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

[4metals]

That patent is quite old, from the 1970’s. It never seemed to catch on in production. If it has, it’s a well kept secret.

 

[James Ball]

Very interesting idea. one concern I have is that the electrolyte would have a kerosine odor associated with it. I do this in my garage and would not want the smell. On the other hand some type of vented hood above the cell would eliminate this problem. It seems to me one could monitor the progress of this extraction by measuring the curpic nitrate in the electrolyte (the blue color intensity should go down) and the selectivity of the extraction by measuring the silver concentration in the cell using the Volhard titration ( which works really well). Got the seeds of an experiment here for sure. I would like to see some data, however.

 

[4metals]

Here’s the thing. There are a good number of refining equipment manufacturers making Silver cells. And all cells have to deal with copper if they refine sterling. (unless they digest, cement, and process cement Silver)
This patent has been around for 50 years. Surely it has been tried, and for some reason no one has made a system using this chemistry to match up with all of the different size Silver cells made to make the copper issue a non issue.

There has to be a good reason for this.

 

[James Ball]

I harvested my silver cell today because it became greenish in color and unusual green-yellow crystals were observed growing in the cell. Has anyone seen these before? These crystals are consistent with needle like crystals of cupric chloride. The problem I have with this is where would the chloride come from in a solution high in silver nitrate?I am treaing my cyrstals with dilutie sulphuric acid. I saw some hissing when these cyrstals first met this acid, I am seeing gas evolution which could be hydrogen gas. I will wait until gas evolution has stopped and then wash the crystals. It would be nice to get some elemental analysis but ICP-MS is pretty expensive.

 

[rusti2]

Very interesting idea. one concern I have is that the electrolyte would have a kerosine odor associated with it. I do this in my garage and would not want the smell. On the other hand some type of vented hood above the cell would eliminate this problem. It seems to me one could monitor the progress of this extraction by measuring the curpic nitrate in the electrolyte (the blue color intensity should go down) and the selectivity of the extraction by measuring the silver concentration in the cell using the Volhard titration ( which works really well). Got the seeds of an experiment here for sure. I would like to see some data, however.

I did not study the subject in depth but a drawback would be that high concentrations of nitrate ion can degrade the oximes and make the consumption of the active compound of the extraction solvent at prohibitive levels. I asked the manufacturers of 2 solvents for copper in nitric acid solutions for information, if they answer me I will let you know.

 

[James Ball]

I think I have an explanation for the greenish crystals. In this run, I added some nitric acid to regenerate silver nitrate in situ. Streetips (aka kadriver) says in a number of his videos that he wants all of the nitric acid consumed in making silver nitrate because nitric acid would dissolve palladium in the slimes. I think that is exactly what I did - dissolved palladium and it crystalized out.

Okay, really like the idea of adding nitric acid to the silver cell to replenish the silver concentration in the cell. All kinds of benefits of doing it this way. 1) you don't spend the time isolating pure crystals and washing them, etc, 2) you don't have to redissolve silver and make sure there is excess silver around (plenty of excess silver in the silver cell). The downside as I see it would be the formation of NOx but that can be handeled with a fan. I really like combining this with the silver titration method. These two methods would allow one to keep the [Ag] at the right amount. I think using cupric nitrate standard solutions is a better way to approximate the [Cu] in the silver cell. Any other downsides to this method of maintaining you silver concentration in the silver cell? What concentraton of silver do you use in a silver cell?

This is why I support this forum. In my opinion, this is an outstanding contribution to my project. Thank you very much,

Jim

ps time to buy some chemicals, buret, lab stand, pipets etc for the silver titration. what fun!

I do NOT recommend adding nitric acid to the silver cell. Streetips said it would dissolve the paladium in the slimes and generate a green solution. I added HNO3 and I got greenish-yellow crystals. This makes sense because we go to great pains to ensure all of the nitric acid in our silver nitrate electrolyte solution is consumed. Why would we add nitric acid then? Live and learn.

 

[4metals]

Why would we add nitric acid then? Live and learn.

It all depends on your feedstock. If you were processing high purity Silver to start (>99%Ag) the Silver would dissolve at the anode and deposit at the cathode and your net consumption of nitric would be negligible. This makes it easy to control. And in a solution with lower free nitric acid and 60g/l Silver, lower concentrations of Palladium tend to accumulate in the anode slimes.

A lot of refiners today, actually most of them, refine coin or sterling silver. In fact the Italian cells advertise you can process Silver up to 80% pure. This is true but the copper tends to build up pretty quick. Seeing as it takes about 3 times as much nitric to dissolve the copper than the Silver, your nitric is consumed and needs replenishment. By adding nitric to the solution you can maintain the Silver levels you need but at the same time you will increase the Copper levels as well.

Some tips to keep the Nitric as low in concentration as possible include slow dosing. If you determine your cell needs, for argument sake, 2 liters of nitric acid, I prefer to add via a dosing pump set to add the requisite dosage over a 24 hour period. Keep the Palladium concentration in the anodes under 1g/kg of Silver as Palladium concentrations in excess of 0.5 g/l tend to favor co-deposition in the crystal.

If a feedstock with lower Palladium content cannot be avoided, separate anode chambers and selective Palladium precipitation with Dimethylglyoxime should be used.

 

[James Ball]

I am refining sterling silver from many sources. I do not have any idea of the Pd content. I typically refine silver shot after HNO3 digestion, Cu cementation and silver shot formation. It should be pretty pure but the Pd would come aloing for the ride.

 

[4metals]

Add some Dimethylglyoxime to test for Palladium, it is selective and very accurate if you have an a analytical balance.

 

[4metals]

Palladium, back in the days when it was cheaper, was used to prevent or slow tarnish on sterling flatware. But since you are digesting everything in nitric and cementing, a simple step would be to add Dimethylglyoxime and drop all of the Palladium out of solution before putting it in a cell.

 

[James Ball]

Good idea. I assume you would add it to the blue silver nitrate solution and then filter it out before Cu cementation. Correct?

This would make sense if I needed to add nitric acid to my silver cell to regenerate more silver nitrate. Pd would stay in the silver shot bag.

I am set up to measure the silver concentration using the Volhard titration. In addition, the amperage on the cell can be used to qualitatively monitor the silver nitrate solution. My plan would be to monitor both of these parameters and make fresh silver nitrate if needed. I have in the past made dry AgNO3 and added this to the cell to avoid adding to much liquid.

I also monitor Cu concentration with standard reference vials for cupric nitrate color.

I think dropping out the paladium would add more sources of contamination with little benefit to the silver cell and it would add another step to the process. It sure sound like a very plausible solution if Pd becomes a problem. My cell looks very blue now with no hint of green.

For my own info I am going to look up the chemistry of dimethylglyoxime and Pd.

 

[4metals]

Good idea. I assume you would add it to the blue silver nitrate solution and then filter it out before Cu cementation. Correct?

yes the Palladium Dimethylglyoxime molecule is very large relatively speaking, that is why it is used to determine small quantities of Palladium in solution. It also drops Palladium as the salt in the presence of nitric acid which makes this easy. Simply filter out the yellow Palladium Dimethylglyoxime and reduce it to the metal when you have accumulated enough.

 

[Barthel732]

Is Jsp nitric acid substitute good? Would it work for dissolving silver for silver nitrate electrolyte

 

[Shark]

Is Jsp nitric acid substitute good? Would it work for dissolving silver for silver nitrate electrolyte

This substitute is sodium nitrate. It would need to be made in to nitric acid, search poormans nitric on the forum.

 

[Barthel732]

Ok thank you. Now I understand why a lot of my experiments don’t work. I assumed that it was real nitric. I’m just gonna buy some from lab alley then. I will read what you mentioned also.

 

[Barthel732]

Have you ever used DIY chemicals nitric acid 67% or Lab alley nitric acid 67%? If so, which would be better

 

[Shark]

I have tried most of them. I haven’t tried the Lab Alley brand, but have used it from Greenway Chemicals, now under new ownership and name change. They are out of Knoxville, Tn. My go to for smaller volumes has been Duda Diesel, out of Decatur, Al. And they are within a comfortable drive for me.
I have also used sodium nitrate, potassium nitrate and calcium nitrate to make both Poormans AR and nitric acid. My preference would be
1- real nitric, distilled or bought from a quality supply house.
2 - sodium nitrate in AR form.
Potassium nitrate then calcium nitrate. In that order, just based on ease of access.

I have never distilled nitric although have the equipment to do it. It was easier to gain access to good nitric than keep making it in quantities I could use. Since I am slowing down more these days, I may try distilling some at some point in time just for the experience.

 

[Barthel732]

I have tried most of them. I haven’t tried the Lab Alley brand, but have used it from Greenway Chemicals, now under new ownership and name change. They are out of Knoxville, Tn. My go to for smaller volumes has been Duda Diesel, out of Decatur, Al. And they are within a comfortable drive for me.
I have also used sodium nitrate, potassium nitrate and calcium nitrate to make both Poormans AR and nitric acid. My preference would be
1- real nitric, distilled or bought from a quality supply house.
2 - sodium nitrate in AR form.
Potassium nitrate then calcium nitrate. In that order, just based on ease of access.

I have never distilled nitric although have the equipment to do it. It was easier to gain access to good nitric than keep making it in quantities I could use. Since I am slowing down more these days, I may try distilling some at some point in time just for the experience.

I found a place called alchemie labs. They have 950ml bottles of nitric for $30 and free shipping. They said anything a liter or more needs hazmat fees but you can have multiple 950ml bottles of nitric in the same box without paying those hazmat fees. I just ordered a bottle so I’ll update on how it is