My gold is black and floats. No matter what I do

Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
As i understand you've dissolved it several times and precipitated with smb. Did you test the solution and the waste with stannous for pgm's?
My best guess is just dirty gold that needs a good wash. Did you cool and filter a couple times through the same filter before dropping the gold?
 
So I'm trying to follow that thread that Martijn posted on this thread. But I'm scared to do all that boiling. Because my hot plate won't boil since I have a catch jar or dish underneath it. And my other hot plate is a simple thing that you're supposed to cook food with so it gets really hot and has broken many glasses of mine. Do you really actually boil it? And that many times?! Don't they break glass too? I'm just hesitant.
I use an electric kitchen hotplate with a stainless steel pan filled with a layer of dry sand to keep the sand at a more or less constant temperature of 100 degrees C. That protects the flask or beaker against extreme heat.
I cap off a small erlenmeyer with a glass cup to keep the vapours condensing back in. Tie a rolled up paper tissue round the neck to catch any accidental droplets on the outside. Keep the sand dry. And use pyrex or labglass beakers and flasks.
 
As i understand you've dissolved it several times and precipitated with smb. Did you test the solution and the waste with stannous for pgm's?
My best guess is just dirty gold that needs a good wash. Did you cool and filter a couple times through the same filter before dropping the gold?
No I used different filters almost every time with every filtration. This picture is of its current state it's no longer floaty anymore and have black water all around it, but it still has a black tint to it. I'm going to attempt to clean it further.
 

Attachments

  • 16721767842662623939154246618131.jpg
    16721767842662623939154246618131.jpg
    1.4 MB · Views: 0
Well I forgot to take a picture of it but after a few HCl boils and boiling water rinses. I was able to melt down and get somewhere around 22kt. Well that's what I sold it for. But it could've been better deal since the testing was limited to the scratch test. But thanks to all y'all. That thread about cleaning the gold. Helped out a lot.
 
No I used different filters almost every time with every filtration. This picture is of its current state it's no longer floaty anymore and have black water all around it, but it still has a black tint to it. I'm going to attempt to clean it further.
For gold drop - there are few crucial parameters needed to obtain nice precipitates.

1. concentration of Au - if your solution is diluted - there will always be light precipitate, if any (when too diluted, say under 0,3g/L). In these situations, it is very wise to use coagulating agent/flocculent. Microcrystaline cellulose works fine, special flocculents, gelatin or polymer based work nicely too. Or use Celite/bentonite to adsorb the microparticles and filter the solution. Then redissolve the gold from the filter cake, increasing Au concentration orders of magnitude.

2. clear solution - discussed many times here. If you have cloudy solution - most likely due to AgCl/PbCl2 or tin compounds, you will obtain light and small particles, which settle just slowly. This is typical black ppt, hard to work with, hard to decant as it always swirls from the bottom when pouring the barren liquid. You need to filter it crystal clear - if the filter paper is not making it, use mentioned adsorbents like microcrystalline cellulose, and preferrably Celite or bentonite.

3. pH during the drop - you want constantly low pH - it helps to prevent any precipitate forming, and also helps coagulate forming gold particles. That meaning if possible using sulfur dioxide gas - as it is acidic and does not require acid to liberate active reagent, like in the case of SMB or sulfite. Also, preferrably SMB over regular sodium sulfite - and not overdoing it with SMB/sulfite - as unnecessary sulfite will start to kill acid in the solution - to liberate now unnecessary SO2. Breaking the crucial AgCl2- anions to plain AgCl - drastically increasing the chance of liberation of AgCl cloudiness.

If you follow this, you start with strongly acidic, crystal clear solution and use preferrably SO2 gas (or at least topple with some few dozen mL of fresh HCL and continue with SMB) - there is little to zero possibility to obtain fine gold precipitates. Only parameter which is hard to adjust is the concentration. In the cases where you are dealing with large volumes of spent AR solutions with little gold (less than 1g/L), it is wise to cement the gold on copper sheet (after de-noxing) and bringing the whole pot with copper to the very slight boiling- this helps to coagulate the gold into bigger particles and kill all possible traces of nitric (seen by yellow/brownish gasses when beaker is covered - in case of this, vent the beaker from time to time). When doing this, try to minimize contact of air with solution - as it lead to undesirable dissolution of too much copper into the solution.

Also, some solutions containing high nickel or PGMs are hard to de-nox with sulfamic acid (NO and NO2 complexing to these metals). In these cases, use of copper as denoxing agent and also precipitant could be also great advantage.

PS: 22k is 91,6%. Even with the dirtiest gold I ever produced, I never gone below 95%. And this gold was obviously dirty and flocculent, floaty - due to conglomerates of tin oxohydroxides and silver chloride. So be careful when selling the other time. And after melting (regular torch melt on the silica dish glazed with borax), it is hard to get less than 97% (if the solution wasn´t totally milky from AgCl) :) like, you need to put a lot of "effort" to produce button with less than 97% Au.
It pays off to re-refine gold :)
 
Last edited:
Well I'm not sure how to deal with that then. I haven't dealt with that. How do separate the gold and the pgms
Easily. Just as regular gold separation - with SMB, or ferrous sulfate. Redissolve the precipitate in AR or preferrably with HCl/ 10-30% H2O2 (no need of de-noxing afterwards) and only gold will drop after applying SMB or ferrous, PGMs will stay in solution.

But be careful with assumptions when obtaining the black precipitate after copper cementation. Black precipitate could easily be just copper oxides flaking off the copper. Very similar look, but stannous test and also colour of the solution after black cement redissolution will tell you the truth :) Happened many times to me, but XRF told the truth in 2 seconds :D no PGMs or other PMs. Double checked with stannous to be surely sure :)

Also good think about where the PGMs may enter your batch - as PGMs are much more scarce in e-scrap than gold. Aside of some special industrial PdAu plated pins, relay contacts and MLCCs and some jewellery white gold alloys, there are little to no common sources of Pd. Like 99% of the times when you do not expect PGMs, they wouldn´t be there :) Or at least not in concentrations worth chasing....
 
Back
Top