Gold nugget Tarnished

[valicek]

Hi all, I'm hoping to get some advice on how to correct a reaction that happened while I was trying to clean a nugget. I put the nugget in nitric acid but now half of it is black. I think there may have been residual hydrochloric acid in the jar that may have mucked it up. Any help would be great because it's a nice nugget and I'd hate to have to aqua regia it
Cheers

 

[valicek]

Cleaner side

 

[valicek]

Black side

 

[Lino1406]

If hydrochloric acid is present, then it is gold precipitate over a reducer, most probably iron compound. If you boil it in hydrochloric acid (after water rinse) it may remove the iron as well as other minerals shown

 

[valicek]

Thanks for your reply Lino, I will give it a try later and let you know the result.

 

[valicek]

Fantastic Lino, it is working. It's been boiling for 2.5 hours now In hydrochloric acid after boiling in water. It's about 80% done now. I assume I keep boiling until nugget boils no more? Thanks so much for your knowledge PS I'll take photos of finished product tomorrow

 

[Lino1406]

Take care not to lose brown powder which may get freed during boiling

 

[valicek]

Hi Lino, I've boiled in hydrochloric for about 4 hours but it hasn't quite got the gold colour on that darker side. Do I reboil until gone or is it time for something else? Much appreciate any input.

 

[valicek]

Showing clean/dull together

 

[Lino1406]

It is suspected as insoluble chloride, I'd test a piece with ammoniak or hot NaOH

 

[valicek]

Thanks for your reply Lino, so pure ammonia into a beaker and let it sit for how long approximately? I'm assuming I do not add heat as it's boiling point is -33 degrees. Thanks again

 

[Lino1406]

Ammonia solution in water is meant. If chloride is there (Pb, Ag) it should act immediately

 

[valicek]

Ok, I will buy some tomorrow and let you know what happens, thanks again

 

[kurtak]

NICE looking nugget :shock: 8) :G :!: :mrgreen:

How much does it weigh :?:

Looks like it is "about" 70 -80 % gold with 20 - 30 quartz :?:

Kurt

 

[valicek]

Hi Kurt, it weighs 23.8g. I haven't done specific gravity yet but will do and will post results.

 

[valicek]

It turns out I went with a hot caustic bath. Boiled in a strong +60% for an hour With no real difference. Any thoughts?

 

[valicek]

On closer inspection there is alot of new cavities and alot more sharp edges. So the hot caustic definitely did something but it has not taken off the dull look on one side. Any thoughts always appreciated

 

[valicek]

It's way more porous and it looks a bit rusty to the eye. Another water boil and hydrochloric
boil ?

 

[valicek]

Ok, now after water boil and then hydrochloric again I was inspecting the nugget and it broke into 3 main chunks and bit coming off. I guess the treatments has eaten away all of the structure that was holding the gold together. Anyway I'm gutted but not too bad. Still would like to make it glisten so any help is appreciated.
I did specific gravity and it's got 20.2g of gold in it.