After some nitric acid baths i have a dense brown precipitate, what is this? (Images attached)

[Ellias]

Hello everyone!

I am processing around 500 grams of PROMs for fun. The process i took was the following:

1. Incinerated until white

2. Grind with mortar and pestle

3. Strain the powder

4. Grind strained substances

5. Incinerated again

6. HCl bath for 2 days

7. Cleaned and washed around 15 times with boiling water and hot water

8. 2nd round of HCl bath under heat for 4 hours (light boil)

9. Washed 15-20 times and made REALLY SURE to clear any residual ash and HCl (HOT water/Boiling water and some very deep spatula stirring)

10. Put in a nitric acid bath and now i am here. And my head is a bit puzzled.

[THIS IS WHERE I STOPPED]

I started the nitric with 50/50 nitric water but had to add a bit more water as the reaction almost got too reactive, too fast

Left reaction on heat for 4 hours. However right now my powder at the bottom slowly turned into a dark brown color (near the beginning prior to Nitric, I saw my line of gold and some black powder on top at first)

My question is - what the heck is this?

And should i give it a shot of nitric acid to clear it up and return it to a more blue color?

I am wondering if this is due to remaining iron in my solution and adding more water turned it to rust or if it was something else. Please let me know what this dark brown substance is (if not rust).

I am going to wait a whole night before decanting and trying to recover silver but please let me in on some insights/solutions or what ive done wrong.

 

[Ellias]

@Shark @Yggdrasil hoping to pike you guys about this one.

 

[BGDOCK]

Do you mind if I ask
Did you use a magnet to seperate any ferrous material ?
Could be some iron hydroxide
Draw a couple of samples off , of that brown compound and add some distilled water ,apply gentle heat see what happens first then add some nitric see what happens to that brown compound ,
Might have to drain the green solution off to attack the brown material
You got this, have patience

 

[Shark]

Stannous test the solution. Always stannous test.

There is a lot of copper in the solution for all the HCl soaking. Did you magnetically remove any material before hand, especially before using nitric? Iron in nitric will often produce iron oxide (I think the oxide is right) basically plain old rust in a very fine state. Filtering can be a nightmare. If this is the case, I would ...
Stannous test. If positive, either drop it or decant and drop separately. Then follow the procedure outlined next...

If negative.

Decant the solution off, and go to AR. Filter, as often as needed to get the solution clear of debris. Drop it, and then move to cleaning the gold.

My first time doing IC's went really well. The second time was nearly a disaster. I spent days trying to find all the missing gold and about week later I finally got most of it back. It sure made me glad I had a stockpot in use.

Looking forward to others opions on how they would proceed.

 

[Yggdrasil]

@Shark @Yggdrasil hoping to pike you guys about this one.

As Bgdock asks, did you separate out the magnetic parts?
If not, the brown will most certainly be Iron in various states.

 

[Ellias]

Stannous test the solution. Always stannous test.

There is a lot of copper in the solution for all the HCl soaking. Did you magnetically remove any material before hand, especially before using nitric? Iron in nitric will often produce iron oxide (I think the oxide is right) basically plain old rust in a very fine state. Filtering can be a nightmare. If this is the case, I would ...
Stannous test. If positive, either drop it or decant and drop separately. Then follow the procedure outlined next...

If negative.

Decant the solution off, and go to AR. Filter, as often as needed to get the solution clear of debris. Drop it, and then move to cleaning the gold.

My first time doing IC's went really well. The second time was nearly a disaster. I spent days trying to find all the missing gold and about week later I finally got most of it back. It sure made me glad I had a stockpot in use.

Looking forward to others opions on how they would proceed.

This worked out! I did not separate the metallic parts. Thank you so much