Silver still in solution and precipitating with gold?

[Notorious]

@goldsilverpro:
Thank you for all your help up until now! Hope to see more in the future )
I'm busy testing all sorts of stuff. I will report back.

@qst42know:
You mean the "black pearls" that won't go into solution because of the AgCl barrier? It's about 30% Au after melting.
If you mean the Au that stays behind in the AgCl, i haven't processed my AgCl yet, but i'm guessing its 1 to 2 %.

 

[Notorious]

Thank you all for your great tips.

How i always get 9999 now:

1. Melt with KNO3 & borax (Na2B4O7.10H2O), create ingot, take sample
2. Remelt for granulation in water barrel
3. Put granulate in rotating reactor
4. Add 1 part HNO3 (60%), 4 parts HCL (34%). (Part: 0.7 liters per 1 kg of fine gold)
5. After no more NOx fumes occur add another part of HCL
6. After 2 hours when reaction is finished, add ice until solution is very cold.
7. pull all the AR with a vacuum through a double filter cloth 1.
8. Add some Ureum until no more NOx fumes develop.
9. pull all the AR with a vacuum through a double filter cloth 2.
10. Precipitate with food grade Na2S2O5.
11. Pull through double filter cloth 3.
12. Leach gold powder with hot distilled water for 30 minutes.
13. Leach gold powder with hot HNO3 60% for 30 minutes.
14. Leach gold powder with hot distilled water for 30 minutes.
15. Leach gold powder with hot NH4OH for 30 minutes.
16. Leach gold powder with hot distilled water for 30 minutes.
17. Melt the gold.

 

[Harold_V]

13. Leach gold powder with hot HNO3 60% for 30 minutes.

It's no secret that those that follow this advice are at risk of dissolving traces of their gold.
Reason?

You are washing gold that came from a chloride solution-----which is difficult to eliminate, even with a prolonged rinse.

Not suggesting, not for a moment, that your process doesn't work---just that it lends itself to problems.

Harold

 

[4metals]

Unless your source of gold is other than karat gold (and therefore you may have some odd metals in the mix) the main contributor to lowering your high purity is silver, which you address by keeping it cold before filtering, and with the ammonia leach. The other metal to be concerned with is copper. Copper comes down at the end of the reaction while the last bit of gold is dropping and comes down as cupric chloride if you over-add the bisulfate. I would replace the nitric leach for the reason Harold stated above, and replace it with a HCl leach, which will dissolve any cupric chloride.

From your process description, mechanical not chemical, are you using a refining machine to process your material?

Also step # 9 after adding Urea, is un-necessary, the urea dissolves completely and you should not have anything on the filter paper if you do filter it.

 

[Notorious]

According to my tests Cu doesn't easily dissolve in HCL, i haven't tried dissolving an isolated sample of CuCl2, i will asap.

I know leaching with HNO3 could be problematic that's why I made it so that the hot distilled water "rotates". It get's filtered and re-demineralised about every minute for 30 minutes on end.

step # 9 after adding Urea, is un-necessary, the urea dissolves completely

According to my tests there is the possibility of some precipitate, i guess Urea nitrate.

Are you using a refining machine to process your material?

Yes, i'am, Italian c**p, there's not much left of the original parts, i hope, in a couple of years, i'll have some budget to buy a custom one build to my specifications.

 

[Notorious]

I received an analytic grade sample of CuCl2.2H2O. I was unable to source an anhydrous sample.

It dissolved in all my tests, HNO3 70%, HNO3 22 Baumé, HNO3 32 Baumé, HCL 32%, NH4OH 24.5%.
They all dissolved the CuCl2.2H2O within 5 minutes at room temperature, NH4OH was the fastest.

Anyone knows if the dihydrate sample is reference worthy to the CuCl2 precipitating with the Au?

Thanks for all the help so far!

 

[Palladium]

You are correct copper metal is not dissolved to any extent with hcl, but copper oxide will. You need an oxidizer to oxidize the surface so the hcl can adsorb it. This can come from oxygen in the air or the solution. It can come from adding H2O2 also. If you’re trying to clean up your gold after the drop it should not have any copper present in the metallic form. Copper chloride will be the contaminate. If that’s the case then a wash in warm hcl will remove it. Once the gold is dropped nitric washes are not recommended.


Harold’s washing method:

First wash should be in boiling HCL and tap water. Boil for a prolonged period of time. Take up the solution with tap water, decant after the gold has settled, then rinse with tap water, which should again be brought to a boil. After it has boiled for a period of time, add more tap water to cool the lot, then decant as before. Rinse again, and do it until the wash water comes off clear. Next, wash the gold with ammonium hydroxide and tap water. Heat it until it boils. You'll notice that the solution gets discoloured. How much is determined by how dirty your gold was when you started. The ammonia evaporates fairly quickly, so you can't boil very long. Add tap water to cool, decant, and follow up with a tap water rinse, again, boiling the water. Add tap water to cool, and then decant. You now repeat the HCL and tap water wash. You'll be amazed that suddenly more contaminants will come off. Boil well, add water to cool, decant, repeat the water rinse, decant, then, and this is important-------start the refining process all over again by dissolving the well washed gold powder in aqua regia. I'll talk about that in a minute, but these are indicators you should have observed along the way, aside from the fact that you could see contaminants being washed from your gold powder.