Dissolving silver

[ldanielrosa]

TL;DR

How dilute must it be to avoid destroying half the acid?

I'm making poor man's nitric acid to refine silver from scrap. I would like to waste as little as possible. I've noticed that about half the acid is destroyed oxidizing the metals, and I'd like to reduce that if possible. One reference mentioned that I lose only one in four in a "dilute solution" instead of half. How dilute must it be to allow the NO2 to disproportionate so that half of it will redissolve and become nitric acid again?

 

[oz93666]

Cold dilute acid will react to produce NO (reacts with oxygen to make NO2)
Hot concentrated will react to give NO2
NO2 will disolve in water SPARINGLY to produce a weak nitric acid ...
Probably safer to go with cold weak acid , catch the NO gas (clear) in a large container , add air to make it NO2 (brown) , add water and shake ... don't expect much yield.

 

[Borek]

This system is rather messy, there are several competing reactions occurring in parallel and difficult to control separately, although some of them prefer higher/lower temperatures, some occur easily in higher/lover concentrations. The only sure way of finding optimal point is experimental comparison of yields varying temp and concentration.

Quick googling found this patent: https://patents.google.com/patent/WO2017009667A1/en so you are definitely not the first one to think about optimizing the process.

 

[Mayhem]

Are you refining silver for purposes other than exploring science? Silver, unlikely gold, is actually fairly cheap and refining silver, even from scrap, does not offset the costs of whatever chemicals and tools you will need to achieve that.

That said, if you are doing it for fun, why are you trying to dissolve the silver instead of everything else? Plastics can be burnt (with proper safety measures and knowledge of local legislation) and sometimes dissolved in organic solcents. Metals less 'noble' than silver and copper will readily dissolve in HCl, which is typically available in hardware stores. Does produce hydrogen though, so be careful!

 

[ldanielrosa]

Thank you oz93666 and Borek. I see that minimizing losses will not be trivial.

Thank you Mayhem for your concern on the financial side, but I don't quite agree with your calculations. I am reasonable confident that it will be an order of magnitude less expensive for me to isolate my own silver from the scrap I have on hand.

That said, I appreciate having other minds to benefit from on this. Thank you all for your time.

 

[tech99]

Also just to mention that silver compounds should not be put into the drainage system as it is very toxic to plants and animals.