Unknown amount of gold in jewelry polish bags

[diverwild]

Hi 2 Question if you never mind
Q 1

I want to end this free nitric acid problem in my AR
I refine polishing bags for my friends which are filled 18K gold
when I burn the bags and go for AR process I had problems evaporating that that sneaky free nitric it took a lot of my precious time and my friends would not tell me how much gold in their bags some times I get 100g, 150, 90
so if I add less than the required amount there are grams not digested if I add more I end up with the free nitric problem

Q 2
how do I know if these brown nitric fumes are gold being digested with AR or it is simply just free nitric acid running out since AR is full of dust which can't give you a hint


I never forget when my first refining attempt that took me three days and nearly 1 liter of nitric acid boliling because I thought brown=digesting so I kept doing and adding and I was happy .

 

[nickvc]

With polishing dust you need to incinerate it with care and with a cover over it as the gold in it is in very fine particles and can be blown out. Once incinerated you need to crush and sieve it to remove any large pieces of metal and then place the powder into your beaker cover with HCl and heat, once the acid is hot add small increments of nitric, allow it to work and the reaction to slow down and then stir the nitric into the rest of the powder, be careful at this point as it can boil over, allow the nitric to complete its reaction and then repeat the same process until you get little reaction, you must keep stirring the powder and try to actually boil the solution, do not just walk away as the beaker will crack, once you have cooled and filtered the solution if you recover 100 grams for example you will have 10 grams still left in the powder if you have done it correctly, if after the second treatment you recover more than 10 percent you didn't process it correctly on the first pass so a third dissolution may be necessary to recover any more of the values.
If you have only processed your materials once I would suggest at least one more attempt to recover values.

 

[g_axelsson]

My advice is to do the digestion in steps. Measure up what you think you need of nitric and add half of it to your reaction vessel. If it stop reacting and there is still undissolved gold, pour it off, this is now gold chloride free of excess nitric. Try to eyeball the reminding mud and add new HCl and less than the amount of nitric you think you need. The lower volume will let the reaction work quite fast again. Pour off and repeat again until you have nitric left when the reaction have died down.

To test for free nitric use a copper wire. If it is covered by a black residue and not dissolved then the nitric is used up and you only have HCl and gold chloride in solution.
If the wire is attacked and forms bubbles then there is nitric left and the gold in your mud should all be dissolved.
Sulfamic acid could also be used to test for nitric acid in solution.

The last batch should be a lot less volume than the whole batch and easier to remove the excess nitric acid.
Using lower volume at the end also makes it easier to detect any reaction. The aqua regia is a lot more concentrated comparing to digesting it with all the gold chloride still in the reaction vessel if done in one go.

Sulfamic acid is also an easy way to get rid of excess nitric acid.

I haven't used this process on polishing sweeps, but it works well with karat gold and gold powder.

Göran

 

[kernels]

Yep, as above, I think the problem you are asking about is excess Nitric acid after dissolving the available gold ? The easy answer is Sulfamic Acid (or sometimes called Sulphamic Acid)

This video is in english, but even seeing what is happening might help: https://www.youtube.com/watch?v=oN8-7q21Cnw

 

[4metals]

You will never get all of the gold by digesting the incinerated sweeps in aqua regia but you can get most of it and what remains will be in the mud along with the silver. I suggest 3 things, 2 of which have been mentioned.

First, use your nitric sparingly.

Second, kill the excess nitric with sulfamic acid.

Third, always take a small spoon full of the mud after you are done and digest it again in an aqua regia solution in a small beaker. Test this with stannous and you will be able to determine from the stain if you need to reprocess. This test is easy to perform and pretty quick as well. Keep a log for each customer and you will be able to predict your acid usage for the same customer with repeat business. This does not mean you shouldn't do the small spoon test after each lot with the residues but after a while you will have the experience to get all that is going to come from the sweeps in 1 digestion.

 

[diverwild]

Thank you guys a lot

one Q for 4metals why can't I get all of the gold by digesting the incinerated sweeps in aqua regia in the first time ? even if I add more nitric than I need and stir it frequently ?

yesterday I recovered 44,5 G of pure gold using SMB which means 96% of what is in the bags then I took a look at the diluted AR I saw brown some kind soft mud or something it has no weight at all, and it's not mud because I filtered, is it SMB and it smells very bad

 

[4metals]

Mostly it is due to difficulty rinsing. You can get better than 96% of it but the sludge is tough to rinse. All refiners save acid refined sludges and ship it out for recovery of the remaining gold and all of the silver.

 

[andy3124fish]

Hi, I have been reading post from this site and am thankful that it is here. I don't ever post anything. I just learn alot from reading. My question is where do people send their built up sludge. I looked on Google, but have no idea where to go. Thanks

 

[snoman701]

Depending on the quantity, you could start by asking 4metals.

 

[nickvc]

Unless you have serious quantities I doubt you will find a decent deal, I’d imagine you are looking at the large refineries such as JM or Metalor although there may be others but asking 4metals would be a good idea as he has dealt with many of the large companies.