# Silver Cell chemistry?



## Lobby (Mar 6, 2012)

Folks,

I've looked all through this silver subforum looking for the overall chemical reaction in the silver cell (graphite cathode, silver anode, AgNO3 electrolyte) yet I couldn't find it.

Can anyone help? 

Without understanding that chemistry (and that of the competing copper reaction) I find understanding the discussions on voltages, current per surface area, and the effect of copper in the electrolyte difficult to digest.

Thanks.


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## element47 (Mar 6, 2012)

I know I have read multiple posts on everything you list....perhaps expand your search to the whole forum vs only the silver subforum? Yeah, I know, it should be in "silver". Dr. Poe had an important caution as to not allowing the applied voltage in a silver cell to get too high, and as I recall, it was pretty sensitive as to voltage...

I believe the primary chemical reactions are listed as a "slate" on Lazersteve's excellent website. 

I have no particular suggestion other than trying a (different, larger) collection of other search terms. I know I have read about everything you cite on this forum.


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## butcher (Mar 6, 2012)

Try using Laser Steve's search on his website. search silver cells.

http://goldrecovery.us/forum_search.asp

http://www.google.com/search?hl=en&as_q=silver+cell+&num=1000&ft=i&as_sitesearch=goldrefiningforum.com%2Fphpbb3&as_qdr=all&as_occt=any

2,680 results


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## Lou (Mar 6, 2012)

You don't want to run your cell at excessively high voltages, for then you run the risk of co-deposition of other metals and the side reaction of splitting water (and/or making NOx).

Most cells take a few days running to equilibrate and operate "right" and they'll run great for quite some time if the feedstock material is of good quality.

It's been my experience that you're changing electrolyte once every month if your anodes are 98-99%+, and much more frequently if they're sterling.

Basically, the cell works as follows:

As electrons flow into the cathode and deposit the silver crystal, Ag+ + 1 e- --> Ag(0).
As the silver deposits and is effectively removed from the system, silver from the anode replaces (anodic oxidation) it to maintain something of a steady state silver ion concentration.

A good analogy is a room with two doors but a long line of people:

As one person exits the room, another person can walk in and replace him. So it is that each person leaving is replaced and the line never changes.


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## Lobby (Mar 6, 2012)

Thanks, folks.

Are there any gasses given off at either the cathode or anode? I mean, as a normal part of the chemical reaction?


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## samuel-a (Mar 6, 2012)

Lobby said:


> Thanks, folks.
> 
> Are there any gasses given off at either the cathode or anode? I mean, as a normal part of the chemical reaction?



As Lou stated, at optimum operation conditions, all you get is a simple ions exchange.
Too high voltage (or too little anode surface = too high voltage) will lead to H2 evolution at cathod and NOx at the anode, co-deposition of other metals and slowly deplete the electrolyte.

Other then that, there's a natural evaporation, as you run you cell at about 70-95F, i would expect fumes to be somewhat corrosive. My cells are under a vent at all times.


edited according to GSP's correction


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## Lobby (Mar 6, 2012)

samuel-a said:


> Other then that, there's a natural evaporation, as you run you cell at about 122-140F, i would expect fumes to be somewhat corrosive. My cells are under a vent at all times.




Are you reading my mind, or what? :mrgreen: In addition to understanding the chemistry of the cell, locating them was also in my thought process.


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## MysticColby (Mar 7, 2012)

Wouldn't there be a reaction at the anode? Since Ag+ gets an electron at the cathode, I would expect NO3- to lose an electron at the anode (then maybe NO3 reacts with Ag to form NO3- and Ag+)?



samuel-a said:


> Other then that, there's a natural evaporation, as you run you cell at about 122-140F, i would expect fumes to be somewhat corrosive. My cells are under a vent at all times.


Why would there be corrosive fumes? Shouldn't all of the nitrate be occupied by metals, never allowing them to evaporate? Doesn't pure silver nitrate with no excess nitric produce no fumes?


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## goldsilverpro (Mar 7, 2012)

I've run many large silver cells and have many books that contain data (and photos) for silver cell operation from many of the largest silver operations in existence. In NONE of these are the cells heated. It's totally unnecessary to do so. *Where did this 122-140F thing come from?* 

For various reasons, there is always at least a little free nitric acid (say, from about 1% to 3%) in the solution. Under a normal 70F with one 30 gallon cell, you will always get a slight amount of acid fumes. Enough to, at least, be able to slightly smell. It should be vented.


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## samuel-a (Mar 7, 2012)

goldsilverpro said:


> Where did this 122-140F thing come from?



I hope you will accept my apology, for some reason , when writing my post, data of copper cell and silver cell commingled at my fingertips.
Silver cell does gain temperature on its own and anywhere from 70 - 95F (which is only slightly warm to the touch) is OK to run at.
I will change my original post accordingly.

Though, it doesn't change what i said what so ever, placing the silver cell in vented area is wise thing to do as evapoartion does occur anyway.






MysticColby said:


> Wouldn't there be a reaction at the anode? Since Ag+ gets an electron at the cathode, I would expect NO3- to lose an electron at the anode (then maybe NO3 reacts with Ag to form NO3- and Ag+)?



Maybe someone else can explain this better then i do. but i'll give it try.
Around the Cathode, which is negatively charged, cations are reduced (Ag+ gain electrons) and leave free anios (NO3-), therefore around the cathode there will be a constant negative potential.
Those (free NO3-) then migrate in the electrolyte toward the the positivly charged Anode (and it's surrounding) where Ag atoms are losing electrons and combime with them to form new AgNO3.
The electrons lost by the Ag at the anode travel up the electrode and out of the cell to complete the circuit.

Does this make sense now?


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## Westerngs (Mar 8, 2012)

Some free nitric is necessary because the pH needs to be kept below 3. Above pH 3, metallic hydroxides (mainly copper) start precipitating out of solution.

GSP,

Having run many silver cells for many years, It has been my experience that they produce more silver at a higher temperature. We keep our cells at or near 120F. We have tried lower temperatures, and all else being the same, we produce 20-50% less silver. We ran a 6 month study about 15 years ago with several banks of cells at different temperatures.


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## Lou (Mar 8, 2012)

They generally heat themselves, particularly the vertical config.


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## goldsilverpro (Mar 8, 2012)

Westerngs said:


> Some free nitric is necessary because the pH needs to be kept below 3. Above pH 3, metallic hydroxides (mainly copper) start precipitating out of solution.
> 
> GSP,
> 
> Having run many silver cells for many years, It has been my experience that they produce more silver at a higher temperature. We keep our cells at or near 120F. We have tried lower temperatures, and all else being the same, we produce 20-50% less silver. We ran a 6 month study about 15 years ago with several banks of cells at different temperatures.



At 100% efficiency, silver will deposit at the rate of 4.025g/A-hr. No matter what the conditions, it will never plate out faster than that. Maybe, the particular mix of metals in your anodes requires this. I always ran at "room temperature" and have never experienced such low efficiencies. With 90Ag/10Cu anodes, I got about 85% efficiency and with 98Ag/2Cu, at least 95%. What is the makeup of the anodes you are running? Can you explain, technically, why a temp increase would give you a higher efficiency? No offense, but it just doesn't make sense to me. Are you running Thum cells or Moebius cells?


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## Westerngs (Mar 9, 2012)

GSP,

I cannot technically tell you why silver refining cells run more efficiently at higher temperatures. All I know is that based on my experience, that is the case.

You are correct when you state that you can only get x amount of silver per amp, but as you know, it is impossible to get a refining cell to work at 100% efficiency, there are many variables.

Just as I cannot tell you why temperature is important, I also cannot tell you why the cell will work better with copper in solution (I use 30g/l) than without it. It just does.

I did find something in Butts and Coxe, pg 101, which states that Cerro de Pasco Corp. ran their refining cells at 45C (113F).


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## MysticColby (Mar 10, 2012)

higher temperatures will have the molecules in the liquid moving around faster, meaning they will mix faster. From how these work, it seems to me there would be an excess of NO3- near the cathode and an excess Ag+ near the anode. You'd prefer homogenized, so heating would mix these two quicker.

how about some sort of stirrer instead?


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## Harold_V (Mar 10, 2012)

Westerngs said:


> Just as I cannot tell you why temperature is important, I also cannot tell you why the cell will work better with copper in solution (I use 30g/l) than without it. It just does.


I don't agree. I routinely started my cells without added copper, secure in the knowledge that it would accumulate fast enough. Deposition was consistently the same---a hard deposit not easy to remove from the stainless cathode, which gradually changed as the copper content rose. The cell went from depositing a film to crystals quickly, and eventually produced crystals that were easily dislodged. Continued operation resulted in a deposit of fine strings of silver, at which time I'd do a wholesale change on electrolyte. 

Copper provides for increased conductivity with a lower silver content, and makes for easier harvesting of the crystals. It would take a serious amount of information to change my mind, having processed the way I did for years on end. My results were consistent. 

As to temperature of the cell, that, too, was consistent, a function of the resistance of the cell. Mine ran barely warm to the touch, and evolved very little in the way of fumes. It should also be noted that I ran my cell @ approximately 15 amps/square ft., which is below acceptable levels. My electrolyte was created by totally consuming free nitric, then just a few drops of HNO3 were added. PH was generally 1. 

Harold


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## Westerngs (Mar 10, 2012)

I think there are so many variables that no one setting is "correct". Silver concentration, free nitric acid, anode purity, amperage etc, all have so many possible combinations that every person needs to look for ways to optimize their operation.


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## MysticColby (Mar 14, 2012)

Westerngs said:


> Some free nitric is necessary because the pH needs to be kept below 3. Above pH 3, metallic hydroxides (mainly copper) start precipitating out of solution.



So if you have a filtered solution of just copper nitrate and silver nitrate (all the nitric has been removed via evaporation), it will form copper hyroxide? What would cause the pH to raise? You'd need to add OH- in order to raise the pH.
Is it that Hydrogen Hydroxide (HOH = H2O) double displaces with copper nitrate? hydrogen IS on that reactivity series... but then one of the products would be nitric acid.


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