# Running Sterling in a Silver Cell



## goldsilverpro (Apr 21, 2012)

With all the recent silver cell threads, I have ended up doing a lot of research. I think I have come up with a way to directly run sterling and never have to replace the main solution. I think this is how the old-timers controlled their cells, although it's not discussed much in the books. This assumes that there is no palladium present and that the only contaminates in the silver are copper and minute traces of gold. If there is Pd, there are ways to handle it, but I won't discuss them in this post. Although the method could be used for small cells, I am thinking of larger operations. To do this right, one must be able to analyze both the silver and the copper in the solution. The silver analysis is fast and easy using the Volhard titration. The copper is more difficult but there are methods out there. I determined the specific gravity after analyzing the silver, and, from graphs I had made, I could then easily estimate the copper.

In general, here's the method.
(1) Determine the copper concentration that you want to start with and maintain in the solution. From the books, the best copper concentration is 60g/l and that's what I will be using for this discussion.
(2) For the silver in this discussion, I am making the solution up at 80g/l and don't want it to fall below 50g/l. When the silver falls to 50g/l, it is time to adjust the solution - reduce the copper and raise the silver.
(3) Analyze the copper and remove enough solution to reduce the copper back to where it started out - 60g/l.
(4) Dissolve enough silver, separately, in 50/50 nitric, to raise the silver back up to the starting point - 80g/l. In this case, it would require 80 - 50 = 30g/l of silver. Add this to the cell.
(5) Add enough distilled water to bring the solution up to its proper level.

At this point, everything is back to its starting point.

I made some calculations, assuming a one liter cell operating at 1.8 amps. I also assumed that the sterling was 91% silver and 9% copper and that the electrode efficiencies were 100% (in practice, you will never get 100%, especially at the anode).

From all this, the Ag would drop to 50g/l after 16 hours. At that point, to reduce the Cu to 60g/l, 128 ml of solution would be removed and, 30g of dissolved Ag (89ml) added, and 39ml of water added. The total silver removed from the cell would be 6.4g and the total crystal produced would be 118g. The silver removed is easily recovered by Cu cementation.

This would be repeated ad infinitum(sp?)


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## Westerngs (Apr 22, 2012)

On a small scale, no problem. On a large scale, easier said than done.


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## goldsilverpro (Apr 22, 2012)

Westerngs said:


> On a small scale, no problem. On a large scale, easier said than done.



I don't agree. Just analyze for Ag and Cu and make the adjustments. Very simple with the proper equipment. I can't see the size making any difference. If I had 10 cells, though, it would take 10 times more work than with 1 cell. With an AA, I could sample and analyze those 10 cells in about 30-60 minutes. If I had a reservoir of AgNO3 already made up, the adjustments could probably be made in an hour.

I have about 10 years experience of working in the electroplating industry. I did this sort of thing on a daily basis and much of it was more complicated than the simple adjusting of silver cells. Some plating baths have 3 or 4 ingredients that require analysis and adjusting. I once controlled, by myself, about 60 different tanks in a large plating facility. Some were as large as 4,000 gallons.


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## 4metals (Apr 23, 2012)

It does work in large cells as well. One large silver refinery I set up the thing we control is the sterling copper content. This is easily done as most bars are 1000 oz and we have plenty of 99% silver from the cementation to bring up the bars that are low. We have on tap electrolyte made up at 8 oz/gallon as Ag made from sterling. Each bank of cells contains about 630 gallons in 6 cells and the level control reservoir. The daily routine is harvest the electrolyte, titrate the silver (via volhard), remove solution and replenish. The fact that we have the anodes all prepared at the same copper content (or very close) makes this routine very predictable and we never have to analyze the copper, the copper forces the silver content lower and that tells you it's time to replace.

In practice the silver cells have a rather large sweet spot where they run smooth so some daily variation still produces good quality crystals. We do titrate the free acid content also, trying to keep it at 20g/l as nitric acid which is maintained with a dosing pump for nitric.

The down side is there is a lot of waste acid to deal with and it's loaded with copper nitrate. Would be nice to either get rid of the waste for free or get paid for copper.


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## goldsilverpro (Apr 24, 2012)

4metals said:


> It does work in large cells as well. One large silver refinery I set up the thing we control is the sterling copper content. This is easily done as most bars are 1000 oz and we have plenty of 99% silver from the cementation to bring up the bars that are low. We have on tap electrolyte made up at 8 oz/gallon as Ag made from sterling. Each bank of cells contains about 630 gallons in 6 cells and the level control reservoir. The daily routine is harvest the electrolyte, titrate the silver (via volhard), remove solution and replenish. The fact that we have the anodes all prepared at the same copper content (or very close) makes this routine very predictable and we never have to analyze the copper, the copper forces the silver content lower and that tells you it's time to replace.
> 
> In practice the silver cells have a rather large sweet spot where they run smooth so some daily variation still produces good quality crystals. We do titrate the free acid content also, trying to keep it at 20g/l as nitric acid which is maintained with a dosing pump for nitric.
> 
> The down side is there is a lot of waste acid to deal with and it's loaded with copper nitrate. Would be nice to either get rid of the waste for free or get paid for copper.


May I ask at what level do you maintain the copper in solution and, what is the copper content of the anode bars that go into the cell?

A long time ago in L.A., an oil company picked up all our waste acid, periodically, for free. It seems they used it, somehow, to flush oil wells. I have talked to other people with the same experience. In this day and age, however.......?


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## Lou (Apr 24, 2012)

They'll still use it.


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## Westerngs (Apr 24, 2012)

My experience is different. 

The copper content varies greatly from as low 10% to as high as 60%. Unfortunately, the copper builds up and the silver depletes so quickly that there is little opportunity to remove and replenish electrolyte. As for makeup silver nitrate, it would be necessary to dissolve nearly 10K t.o. per day and the capacity is just not there, not to mention needing to scrub the NOx produced.

4metals, there are copper smelters that will pay for the copper hydroxide produced from precipitating the copper from nitric acid. I can point you in the right direction if needed.


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## MysticColby (Apr 24, 2012)

hmmmm. I had a thought: you keep voltage low so that copper doesn't co-deposit with the silver. what if there were 2 cathodes. one running 3 volts, the other like 20 or w/e it takes to primarily deposit copper. These would be at opposite ends of the cell, with the collective anode in the center. The idea being: copper is deposited on one side, silver is deposited on the other. You'd really only need to turn the copper side on if the copper content got too high, and you'd need to isolate each side from each other with filters. I'm sure some silver would get caught with the copper, but you wouldn't have to change the electrolyte - ever. Just harvest each side when it fills up, as you would have to do normally.


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## Lou (Apr 24, 2012)

We've had success on the small scale with a regenerable resin that ignores monovalent silver and goes for copper, nickel, and palladium (all of which can be eluted off).



Lou


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## Lobby (Apr 24, 2012)

Thanks for the posts, folks. Good stuff, as I'm getting ready to start up a silver cell.


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## publius (Apr 24, 2012)

Sticky this please!

I am running a 1 liter silver cell right now. It seemed to stall. But after titrating silver and copper in my cell that seemed to stall, I found that my anode was passivated by a black coating. scraping the slime off the anode started up the process again.


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## Lobby (Apr 24, 2012)

With sterling silver, we can be pretty confident that all we have is silver and copper. But with sterling jewelry, there's all sorts of stuff there (lead from solder, for instance). Any thoughts on processing this Ag material with this method?


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## Lou (Apr 24, 2012)

That's where the other part becomes important: proper rinsing of the crystal.


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## 4metals (Apr 24, 2012)

> May I ask at what level do you maintain the copper in solution and, what is the copper content of the anode bars that go into the cell?



I like to see copper under 60 g/l and all bars go into the cell at 8 - 9% copper. The 80 % material is brought up by the cemented 99% material. It's not that less copper goes into the system but it is consistent and it makes for easier control. 

Electrolyte is replenished often and the biggest NOx load comes from the electrolyte production. It is not unusual for the cemented out quantities to be very close to then replenishment quantities as far as silver content goes. So there is plenty of silver to upgrade bars with. Large digestions of over 5000 oz for daily electrolyte production are digested over 24 hours adding nitric to the warm water in the tank slowly with a dosing pump to spread out the NOx generation from over 50 gallons of nitric to make the scrubber deal with a more consistent load rather than a dump it all in and hope nobody drives by like in the old days.


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## Lou (Apr 25, 2012)

> Large digestions of over 5000 oz for daily electrolyte production are digested over 24 hours adding nitric to the warm water in the tank slowly with a dosing pump to spread out the NOx generation from over 50 gallons of nitric to make the scrubber deal with a more consistent load rather than a dump it all in and hope nobody drives by like in the old days.



I can't help but find that hilarious.


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## Smack (May 28, 2012)

4metals said:


> The down side is there is a lot of waste acid to deal with and it's loaded with copper nitrate. Would be nice to either get rid of the waste for free or get paid for copper.



Have you ever tried to pull the CU out of waste solution using electrolysis?


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## Lou (May 29, 2012)

Big issue is that nitrate ion might undergo its own redox...copper, nickel, and cobalt are typically plated from sulfate milieu (which for standard purposes is an inert anion).

Not to say it won't work.


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