Slow and incomplete drop of gold

[resabed01]

I have my gold bearing solution from stripping gold from dishware and glassware, several hundred pieces. I used HCl-Cl as the stripping solution and I've tested with stannous so I know it's pregnant. Because I had rinse waters that also contained auric chloride I added the rinse water to the stripping solution then reduced the volume by evaporation (not boiling) to remove excess water. Reduced the solution down to about 400ml. With the heating I'm pretty sure the chlorine is now gone. The solution had a nice yellow color to it. I have no idea how much gold it contains.

I let the solution sit for a few weeks because I was busy with other things and when i came back I noticed there were tiny golden metallic flakes in solution. Not that it mattered because I wanted to drop the gold from this solution anyways but I thought that was interesting.

Yesterday I added Sodium Metabisulphite in dry powder form to get the gold to drop, up to two teaspoons. It fizzed and the solution went slightly cloudy but did not go from yellow -> clear -> muddy brown as expected. A strong sulphur odour was present when I mixed in the SMB. Some gold dropped but not all.
After 24hrs the solution is still yellow and cloudy with precipitated gold on the bottom. I tested with stannous and it's still positive. And maybe has other PMs in solution? I'm not sure but the stannous test showed yellow before it shifted to purple.

What's the solution to getting all the gold to drop? Add more SMB? This SMB I purchased at a wine making shop and is a couple of years old at least.
Did I do anything wrong in all my steps?

Thanks

Trevor

 

[philddreamer]

Maybe with all the evaporation, plus sitting for a while, you might need to add some water. SMB needs water in order to work properly. Has the SMB been opened for 2 years?
Phil

 

[resabed01]

The SMB was in a closed container but not sealed. It caked but if I knock it around with a spoon it easily breaks up into powder again.
I'll mix up a solution of SMB, this time with more water and try as suggest. Thanks.

 

[maynman1751]

You may also want to GENTLY heat the solution. It sometimes aides in dropping.

 

[Golddigger Greg]

I might be wrong but your SMB may be bad. I seem to recall a post on the forum that said if left exposed to air SMB will clump as it converts to a Sodium Bisulfate. Try a diluting a small sample of your solution and try to drop with your warmed SMB solution. If that doesn't produce results you know it is expired, and you won't have added more to your main liquor.

 

[resabed01]

It's possible my SMB is past due. I notice when I mix it with water I need to be careful and have good ventilation otherwise I'll get knocked back by the sulfur dioxide that's produced.
That smell takes me back to when I was a kid and we used to light chunks of sulfur on fire. Very unpleasant and harmful too no doubt.
It is cool the last few days... about 10c at night and 15c during the day. I'll try heating the solution.

 

[resabed01]

Another question on the same related topic.
On my latest batch, this time it was the flakes/mud from a batch of pins that were in a crock pot.
I dissolved the gold flakes with HCl-clorox and had a nice transparent orange liquor after filtering. I was anxious to see dropped gold powder so I heated this auric chloride solution to about 70 deg C where I noticed it started to fizz much like soda pop. I assumed this was the chlorine being released. Being careful not to inhale, I would stir it every few minutes to help it along. This went on for about 20 min until the fizzing started to slow down. After which I pulled it from the heat to let cool. When the solution was down to 25 deg C, I mixed up about 7 grams of SMB and water and added it to start the drop. I estimated maybe 3 grams of gold from my batch of ~800g pins but I really had no idea.... it could have been more ... it could be less. With the addition of the SMB I expected the solution to turn from orange to clear before turning a muddy brown but it did not. It turned from orange to yellow before going cloudy brown. I let it settle overnight.

Today the solution has settled and cleared and it's still a rich yellow color. I pour off the main portion of the solution to collect the dropped gold powder which weighed out at 1.20 grams and melted into 1.17 grams. :mrgreen:

I'm looking at the spent solution and I think there is still gold that hasn't dropped. I test with stannous and I get a instant dark brown result. I assume this is a false positive from the excess SMB I added?

I heat the solution again, this time taking it to about 85 deg C, just below boiling. More gas is released, this time I'm thinking it's sulfur dioxide along with some residual chlorine? As I was heating it the solution went slightly cloudy again and dropped a bit more gold, not much. Once it cooled a bit I mixed up a couple grams of SMB with water and added. At this point I forgot to test again with stannous before adding the SMB. The solution slowly darkened and is now precipitating as I type this.

I know you can't tell if gold is in solution from looking at it but something was telling me all the gold didn't drop. And in this case it appears my hunch was correct. Now I'm questioning my previous solutions which I thankfully kept in a jug.... I'm seeing fine black powder collecting on the bottom of the container.

How do I know when all the chlorine has been liberated from my solution so I can move onto the next step of dropping gold?

 

[butcher]

A test for chlorine in solution.
Heat the suspect solution until vapor fumes appear, pour some ammonia in a bottle cap (the ammonia in this cap will vapor), hold the cap full of ammonia next to the vapors emitting from your solution, when chlorine vapors and ammonia vapors come into contact they make a white smoke of ammonium chloride gas.

 

[resabed01]

Thanks Butcher, I'll remember this for next time.