I have tried to refine 18k gold to 24 k, I used Aqua Regia solution,
left the solution work over night, in morning gold pieces were covered in black, but did not dissolved.
That is what happens when the Silver content in the Gold is too high
I spoke to local jeweler and he told me that local gold has more than 15% of silver in it
and has to be quatered before refining with silver or copper, I have ask him if he can sale me silver to do so,
but he did not have any at that moment and suggested that I use copper, so I did.
It is completetely ok, to use Copper instead of Silver, but it the Copper needs a about 4es as much Nitric as Silver to dissolve.
Pieces which I quatered I submerged in solution of nitric acid/ distilled water 50:50 left it work for about 6 hrs.
It is beneficial to do this under almost boiling temperatures, and continue till there are no more reaction. Add more Nitric until there are no more reaction.
I think this was not completed, since you have blue in your end solution. Pour off all liquids and collect it in another container.
Wash the remains until the wash water is clear or almost clear.
than I have added hydrochloric acid in ratio 4:1 to nitric acid and left it work again over night.
This is your first big mistake.
We do not premix the AR, add enough HCl to cover what you are dissolving, then add small increments of Nitric untill all is dissolved.
Adding more Nitric when the reaction stops, or more HCl if that do not work. This is best done hot, but not boiling, never boil Gold solution.
When all solids are dissolved, the liquid should be orange or slight greenish. Cool the solution with ice and dilute it with some water
Then filter it until crystal clear which here means you can read text through it.
In morning solution turn green and after few hrs. turn brown black and al gold/coper pieces were dissolved.
There should be no Copper left after the Nitric. I don't quite understand the brown black you are describing.
I waited few hrs till all chemical reaction stop and add bicarb soda to cleared the solution and added some urea,
solution did not cleared but turn dark blue,
I added more bicarb soda and urea and heated solution in boiling water until all chemical reactions have stopped.
Why did you add Sodium Bicarbonate?
And Urea is not used for refining here in this forum, it is not effective to destroy the Nitric and its salts completely
and sometimes can create explosive compounds. Preferably we use so little Nitric it don't need to be denoxed.
If we need to denox we use Sulfamic acid.
Yesterday I have drain excess white liquid and partly dehydrated solution, now I am left with blue mud.
Hard to say, but you may have added too much bicarb and created a hydroxide mud, I see no reason to increase the pH this time.
It can create a lot of confusion. Your mud can be undissolved salts of kinds too. Anyway, it should not be blue.
That means you did not dissolve all the copper in the Nitric step. By the way, what kind of Copper did you use?
Are you sure you did not use some kind of Bronze?
