Any time I can, my choice is to cement the silver from the silver nitrate solution with copper metal.
In Ideal conditions I prefer a thick solid piece of copper electrical buss bar, I also like the ones which are silver plated, so I can also recover that tiny bit of silver.
There are times where I may use other copper items, much depends on what process the silver is recovered from and how large the batch...
Some copper things I have used to replace the silver in solution:
Cathode copper, which comes from recovery of silver from silver brazed copper and silver-plated copper, in copper electro-winning copper sulfate cell project
Copper powder, usually at the beginning of the cementing process, and switching to thick solid copper to finish up the reaction, this copper powder is a byproduct of other recovery processes.
Very fine copper wire (finer than human hair) from small transformers, this fine wire after incineration and washing is similar to the powder only finer, and is used like the powder at the beginning to consume the fine copper completely before finishing up with a larger buss bar of copper.
With powder or finer pieces of copper, I only use it in the beginning of the reaction, and make sure all of the fine copper dissolves before all of the silver is cemented out of solution, crushing any clumps and good stirring are important to make sure you do not have bits of copper metal mixed with silver metal cemented powders, (slight excess of free nitric is also helpful) before all of the silver is finished cementing and adding the buss bar to complete the process.
When using just the thick buss bar you will not have to worry about bits of copper mixed with your silver metal you cemented out.
Clean copper plumbing pipe, 1 1/2" to 3" diameter about 6" long split lengthwise (use hack saw or large tin snips), and hammered out flat, lightly sanded, or cleaned with a wire brush (heating with a torch and rinsed off with water just prior to use. Sometimes you will want to cut this slab of copper again to better fit vessels using large tin snips, the larger diameter pipe is easier to cut and open up flat, and is thicker than small pipe would be, the horn of an anvil and a hammer makes easy work of unrolling the copper pipe. I do not like the idea of just smashing the copper smaller piece of pipe flat, although it will work.
Copper electrical wire, grounding-bonding wire in larger diameter, or sometimes even 10AWG for cementing small batches.
Copper arms from contactors or breakers, many times these will have some silver or silver plating, I only use the larger heavier pieces.
Silver-plated copper dinnerware (if using this be sure its copper and not brass or a white metal)...
1 gram of copper will cement 3.4 grams of silver, I am guessing I could sell my scrap copper at about $2.50 per pound (453.5g), silver around $20.00 per troy ounce (31g), so if I cemented 3.4g of silver for every gram of copper in that pound of copper worth $2.50, I could cement 1541.7 grams of silver, or about 49.7 troy ounces of silver.
So I could sell my scrap copper for $2.5o, or cement silver with it and get about $994.7 worth of silver (darn I wish I had that much silver nitrate, I would be out there dissolving a copper buss bar right now).
Now, if you over used your nitric acid, or did not completely consume the acid, you would use more copper than needed, reacting the free nitric acid (in your silver nitrate) just to dissolve copper into solution instead of cementing silver, nitric is not cheap or easy for me to get, so I am careful of with my use of HNO3, whether I buy it or distill my own.
About 1.2ml of 70% HNO3 diluted with equal volumes of water will dissolve a gram of silver, and it takes about 3.4 times this much nitric to dissolve a gram of copper.
To state this backwards a gram of copper would consume about 4.15ml of excess HNO3 in your silver nitrate solution, so if you do not get too carried away with your use of nitric acid when putting the silver into solution, and use heat to be more wise with its use, it would not take much copper at all above the needed amount to cement your silver, although we do want to be sure the solution is slightly acidic when we cement silver, we do not need large amounts of free nitric in the silver nitrate solution.
If silver nitrate is too concentrated, especially with more copper nitrate already in solution the cementing process is more slow or difficult, than when solutions are more dilute.
The copper nitrate by product I can use in many different recovery operations, or convert it to another form of copper salts for use, and actually I will eventually get my pound of copper metal back, so the that buss bar (or the tiny portion of it that dissolved, I do not have enough silver to dissolve the whole 1# bar) was not wasted in the process of cementing silver.
I actually hate dealing with silver chloride, I am not that fond of the conversion methods, But I do seem to find myself with silver chloride much more often than I would like, mostly from recovery processes where I cannot use, or do not want to waste my nitric acid, I not only feel dealing with silver chloride is troublesome, and easier to loose silver in the processes, more trouble melting back to silver,
I do not get excited at the reaction of making silver chloride, or converting it.
Cementing silver with copper is always just plain exciting to me, and melting silver metal from the silver cement is another pleasure.
I am very tired, rambling again
Edited, (after a few hours of sleep), I meant to say silver nitrate where I said chloride, The ratio numbers (I am not good at remembering) and have made notes, these numbers do vary a little, but the Numbers I got from GSP have served me very well.
Actually when it comes to numbers, silver, and learning to recover or refine precious metals, GSP's posts have been, and are still invaluable to the success of the forum and to the members here who wished to learn this art.
I recommend reading GSP's posts, his well written book, all of the information he has provided, and his equations (many of which I still cannot compute).
The forum and its members, owe Chris (Gold Silver Pro) a giant Thank-You, for our success and education.
