Nitric turned to brown color

[autumnwillow]

Not really sure why nitric became brownish in color, silver is clear, copper is bluish, nickel is greenish, brownish is?
The processed lot was bench sweeps.

Pyrolized, incinerated then digested in nitric.

It was kind of sludgy.
I think this happens when the gold or lot being processed is too fine.

If I went for direct AR would it also be a mess?

This is only my 2nd attempt processing bench sweeps without smelting involved. I usually pyrolize, incinerate, smelt then inquart. I decided to process this lot without inquarting due to the absence of large pieces.

 

[danieldavies]

it looks like there is palladium in solution. try stannous chloride test.

 

[autumnwillow]

Update on this.
Stannous test on nitrate solution is negative and I do not think stannous is used to check for palladium, it should be DMG.
Proceeded with AR. Stannous test in AR is positive for gold.

On the brownish nitrate solution, I took about 40ml sample and used copper to cement. After about 30 mins it probably precipitated silver and the solution turned to the familiar green color.

The metals present in the lot should only be iridium, tin, zinc, nickel, magnesium, silica, manganese, germanium, gold, silver, copper, iron and indium. I do not know which one of these elements made the nitrate solution brownish.

I'm still not sure what is happening, but I'll proceed with finishing the refining even if there are complications already so as board members who experience same may follow the same method.

Next is filtering, precipitation, washing then probably re-refine if the washed powder is not clean.

 

[danieldavies]

stannous chloride can be used to test for palladium in solution. DMG can also be used, but it is a more expensive.

 

[Topher_osAUrus]

Only problem using stannous to check for palladium, in this case anyway, is the nitrate will keep oxidizing the sample result, and may give a false negative.

 

[Lino1406]

Iron +[O] = Fe2O3 (brown)

 

[autumnwillow]

All went well.
Except that, it was hard to filter, AR solution was green with soapy bubble, it was still green after precipitation of gold and there were lots of gold that were too fine.
Melted gold needs to be re-refined.