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.
- 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)
- 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
- 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.