Issue in gold precipitation

[alpnilam]

Dear friends
I have the powder scrap containing gold, silver, copper & zinc and the task is to refine gold & silver out of it.
I have tried as per the process read in this forum but I am not getting a gold precipitate. I followed the process given below correct me if I was mistaken.

the 100gm powder was taken in glass bottle + 78 ml nitric acid, hold 10 min - it gives red fumes + 312 ml HCl (1:4 ratio by volume) aggressive reaction gives a green foam
Hold overnight which gives dark green colour+ filtered the green solution + heated at 100c to remove nitric oxide + 20 ml green solution was transferred to test tube and SMB was added- brown colour reaction observed at point of addition and clears at the end I get white precipitate instead of brown gold precipitate and solution became light green

I don't understand what happened to gold it was expected 150mg out of solution.

As I understood white ppt was maybe CuCl2 than how to get rid of copper issue

Thanks in advance

 

[everydayisalesson]

Sounds like your gold is redissolving. Need to neutralize your nitric. You can use sulfamic acid or urea to do this. Search those 2 terms and read up on them, also a few videos out there if you look for them. Hope this helps.

Mike

 

[Yggdrasil]

Hi Alpnilam!
You have used way to much nitric. But you are in luck, Kadriver aka Sreetips posted this today.
Watch and learn

https://youtu.be/PNMkR-opWvI

So you need to get rid of the excess nitic with evaporation, sulfamic or such.

 

[FrugalRefiner]

I have powder of scrap containing gold, silver,copper & zinc and task is to refine gold & silver out of it.
I have tried as per the process read in this forum but I am not getting gold precipitate. I followed below process correct me if I mistaken.
100gm powder was taken in glass bottle + 78 ml nitric acid, hold 10 min - it gives red fumes + 312 ml HCl (1:4 ration by volume) aggressive reaction gives green foam

I may not understand what you've done, but your process as you described it isn't quite right. I would have just started with a nitric acid leach. I would have added perhaps 50 ml. of distilled water and 50 ml. of nitric acid. I would have heated this and allowed it to work for a while. The nitric acid will dissolve the silver, copper and zinc, leaving the gold undissolved. When the reaction stops, I would add a bit more nitric to see if there was any further reaction. If there is, add small amounts of nitric and allow it to react, then test again. When there is no more reaction, I would decant the solution leaving any powder behind. The remaining powder should be fairly pure gold.

The silver can be recovered by cementing with copper, or dropped as silver chloride (AgCl) by adding HCl or salt (NaCl).

The gold can be digested by covering it with HCl and adding tiny amounts of nitric till it dissolves. Then drop it with SMB, copperas, etc.

By dissolving the base metals and removing them before you dissolve the gold, the gold will be much cleaner when you dissolve it and drop it.

I don't understand what happen to gold it was expected 150mg out of solution.

150 mg of gold isn't much. It can be difficult to see.

You didn't mention testing at any point with stannous chloride. Without testing, you can never be sure if you have gold in solution, or if you have completely precipitated it after it has been dissolved.

Dave

 

[alpnilam]

Hii Dave,

thanks for the information

no, I didn't test with stannous chloride as it was not available with me

I have one more query how to deal with presence copper II chloride(white precipitate), should I filter the precipitate and again try the solution with SMB for precipitation of gold?

 

[FrugalRefiner]

no, I didn't test with stannous chloride as it was not available with me

Stannous is available to everyone. You can make it by dissolving some tin bearing solder in HCl.

I have one more query how to deal with presence copper II chloride(white precipitate), should I filter the precipitate and again try the solution with SMB for precipitation of gold?

I can't answer that question since we don't know if you have any gold in your solution. Make some stannous and test it.

If the white precipitate is a copper salt, it would be copper(I) chloride (CuCl), not copper(II) chloride (CuCl₂).

Dave

 

[goldsilverpro]

Dave has summed up a correct method (first leaching in nitric acid) for working your material.

I don't think that excess nitric acid was your problem. I think it was that you had an extreme amount of base metals and silver relative to the amount of gold (667 to 1). This can cause all sorts of problems in the final collection of the gold, as you have seen - i.e., other materials precipitating with the gold; loss of gold; dirty gold; etc. With all of that contamination, that tiny amount of gold can get lost in the shuffle and, even if you were able to collect all the gold, it would be terribly contaminated and would require a 2nd refining. If possible, it is most always best to eliminate the non-gold metals before dissolving the gold. Even with karat gold, which, in the US, averages out about 50% gold, it is more trouble free to inquart and dissolve out the silver and base metals with nitric before dissolving the gold with aqua regia. As Dave also said, the silver can easily be recovered from the nitric solution with by cementation with copper.

Were it me, I wouldn't waste time worrying about the $6 worth of gold in your solution because, if you do things right in the future, you won't have this problem again.

I might mention that, unless you are paying next to nothing for the nitric or, if the silver content is quite high, you will have a problem profiting from this method with such a small amount of gold.

 

[alpnilam]

Thanks Goldsilver pro

I discarded the privious solution considering wrong process, yes you are right this contain less gold and much base metal.
in second try I came to know that it also contain some iron and artificial stone. by rading C.M. Hoke's book I understand that iron can be removed by magnet and process with HCL treatment. any advide to remove artificial stone?
As this scarp I get from market claiming have 0.15% gold, this mixter is unknown to me and making new trouble with every try
Does stannun chlorie test give positive with low concentration (about 0.1%) gold containing solution?

If anyone have similar excpirience -pls guide