Sometimes it is brown, sometimes it is black ...

[Renaldas]

Precipitating gold from AR solution with SMB, usually I get fine brown gold powder. But sometimes my precipitate seems almost black, or very dark brown. Can you tell me, why does this happen?

 

[jimdoc]

I think you will have to give more info,like what went into your AR solution to get a good answer.

Jim

 

[goldenchild]

Generally, the reason for a darker precipitation is a dirty AR solution aka drag down. Filtration is very important after digesting all your values. It could be the difference between needing to refine your gold once or twice. Did you remove all the base metals before going to AR or did you go straight to AR?

 

[Renaldas]

I think you will have to give more info,like what went into your AR solution to get a good answer.

Jim

This happens quite often, last time it happened today, processing 10 Pentium Pro's.

 

[Renaldas]

Generally, the reason for a darker precipitation is a dirty AR solution aka drag down. Filtration is very important after digesting all your values. It could be the difference between needing to refine your gold once or twice. Did you remove all the base metals before going to AR or did you go straight to AR?

No, i was processing without previously removing base metals. I precipitated the gold, tested with SnCl2, it shows, that there was a little amount of gold remaining. I poured the solution to second bottle and add a little SMB again. Gold in first bottle was fine brown, in the second bottle it was almost black.
There are some base metals dragged down with gold?

 

[Harold_V]

There are some base metals dragged down with gold?

Read Hoke!

Harold

 

[chemist]

How you refine depends on what you want as the end product.
Harold is right. Hoke gives you the proper procedures for getting to near 99%. The forum members here can provide you with the techniques for pushing past 99% to 99.99%.
But, if all you want is to concentrate the gold (let's call it 95%), then the dragdown of other metals from dirty AR is acceptable.
What level of fineness do you want?

 

[butcher]

base metals in solution of aqua regia, that is not refineing but recovering the gold.
I presume the more base metals in solution the more gold it will retain left in solution, even after dragging some of the base metals down in the precipitated gold, if working with small lots of gold, you should keep a good stock pot, or cement out with copper and refine the gold.

 

[chemist]

...I presume the more base metals in solution the more gold it will retain left in solution...".

Why can't you just keep adding SMB until the Stannous chloride test tells you that all of the gold has dropped from the AR (along with some base metals)? The powder would contain base metals, but it should also contain all of the values.
All AR processing leaves behind some base metals in the solution. After all, the purpose of the AR process is to do the final separation of gold from residual base metals.

 

[Renaldas]

How you refine depends on what you want as the end product.
Harold is right. Hoke gives you the proper procedures for getting to near 99%. The forum members here can provide you with the techniques for pushing past 99% to 99.99%.
But, if all you want is to concentrate the gold (let's call it 95%), then the dragdown of other metals from dirty AR is acceptable.
What level of fineness do you want?

I prefer to achieve 995 and higher.
If I took this black powder and boil it in HCl several times, rinse it, it becomes nice brown powder. Dont you think this is enough to get 995 and higher?

 

[g_axelsson]

To dissolve all the material in AR gives you a lot of volume to work with. The added base metal salts will make it harder to detect gold and decide when chemical reactions have come to an end, making it easier to overdose on chemicals. The larger volumes also dilutes the reagents and makes your reactions take longer time.
A lot have been written already about going directly to AR with base metals present. It can be used as a recovery process but to do that successfully you need to know the basic reactions and have a lot of experience. Search the forum, it's all there.

If you are aiming for higher purity just collect all your powders and re-refine it. Don't melt it because it will be a lot harder to dissolve it then. The volumes are small now so it should be easier to get all the gold out of the solution and the gold dropped will be easier to clean and melt in the end. It's easier to correct an error in the beginning of the refining than to solve it with washing in the end.

/Göran

 

[butcher]

Good point Goran, using chemicals to precipitate gold from a highly contaminated solution of base metals, I feel would be a waist of chemicals, remember gold will plate to copper, I believe it will even plate to the copper salts left in solution so unless you drop all metals from solution with chemicals you are possibly not getting all the values, as an example look at the stannous chloride test see how tin can hold your gold in the violet colored solution.

Using a copper buss bar (see reactivity series) would make more sense to me for recovery of the gold from those contaminated solutions, but even then in small lots some gold may remain on buss bar (so always use same bar), eliminating base metals needs to be done any way, so it only make sense to do that first and get all of the gold and a more pure state.
Aqua regia can be challenging anyway add base metals your asking for trouble if you want to get your gold back.
Eliminate the base metals first.

 

[HAuCl4]

How you refine depends on what you want as the end product.
Harold is right. Hoke gives you the proper procedures for getting to near 99%. The forum members here can provide you with the techniques for pushing past 99% to 99.99%.
But, if all you want is to concentrate the gold (let's call it 95%), then the dragdown of other metals from dirty AR is acceptable.
What level of fineness do you want?

I prefer to achieve 995 and higher.
If I took this black powder and boil it in HCl several times, rinse it, it becomes nice brown powder. Dont you think this is enough to get 995 and higher?

With near complete certainty: YES. Unless you have lead and/or tin (which you shouldn't), that triple-washed gold should be 995+, and probably closer to 999, if you filtered the silver chloride well before doing the SMB drop. IMHO.

 

[goldsilverpro]

The goal should be at least 99.95% (999.5 Fine), which is not that difficult if you know what you're doing. Anything less will have to be ultimately refined by someone, in order for (most) new products to be made from it.