Electrolyte for silver cell questions

[Cmarett]

Hello everyone, I am about to put my first silver cell into operation and have a few questions on the electrolyte. I have searched for these answers, but the information I find is either very conflicting with other information I find, or very scientific speak and hard to understand and follow. Hoping the group can help. Thanks in advance.

Question #1 / How do I know the amount of impure silver that I can run through a cell before the nitrate solution is used up or becomes too contaminated with copper?

Question #1.5 / How do I know at what point the cell has become too contaminated, and the nitrate solution needs to be changed?

Question#2 / Assuming my silver nitrate solution is 90% pure and 10% impure, What should I be using as a ratio on this silver nitrate solution per liter of distilled water?

Again, thanks in advance for any help.

 

[command2001]

Hello everyone, I am about to put my first silver cell into operation and have a few questions on the electrolyte. I have searched for these answers, but the information I find is either very conflicting with other information I find, or very scientific speak and hard to understand and follow. Hoping the group can help. Thanks in advance.

Question #1 / How do I know the amount of impure silver that I can run through a cell before the nitrate solution is used up or becomes too contaminated with copper?

Question #1.5 / How do I know at what point the cell has become too contaminated, and the nitrate solution needs to be changed?

Question#2 / Assuming my silver nitrate solution is 90% pure and 10% impure, What should I be using as a ratio on this silver nitrate solution per liter of distilled water?

Again, thanks in advance for any help.

No answers???? I could use the information myself.

 

[4metals]

I am used to Silver cells on a much larger scale than your setup. Larger cells use a daily titration to determine the concentration of Silver in solution and add nitric acid accordingly. Obviously, small cells are not going to be routinely titrated so some accommodations need to be made.

I can write a spreadsheet to help you to get started but there will have to be some guesstimations to determine how much Silver is in solution. The problem is sterling Silver is 7.5% copper and copper takes 3.4 times more nitric to dissolve. So as your anodes dissolve, the nitric available to continue to dissolve new silver at the anode diminishes. This causes your silver nitrate concentration to drop.

To start out, what is the volume of your cell? And how much refined Silver can you remove daily? (or every couple of days). From these numbers we can work backwards to figure how much nitric you need to add to make up for the excess consumption by the copper in the alloy.

As far as how much copper can build up in the solution, classic cell chemistry allows the operating Silver content, which you want to maintain at 60 grams. per liter defines how much copper can be in solution before the copper starts to cross over and contaminate your refined Silver. By tracking your anode consumption, you can determine the copper in solution based on the amount of anode dissolved.

As I said, I have never operated a small silver cell so the controls I suggest may not be do-able for you. So if some other members whose expertise is in small cells chime in, maybe we can come up with some documented guidelines for future use by everyone.

 

[nickvc]

When I ran my cell I made up the electrolyte using cement silver so it was contaminated with a little copper and I added nitric based on the color of the electrolyte as it ran , my feed stock was sterling much gold plated so I was after the slimes but it produced around 100 + kilos of fine silver and the slimes were worth chasing.

 

[4metals]

This is a spreadsheet used for the smallest cell I ever worked with. It is a cell which produces 3000 ounces of Silver per week (7 days) of continuous operation. I realize your small will not be titrated so we have to come up with a work around. I have entered the volume of the cell based on what I think your volume will be.

 

[FrugalRefiner]

I use sterling to make up my electrolyte. Some copper is desirable in the electrolyte.

I made a series of copper nitrate solution samples from 10 grams per liter to 50 grams per liter. When the color of the electrolyte matched the color of the 40 grams per liter sample, I treated the electrolyte to remove some copper.

Dave

 

[Master Nater]

I use sterling to make up my electrolyte. Some copper is desirable in the electrolyte.

I made a series of copper nitrate solution samples from 10 grams per liter to 50 grams per liter. When the color of the electrolyte matched the color of the 40 grams per liter sample, I treated the electrolyte to remove some copper.

Dave

what kind of treatment did you give your electrolyte to remove copper?

 

[FrugalRefiner]

I remove part of the electrolyte and replace it with fresh.

Dave

 

[Cmarett]

I am used to Silver cells on a much larger scale than your setup. Larger cells use a daily titration to determine the concentration of Silver in solution and add nitric acid accordingly. Obviously, small cells are not going to be routinely titrated so some accommodations need to be made.

I can write a spreadsheet to help you to get started but there will have to be some guesstimations to determine how much Silver is in solution. The problem is sterling Silver is 7.5% copper and copper takes 3.4 times more nitric to dissolve. So as your anodes dissolve, the nitric available to continue to dissolve new silver at the anode diminishes. This causes your silver nitrate concentration to drop.

To start out, what is the volume of your cell? And how much refined Silver can you remove daily? (or every couple of days). From these numbers we can work backwards to figure how much nitric you need to add to make up for the excess consumption by the copper in the alloy.

As far as how much copper can build up in the solution, classic cell chemistry allows the operating Silver content, which you want to maintain at 60 grams. per liter defines how much copper can be in solution before the copper starts to cross over and contaminate your refined Silver. By tracking your anode consumption, you can determine the copper in solution based on the amount of anode dissolved.

As I said, I have never operated a small silver cell so the controls I suggest may not be do-able for you. So if some other members whose expertise is in small cells chime in, maybe we can come up with some documented guidelines for future use by everyone.

Thank you for the reply. Wow, you were/are processing a lot of silver! I'm a little confused when you mention the amount of nitric in the electrolyte as I am under the impression that you do not want any free nitric in the electrolyte as it will dissolve the silver crystal that is being produced. Possibly I misunderstood what you meant, can you elaborate. Thanks again.

 

[Cmarett]

This is a spreadsheet used for the smallest cell I ever worked with. It is a cell which produces 3000 ounces of Silver per week (7 days) of continuous operation. I realize your small will not be titrated so we have to come up with a work around. I have entered the volume of the cell based on what I think your volume will be.

Thank you for this. I will look this over and I'm sure have questions. To answer the questions you first asked, the volume of my cell is 11 liters. As for how much refined silver I can remove, that is one of the questions I'm trying to answer. I believe that answer comes from having a better understanding of how quickly the electrolyte becomes contaminated.

 

[Cmarett]

I remove part of the electrolyte and replace it with fresh.

Dave

Thanks Dave. I like this idea a lot!

 

[Cmarett]

When I ran my cell I made up the electrolyte using cement silver so it was contaminated with a little copper and I added nitric based on the color of the electrolyte as it ran , my feed stock was sterling much gold plated so I was after the slimes but it produced around 100 + kilos of fine silver and the slimes were worth chasing.

Thank you for the reply. Won't adding nitric to the electrolyte dissolve the silver that is forming?

 

[Yggdrasil]

Thank you for the reply. Won't adding nitric to the electrolyte dissolve the silver that is forming?

As the cell is running I think it will not.

 

[4metals]

I am under the impression that you do not want any free nitric in the electrolyte as it will dissolve the silver crystal that is being produced. Possibly I misunderstood what you meant, can you elaborate.

In a perfect world your impression is correct. If your anode is almost pure .999 Silver, when Silver Nitrate gives up it's Silver at the cathode, that now single nitrate ion picks up a single molecule of Silver at the anode. And this repeats itself ad infinitum.

Now for the real world. Since your anode material is not high purity Silver, the other metal in the alloy, typically copper, also dissolves at the anode and goes into solution. Except copper is a nitric hog, it takes over 3 times as much nitric to dissolve a mole of copper as it does to dissolve a mole of Silver. (actually the number is 3.4 times if my memory serves me well). So what happens is the copper content in solution increases and the amount of available nitric to liberate more Silver decreases as well. In big systems a titration will tell you how much your silver concentration drops and you pick a column off the sheet I sent which tells you how much nitric is required to replenish the Silver to optimum. This process continues until your solution develops the color as Dave mentioned to guesstimate the copper concentration by comparison at which point you change out a percentage of the solution or in a small cell, start over.

I never hear the small Silver cell folks discuss adding nitric to replenish the nitric depleted from refining sterling. Perhaps they don't and when the cell production drops off they change out the electrolyte and start over. When you can come up with a number like every X days, I remove about Y grams of Silver from the cell we can back into that number and replenish the nitric to keep up the cell longevity.

Adding nitric too quickly can bring up the free nitric too quickly and have an undesirable effect of putting any Palladium into solution rather than keeping it in the anode bags where it ends up when free nitric is lower. In larger systems a timed dosing pump is used because some systems need to add 10 gallons a day, which is best done spread evenly over an entire 24 hour period. In a small cell, maybe an IV dripper can deliver diluted nitric over a few days for the same effect.