"foggy" solution after precipitation, too much SO2 ?

[MicheleM]

Dear all

After gold precipitation from the yellow solution in with potassium meta-bisulfite (Image1 :left and center), the resulting solution (image1, right) appears slightly yellow with micro-bubbles of gas that make the solution non completely transparent. Maybe too much sulfite?
Image1:


I did a stannous test and the result is negative to gold and moreover without colors, nut i'm not sure that i can trust it because this time to produce SnCl2 i used 34% HCl and tin coming from solder wire (with 5 %or 10% of Pb. i do not remember exactly)

Any comment is welcome, thank you and have a good day!

 

[nickvc]

Just a guess but the cloud you can see could well be your gold precipitating from your solution, looking at your last photo that brown powder could well be your gold.

 

[MicheleM]

thank you nickvc for your kind reply,

Yes, the brown powder has a certain percentage of gold but it looks brown, dark brown, so maybe i should re-refine it.
I filtered the barren solution that is now crystal clear (yellowish color) , i see that the fine brown dust in that i collected in the filter is much harder to re-dissolve with HCl-Cl.
i am going to use less potassium metabisulfite in the next days
thank you again,

 

[Martijn]

To test if your stannous is still working and good, you can make a reference liquid that holds just enough gold to get a faint reaction with your Stannous Chloride.
Take a little bit of gold chloride before precipitating, and dilute until just weak enough to get a result.

The foggy liquid from the gold powder:leave it for another week or so until all is dropped.
Fine gold particles will not give a positive test, SnCl₂only shows gold in solution. There may be ultra fine particles floating around.

If gold particles do stay suspended, add a bit (20ml) of H2SO4 and boil. The particles will clean, clump together and fall to the bottom. > tip from Geo

How to clean 'Dirty" gold powder/ "Get pure shiny gold": https://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=325
It should be a nice light brown powder before melting.

Martijn.

 

[MicheleM]

Thank you Martijn,

after the filtration the liquid was crystal clear and it has no more particles or bubbles. i i am going to read the link in your comment before any further action.
have a good day!

 

[MicheleM]

Good morning everyone,

yes i think that i was right to not completely trust my previous stannous test:

i left a copper bar in the solution for 24 hours, then i filtered again the solution and i washed well the copper bar. i collected a very small amount of black powder then dissolved in HCl-Cl. As you can see in the figure below: left, the solution is clear with just a greenish color , right: the black powder dissolved in HCl-Cl
Figure:


i read carefully the standard washing procedure for gold powder, but this is the most difficult step for me because i have only one 100 ml boro-silicate glass item and not others heat-resistant glass containers. I will find a way to do it properly using my available tools.

Again thank you Martijn and Nickvc.
Have a good day!

 

[nickvc]

You can use Pyrex for heating but I would advise using a sand bath to spread the heat so the glass does not fracture or shatter, for cleaning up your powders that should suffice.

 

[MicheleM]

thank you nickvc,
the sand bath is a good idea, i am going to use it.

Have a good evening

 

[Martijn]

For the washing steps you just need to cover the powder with a bit of acid. A small beaker in a sand bath will do fine for a couple of grams of gold.

 

[MicheleM]

Thank you Martijn,
i am going to do a water-acid-water wash
as soon as the "sand-bath setup" will be ready,

Thank you very much guys i really appreciate the time that you spent to answer me

Have a good day/night!

 

[MicheleM]

Hello everyone,
i do not know exactly how very fine gold powder should appear, but looking to the colors from the picture below (i did the harold washing procedure, except for ammonium hydroxide) i guess that i am a little bit far from the right color, i would like to know your opinion,

thank you! have a nice day

 

[nickvc]

Looks pretty good to me 8)

 

[MicheleM]

Happy Easter and thank you again for your support,

maybe not the best result (i should improve my washing procedure and other minor details) but in the end i am very satisfied , 0.33 grams from 240 grams of pins (60 g,full plated, 180 grams not full plated) and foils from more or less the equivalent of 18 RAM sticks



Have a good day!