Cleaning "Dirty" Gold

[Lobby]

Folks,

I've just started my 1st two batches refining gold.

Batch 1 = 10k 88.5g of 10k
Batch 2 = 110.8 g of 14k

Inquarting was fine, but the actual dropping of the molten, inquarted gold was in too short a pail. I ended up with blobs of gold, not the pretty corn flakes.

Well, I went ahead with the nitric dissolution. Naturally, there were still big chunks of goldish metal left in the flasks. For each batch. So I removed the large metallic chunks and re-dissolved them with nitric.

The 10k batch seemed to break down the metallic chunks well. The 14k batch didn't completely.

I proceeded with AR (using GSP's method) and got some interesting results:
- the 10k batch produced a pretty yellow solution
- the 14k batch was a dark, dirty, muddy mess

I've dropped the 10k batch with copperas and am letting it stand overnight. The 14k batch is waiting copperas addition.


Question:

I'm sure I've carried over silver and copper into the AR step (on the 14k batch). I guess the next thing to do is to go ahead with the copperas drop, and then clean the gold.

Any suggestions?

 

[nickvc]

Let your solution cool and add a little sulphuric and then let it settle, filter your solution and then precipitate your gold. Check your solutions with stannous to be sure you have removed all values.
Keep the filter papers and remove any large obvious pieces that might not have dissolved for the next batches, you might need to re refine your powders but try Harolds rinsing methods first they might work.

 

[Lobby]

What should the sulfuric do? (I like to understand the chemical basis for the the steps I take. Thanks for your patience).


Here's a few pics:

Here's Batch 1, after the Ag / Cu dissolving with HNO3

Note the big chunk at 11 o'clock. I took it out, along with a few others and redissolved it.

Here's batch 2, after the Ag / Cu dissolving with HNO3. Note the cool silver (or is it copper) nitrate crystals. I obviously didn't add enough water. They quickly dissolved with a bit of water. :mrgreen:

Here's the redissolving with HNO3 of the large chunks. The beaker whose watch glass I'm holding is Batch 2. It had some large chunks of 25% gold

Batch 1 after AR reaction. Note the pretty yellow color.

But here's Batch 2 after AR reaction, filtration, and 3 volumes of water addition. Man, it's ugly.

It's now stood overnight.

 

[goldsilverpro]

Folks,

I've just started my 1st two batches refining gold.

Batch 1 = 10k 88.5g of 10k
Batch 2 = 110.8 g of 14k

Inquarting was fine, but the actual dropping of the molten, inquarted gold was in too short a pail. I ended up with blobs of gold, not the pretty corn flakes.

Well, I went ahead with the nitric dissolution. Naturally, there were still big chunks of goldish metal left in the flasks. For each batch. So I removed the large metallic chunks and re-dissolved them with nitric.

The 10k batch seemed to break down the metallic chunks well. The 14k batch didn't completely.

I proceeded with AR (using GSP's method) and got some interesting results:
- the 10k batch produced a pretty yellow solution
- the 14k batch was a dark, dirty, muddy mess

I've dropped the 10k batch with copperas and am letting it stand overnight. The 14k batch is waiting copperas addition.


Question:

I'm sure I've carried over silver and copper into the AR step (on the 14k batch). I guess the next thing to do is to go ahead with the copperas drop, and then clean the gold.

Any suggestions?

Assuming you used enough nitric, it sounds like you either didn't add enough silver and/or you didn't get the molten alloy well-mixed during the 14K inquartation. With proper inquartation of both, the 14K should react the same as the 10K with nitric - everything should dissolve but the gold.

By my calculations, 147.72 g of silver should have been added to inquart the 110.8 g of 14K. Is that the amount of silver you added? How much nitric did you use? Was the silver you used for inquartation pure or an alloy, such as sterling?

Of course, your improper shotting (= granulation; = pouring molten metal into water) made things slower and more difficult.

You said you were using my AR method. What do you mean by that? If I had inquarted 14K with pure silver and, after nitric, there were still solid chunks, I would never use AR at that point because it wouldn't work. These chunks now contain about 70% silver (actually less, since it wouldn't dissolve in HNO3). To dissolve a gold alloy in AR, the silver content cannot exceed 10% or a little less. Anything higher and the silver chloride formed on the surface blocks the penetration of the AR.

As always, I hope I got the math right.

 

[Lobby]

You got the math right.

for 110.8 g of 14k, I added 147.2 g of sterling. This resulted in:

64.2 g gold (24.9%)
149.5 g silver (57.9%)
44.2 g copper (44.2%)

(I think I assumed the 14k was 25% Ag and 16% Cu - this came from the XRF of a prior batch of 14k)

As I mentioned, I dissolved with HNO3 twice. 1st time used 365 mls of 67%, saw metallic chunks that would not break with a glass rod, so re-dissolved with HNO3. About 110 mls.


By using your AR method, I meant covering the gold dust with HCl (240 mls). Then adding HNO3 in 4 ml increments till I got to about 35 mls. Reaction stopped. I increased temp to a very slight boil, added 2 mls of HNO3 and nothing happened.

Then I cooled it down, and filtered. After filtration (and 3 fold water increase) I got that dark pot.

Hmmm.

I'm gonna go filter the 1st batch. The pretty one.

 

[dtectr]

Read GSP's post again. If you have "chunks of metal" you did not mix your alloy sufficiently during inquartation - thus process will be incomplete.
you messed up your process - stop trying to make it ok and follow the voices of experience. 10k worked and 14k didn't. Redo it and learn. Drop with Cu and start from scratch.

 

[Lobby]

Thanks.