suggest the best method for dust refining

[gambit2006]

our jewelry factory mainly manufactures in 10 kt & 14 kt white gold e gold jewelry.
the white gold alloy we use contains 20%silver of alloys wt.
what is the best method for recovering pure gold from dust batches (filing dust, setting dust,polishing dust)
our factory manufactures jewelry in sterling silver also.so silver dust also gets mixed with karat gold dust.

 

[FrugalRefiner]

Since you've mentioned the silver content of your gold alloys, I'm guessing you understand it could cause problems in AR. But if you're only dealing with very fine particles, it might not.

If it were mine, I'd do a test on a small batch first. I'd add 50/50 distilled water/nitric acid to it. That will dissolve any of the sterling dust, and it will dissolve at least some of the silver content of the gold alloy. When the reaction is done, filter the remaining dust, and try an AR digest. If the particles are fine enough, you may be able to successfully dissolve all the gold.

If there is any undissolved material remaining, it may just be silver chloride, or it may be silver chloride with some gold entrapped in it. You can test this by dissolving the remains in ammonia. If there is anything undissolved after the ammonia treatment, filter it out and take it back to AR and test this second AR for gold. Be sure to acidify the ammonia solution promptly.

If there is gold in the second AR, then you would probably be better off inquarting all the material right off the bat, digesting the silver in nitric, then the gold in AR.

Dave

 

[upcyclist]

Hoke's book (In Dave/Frugal's sig block above) is specifically geared to the small jeweler/refiner--be sure to give it a read. Depending on what you use for polishing, you may want to refine the polishing sweeps separately (oil-based rouge polishes, for example, call for incineration).

 

[4metals]

You must incinerate the material and sift the ashes first before doing as Dave suggests. Your best option is as Dave has suggested as inquarting an ash powder is not an option. Since a good portion of the silver was in a gold alloy the silver may be too high for aqua regia and not high enough for nitric.

Your option then would be to flux and melt the sweeps to collect a mixed alloy bar which can be inquarted and processed by classic methods.

 

[FrugalRefiner]

upcyclist and 4metals are right. I neglected to mention the need to incinerate your material. Thanks for keeping me on my toes guys. :wink:

Dave

 

[nickvc]

Incineration as pointed out is a must with all this material.
The polishing dust will probably be best recovered after incineration and sieving by using dilute nitric acid on heat with good stirring to remove the silver and as much base metals as possible, you may need to do this several times if the value warrants the time or costs, then filter the remaining powder and rinse well with distilled water, the remaining powder can then be treated with AR to recover the gold, this process will almost certainly need doing at least twice as if you recover say 100 grams first time the second recovery should be around 10 grams, if it's more then you aren't allowing the acid to get to all the material.
If your filing dust is from carborundum wheels the same procedure as above will work as the material should be fine enough to allow the nitric to remove your silver, if it is from filing then put it with your setting material and melt adding more silver to make the alloy only 25% maximum gold and then part with nitric to recover the silver before using AR to recover your gold, the reason for this is if the pieces are too big the gold content will stop the nitric from working and the silver content would do the same with AR.
Hope that helps.