AR Help

[LostDutchman]

Hi guys! I've been reading the forums for a while and experimenting.

I currently have a batch of gold filled watch cases processing. I used 8oz of Sodium nitrate dissolved in 475ml of hot water and 975ml of muratic acid to form my AR. The batch originally weighed 287g. Problem I have run into is that at first the process was rocking... gassing well and seemed to be going fine. Problem is that the reaction seems to have stopped while leaving undissolved gold both on the surface of the AR and undissolved pieces in the bottom. Is there anything I can do or add to continue the reaction or should I filter and add this stuff to a smaller batch?

Any help would be appreciated.

 

[FrugalRefiner]

Hi guys! I've been reading the forums for a while and experimenting.

I currently have a batch of gold filled watch cases processing. I used 8oz of Sodium nitrate dissolved in 475ml of hot water and 975ml of muratic acid to form my AR. The batch originally weighed 287g. Problem I have run into is that at first the process was rocking... gassing well and seemed to be going fine. Problem is that the reaction seems to have stopped while leaving undissolved gold both on the surface of the AR and undissolved pieces in the bottom. Is there anything I can do or add to continue the reaction or should I filter and add this stuff to a smaller batch?

Any help would be appreciated.

You would have been better served by dissolving and eliminating the base metal before you tried to dissolve your gold.

If you still have solid metal remaining, and the acid is exhausted, you probably don't have any gold in solution. Have you used any heat to drive the reaction to completion? If not, heat it up. When you're confident the acid has been consumed, test the solution with stannous chloride to see if you have any gold in solution.

Then, if you still have undissolved metal, you can decant off the solution and add fresh acid to the remaining metal. If the solution was barren, treat the waste and discard it. If there was gold in solution, drop it with your agent of choice, then treat the remaining waste solution.

Dave

 

[Geo]

The only thing I would add to what Dave said would be to add a small amount of fresh HCl to the warm solution and undissolved metal. If the solution has free nitric and no free HCl, the reaction will stop. This will either restart the reaction or have little to no reaction.

 

[FrugalRefiner]

Good point Geo. I've never had to resort to poor man's AR, so I don't know if his original mix had excess HCl or not, but adding a bit more HCl will do no harm.

Dave

 

[4metals]

You never said if you tested the solution with stannous chloride when the reaction stopped. Given the weight you started with and the volume of acid you started with, there likely was not enough acid to dissolve the batch entirely. What would happen in this case would be any gold that did go into solution will be forced back out of solution by the base metals.

Testing will tell you if this is the case. If your test indicates no gold in solution you can filter the solids and save the solids and treat your barren acid as a waste.

This procedure is much better if you use a nitric leach to get rid of the base metals and silver first and only use aqua regia for the last dissolve after all of the base metals are gone.

 

[LostDutchman]

Thanks for the tips guys. The solution did not contain gold so I filtered and melted the solids into a useable form. I knew there had to be a step I was missing. I've had no problems doing karated gold with this mixture and produced good results. In the future I'll remove as much base metal as possible.

 

[4metals]

Melting the undissolved didn't give you much of an advantage unless it was crusted over chunks of metal. Generally after parting to rid yourself of base metals, the remaining particles are easier to digest as they emerge from the parting process. Melting only reduces surface area for reaction.

 

[LostDutchman]

There were a lot of fine particles and very small stuff I'm afraid I would have lost if I didn't get them together.

 

[4metals]

Settle and decant, you are working on a small scale, nobody rushing you so let it settle. If it's that fine you will likely blow it away with a torch too.