Measuring gold precipitation

[KatrienA]

Dear sir/madam,

I would like to ask a question. If I am precipitating gold with Sodium Metabisulfite is there a possibility of measering the reaction. For example the redoxreaction with an electrode or something like this. I do not know if this question sounds logic

Thank you in advance,
Kind regards,

Katrien Achten

 

[lazersteve]

Stannous chloride solution will allow you to sample the solution to determine when all of the gold has been precipitated. The test is based upon the color change of the sample when the test solution is applied. The intensity of the color of the test can be an indication of gold concentration in the solution.

Steve

 

[philddreamer]

Hi Katrien!

If your question is, how much SMB is needed to precipitate all your gold in solution, then you need to add 1 gram SMB for 1gram of gold. In other words, for example: you expect 10 grams of gold, add 10 grams of SMB. A 1:1 ratio. (I always add a bit more.)
If you don't know how much gold is in solution, then add SMB in increments; let sit for 10 minutes; check with stannous Cl. If positive for gold, add another increment of SMB. Do this until negative test. Add up the amounts added of SMB, and that should give you an idea of how much gold you precipitated.

I hope I understood your question right.

Kindly,

Phil

 

[KatrienA]

Thank you for your reactions! I will look into the action of the chloride solution.
In my experience, if I want to recover pure gold, there is a point where my pureness of my gold declines. I want to stop adding SMB when I am at my highest pureness. My question is: can I measure this during the reaction, so that I can see when I am at this point?
I want to stop at this point and begin a second round of precipitating with the rest of the solution. Do you know what I mean?

Kind regards,

Katrien

 

[philddreamer]

I understand now what you mean.
My expirience with achieving pure gold is that the purity is based on how well you rinse the gold powder, not the stage of precipitation. So, precipitate ALL the gold. Rinse. Re-dissolve your gold & rinse again. I garantee you'll have .999+ gold as a result.

What is the source of your gold & how do you separate the gold from the base metals?

Phil

P.S.
Rinsing steps recommended at GRF:
1. Let the gold powder settle to the bottom of the beaker over night.
2. Siphon or gently pour off the used SMB solution into an old milk jug labelled Used SMB. Save in your stock pot or properly dispose of.
3. The gold powder stays in the same beaker you precipitated it in.
4. Add just enough water to cover the gold powder and boil for 5 minutes.
5. Let settle and pour or siphon off the water into the stock pot.
6. Repeat three times.
7. Add just enough muriatic acid to cover the gold powder.
8. Boil for 5 minutes and pour or siphon off into the stock pot after testing with stannous. If gold is present keep in separate beaker to precipitate later.
9. Repeat until the acid is no longer discoloured by the process.
10. Repeat the water rinse as above.
11. If you suspect silver is present as a contamination, repeat the process with hot 3% household ammonium hydroxide (unscented- clear). Put these rinses in a separate container and add muriatic acid until no more white silver chloride precipitates. You have added enough HCl when there are no more white fumes coming out of the liquid. (Any karat, dental, CPU lid, or gold filled scrap will have silver as a contaminate.)
12. Finish up the rinses with three more hot water rinses. Put these rinses in with the ammonium hydroxide rinses.
13. Gently heat the beaker containing the gold powder while swirling the beaker. As the gold dries it will begin to clump and move around the beaker freely. Don't allow the gold to stick to the beaker.
14. When the gold is 100% dry it should be a nice light tan color, if not re-dissolve it and precipitate again with SMB. Repeating the above cleaning process after precipitation. Good clean gold settles very quickly when precipitated and clumps into nice balls when dried. No gold should be stuck to the beaker when you are done.
15. When completed transfer the gold to a properly prepared melting dish and melt into a button. per LazerSteve

 

[glondor]

From what I understand from Harold's tutorials, The first to drop is the cleanest gold. Perhaps you could develop a time method. Do your SMB routine and decant after a few minutes when the "first and fastest" gold drops and decant the "slow and dirty" the next day. Just a thought. Escrap always results in dirty gold.

 

[Harold_V]

It is my opinion that all gold should be precipitated, regardless of how clean or dirty it may be. The time saved in tap dancing around precipitated gold that has dragged down gold chloride, as well as other contaminants, makes the idea of partial precipitation not very attractive.

Once down, a proper washing, then re-dissolution will yield exceptional results, assuming one uses good hygiene and practice. Why complicate a process that has been used successfully?

Harold