Measuring cupric nitrate in solution in a silver nitrate/silver electolysis cell

[FrugalRefiner]

The downside as I see it would be the formation of NOx but that can be handeled with a fan.

A downside is that you're dissolving some of the crystals you've already purified through the cell. I prefer to dissolve some feedstock (for me, that's usually sterling) and add that to the cell. It adds some copper too, but that's going to get there whether I dissolve it in some nitric or process it as anode material.

Dave

 

[James Ball]

Streetips (aka kadriver) did a nice peace of work with cupric nitrate derived from copper using a Spec 20. He also uses about 150 g Ag/L to increase his amperage.

The gravimetric method for copper concentration seems pretty laborious compared to visual comparisons. How well did the gravimetric method compare to AA?

I would like to see your spreadsheet if you can find it.

I do not see much of a downside to adding HNO3 to the silver cell. I would add more cement silver shot to make up for the silver dissolved by nitric acid. This seems a lot easier than isolating pure silver and digesting in nitric acid and then adding it to the silver cell.

 

[4metals]

I would like to see your spreadsheet if you can find it.

 

[4metals]

the spreadsheet has 3 sheets, one for the titration, one for making up a new tank of silver nitrate, it is set for a volume of 275 liters as that is the volume of the smallest Italimpianti system. The last sheet tells you how much nitric to add to balance the electrolyte. Again it is set for a 275 liter cell but you can change the variable by unlocking the cell. The password is 4metals. If you have questions I can answer them here.

 

[4metals]

How well did the gravimetric method compare to AA?

Precipitation of the insoluble thiocyanate complexes makes this procedure non selective for Copper as a result Lead, Palladium and Mercury interfere as insoluble Pb(SCN)2, Hg(SCN)2, & Pd(SCN)2 these will result in higher results for copper but the only consequence is changing out of the solution sooner which still guarantees the purity of Silver required.

Overall with the cells I ran this test with the results never varied more then 2% from the Atomic Absorption. But if you have an Atomic Absorption you're not running this test for copper anyway. This is a work around for those without the benefit of an Atomic Absorption.

 

[James Ball]

My silver cell changed color today. I thought I was pretty far from Cu co-prectpitation. I stopped the electrolysis and will harvest the silver I have and make fresh electrolyte. Have you seen anything like this? I added conc nitric acid last week to boost the [Ag] but did not see any NO2 coming off. Can dil HNO3 dissolve stainless steel causing this color change?

 

[4metals]

Can dil HNO3 dissolve stainless steel causing this color change?

Nitric doesn't dissolve stainless steel. That color looks perfectly fine to me for a Silver cell electrolyte. Caribbean blue is my favorite electrolyte color, not indicative of high copper.
I always preferred to add the required nitric over time because high concentrates of nitric tends to favor dissolving any Palladium in to the electrolyte whereas slow additions favor Palladium remaining in the slimes.
I always prefer to have a glass bottle with a stopcock that is set for a slow drip and I added the nitric to that and let it drip in slowly. Larger systems actually have dosing pumps that can be set to liters per hour so nitric additions could easily be added slowly.
My favorite shade of blue!!!!!!

 

[James Ball]

I am not cocerned about the blue, but more the yellow-green at the bottom of the tank. Nice commercial setup!!

 

[4metals]

Have you tested your solution with Dimethylglyoxime? Palladium turns a solution green. And only a few PPM of Palladium in the electrolyte plates out in the crystal.

 

[James Ball]

I was wondering about that. Tomorrow I will measure the copper conc using standard reference vials and the silver content using the Volhard titration. If both of those come out okay I will keep going. I have about 3 amps at 3.5 V

 

[cejohnsonsr1]

I know this suggestion is inexact, but you might want to take a look at one of Sreetips silver cell harvesting videos and note the color of the electrolyte. He usually gets 2 runs of about 2 weeks with replenishment with the same electrolyte as the original charge. Shouldn’t be a difficult search. He has recent examples of reusing after a 1st run and replacing after a 2nd run.

 

[James Ball]

thanks I have seen those videos. Streetips' videos is what got me going on this hobby. Having said that this forum is the one Kevin used for his information. I am going with the idea that copper doesn't co-precipate until one gets to 50 or 60 g/L. My current cell has about 10 g/L based on comparison to known reference standards (see picture). I also did a Volhard titration of the silver content of the electrolyte. I used two different concentrations of KSCN (~1 and 0.1 M) and got the same result: 234 g Ag/L. I had no idea I had that much silver in my cell. Is there such a thing as too much silver nitrate?I suspect there is but Streetips uses 150 g Ag/L so I am not off by more than a factor 2. Bottom line: I am going to keep my cell going. As 4metals suggested, the yellow-green color could be paladium as I have no control over the composition of my sterling silver.

 

[rusti2]

Nitric doesn't dissolve stainless steel. That color looks perfectly fine to me for a Silver cell electrolyte. Caribbean blue is my favorite electrolyte color, not indicative of high copper.
I always preferred to add the required nitric over time because high concentrates of nitric tends to favor dissolving any Palladium in to the electrolyte whereas slow additions favor Palladium remaining in the slimes.
I always prefer to have a glass bottle with a stopcock that is set for a slow drip and I added the nitric to that and let it drip in slowly. Larger systems actually have dosing pumps that can be set to liters per hour so nitric additions could easily be added slowly. View attachment 60307
My favorite shade of blue!!!!!!

Is it common to use Mobius cell extraction solvents to periodically remove Cu?

 

[4metals]

Is it common to use Mobius cell extraction solvents to periodically remove Cu?

Are you speaking about selectively removing copper from a silver nitrate electrolyte?
Please describe the process you think that will do this.

 

[rusti2]

¿Está hablando de eliminar selectivamente el cobre de un electrolito de nitrato de plata?
Describa el proceso que cree que hará esto.

Are you speaking about selectively removing copper from a silver nitrate electrolyte?
Please describe the process you think that will do this.

Remove the electrolyte or part of it and subject it to an extraction with a selective solvent for Cu and reuse this electrolyte again with the Cu removed, on the other hand recover a Cu salt with a high degree of purity.

 

[rusti2]

It also increases the nitric acid in the treated electrolyte and when the cell begins to operate it would raise the concentration of silver nitrate.

 

[James Ball]

I do not know of any solvent that would selectively remove cupric nitrate and not silver nitrate. Ion exchange resins would be pretty nonselective as far as I know. Interesing idea if one could come up with a clever way of doing this.

 

[4metals]

Interesing idea if one could come up with a clever way of doing this.

Interesting and valuable, I do not believe anyone has come up with a viable method yet.

 

[rusti2]

Interesting and valuable, I do not believe anyone has come up with a viable method yet.

I am not a specialist in electrolytic refining of Ag, I thought that solvent extraction of Cu could be used in the Ag electrolyte, I share a patent that explains a procedure in general terms that seems viable but does not describe any detailed experimental development that does so more plausible, we know that patents must be looked at with a critical eye. I have some experience in extraction with solvents and both the extraction with agitation, the separation of the phases, the washing of the loaded organic phase and the stripping of the organic phase on a scale of a few tens of liters can be done with equipment that requires minimal investment, in the patent they describe 3 types of extraction solvents that could be used:
Yo. 2-hydroxyl benzophenone oxime derivatives sold by General Mills Inc. under the trademark "LIX";
ii. 8-hydroxyquinoline derivatives sold by Ashland Chemical Co. under the trademark "KELEX", especially KELEX 100 which is a 7-dodecenyl-8-hydroxylquinoline; and
III. 2-hydroxy 5-nonyl acetophenone oxime available from Shell International under the reference SME 529 (previously RD539)
to which ACORGA M5640 could be added another oxime from the company Solvay S.A.
The advantage of this procedure is that it allows the copper to be eliminated selectively, it avoids having to add fresh solution of silver nitrate or nitric acid periodically and when the copper is removed with SX, nitric acid is released which subsequently increases the concentration of silver nitrate, it could be also work with anodes with lower silver content. Take a look at it.

 

[rusti2]

It also avoids having to periodically eliminate part of the electrolyte with copper content at its limit and the recovery of its contained silver.