_V (Nov 14, 2008)

Lino1406 said:


> Silver concentration with DMG?


You don't, at least not to my knowledge. The DMG test would be used to determine the presence of traces of palladium----a test that could prove valuable when the solution is not blue. 

Harold


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## Oz (Nov 15, 2008)

Speaking of testing…

Does anyone see a possibility of silver remaining in a solution of nitric if it is saturated with copper to the point no more Cu will dissolve and inserting a clean piece of copper there is no accumulation on it? Having said that the small traces of silver left would be of little significance other than the fact that much of my silver is from inquartation and the PGM traces will cement after the Ag.


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## Harold_V (Nov 15, 2008)

I'm of the opinion that if you had such a solution, copper nitrate crystals would form, allowing the balance of the silver to be cemented by the copper that would replace that which was crystallized. 

Sheer speculation. We need the expert opinion of Lou or GSP. 

All I can say is in all my years of refining, I never failed to recover all of my silver by cementation, regardless of the degree of saturation. That, however, may not be a reasonable measure. It could be I was nowhere near the point of saturation. It does give me a hint that your proposal is a non-issue, however. 

Harold


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## Lino1406 (Nov 15, 2008)

In solution is negligible, as long
as silver + copper nitrate is more
stable than copper +silver nitrate


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## Lou (Nov 15, 2008)

Generally speaking, this electromotive effect between copper and silver takes best in an acidic environment. Also, copper nitrate is happiest in acidic conditions.

If you think you've cemented out the values and you add a crystal of KI or NaBr to your solution and see a precipitate, there is still silver in solution. Likely, it is so very dilute, it is indeed negligible, but if one is really concerned, or doing this on such a scale that leaving a tenth of a percent (think 1 ounce in solution per 999 cemented), the it can be filtered, evaporated, and recovered with sodium bromide. 


Some of the issue you saw Harold is the fact that there is so much copper in there, it is very difficult for the silver ion to latch on to the copper bus bar and reduce itself. Also, there is silver ion stuck onto the surface of the reduced silver metal. To top it off, there is likely a silver ''plate'' adhering to the copper that makes it very difficult for these few remaining silver ions to get to the surface of the copper. Agitation and mechanical scraping of your copper source are the keys to success in this case.


Lou


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## Harold_V (Nov 15, 2008)

Lou said:


> Generally speaking, this electromotive effect between copper and silver takes best in an acidic environment. Also, copper nitrate is happiest in acidic conditions.


That parallels my experiences. There were times when I had to add a few drops of nitric to my solutions in order to achieve the desired reaction. 



> If you think you've cemented out the values and you add a crystal of KI or NaBr to your solution and see a precipitate, there is still silver in solution. Likely, it is so very dilute, it is indeed negligible, but if one is really concerned, or doing this on such a scale that leaving a tenth of a percent (think 1 ounce in solution per 999 cemented), the it can be filtered, evaporated, and recovered with sodium bromide.



I had a policy of decanting, then adding (rock) salt to the spent solution. That way, if there was a trace of remaining silver, often liberated from the cemented silver as the copper was being removed, it would be recovered as chloride. That, too, gave the decanted solution time to settle adequately, on the outside chance that I had decanted traces of suspended silver with the solution. Only after allowing the solution to settle well (at least one day) did I then decant and send the copper nitrate to my copper recovery barrel. 



> Some of the issue you saw Harold is the fact that there is so much copper in there, it is very difficult for the silver ion to latch on to the copper bus bar and reduce itself. Also, there is silver ion stuck onto the surface of the reduced silver metal. To top it off, there is likely a silver ''plate'' adhering to the copper that makes it very difficult for these few remaining silver ions to get to the surface of the copper. Agitation and mechanical scraping of your copper source are the keys to success in this case.



Again, proven in practice. There were times when the silver was attached so rigidly to the copper that it was not possible to remove it, even with vigorous scraping. In such cases I scraped the copper as best I could, but left some of the silver. As the copper was eliminated in cementation, it exposed the edge of the hard plated silver, allowing it to break away. In time, all of the copper was consumed. It was easier than wrestling with the silver coated copper. 

I found that this condition was exacerbated by having the silver nitrate highly concentrated, with a higher pH. Diluting the silver alone would often improve conditions such that the cemented silver would slough off of it's own accord. I found that to be the most desirable condition, which goes without saying. 

Harold


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## Oz (Nov 16, 2008)

Thank you both for your thoughts and experience. I too have found that a solution higher than necessary in nitric acid would “plate” the copper with Ag and greatly slow the copper from being able to go into solution, almost like pacification of the surface. Time remedies this condition.


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## hungry (Dec 24, 2008)

OZ

First I would like to thank you for the great photos. They give me a visual clue as what to expect when dissolving silver/copper in a nitric solution. I currently have buss bar contact points (one pound) in an approximately 50% solution of nitric acid (1400 ml) and have a few questions, if I may. First did you use heat to initiate the reaction and at what temp. if so? I noticed you have your solution in a mason jar. Can you apply much heat to those and get away with it? I've never taken the chance as I use beakers when applying heat. How much did the initial scrap weigh?
I have no idea what % of silver is in these contacts and I was wondering if the excees copper in them could cause the silver to precipitate out prematurely as the silver was dissolving. Before I added heat it sat out in the cold for about two weeks. I used Lazersteve's recipe (840 ml) plus 200 ml 70% nitric and 300 ml distilled water. Reaction was slow because of the cold. I have a green solution that is very slightly blue with a lot of grayish-white sediment which appears like silver from what I see in your photos or could it be more of the sulfate from the poor man's nitric?
Today I finally got around to heating it. Not very hot but hot enough to get the nitric vaporizing from the bottom up. The sediment is starting to dissolve getting the solution greener but no bluer. I am thinking about adding a bit more nitric to it. There is still a bit of solid pieces left. I am sorry I can't supply photos to help, but I have not gotten around to buying a camera yet. I need to know if I am getting this close to being right or not.
I would appreciate any feedback or enlightenment from you or anyone else.

Thanks' 
ED


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## Harold_V (Dec 24, 2008)

Your solution should be green, not blue. Silver dissolved in the presence of copper in solution will be green, although not a dark green. There will always be copper present, from the solder used to attach the contacts to the buss bars. 

Heating is key to success-----unless you have the rest of your life to dissolve contacts. 

There are two types I found routinely----one of them has a waffle pattern on the back, or soldered side. They contain less than 50% silver, the balance being tungsten. They are difficult to process in that the tungsten shields the silver from exposure to your acid solution, but it just slows down the process, it does not cease. My comment is based on the idea that you actually boil your solutions---where the vigorous stirring of the solution from boiling penetrates the contacts, although slowly. I processed thousands of ounces that way with success. 

You can check your progress by attempting to break one of the contacts. If it snaps under thumb pressure, and has no distinct line in the center, you can safely assume you have extracted the silver. If you have not, there will be a dark gray line in the center, which is the contact material that has yet to give up the silver content. They break readily when barren of silver, and are difficult to break when they are not. 

The other type of contact I encountered yielded a white/yellow flocculent material, along with silver. I have no clue what the material would be, but it settles readily, or can be filtered to separate it from the pregnant solution. Contacts of this type yield a much higher percentage of silver, but I can't say how much. I ran my contacts mixed, not being concerned about specific yields. 

When you cement the silver from solution, using copper, as the silver content diminishes, you should expect your solution to shift from green to blue. When it is barren of silver, it should be a beautiful sky blue color so characteristic of copper. Be certain to test the solution with a drop of HCl or salt when you feel the operation is completed. If you still have a little silver in solution, you'll get a showing of silver chloride. 

Hope some of this helps.

Harold


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## hungry (Dec 24, 2008)

Hi Harold
So, what I gather there will be porous copper left over even after the silver is all dissolved. That means silver dissolves before the copper. 
What I am curious to know is can that copper pre-cement out the silver and if so at what point does it stop.
I guess my nitric solution was alright as you did not have any comment to the contrary.
It has been nice exchanging words with you again as it has been a while.

Thank you much,

ED


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## goldsilverpro (Dec 24, 2008)

Forget about the colors. If you test the solution with a drop of HCl or a drop of NaCl, and it forms a white cloud, the silver cementation is not complete. Stir it and leave it awhile longer. When no white cloud appears, all the silver has been precipitated.

Immersion silver (cementation) will slow down or stop when the copper is heavily coated with silver. This usually doesn't happen, because the silver falls off. If things slow down, scrape the copper down with a plastic scraper. This will expose fresh copper and allow further cementation. For every gram of silver that cements, 3.4 grams of copper must dissolve. If the copper is covered with silver, the acid can't penetrate and dissolve the copper and everything slows down. Stir the solution often. This dislodges the silver and also provides acid to the copper. The speed of the cementation reaction is proportional to the surface area of the copper. The more, the merrier.

Since the reaction requires acid to dissolve the copper, a little free nitric is necessary. If, at first, nothing happens, add a few mL of nitric, You should only have to do this once.

Forgive me Harold, but, in my experience, when dissolving Ag/Cu alloys, added heat is not necessary, even in a cold climate. The solution will heat up quickly due to the dissolving reaction. I have dissolved 1000s of pounds of large contact points. They average about 81% silver. After sweating them off the copper buss, I would put about 5# of points in a 5 gal plastic bucket. I then calculate that I need about 1.1 gallons of nitric plus 1.1 gallons of distilled water to dissolve the points (hope I got the math right). I cover the points with all the water and add about 1/4 of the acid. Soon the action (foam and fizzing) will start and the solution will heat up. When the action slows down, I stir and add 1/4 more acid. I repeat until all the acid has been added. The bucket will feel very hot. I then loosely cover the bucket and go home. In the morning, the points are dissolved, if I calculated the correct amount of acid. If some undissolved points remain, decant the solution and dissolve the remaining points in a small amount of nitric and water. I use the same procedure for sterling. Works every time.

Very simple. Don't make it complicated.


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## hungry (Dec 24, 2008)

Hi GSP
I haven't reached the cementing part yet. I am still dissolving the contact points. I have not done it before and I was wanting to know if I was headed in the right direction. I have a question or two for you. Does all the copper dissolve if I wait or is it not necessary to do so? And will the undissolve copper pre-cement some of the silver out of the solution? If yes should I try to diisolve all the copper?

Thank you for your response.

ED


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## Lou (Dec 24, 2008)

Harold_V said:


> The other type of contact I encountered yielded a white/yellow flocculent material, along with silver. I have no clue what the material would be, but it settles readily, or can be filtered to separate it from the pregnant solution. Contacts of this type yield a much higher percentage of silver, but I can't say how much. I ran my contacts mixed, not being concerned about specific yields.



This sounds very familiar to me with regard to the flocculent yellowish white precipitate. In fact, it sounds very similar to what molybdenum does with nitric acid.

Lou


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## butcher (Dec 25, 2008)

Hungry I would unsolder silver from copper, large amount of copper will use up your acid.


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## hungry (Dec 25, 2008)

Hi Butcher

I did unsolder them. I was concerned about the amount of copper that is in the contact point themselves. I also just turned off the heat from under the beaker and I am seeing chystals of sulfate form up the sides of it. (I think it is sulfate from the poor man's nitrate.) It is in the low 30's here. I am thinking I need to add some of my reagent grade nitric to it to boost the reaction. Of course I am just guessing.

Thank you for your feedback.

ED


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## butcher (Dec 25, 2008)

heating may have evaporated some acid and when cooled the salts ppt.lil more acid wont hurt. 
even a weak sulfuric acid freezes here when temperature gets cold,sometimes just a little sulfuric acid will remove ice from my solutions.(raising specific gravity and hydrogen bubbles I'm not sure)


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## hungry (Dec 25, 2008)

Thanks Butcher. I appreciate your time.

ED


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## Harold_V (Dec 25, 2008)

goldsilverpro said:


> Forgive me Harold, but, in my experience, when dissolving Ag/Cu alloys, added heat is not necessary, even in a cold climate.


Not a problem, Chris. I agree-----a silver/copper alloy will readily dissolve, creating its own heat-----but I rarely had the opportunity to allow things to happen on their own. I heated in order to accelerate processes-----all processes-----but the tungsten contacts are a different problem. I'm not convinced you'd leach all the silver without heating. With heat it was a process that took a few hours. Because of the isolation of the silver by the remaining tungsten, the process slowed to a crawl as the silver was leached. The last traces were slow to extract. I can't help but think it would have been all the slower without heating. 

I do admit----I never tried it without heating---I could be wrong. One thing I know, however----heating worked very well. 

Lou----Interesting comments on the yellow/white material being moly. Not being a chemist, I had no idea what it might be----I just knew I didn't want it in the end product.

Harold


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## Harold_V (Dec 25, 2008)

hungry said:


> Hi Harold
> So, what I gather there will be porous copper left over even after the silver is all dissolved. That means silver dissolves before the copper.
> What I am curious to know is can that copper pre-cement out the silver and if so at what point does it stop.


Because both silver and copper are soluble in nitric, I don't believe the scenario you describe exists. The moment you start dissolving the alloy, even if the copper was inclined to remain as a solid, it would immediately start cementing silver, so one way or the other, both of them are digested. 

You need not fear having copper left over when dissolving contacts. There is no copper in the silver, although there is some in the solder, but the percentage as compared to the mass of the contacts is very small. Your solution will be tinted green, thanks to the traces of copper, but you will have very little copper in solution because there is very little present. 

You mentioned you had removed the contacts from the buss, so I'm of the opinion that even if the acid level diminishes to the point where you won't further dissolve silver, none of it will cement from solution because, in theory, you have no free copper. No harm done in trying, however. Use a small amount of nitric/water and allow it to be exhausted----then see if you see any cementing. If so, further addition of nitric/water will dissolve what has cemented, so no harm done, and the cementing process will have further dissolved the copper. It might be a good report for the board if you find I'm wrong. For me, it was never a problem. But then, I also heated my solutions, always, and was aggressive in my application of acid. Time, for me, was of the essence. 



> I guess my nitric solution was alright as you did not have any comment to the contrary.


The ratio isn't really critical----as long as you include some water. If you use too much, the reactions will be slowed, but the amount of work done will be the same. 

It's nice to not have the nitrate solution too concentrated, otherwise you have problems in the cementing process. Heavily concentrated solutions sparse in free nitric are inclined to cement out as a solid film, which often adheres doggedly to the copper. It can be so solid as to render the copper ineffective for further reduction of silver. A little free nitric and a dilute solution will prevent the problem. 

Nice to hear from you again, Ed. 

Harold


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## hungry (Dec 25, 2008)

Thank you Harold, you have resolved my concerns completely.

Thanks to all of you for your great replies. I appreciate all your help.

ED


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## hungry (Dec 25, 2008)

I have taken some of the fine powder from the bottom of the beaker and subjected it to bright sunlight and it turned purple. From what I understand this is indicative of silver. I've added more nitric and water and increased the heat, as you stated Harold. I am getting brown fumes although lightly. I am seeing fine silvery particles throughout the solution as well as the fine powder settling to the bottom again. There is less of the powder than earlier. As I stated before I have never done this before and I want to understand what I am observing for the next time I attempt this procedure.
I know I am monopolizing this thread and to others I may be complicating the process, but I find this interesting. I still have a lot of sterling to do, then I can get back to my gold.

ED


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## Harold_V (Dec 25, 2008)

hungry said:


> I have taken some of the fine powder from the bottom of the beaker and subjected it to bright sunlight and it turned purple.


That is likely the result of silver nitrate still in solution. When the silver has been totally cemented, that shouldn't happen, although if you have sulfur in the atmosphere you can expect darkening of the silver crystals. They should be well rinsed with distilled water, although if you have extracted all of the silver nitrate you can use tap water with adequate results. That's all I used for rinsing cemented silver. It often leaves a little mineralization that leaves the surface of the silver crystals somewhat coated. No harm done, it is eliminated in melting, it just doesn't look as good as crystals rinsed with distilled water. That is particularly true of crystals removed from a silver parting cell, where you have much larger and brighter surfaces. 



> From what I understand this is indicative of silver. I've added more nitric and water and increased the heat, as you stated Harold. I am getting brown fumes although lightly. I am seeing fine silvery particles throughout the solution as well as the fine powder settling to the bottom again. There is less of the powder than earlier.


Can I assume that you still have what remains of the contacts included? If so, more nitric and a longer heating period will dissolve everything that is soluble. My practice was to boil until there were no fumes, then decant the solution and start with more nitric/water. It is possible that some silver is cementing on the remaining contacts, although that is not something I experienced. Could be because I didn't allow my solution to remain with the contacts, however. I simply don't know. 



> As I stated before I have never done this before and I want to understand what I am observing for the next time I attempt this procedure.


If you want to insure that you extract the silver without any recycling, eliminating the chance of some of the silver nitrate cementing, you might try doing what I did. Heat the contacts and allow them to boil, then when you see the end of fumes, pour off the solution and start with more acid and water. That way you are assured of not cementing prematurely. 

I suggest you allow the pregnant solution to settle. What ever is alloyed with the silver (Lou suggested moly), along with traces of tungsten, will pour off with the solution. Allow it to do so. After it has settled, decant with a hose and cement the values. Rinse the solids that remain behind and decant, finally filtering to extract the last of the values. I recycled all of the solids by incineration and combining with my other waste materials for future processing in the furnace. That way traces of silver are recovered, with the unwanted substances absorbed by the flux. I don't suggest discarding the filter. 

You're not dealing with a great amount of value with silver, so a little experimenting on your part should yield a process that suits your capabilities. Remember, I worked out of a fume hood, so I had the advantage of rushing processes without being exposed to fumes that were undesirable. If you work out of doors, or in a protected area but have no means of eliminating fumes, you may be forced to proceed in a different direction. There is no right or wrong in this issue, not as long as you recover all the values and do so safely. Chris' method would be adequate-----I just didn't like working out of plastic containers, therefore I don't encourage the process. I used them only for my stock pot, for cementing copper, and for cementing silver. Nothing else. 



> I know I am monopolizing this thread and to others I may be complicating the process, but I find this interesting.


It is all a part of learning. You may feel you are monopolizing the thread, but the information that is being dispensed can and will prove useful to others. There is no better way to learn that to enter in to a good, constructive conversation. You're fortunate to have others that are willing to do so with you. Remember---guys like me had no resources aside from Hoke's book. It's good, but doesn't answer all questions. 



> I still have a lot of sterling to do, then I can get back to my gold.


Unless you expect to never process karat gold, I'd recommend you do NOT process sterling for the sake of processing. It is a valuable asset for those that inquart, where it serves a purpose, not being refined simply for the sake of refining. Dissolving silver, as Chris mentioned, is dead easy--it is eager to dissolve, and does so with a minimum of acid. It is also very easy to separate from gold, so the combined benefits make it the element of choice when it comes to inquartation. 

Harold


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## hungry (Dec 26, 2008)

Harold I was wondering if the solution could become over saturated and just stop dissolving the silver? I have like 1500 ml of solution including whatever solids are left.


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## Harold_V (Dec 26, 2008)

If it helps you any, when I made my electrolyte for my parting cell, I dissolved 30 troy ounces of silver in a liter of nitric, along with a liter of distilled water. The solution was so concentrated that it grew silver nitrate crystals immediately as it cooled. You could watch it happen. 

Considering you started with only a pound of contacts, some of which is not silver, I don't think that's an issue in your case. 

If you're curious, you might try siphoning some clear solution to another container and allow it to cool. If it is inclined to grow crystals, you'll see them. In the process, the crystals will reject most of the copper. It's one of the ways you can purify silver. 

Harold


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## goldsilverpro (Dec 26, 2008)

Harold,

The way I read it, I don't think Lou was suggesting that molybdenum was alloyed with the silver. I don't that they will alloy. Moly and tungsten have similar properties and I think he was saying that moly produced a similar yellow ppt. in nitric. All of the waffled points I ran contained tungsten and I got the same yellow ppt. I think they are made by compacting silver and tungsten together and then sintering. The only moly I remember dealing with were gold coated moly disks from a certain type of rectifier. When I put them in acid, I got the yellow ppt., although I seem to remember it being somewhat less yellow than the tungsten ppt.

Considering that you were very diligent in returning 100% of your customer's material, I understand why you didn't use plastic buckets. They scratch easily and the scratches retain gold powder. I rarely did things on a refining basis and, therefore, I owned most of the stuff that I ran. I could care less if a tiny amount of gold was stuck in the bucket. It would eventually be recovered. To keep it at a minimum, I used a 1 sq.in. piece of a green Scotchbrite pad, with a little water, to scrub down the pure gold powder inside of the bucket - took less than a minute. I then rinsed it with a squirt bottle and transferred it to the filter. The amount left in the bucket was very small. I used the same green pad until it wore out and it was only used for the pure gold. I had 2 or 3 buckets dedicated for dropping gold.

When I first started, the places that I worked for used 5 or 7.5 gallon Pyrex battery jars to dissolve gold, with heat. They usually used a restaurant grill covered with thick asbestos cloth to cushion the jars. One place had a flat titanium steam plate fabricated to heat the jars. The problem was that battery jars aren't supposed to be heated. The bottoms weren't of uniform thickness and they tended to occasionally break from thermal shock. One place set the jars in a 1/4" thick, deep lead tray while heating, to catch everything if they broke. The advantage of these is that you could run 100 oz, or more, of gold in them, at one time. Another disadvantage was that they were very awkward to handle, although some had handles indented into the glass. The best large Pyrex jars I've used were of 3.5 gallon capacity and were made by a local glass-blower, in L.A. They were of uniform thickness and never broke unless you banged them on something.

From that point on, I used 4 liter beaker everyday for the small stuff. For the big stuff, and for dropping gold - I usually had several gallons of AR - I used buckets. It worked. I got pure gold. I lost nothing. For dissolving gold, it is easy to rig up a hot water bath to put the buckets into.

I'm experiencing deja vu (all over again), Harold. I think you and I have had this discussion before.


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## Harold_V (Dec 26, 2008)

goldsilverpro said:


> Harold,
> 
> The way I read it, I don't think Lou was suggesting that molybdenum was alloyed with the silver.


I'd like to hear Lou's view on that. I was discussing what ever came from a type of contact that doesn't have the waffled backside. I processed enough of the waffle type to know that the yield was under 50%, yet the average yield (including all types of contacts) was well above. Small contacts appeared to be alloyed with cadmium, but the larger contacts that didn't have the waffle pattern yielded the yellow/white flocculent product----so it was obviously not tungsten. I think Lou alluded to that contact, which is distinctly different. 

I agree----tungsten/silver contacts are likely a powder metallurgy process. The melting point of tungsten is far too high for them to be melted, and silver and tungsten may or may not alloy in any case. 

While I didn't return 100% to my customers (I refined on a percentage basis, which I took in metal), it was important to me to have 100% accountability, which is one of the reasons I didn't use plastic in the precipitation process. Assaying was never a part of my refining process, thanks to running flagged individual lots. The values of one customer were never mixed with the values of another. Further, by using beakers, there was no need to handle the gold until it was finished. Once the gold was filtered, it didn't leave a beaker until it had been washed and dried. If, by chance, a beaker had any anomaly that permitted gold to adhere, it was immediately demoted to service in parting inquarted gold. 

I'm not suggesting that my process should be a proper example for others to emulate----it was just the method I chose, especially considering my lab was open to inspection by curious customers. I didn't want to present an image of anything slip-shod to destroy an image of professionalism. Sort of reminds me of the Modern Jazz Quartet, where they took the stage wearing tuxedos. They projected an image of excellence, matching their stellar performance. 

Again, that's just me-----others need not share my views. 

I had one of the Pyrex handled jars, one that was about 5 gallons in size. It came from a closed lab. I traded for it by making a few molds for a fellow refiner. He had no use for the jar, but I did. It was used for processing carpets, and also for converting silver chloride to elemental silver. I never heated the jar, but it was nice to have one that tolerated heat. Both of the applications for which it was reserved were exothermic, and often achieved the point of boiling. While it was well worn when I sold the lab, it was still functional, and was part of the sale. It was one of the more valued of vessels I had. Replacement cost is in the hundreds. 

Harold


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## Lou (Dec 26, 2008)

There is no alloy between silver and molybdenum in use to my knowledge, nor do I know if one such exists. Just because there is a silver core sintered into the tungsten or molybdenum support it does not mean that it is an actual alloy. A sintered product does not an alloy make. Molybdenum, like tungsten is hard, heavy, and is called a refractory metal. This means it melts at a very high melting point. In my experiences in the laboratory, tungsten, molybdenum, and tantalum were often interchangeable as they have much the same properties. Thus, it is pure speculation on my part, but it is based off of what I've experienced in the laboratory.


Granted, there are thousands of yellow-white precipitates in the world. I'm merely thinking molybdenum because I've dissolved much of it and the yellow-white molybdic oxide sloughs off. This only works with a certain concentration of nitric--too high of a concentration and it will passivate the surface with a film that sticks with tenacity, preventing further dissolution.


I know nothing of the sort about processing contacts--I merely know what they do and what they are for and thus why they are made from a refractory metal like tungsten. My recommendations would be made from commonsense and chemical intuition.

All manipulation of pure tungsten, molybdenum, tantalum, or others in the general vicinity must be done via powder metallurgy, as Harold mentioned in brief. This means they are sintered, usually under hydrogen gas (that's how I do it) or a mix containing it. Melting such metals is done via arc melting or electron beam melting. Induction isn't often used.


As far as dissolving metals goes, I use a round bottom reaction flask with overhead stirring for large things. Otherwise, 2, 4, 6L Pyrex beakers serve well. The only problem with using beakers is the spatter as things boil down or as a vigorous reaction occurs. To avoid this, one may react in an Erlenmeyer flask and then transfer to a beaker which has much more surface area. If one is really well equipped and wants to greatly speed the evaporation process, using a rotary evaporator is second to none for handling precious metals solutions. What takes hours in a beaker will take minutes in a Rotavapor. 

Lou


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## goldsilverpro (Dec 26, 2008)

You're probably right, Harold, concerning the contact points. When I ran them, I just assumed that they were all tungsten/silver. According to the internet, they also make tungsten carbide/silver and moly/silver. Maybe the non-waffled thin hard ones were moly. Maybe that's where the yellow color came from. When I ran points, I first separated the 90% silver ones from what I thought were the tungsten/Ag ones. Some were waffled and some weren't and I ran them all together.

I think that most of the high silver ones were coin silver (90/10 Ag/Cu+other metals). When sweating them off, Cd, Cu, etc., are picked up from the braze and the copper buss. I ran many 100s of pounds of them and averaged an 81% silver yield, +/- about 2 or 3%.

Karat gold and sterling casting alloy is available from jewelry supply houses. These are added to pure gold and silver. There are many different manufacturers and many formulations, karats, colors, and shades of colors. Everyone claims theirs is the best. Much of it contains various oxygen scavengers and anti-tarnish ingredients, such as Si and Ge.


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