# boiling off nitric acid



## leondavids (Nov 27, 2011)

Hi GREAT forum , i have been doing lots of reading and am taking slower steps now .After dissolving a watch casing in nitric acid all that remains is the gold foil .should i filter this and then put the foils into solution or boil off the nitric acid first before putting gold into solution.My idea being that i could boil the nitric solution to save time later as boiling the gold solution is not recommended.( filtering the solution once i have gold dissolved in aqua regia) and then evaporating the exess nitric acid out of the solution .Many thanks in advance!


----------



## martyn111 (Nov 27, 2011)

I would allow your solution to settle, decant the liquid off your foils, rinse using distilled water at least a couple of times (tap water could produce agcl if silver was in solution), dissolve your foils by whichever method you choose, precipitate and wash as per Harold's wash proceedure, re dissolve your gold, precipitate, wash, dry and melt.
If you were to boil off the nitric you would concentrate the contaminates rather than removing them.


----------



## qst42know (Nov 27, 2011)

Don't put the foils in a filter. Hot water washes and decanting to remove any color should be enough. The foils don't leave the vessel until it's time to dissolve, dilute, and filter.


----------



## Geo (Nov 27, 2011)

dont forget about a major step here.if you decide to use hcl/cl incinerate the material first.never go from a nitric solution to a hcl solution or hcl solution to a nitric solution without incinerating the material first.iheres no real problem with filtering the foils just dont throw your used filters away.they can be incinerated later to recover any values.if you filter it will go alot faster and just let the foils dry in the filter.after its dry the foils will be loose.


----------



## leondavids (Nov 27, 2011)

Thanks for the swift reply , i will attempt the distilled water wash and decant through a filter.
Geo , should i incinerate the foils before i dissolve them in aqua regia .Is this what you meant ?

Thank you once again.


----------



## qst42know (Nov 27, 2011)

Geo said:


> dont forget about a major step here.if you decide to use hcl/cl incinerate the material first.never go from a nitric solution to a hcl solution or hcl solution to a nitric solution without incinerating the material first.iheres no real problem with filtering the foils just dont throw your used filters away.they can be incinerated later to recover any values.if you filter it will go alot faster and just let the foils dry in the filter.after its dry the foils will be loose.



There is no reason to destroy residual oxidizers if the next step is to add oxidizers and dissolve. If you expect tin that's another story, then incineration is necessary.

I don't like using filters till I must, tying up fines in a filter is more trouble than rinsing a solution through.


----------



## Geo (Nov 27, 2011)

since aqua regia is a nitric acid compound there's no need to incinerate.if you have time and there's no rush rinses work fine though i have found that decanting rinses through a filter catches a small amount of foils that would otherwise be poured down the drain.i suppose it comes down to personal preferences as i don't mind tying up a small bit with the knowledge of a small amount of gold when i incinerate my filters (kind of like found money) :lol: my wife said that could be our Christmas fund for next year. 8)


----------



## qst42know (Nov 27, 2011)

Decanting through a filter can be a good safety measure to prevent losses.


----------



## Dr. Poe (Nov 28, 2011)

You should know that coffee filters are made with some barium carbonate. Barium salts decompose when sintered to barium peroxide. Both gold and platinum dissolve in strong alkalies when smelted with oxidizers. To avoid losing some gold to this phenomena, add carbon to your flux. Hydrogen peroxide is manufactured commercially by treating barium peroxide with diluted sulfuric acid. Barium sulfate precipitates to be used again and pure H2O2 is produced. The concentration of H2O2 is predetermined by the dilution of the sulfuric acid. Caution: concentrated H2O2 is explosive (Rocket fuel) ! Dr. Poe


----------



## leondavids (Nov 28, 2011)

Thanks for all the good info great forum , i will proceed with caution and will inform you of my results.
Thanks again.


----------

