kurtak said:
As far as when your electrolyte becomes corrupted to the point that it starts co-depositing copper (or other metals) its hard to say because you don't know "for a fact" the purity of the silver (anode) going in --- this is going to be a learning curve on your part by running the cell - then testing the finished silver - to determine the what & how in the running of "your" cell
Kurt
And---what you learn from one anode (or batch of shot) may or may not be representative of the following anode or batch. It's all reliant on the amount of contamination forwarded with the recovered silver. Part nothing but pure silver and the lifespan is endless. Part contaminated silver and it may not get through the first attempt. No one can predict how much electrolyte will yield, as they have no way of knowing the purity of the anode.
For what it's worth, here's some of my thoughts.
My experience indicated that when my cell started growing long hairy deposits of silver (much like steel wool), it quickly started co-depositing copper. I would use the last silver recovered for making the electrolyte for the succeeding session. If it came out discolored (a hint of green), that was a sign of co-deposition. It was then tested to determine if the contamination was palladium or copper.
Silver nitrate solution that has not been heated to a slow boil will often contain traces of nitrous oxide. That, in and of itself will give the solution a tint towards green. That was a common occurrence for me when I made electrolyte. I expect it does no harm, but it masks the true color of the electrolyte, which, for me, was the only method at hand for proving the purity of the silver I was refining.
For my electrolyte, I dissolved 30 troy ounces of silver crystal in a liter of 68% nitric, diluted with a liter of distilled water. The resulting solution would readily crystalize upon cooling, so it was further diluted with water when the silver was fully dissolved. The silver nitrate solution was diluted to about 2½ gallons when introduced to the cell. With this amount of electrolyte I could part an anode of roughly 175 troy ounces. Each anode was different, so the yield from batch to batch varied, as some were contaminated heavily with palladium. All contained some copper. Palladium will co-deposit, just as copper does, assuming it's concentrated high enough in the anode. While I did no study of the problem, I am of the opinion that palladium co-deposits because it creates isolation at the anode, to the point where silver can no longer be transferred. At that point, palladium is. So long as the slimes aren't hard enough to require scraping to be removed, that shouldn't be a problem. I suffered that problem only once, and had to re-refine a couple hundred ounces.
I brought my electrolyte to a boil (covered with a watch glass) after dissolution. I learned, from repetitively making the electrolyte, that I consumed all of the nitric by doing so. It was common for a few bits of silver to remain, undissolved, verifying that all nitric had been consumed. When the electrolyte was introduced to the cell, I added several drops of nitric acid. By doing so, I ensured that the pH was 1, or slightly lower.
Harold
