Gold Bromide

[OMG]

I used HBr-Br instead of HCl-Cl for dissolving some gold from escrap, Works nicely btw. (using a sealed container!).
I had leached most base metals first using CuCl2.
So now I have all the gold and trace metals as filtered bromides (along with NaHSO4 salts and some chlorides and whatnot.. I had used H2SO4 + NaBr to make the HBr-Br, and I had stuck the CuCl2 dirty filter with all the gold flecks directly in the HBr-Br)

I thought I read somewhere that AuBr3 will decompose to metallic gold and bromine at 160C or thereabouts.
So I was thinking of letting my bromide mix just evaporate to dryness, then heating it up past 160 to make the gold bromide decompose leaving gold metal and the rest of the salts unchanged.
Then I could wash away the salts with water leaving the gold behind.
(Right now I'm letting it evaporate via the sun so it will take a few days.)

Do you think this is a good way to do it (so I don't have to mess around with filters, and so that I can test with small amounts of gold without having to try to precipitate)?
Will I have issues when I heat the salts up to 160? Will the metallic gold get 'vaporized' all over the place, etc?

I'll give it a try anyway and post my results, but If someone sees problems I will have, please let me know.

Thanks

 

[machiavelli976]

the lower the gold halide , the easyer to decompose it. you will not lose any values but your method can be named a anti-refining process. too many salts might run everything into a nice mess.

 

[Lou]

I think it's a bad idea.

Namely because the decomposition of the gold (III) bromide has several pathways.


Let me make this clear to everyone here:

DO NOT HEAT YOUR ACID GOLD HALIDE HAUX4 (X=Cl, Br, I) UNTIL DECOMPOSITION. GOLD WILL BE LOST TO THE PROCESS.

 

[machiavelli976]

in his situation shouldn't gold be caught by the other salts? it is going to vanish anyhow?

 

[butcher]

I would think gold bromide in bright light should turn to gold metal, as it is used in photography, why not just precipitate the gold from this halide solution?

here is a little on bromine leach, http://www.mine.mn/Robin_Grayson_gold_recovery_method05.pdf

 

[OMG]

Ok, so it will be too lossy. Thanks for the advice.

 

[butcher]

clorine is above bromide, and will displace bromine,
changing the gold bromide salt in solution to gold chloride (s) and bromine (aq)

make gold chloride out of your gold bromide.

 

[OMG]

I liked how the bromide leach worked on the escrap gold so I tried it on some bigger stuff.
Here's what I did:

in a 1 L glass container (sealable)
500 ml ~40% H2SO4
120g of dental scraps, mostly au, some pd, pt, ag, cu, etc - according to the manufacturers alloy paperwork (organics were almost completely removed, the porcelain was still there though)
250g NaBr (dry)
maybe 50ml of bleach to get it going
and a total of probably 150ml of 3% H2O2, added a little bit at a time over the duration (4 days).

within about 5 minutes the solution turned very dark brownorange.
I kept the container sealed, so there were essentially no fumes
It has been sitting at outside temperatures (avg 15-20 C) for 4 days. A couple of times I put it in a heated water bath (maybe 60 C) for probably a total of 12 hrs.

The color is now extremely brown. can barely see a few mm through the liquid.
It gives a very dark purple color with the stannous test.
There is also next to no bromine fumes in the top of the sealed container, the bromine seems to either be used up or absorbed.
I think the solution is loaded up too much and can't dissolve any more, so I'll probably filter and precipitate with zinc this weekend.
I wasn't really expecting it to dissolve all the metal, or even if it could, I figured it would take a long time (like weeks) since some of the metal is pretty thick.

I like this bromine method a lot and am wondering if anyone can help me make it better.
Advantages
- all the chemicals are very common and cheap
- there are essentially no fumes during digestion since it can be sealed
- don't need to use nitrates
- i think the H2SO4 and bromine keep fighting each other trying to be either H2SO4 + HBr or SO2 + Br2 + H2O (and maybe that helps the digestion - if the bromine is being continually generated and absorbed in situ)
Maybes
- apparently AgBr is soluble in cold strong aqueous KBr (maybe its the same with NaBr)
- Br2 doesn't attack the pt normally, but apparently with H2O2 it will
- may have more trouble precipitating with SO2 than would have if it was chlorine
Disadvantages
- takes a long time (to digest large pcs of metal)
- if H2SO4 level is to high, gold will keep getting precipitated by the SO2 in the solution, so it might be easy to screw up and lose values.

If anyone has experience with this kind of stuff or would like to see if this could be developed more, please post.
(I'm sure it has already been developed years ago, and the old timers aren't giving up their secrets, and I can find very little on the internet)
I'm specifically looking for ways to make this faster (while still keeping it easy and without attention required), or to know how much chemicals of each would be required, and also what would be good for precipitation.

Unless I learn something good before the weekend is over, I think I will just filter and precipitate with zinc so i can see how much weight was actually dissolved.

edit: I have pics I will post also.

 

[OMG]

Here's a little update on my progress with some questions.

The bromine leach seemed to work pretty good, but even after more than a week it probably didnt dissolve any more than 1/4 of the metals.
Since my last post, I have precipitated with zinc, washed several times, including heated hcl leach/wash.
A black powder remained. Now I am attempting to dissolve using hcl-cl and do the normal precipitations for gold (FeSO4) and platinum (NH4Cl).
(I wasn't too sure about precipitating them straight from bromide leach so I figured I'd just redissolve them as chlorides)
But I am having a heck of a time getting all the black powder to dissolve. I will put the pics below, but I am using a coffee carafe for the reaction and the bottom (smaller indent) circular area was full of the black powder, actually it went a bit higher but not much. (So you have an idea of how much powder I am trying to dissolve).
So far using hcl-cl and heat I've only got about 1/4 of the powder to dissolve. (tests positive for pt)
Is it really hard to dissolve platinum in hcl-cl or am I missing something? I also added a small bit of peroxide to see if that would help. I don't think it did anything.
Any suggestions on what I should do? (I have no access to nitric and even nitrates are very hard to find - I've only found a bit of ammonium nitrate)
Should I continue trying to dissolve with hcl-cl? Do I not have enough liquid to dissolve all the powder?
If I were to go back to bromine and leach it that way, what would I use to precipitate Pt ? I thought I read somewhere that bromine and ammonium shouldn't be used together.

Here are the pics

This is the starting material (dental scraps).
http://img405.imageshack.us/img405/4611/initial.jpg

This is the coffee carafe with the partially dissolved powder (it was recently stirred thats why it looks like there is so much black). I tried to take an angled shot so you could see the deep yellow color of the liquid.
http://img139.imageshack.us/img139/9536/chloridesdiagonal.jpg

This is a picture of the test swabs before I rubbed them together. ( 1 has stannous on it the other has the dissolved pms)
http://img189.imageshack.us/img189/5338/chloridespretest.jpg

This is a picture of the swabs after I rubbed them together. (shows high platinum content, but I don't see any purple)
http://img25.imageshack.us/img25/6210/chloridestest.jpg

On a side note, I was amazed how much affinity the bromine leach has for dissolving platinum. In the pic below is the glass container I used for the bromine leach, The container was initially full of a dark brown liquid after the week or so of leaching (described in my previous post), and I had poured off almost all the liquid; the only liquid remaining was just enough to barely cover the remaining dental scraps. I then filled the container half full with water (where it is in the picture), and the next day the orange-brown color had already returned. So i did a stannous test, and it showed Pt to my amazement. The bromine/acid levels must have been really weak since 90% of the volume was the water I poured in. But it seemed to dissolve platinum without any problem and without heat.
http://img46.imageshack.us/img46/310/bomidesandtest.jpg
and heres a closeup of the test swabs (the lighter one was the one that had only stannous on it initially)
http://img683.imageshack.us/img683/704/bromidestest.jpg

I guess there must have been alot of oxidizer still in solution because the orange and brown colors faded after a while.

So anyway, how should I proceed? (keeping in mind I have pretty much no access to nitrates)

Your help is appreciated.
edited to make more readble

 

[lazersteve]

It's hard to decide which way to go without knowing what we are dealing with. The unknown black powder looks to contain PGMs, so you will need to test to see which ones are present.

Take a sample of the black powder and place it in a test tube with concentrated sulfuric acid. Give it a boil for 10-15 minutes and see if the solution shows any color.

If you have DMG test a second sample of the liquid in another test tube with the DMG. If the DMG shows positive (yellow precipitate) then add a little extra to be sure you have removed all of the Palladium. Now test the left over solution from the DMG test with stannous to confirm their is still Platinum present.

Steve

 

[OMG]

Ok. I will test with sulfuric. What is being tested for with this? Rhodium? According to the alloy spec sheet, if there were rhodium it would be negligible (I wouldn't recover it - maybe just save it in my used filter container if possible)
Getting DMG would probably be a hassle. I guess I could try using ebay. I don't like ebay, but if I really have to I will. (I am looking into it now)
I am only really concerned with recovering the gold, platinum, and palladium. (all of which should be present in the dental scraps)
Thanks

 

[Lino1406]

I would try ascorbic acid (vitamin C)