Half gold chloride didn't drop gold

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chrisjames

Active member
Joined
May 12, 2015
Messages
29
Hi guys,

I think I need a bit of help if possible.
I have been refining various k jewellery and have followed instructions to the letter. All has gone fine apart from the final gold drop. I had a large jug of gold chloride which I allowed settle for 24 hours before filtering (using coffee filters as I had no lab ones) I then divided the solution into two coffee pots to precipitate. This is where I messed up...
I put a spoonful of smb in a cup of distiller water and added it to pot one then did the same to pot two, however added two tea spoons of smb (I think) the first pot started to drop immediately but the second one only partially dropped then stopped, the solution is still yellow where as the first pot is mostly clear minus some blue from copper (I did enquart however there was some 22k gold that I didn't bother with so assume that's where the copper came from)
The solution has around 40g of gold in so I'm keen to get it dropped.

I've read hoke previously and trawled smb questions but can't find this exact question asked.
I've left the solution for 24 hours but it still hasn't changed. My first thought was to lightly boil the solution and reduce it as I put some water in with a second load of smb (I know I messed up) there's way too much smb in solution I know but when I put smb in it almost goes to precipitate then re-absorbs the gold.

My feeling is that the solution is way to alkaline from the smb so should I boil to reduce, add Hcl and try to drop?

Any help would be great, thanks in advance.

Kind regards,

Chris
 

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Weird, it's the same solution. But just out of curiosity, did you denoxed? Did you test with stannous chloride?

Marco
 
I didn't denox as I was pretty sure it had completely stopped reacting and I tested a small bit to see if it would drop and it did you I did it to the entire batch. It was definitely sodium metabisulphite. They were in the same jug, I separated them out and then added the smb, one dropped and the other started to then drew back in the gold.
I'm actually waiting for the stannous chloride to be delivered but if one went clear I don't see why the other one didn't. I've been going over it in my head and the only difference is that I added two scoops of smb to the pot that didn't react. I think I need to reverse what I've done there but I'm not entirely sure how! It really has me scratching my head. I'm assuming it must have become alkaline from the smb and unable to react.
That's why I thought if I add Hcl it would acidity it and then be able to drop with smb?

It's the weirdest thing!
 
If I was in you I would cement with copper, wait for the stannous to arrive and the go with HCl/CL. Maybe seniors have a different/better way to go.

Marco
 
I was afraid of that. I'm not too au fait with that process. I know the Aqua Regia process pretty well but that's a new load of learning to do :|
I was hoping there was a way of saving it the way it is. I was most likely going to re-dissolve in AR and then precipitate again to clean it up a bit but was hoping to avoid adding too many more steps!
 
The two pots are not the same quantity of solution. If you have not diluted the yellow one further, and if you put the same amount of SMB into each jug, then you have put a lesser concentration of SMB into the yellow pot.

I know the Aqua Regia process pretty well
Alas, not well enough. You have excess nitric in solution; of this there is little doubt. Partial precipitation followed by immediate redissolving is a dead giveaway.
A little excess nitric can be swamped by more SMB, within limits. Before you start over, you have little to lose by adding another spoon of SMB directly to the yellow solution. I would not predissolve the SMB.

If by two spoons you see no effect, I'd stop adding it and move to cementing on solid copper.
 
At the time the reaction froze the pots contained the same amount of solution. It's only since then I added the second smb with distiller water, that's why there's more solution in the second pot.

The pots were almost exactly identical at the time of reaction. The only difference was that I added more smb. I know it seems that it's because of excess nitric but I don't know why one worked and one didn't. That's the weird thing. After the reaction froze I tried a few more spoonfulls of smb but it fizzed and then nothing.

would heating and reducing the solution make any difference do you think? I tried a light boil for a short time last night but not enough to start reducing. I assumed if I concentrated it that may make a difference?
 
chrisjames said:
would heating and reducing the solution make any difference do you think? I tried a light boil for a short time last night but not enough to start reducing. I assumed if I concentrated it that may make a difference?
Stop guessing and experimenting, unless you know the expected outcome and the reason for it. Playing will compound your mess.

Boiling is not a good idea. We gently evaporate solutions down, but except in specific circumstances, we don't boil them. We don't even like the word. The last thing you want is your gold splattering all over the place.

If a few more spoonfuls of SMB did nothing, my best advice is to cement on copper. Stannous chloride will tell you when it's finished.
Start over. Add nitric slowly.
 
On the other hand, if you want try experimenting with evaporating it down, or even more SMB, added HCl; take a small sample, say 10ml or whatever is convenient. Rather that is, than play with a batch that has perhaps 20 grams of gold in it.

Record everything you do, in weight and measure. If it works, you can transfer it to larger scale.

You can also get up to speed with cementing on copper that way.
 
I'm not guessing or experimenting. I've read on here from other members that heating the solution can help push out the gold. As I said I tried, it didn't work so I'm asking. I get it to a gentil boil, barely enough to have bubbles break the surface.
All of the things I've mentioned I've seen on other posts on here apart from adding the extra H2o, that ones on me.

I guess I'll have to go down the copper came ting route then. Thanks
 
Wait on the stannous and test it if theirs gold then I would add dry smb stirring vigorously until it dropped. The smb will eventually kill the nitric. The stannous will tell the tell.
 
I agree with Ralph, the SMB will drop the gold, and if there is free nitric in solution it will re-dissolve the gold and you will produce the red fume, this will continue as you slowly add SMB until the free nitric is consumed, then the gold will remain at the bottom of the flask.

What you risk is adding too much SMB, but it will dissolve in hot water after the gold is down and sitting in a pile of excess SMB (try to avoid this). You also may precipitate copper as a chloride from excess SMB but it is still better than cementation at this point. You can always cement with copper if all else fails.

I agree with Ralph in adding the SMB as a dry powder. I never dissolved it before using it, no sense making more waste. Just add it slowly with stirring.

This entire issue is further complicated by lack of stannous. The stuff is worth having around! Ya think?
 
I went for more smb. I think I've gone over the top with it. It must be 6 tea spoons full. It reacts by fizzing but then dies down within seconds and goes back to clear yellow. No gold is dropping out.

What happens if I've added too much smb and what's the recommended next step.

Also I must say that I'm doing his as a one off project to make some jewellery from the recovered gold so I'm by no means well read on the subject so any help to get me through this would be much appreciated. Thanks guys
 
Hi Jon, no I'm waiting for the delivery.

I've just put 100g of smb into the solution and it has started to precipitate the gold, very very slowly whilst giving off the tell tell brown/red smoke. The solution still reacts to the smb so I'll have to get more in the morning and keep adding small amounts until it stops reacting.

I'm still confused as to why one dropped instantly with only 1 teaspoon and the other needs so much when it's from the same batch. The only thing I can think of is that the pot that precipitated instantly was from what I poured off of the solution first. Does nitric in solution sink to the bottom? That may cause concentrated nitric in one and not the other??!

Regards

Chris
 
chrisjames said:
I'm still confused as to why one dropped instantly with only 1 teaspoon and the other needs so much when it's from the same batch. The only thing I can think of is that the pot that precipitated instantly was from what I poured off of the solution first. Does nitric in solution sink to the bottom? That may cause concentrated nitric in one and not the other??!

Regards

Chris

It's not likely that the nitric separated.

Check your first solution with stannous when you get it and see if you don't have a positive test for gold. If you don't have a positive test still take a piece of copper and put into the solution and see if anything cements onto the copper.
 
He mentions adding hcl earlier on in the thread, but I'm not sure if he did or not. I've had super saturated silver solutions that would not start to drop from copper until you add a little free nitric to kick it off. That usually happens with concentrated solutions though and not so much with diluted. Sort of like vapor lock. Lol
 
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