Completely evaporated Nitric

[warrendya]

Does complete evaporation ensure the nitric acid has been killed?

I have some pins that have been a complete bear to dissolve. Two weeks in AP didn't even touch them. I rinsed them and tried 50/50 poor man's nitric and water and that is slowly dissolving the base metals. I have the beaker outside firstly to keep the vapors out of the garage and secondly so the hot Mojave sun can speed the reaction. Anyway, I left them out one day too long and all of the liquid evaporated, leaving what I presume are nice blue copper nitrate crystals. Rinsing with water dissolved the crystals, leaving a blue solution over the remaing pins and a grey powder which I believe is metastannic tin (a sample of the grey powder instantly dissolved in HCL).

So, my thought was this would be a great time to add some HCL to the main solution to get rid of that troublesome grey powder. But I wouldn't want to accidentally make some AR and dissolve some foils. I follow the logic of repeatedly boiling down AR syrup and adding HCL to drive off the nitric, my question is whether this is still required after the Nitric was completely evaporated?

Thanks, Dan

 

[Harold_V]

I follow the logic of repeatedly boiling down AR syrup and adding HCL to drive off the nitric, my question is whether this is still required after the Nitric was completely evaporated?

Thanks, Dan

Dan,

I am not familiar with the characteristics of poor man's nitric, but if you have any doubts, one of the things you can do to insure that you have killed the nitric is to incinerate the solids. If any remains, you'll see it go off as brown fumes when the solids are hot enough. I normally heated to a dull red heat, but less will work nicely.

You do have one other option. If a small amount of nitric remains, as well as base metals, the introduction of a little HCl will create AR, which will dissolve some of the remaining metal, but as the nitric is exhausted, assuming you still have some base metal left undissolved, it will precipitate the gold as fine powder, dark brown to black in color. Once that has occurred, you should be able to boil the lot with HCl to remove unwanted substances with reckless abandon! :lol:

When you have finished with the HCl wash, and wish to return to nitric to remove the balance of the copper alloy, you would be well advised to incinerate once again, or follow the same routine, allowing what little HCl that remains to form AR, which will dissolve more metal, with the resulting values that may get dissolved precipitated on the base metals once again. Be certain to check your solutions with stannous chloride that is known to be active before decanting and discarding any of your solutions.

Luck!

Harold

 

[Lino1406]

How many? gold is
0.5pct at most