Need help with black powder from cell

[mocodos]

Hello at all,

i need yor help:

after first run on my sulfuric cell, i want to test te black powder.

After washing with hcl an wather, next step was a AR disolving step.

After disolving in hot AR, 2 hours later i added UREA and after SMB.

Now, ist strange: there are some crystals on the gound with some brown powder.

But the stannous chloride test shows brown. First was dark brown color.

Which was my mistake?
How can i save this?

Thanks for comments.

mocodos

 

[lazersteve]

Mistake number one was using urea in my opinion. That's also likely the source of your crystals. They should dissolve in water. Urea is an added expense that is easy to avoid. Use controlled amount of reagents when dissolving your values. Get in the habit of knowing your scrap (keep logs of yields) and doing the math as to how much of each reagent (eg: Nitric acid) you will need before you do any reaction.

The simple step of doing the math will give you insight on what is too much verses what are the right amounts of chemicals to use. Armed with this information you can accurately add the reagents in controlled doses to dissolve your material.

If the solution is still positive evaporate it down to 1/3 of it's volume or until salts form, rehydrate with HCl and repeat two more times.

After the third cycle dilute to three times it's volume with water, filter free of particulate *, and add dry SMB with lots of stirring. Your gold should precipitate then.

Welcome to the forum,

Steve

*=edit

 

[mocodos]

Hello Steve,

thanks for advice.
i will try it today, and send some pics of the procedure.

Greetings

mocodos

 

[mocodos]

Hello all,

now i can post the results:

I think the are some looses of gold from evaporating of the hcl and after the water? Is that right?

After adding dry SMB the stannous chloride test shows little brown/orange color?
Palladium = Is it possible with the cell?

Thanks for helping Steve and best regards

mocodos

 

[lazersteve]

If the color on the swab darkens to blue-green suspect Pd, it is possible with the cell. DMG is the definitive test for Pd.

If the color stays orange/brown I suspect traces of gold and/or a false positive. Excess SMB in acid solution forms Sulfurous acid. When stannous chloride is added the sulfurous acid solution can form H2S and/or Sodium Sulfide both of which are non-selective reducing agents that can lead to dark colors and are the source of the false positives.

There is a document on my website about sulfurous acid that may help to make this more clear.

If you want to be certain you are not tossing any values, boil the sulfurous solution to drive off the SO2 gas and retest. If you still get positive results pursue them further.

Steve