Testing for copper content in electrolyte.. and how much is too much?

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speed

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Aug 13, 2017
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Apologies if this has been asked already but I couldn't find an answer.

Is there a method to test silver cell electrolyte to monitor its copper content that isn't going to cost a fortune?

I currently only run my cell to purify silver from 98/99% to 999 so I get a reasonable throughput before the electrolyte goes blue and I swap it out. I am currently simply using the colour of the solution to give an educated guess at copper content (and to some extent palladium contamination.) However I am now looking to set up a cell to process 92.5% Stirling. I am told this will be more economical than nitric dissolution (certainly saves alot of time!). My problem is ofcourse that its alot more copper going into the electrolyte and for the economics to work out I want to be getting the most use out of the electrolyte before it is recycled.

I'm guessing I will be able to determine how much copper in solution is to much by experimentation but it's how to quantify copper in solution that is puzzling me at the moment.
 
I have found that the more contamination, the larger the crystals you produce.
So I tend to run my main cell quite clean, so I produce very fine small crystal that form mostly sheets of product that is almost white.
This is better for running a cell as small crystals do not reach for the anode quite as fast as larger crystals do, the main danger of running a cell being a short circuit.
I have run smaller cells deliberately high in contamination to produce larger, more interesting sample crystals.
As most of my silver has been used as inquartation my main concern is Pt and Pd.
As every inquartation is quite unique, you have to monitor your cell closely and simply run a silver nitrate refinement through evaporation to crystal before the crystals become too large, If you get it wrong you simply have to cement all the silver and remelt your anode.( Please note the difference between crystalline silver nitrate and electrically deposited elemental silver crystal.)
The recovered liquor can be processed for Pt and Pd with DMG giving you a clean silver to put back through the cell.
Or convert the AgNO3 to AgCL and then drop the Pd and Pt which will mean a further process for the silver.
 
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Is there a method to test silver cell electrolyte to monitor its copper content that isn't going to cost a fortune?
I use a very simple method. I created a 100 grams per liter solution of copper nitrate by dissolving 10 grams of copper in 100 ml of solution. Then I made dilutions ranging from 10 grams per liter up to the original 100 grams per liter in 10 gram increments. It's easy to compare my "standard" solutions to the electrolyte (be sure to put a sample of the electrolyte in the same size container as the standard solutions).

There are other, more sophisticated, ways to determine the copper content, but my sample solutions work for me.

Dave
 
*edited for clarity
I once saw a rule of thumb that running the cell at less than 50/50 silver to copper was undesirable.
If you don't have nearly clear electrolyte (light blue) you may need to run it again to get to 999.

If you begin with 100g of sterling dissolved in your electrolyte, the ratio of silver to copper is 925 to 75 (92.5 grams of silver and 7.5 grams of copper). Each time you process 100g more, the ratio changes. With sterling silver, after about 500g you will be near that 50/50 ratio(about 55 grams of silver and 45 grams of copper in the electrolyte), so you might want to make new electrolyte. Just keeping track of what you ran requires no further steps at all.

I had another idea for another test, but I didn't write it very eloquently, per Frugal's flame post below. I've removed it, since even though it seems like it could be accurate it's overly-complicated.

If you watch Sreetip's videos on his silver cell, his final run has clear electrolyte (silver only with almost no color). IMO if you want highly pure silver - which is the whole point of the post - then I'd think your final run is with only pure silver in the electrolyte, and nearly pure silver in the anode.
 
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Dave’s solution to the problem is easy and frugal. Perhaps not the most accurate, but definitely easy and frugal. Most importantly, it is adequate to the needs of most of our members.

Time for more coffee.
 
I once saw a rule of thumb that running the cell at less than 50/50 Au/Cu was undesirable.
Well, that's confusing. Granted, Au is only one letter different than Ag, but it's a big difference for those who may be new to this. Please proof-read your posts before pushing the "Post reply" button.

If you don't have nearly clear electrolyte you may need to run it again to get to 999.
So if you directly go /w let's say 100g of sterling in the electrolyte, You'll be at 925, then 850 (@100g), etc until your solution is 550 (@500g). So you can theoretically process 5x the amount of sterling in your electrolyte at the start. Easy.
Huh? Again, that's confusing. Please don't use abbreviations like "go /w let's say". It's not that difficult to type out the word "with" instead of "/w". Remember, many of our members have to use translators to read the forum, and abbreviations don't translate well.

Beyond that, I'm not sure what you're trying to say with your 925, then 850, 550, etc. My electrolyte is always somewhat blue. You want some copper in your electrolyte to keep lead from dissolving into the solution and to help crystal formation. I typically run my cell till the copper level reaches about 50 grams per liter.

To test for copper content in a given volume, the acid needs to be a known quantity (e.g. "I have 20% nitric in my electrolyte") and it can hold Xg of copper and Yg of silver. Precipitate the silver /w a known amount of copper and either measure the dissolved copper or precipitated silver. Or do both to validate your math (maximum fun). The key is to standardize your electrolyte, which shouldn't be hard for you. Personally I like the color-based solution above.
Again, I'm not sure what you're saying. I create electrolyte by dissolving sterling silver. I add a tiny bit of excess nitric when I start the run. It quickly balances as the cell runs. Silver deposits at the cathode, making NO3- available to dissolve more silver at the anode. I try not to overthink it.

Dave
 
Thanks. The 'colour chart' option seems like a good way to improve my current process so il have a go at that.

Also I can see how keeping track of weight of feedstock going into the cell can help if it is all known 925 alloy.

My cell current cell is a similar design to 'streetips' but I will be building some new larger cells with removable cathodes as having the container itself as a cathode is a pain for continuous production.

I too run my final product through the cell until i see no colour change to ensure purity. It seems to work!
 
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