# Ideal AgNo3 strength for electrolyte?



## mikeinkaty (Mar 17, 2013)

If you were going to try to maintain a constant silver nitrate concentration for your cell, what would it be, and why?

Not knowing why and because I didn't have much silver I started with dissolving 8 Ozt silver in nitric acid then diluted it to 3.5 liters. According to my calculations, that would have been about a 0.26N Molar concentration of silver nitrate. That first cell lasted for a little over 100 ozt of 990 anodes. I figure I was down to about a 0.1N solution when I took down the cell and dropped the remaining silver.

So now I'm wondering if there is an ideal strength. And for that I guess one would have to define Ideal and what it entails. Cell efficiency or crystal characteristics?

Mike


----------



## samuel-a (Mar 17, 2013)

It is less about silver conc'....
More so about copper.


----------



## samuel-a (Mar 18, 2013)

Sorry... I worte the above from my phone. Hard to write with that.

What i meant to say was, that if you really intend to monitor something, you should monitor the contaminants such as nickel and copper.
Maintain the above at lower then 6-8g/l and you are golden. By circulating the solution via cleanout process (solvent extraction for example), there basically should not be a major drop in Ag conc'. No matter what it is.


----------



## mikeinkaty (Mar 18, 2013)

samuel-a said:


> Sorry... I worte the above from my phone. Hard to write with that.
> 
> What i meant to say was, that if you really intend to monitor something, you should monitor the contaminants such as nickel and copper.
> Maintain the above at lower then 6-8g/l and you are golden. By circulating the solution via cleanout process (solvent extraction for example), there basically should not be a major drop in Ag conc'. No matter what it is.



Well, you can get a close approximation for the copper concentration by keeping track of the total weight and type of anode bars consumed. And to some degree by watching the color of the solution. I don't know about nickel. My anode bars have been running 990 or better so my solution will go a long time before having to much copper (approx 600+ ozt processed).

I'm just wondering if there is a particular AgNo3 concentration that is more efficient. Of course the more silver you put into the solution the longer it will last. But, for a particular anode being processed would a .2N, .4N, .8N, or whatever, AgNo3 concentration be best? Or, does there just need to be enough silver nitrate in the solution to make the electrolysis happen?

If someone were to tell me that a 0.4N solution, for example, was best then I would occasionally add AgNo3 to try to keep it at that concentation. If not, then I'll keep adding 8 Ozt of silver to the solution for every 100 ozt of anode bars fed in. If I had a lot of silver laying around then I wouldn't be so stingy!
Mike


----------



## mikeinkaty (Mar 19, 2013)

samuel-a said:


> Sorry... I worte the above from my phone. Hard to write with that.
> 
> What i meant to say was, that if you really intend to monitor something, you should monitor the contaminants such as nickel and copper.
> Maintain the above at lower then 6-8g/l and you are golden. By circulating the solution via cleanout process (solvent extraction for example), there basically should not be a major drop in Ag conc'. No matter what it is.


Sam -

You said 6-8 g/l. Didn't you mean 6-8 oz/gal?

Mike


----------



## mikeinkaty (Mar 20, 2013)

Amesametrita gave me a publication with several charts. One shows that a silver concentration of 50 grams/Liter, or greater, produces essentially the same quality of Ag at the cathode. Below 50 the quality of the silver at the cathode drops quickly. ( 1 DM3= 1 Liter) So, the optimum concentration is anything above 50 gm/liter.

In my cell where I have been using 8 ozt silver per 3.5 liter water, I could therefore expect the silver concentration to get too low after I have processed about 60 ozt of 990 anodes. If I were processing 995 anodes it would last twice as long or 120 ozt processed. Conversely, if running 980 anodes then I would expect to only process 30 ozt.

http://www.ams.tuke.sk/data/ams_online/2005/number1/mag10/mag10.pdf

Are there other publications around with similar type charts?

Mike


----------



## samuel-a (Mar 24, 2013)

You could run it with 40-60 g Cu/l
but then your reach the co-deposition threshold rather fast... (at 50-60 g/l Ag) 
Copper ions are better conductors than silver, but that doesn't mean you need a whole lot of it.

See, you could run a silver cell even at 2 g/l silver, assuming you run 995+ Ag anodes, but at somepoint, the copper concentration will be high enough to co-deposit. And it won't be at 50 g/l...

So it is not only the absolut content of each coponent (metals ions), it is also the ratio.
As rule of thumb, keep Cu + Ni content, but keep it low. That's about it.

Of course there are other variable that takes part here, namly current density, voltage and spacing.


----------



## mikeinkaty (Mar 24, 2013)

samuel-a said:


> Of course there are other variable that takes part here, namly current density, voltage and spacing.



Speaking of current density, here is a good reference: See page 240.
http://books.google.com/books?id=E_...&ved=0CDgQ6AEwAg#v=snippet&q=moebius &f=false

It says 20-40 Ma/sq-cm max for the current density. I put a new cathode in my cell with an area of 68 sq-in or 440 sq-cm so that means I could run at up to 9.0 - 17.5 amps and not exceed that stated limit. They didn't say anything about the current density for the anode though. Is there a max there too? I can run at 9 amps without the voltage getting over 2.5V. I'm still experimenting with the new cathode to see how fast I can run it and still get good crystals and no co-deposits. The only problem with 9 amps that I have seen so far is the edge effect where it was growing long thin crystals. I stopped that by fitting plastic report binders over the edges. It runs 1.5V at 6 amps so I will try that for a while. It runs 1.0V at 4 amps. With my old cathode of 20 sq-in I was getting close to the max current density at 4 amps.

The guys with the SS bowls (no edge effects) for the cathode probably could run their cells at 15 amps as long as the voltage stayed below 2.5 volts and the electrolyte didn't start boiling. If processing silver shot like Kevin, one would have a much higher anode area (lesser current density at the anode). 

With the new cathode I'm getting silver 'sand' deposited on the cathode. I've been cleaning it out after each anode bar (5-6 ozt). I think that if I let it go without cleaning it out so often I could get bigger crystals (nodules instead of sand). I've got about 20 ozt left to process with this batch so will try it.

I was thinking amps controlled the type crystals obtained but I now believe it's the amps x the area of the cathode + the length of time they are allowed to grow. I still need to find a discussion on what role voltage plays. The referenced paper, above, mention running cells at between 1.5V & 2.8V. I think voltage comes into play with the types of base metals expected. A voltage to low or to high probably makes the other metals start depositing on the cathode.

Mike


----------

