Method for Ultra High Purity Gold

[Lou]

You want to know why?

Why quartz?

Pure transparent quartz is usually metals free and comes in a high grade. It's leached with the acids you're working with before hand to remove any surface metal cations that may be present in the quartz. Most anions like chloride and sulfate are not problematic in the refining of gold because they are thermally labile (go off when the gold is melted) but they are to be avoided because they usually contain a base metal counter ion (the cation, a positive ion that is a oxidized metal species in this particular case). Trace metal acids are very pure acids that are very expensive (they have part-per-trillion levels of base metals). The conductivity water is used for the same reason--no conduction means no metal ions acting as electrolytes.


Who? It's a German procedure, I don't know who, but it's quite similar to that in Georg Brauer's collection but it must be a newer modification because the technology to analyze gold to that purity (which is practically at detection limits) didn't really exist til ICP-MS came into its own.

Sulfur dioxide by itself gives a high quality precipitate, but is prone to reduce copper (II) to copper (I) which we see as a white-gray chloride. Any silver is removed by the decantation procedure and by filtering. In this case, the gold is already very pure, so any copper that is inadvertently reduced will remain in the acidic solution as a chloro complex. Doing it over multiple times will ensure that all the copper is removed. Any palladium present will be a ''rider'' with the gold that comes down. To remove that, oxalic acid is used. The ammonia is used to adjust the pH to get complete precipitation.

 

[Chumbawamba]

Hey Lou.

I still can't say I understand all of it, but your explanatory paragraphs certainly help in bringing me closer. Thanks for taking the time.

 

[HAuCl4]

Ferro in page 10 of their BDG document claim 6N gold purity can be achieved with a certain oxalic acid mole concentration in the reduction phase. I don't know if that claim is true, but that may help cutting some corners and some costs to obtain UHP gold.

I'd love to read Lou's comments regarding that claim on page 10 of Ferro's document.

I imagine very specific extractants are also available for UHP Pt and Pd, and probably every other metal in the periodic table.

 

[BGT]

So I have gold precipitate from a gold drop using SMB (sodium meta bisulfite) 75 grams smb to a 500ml AU cloride filtered solution.

How do you get it to a dry powder after this? (steps to dry powder) Also, I have tried to torch the precipitate directly after it settles for 24 hours and while still wet and it just turns into black beads. (borax and argoflux were added) Should there not be any flux or borax in the melting dish? Which Step is missing?

Thanks.

 

[Harold_V]

How do you get it to a dry powder after this? (steps to dry powder) Also, I have tried to torch the precipitate directly after it settles for 24 hours and while still wet and it just turns into black beads. (borax and argoflux were added) Should there not be any flux or borax in the melting dish? Which Step is missing?

Thanks.

Read Hoke.
I saw no mention of any attempt to wash the recovered gold.
Why is that?

Harold

 

[lazersteve]

So I have gold precipitate from a gold drop using SMB (sodium meta bisulfite) 75 grams smb to a 500ml AU cloride filtered solution.

How do you get it to a dry powder after this? (steps to dry powder) Also, I have tried to torch the precipitate directly after it settles for 24 hours and while still wet and it just turns into black beads. (borax and argoflux were added) Should there not be any flux or borax in the melting dish? Which Step is missing?

Thanks.

Did you confirm you had gold in solution with stannous chloride befroe adding all that SMB?


That's a lot of SMB unless you had several ounces of gold in the 500mL. Copper I chloride will precipitate with SMB if a lot of copper is present in the solution when the SMB is added. Copper will turn black when the torch flame is removed.

It's likely you precipitated a combination of gold and copper I chloride, melted it and now have dirty gold beads. Try sanding the black coating off of one of the beads with an emery board to see if it has a golden core. If not, it may all be copper and or base metals.

Steve

Steve

 

[BGT]

I started using a separatory funnel with BDG. Tested with Stannous Chloride from beginning to end. Gold was there. Followed and separated 3 times with 32% hcl wash. Used oxalic in a magnetic stirrer for 5 hours at 85C. Placed contents in Buchner Funnel and got 3 filters worth of brown powder. Torched the powder/filter with a MAPP torch and got black rocks. Sanded the surface and saw shiny gold underneath, but it is so embedded within the rock like substance that my question is what is the best way to free it up again? Should I place the rocks in sulphuric? Should I AR it all over again?

Thanks.

Mark

 

[lazersteve]

The black is oxides from the base metals you pulled over from not following the proper process. Your HCl wash was way too strong and your pregnant solution was not diluted first.

Here's a step by step process that works for me:

** Process using BDG

Here's the general procedure:

1. Dilute the pregnant solution to 25% concentration (1 part solution to 3 parts water).
   
   • Filter/Settle & Siphon out any sediments that form.
2. Add a portion of the diluted pregnant solution to your clean funnel (500mL).
   
3. Add enough BDG to hold the expected gold in the pregnant solution (BDG holds ~50 gm/L max). 250 mL of BDG will can strip out 12.5 gm of gold maximum.
   
4. Stopper the funnel and vigorously shake for several minutes.
   
5. Let funnel sit to until the two layers completely separate. The top layer should not be cloudy. The patent mentions a centrifuge, this would speed the separation greatly.
   
6. Funnel off the lower layer into a separate glass vessel.
   
7. Repeat with each portion of the solution until all the solution has been processed using the same batch of BDG (Up to the 12.5 gm limit).
   
8. In a separate beaker mix a solution of HCl (Muriatic 31.5%= 10 Molar) with distilled water 20 parts water: 1 Part HCl.( 19 mL H2O per 1mL HCl). You will need a total of 3 times the amount of BDG you used of this diluted acid. If you used 250mL of BDG you need to mix up 750 mL of this rinse acid (712.5 mL H2O to 37.5 mL HCl). You will be running three rinses of equal volume to the BDG (250 mL). I only used one rinse when I did my experiments. The better you rinse the cleaner your gold. The patent states three to five rinses.
   
9. Add an amount of the diluted acid from the step above equal to the volume of BDG used to the funnel. If you used 250 mL BDG then add 250 mL of the diluted acid.
   
10. Stopper and shake vigorously for several minutes.
11. Let separate as before and drain off the acid wash into a separate vessel ( not the same one as before ).
    
12. Repeat steps 9-11 two more times. You can combine the rinses in the same vessel.
    
13. Dissolve 90 gm Oxalic acid per 100 mL of distilled H2O. Use the formula Lou has posted here to determine how much you will need. Place 250 mL (equal volume to BDG) of this solution in a 1L pyrex beaker with a magnetic stirring rod (not required). Put the beaker on a hotplate. Heat to 80C and turn on the stirrer (if available) to a very slow speed. Oxalic acid is hazardous READ THE MSDS!! Here is a link to some follow up on Oxalic acid use.
    
14. Carefully filter the BDG from the funnel into the 1L Pyrex beaker with the Oxalic acid warm.
    
15. Heat (with stirring) for 2-3 hours. The gold will drop as beautiful gold flakes or a fine brownish mud. The BDG will be clear when it is depleted of gold.
    
16. Filter the gold out and wash with full strength hot muriatic acid.
    
17. The gold should be 99.9%+.

The above is a method I formulated and tested from the BDC patent.

Steve

 

[BGT]

Thank you so much for the detailed BDG information! Already starting it right now.

Just a few quick questions. How do you rinse the filter paper with the hot muriatic acid? Do you leave the round filter paper in the buchner funnel with the brown powder sediment on the paper and pour in hot muriatic acid into the buchner funnel, wait for it to drain and then remove the filter paper out? After removing the filter out of the buchner funnel, Is it better to let the paper air dry or just torch it right away, or scrape off the powder from the filter when it is dry?

Mark

 

[lazersteve]

Mark,

You could do it the way you suggest or you can wash the gold into a beaker with a spray bottle and add the HCl then heat. Pour off the acid after the color of the acid no longer changes any darker.

Steve

 

[HAuCl4]

Thanks for posting the BDC detailed process Steve. Do you use the process regularly?. The drop is faster using ammonium oxalate in slightly acid solution and shaking it. I never did more than a few ounces at a time though. And have no idea how to scale it up. :roll:

 

[lazersteve]

I used the process quite a bit several years ago when I was learning how to properly use Dibutyl carbitol (BDG). Lately, I turned my attention to it again as a means of quick stripping gold plating when mixed with a selective solvent for gold. The real issue when using it like I'm trying to do now is that the gold has to be fully stripped from the parts without any water in the reaction for the reagents to be selective and extracted into the ethereal upper layer.

I'm still working on this process, so I will not disclose any details about the process until I have more experimental data on it's usefulness. It involves an easy to make reagent that looks to be easily recycled so it's well suited for use with BDG.

Once I have enough experimental evidence to back up my ideas for the selective stripper and a complete process, I will post more about it.

I have used potassium oxalate to reduce the gold from BDG as well as straight oxalic acid.

Steve

 

[HAuCl4]

Interesting Steve. Thanks. The DBC process felt lengthy and cumbersome to me. Almost prefer to dissolve twice, and precipitate once with SMB and once with oxalate, to obtain a very pure product but maybe not as good as with DBC. If it could be made simpler and faster, I'd like to learn about it.

 

[Lou]

Liquids to liquids.

http://www.chemglass.com/images_product_1/CG-1375-01.jpg

 

[HAuCl4]

Interesting gadget Lou!. 8)

 

[HAuCl4]

Is there some type of additive, like corn starch or egg white or something, that will help cleaning the AgCl faster than waiting for days to settle completely, before dropping the gold?. :?:

 

[BGT]

Is there a better way to torch the filter paper in the melting dish?

I am using a MAPP torch and treating the the dish with heat from the torch then sprinkling on some anhydrous borax on the melting dish then place the filter paper on the dish and then torch the paper. Is there anything that can be better within these steps. The residue gold is from a bdg/oxalic method so I have ultra pure going into the dish already.

Thanks,

Mark

 

[Barren Realms 007]

Is there a better way to torch the filter paper in the melting dish?

I am using a MAPP torch and treating the the dish with heat from the torch then sprinkling on some anhydrous borax on the melting dish then place the filter paper on the dish and then torch the paper. Is there anything that can be better within these steps. The residue gold is from a bdg/oxalic method so I have ultra pure going into the dish already.

Thanks,

Mark

Pour some alcohol on the filter paper and light it and let it burn and then tourch it.

 

[joem]

Is there some type of additive, like corn starch or egg white or something, that will help cleaning the AgCl faster than waiting for days to settle completely, before dropping the gold?. :?:

:shock:
I'm not eating an omlette at your house

 

[Harold_V]

Is there a better way to torch the filter paper in the melting dish?

I am using a MAPP torch and treating the the dish with heat from the torch then sprinkling on some anhydrous borax on the melting dish then place the filter paper on the dish and then torch the paper. Is there anything that can be better within these steps. The residue gold is from a bdg/oxalic method so I have ultra pure going into the dish already.

Thanks,

Mark

I'm at a loss to understand why you got the gold on or in a filter in the first place. That is an unneccessary operation that leads to problems. Problems about which you are asking for a solution.

What am I missing?

Harold