Lose of gold, at the time of parting

[crauther]

Loss of gold, at the time of parting

Is there any chance for the gold to segregate from the cornet at the time of parting? Using 1.2 & 1.3 HNO[SUB]3[/SUB], Specific gravity (3:2 & 2:3, H[SUB]2[/SUB]O- HNO[SUB]3[/SUB]), and the parting time is fifteen minutes for each acid. Temperature of the hot plate is adjusted to 60[SUP]o[/SUP]C. After the parting, added NaCl to the 1.3 density acid, and the color of the solution got changed to yellow. Is this because of the gold, segregated from the cornet, that react with the halides and forming gold chloride solution. If yes, anybody could suggest a method to minimize the lose of the gold from the cornet, and to extract gold from the gold chloride solution. Should i need to keep, the parting acid, boil for entire 15 minutes or just below boiling.

 

[fireguy]

Is there any chance for the gold to segregate from the cornet at the time of parting? Using 1.2 & 1.3 HNO[SUB]3[/SUB], Specific gravity (3:2 & 2:3, H[SUB]2[/SUB]O- HNO[SUB]3[/SUB]), and the parting time is fifteen minutes for each acid. Temperature of the hot plate is adjusted to 60[SUP]o[/SUP]C. After the parting, added NaCl to the 1.3 density acid, and the color of the solution got changed to yellow. Is this because of the gold, segregated from the cornet, that react with the halides and forming gold chloride solution. If yes, anybody could suggest a method to minimize the lose of the gold from the cornet, and to extract gold from the gold chloride solution. Should i need to keep, the parting acid, boil for entire 15 minutes or just below boiling.

Is the reaction completed after 15 minutes? What is the purpose of adding the NaCl?

 

[crauther]

Is the reaction completed after 15 minutes? What is the purpose of adding the NaCl?[/QUOTE

Addition of NaCl : In order to check whether the gold is losing at the time of parting. Yellow AuCl will form when gold react with halides ( Cl, Br) (Ref: Inorganic chemistry Catherine E Housecroft and Alan G Sharp.) NaCl has no role in parting.

We just give fifteen minutes to first parting and another 15 minutes to second parting. During the first parting, within 6-7 minutes, the evolving brown fumes from the acid will cease, but we allow the acid to boil for 15 minutes, as our mandatory procedure. Being a rookie my knowledge in parting is very limited.

 

[fireguy]

Is the reaction completed after 15 minutes? What is the purpose of adding the NaCl?[/QUOTE

Addition of NaCl : In order to check whether the gold is losing at the time of parting. Yellow AuCl will form when gold react with halides ( Cl, Br) (Ref: Inorganic chemistry Catherine E Housecroft and Alan G Sharp.) NaCl has no role in parting.

We just give fifteen minutes to first parting and another 15 minutes to second parting. During the first parting, within 6-7 minutes, the evolving brown fumes from the acid will cease, but we allow the acid to boil for 15 minutes, as our mandatory procedure. Being a rookie my knowledge in parting is very limited.

Your industry may be different, but it is not typical to add the NaCl. I would recommend you follow more normal practices similar to the ASTM Bullion method:
http://www.astm.org/Standards/E1335.htm

The SMA methods committee worked extensively with ASTM on developing this method, and Volume 2 gives extensive and specific information on this:
www.lmine.com/product/9051x.html

 

[wotavidone]

Is the reaction completed after 15 minutes? What is the purpose of adding the NaCl?[/QUOTE

NaCl has no role in parting.

New member here reading through old threads for fun.
Pardon me for asking the obvious, but are you adding the NaCl while the cornet is still in the parting vessel?
Adding NaCl, giving you free chloride ion, to nitric acid effectively results in aqua regia (sort of - the proportions aren't the same, obviously). So, if you haven't decanted this solution off the gold, you will dissolve some of the gold by adding the NaCl.
Regards,
Mick

PS, if you do have some solution with gold chloride in it, sprinkle in some zinc dust, the gold will be displaced from solution.

 

[Auassayer]

I agree with Mark, 15 minutes is not long enough to part the coronet. Your loss of gold is either a bit of chlorine in your water, or you "saw-toothed" the coronet.

You should allow the coronets to part for 45 minutes for each stage. I tell my assayers, minimum 45 minutes and a 20-25% loss of solution. Second, if you are buying distilled or de-ionized water from a local supplier, then it is very possible that there is a bit of chlorine left in the solution, and will cause a gold loss. With the fast pace of todays gold labs, I very highly recommend you purchase a 4 stage water purification system yourself, or have one custom fit to your situation. Saw-toothing is the most common error Assayers make when assaying bullion. Saw-toothing is when you roll down the dore to form a coronet and do not anneal correctly while completing, the edges of the coronet may become jagged and when you part, small almost unseeable pieces of the gold sponge will break off and get washed away. I eliminated having my assayers make coronets years ago in favor of simple cleaning, heating and flattening with a hammer. I have seen significant improvements in quality doing this. In the old days, they only used to make coronets to speed up the parting process. Also you want to make sure your silver to gold ratio is 3:1 (in a pinch you can get away with 2.5:1) but I recommend staying right at the 3:1 ratio. As for the color of your solution after you precip the silver out, it is NOx.

 

[Auassayer]

Actually, most people do not even recover the silver anymore, it is simply placed in the facilitys benefication system.