Temprature, disolving and precipitating gold

[old thompson]

hi guys, I have a new batch of foils and am going to dissolve them in HCL/bleach. I am working outside in about 20 degree F. weather, but no worries- I have an electric hot plate. I understand that HCL will dissolve gold when heated or when an oxidizer is added, but that when bleach is used the gold is attacked by CL2. I also understand that cold water holds more O2 than warm water and presume that HCL solution will hold more CL2 than warm HCL solution?

What is the optimal temperature of an auric chloride solution before adding SMB to make SO2 force that auric chloride to give up the gold? I am pretty sure that it varies with the concentration of the auric chloride, but has anyone compiled a graph? Also, it seems to be an exothermic reaction, so volume plays a role as well?

I am just a dumb carpenter and would like to understand exactly what is going on. Thanks- o.t.

 

[Harold_V]

What is the optimal temperature of an auric chloride solution before adding SMB to make SO2 force that auric chloride to give up the gold? I am pretty sure that it varies with the concentration of the auric chloride, but has anyone compiled a graph?

No graph, at least of which I'm aware. With SMB (SO2 gas), temperature isn't critical unless your solution gets too hot.

Also, it seems to be an exothermic reaction, so volume plays a role as well?

No, but concentration does, as it is an exothermic reaction, with a higher level of concentration, more heat is produced.

As best I can, I'll address the temperature issue. I'll speak from experience in precipitating from concentrated solutions.

I never found temperature to be an issue unless you tried to precipitate from hot solutions, which I can't see happening under normal circumstances. If you precipitate with a level of concentration that is 3 ounces/liter or less, you should enjoy success precipitating from ambient temperatures, assuming ambient, for you, is not 100° F.

I routinely iced my gold chloride solutions prior to precipitation. If the level of concentration exceeded about 4½ ounces/liter (including ice), by the time the gold was down, the solution was quite hot---too hot to handle comfortably. There were occasions where precipitation ceased, while some gold remained in solution. All that was required to precipitate the remainder was to introduce more ice.

Keep your concentration at two ounces/liter or less, and you'll have no problems. If you prefer a higher level of concentration, you'll learn to use ice.

Harold

 

[Pantherlikher]

Good to know as a general rule all around.

You did forget to mention the safety factor so...
Be extremely careful of glass and extreme temperatures.
Cold glass on a hotplate will explode or fracture. Glass has zero tollerance for expansion and contracion caused by changes in temperature.
The bottom of the glass can warm up too fast and the cold air can hit it to cause failure.

It might help doing everything inside a plastic tub. Air around will warm up with hot plate. It should be good enough but in case of fracture, at least the tub will catch spilt solutions saving your PM.

B.S.

 

[old thompson]

Thanks guys!

 

[old thompson]

Dropped about a 1/4 teaspoon full yesterday outside in the cold, around 10* F. The auric chloride solution cleared up as soon as I added the precipitant. Nothing dropped at first but as soon as I gave it stir with a cold plastic knife the sponge seemed to fall off the knife. It was all out in about 30 seconds and tested to be bare with "solution A" about twenty-five minutes later. It really dropped fast compared to the my first try in the summer, the solution never looked gray, just sponge dropping off the knife, nice and brown, and clumpy. Very good!

I will attempt to post a picture of my meager results in the gallery when possible. I still don't feel comfortable melting it into a bead though. Doing a search on the mini-fire brick furnace now, looks like the way go with very small amounts.

 

[butcher]

Of coarse "solution A" (stannous chloride solution) was a name C.M. Hoke gave in here book explaining the stannous chloride and the test used to see your values in solution.

I refine it twice with washing procedure taught by Harold before melting.
Looking forward to seeing those pictures.

 

[rickbb]

For really small amounts you'd be better off with a melting dish and small mapp/O2 torch.

 

[butcher]

Yes a melting dish in the mini-fire brick furnace would work just fine.