Black Silt in precipatated gold

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donl001

Member
Joined
Apr 25, 2008
Messages
18
Location
Pa
Gentlemen,

Once again I would like to ask for assistance from the experts.

I processed a batch of gold filled jewelry using the process outlined on Lasersteve's DVD.

On the last two batches, when it came time to percip. the gold out of solution using SMB, I ended up with gold and approx. an equal quantity of a black silty material. The unknown material is significantly less dense than the gold, but, is an extremely fine powder. The powder is light, but, is mechanically carried along with the gold. I can post photos if needed, but, any guesses of what the material my be?

The gold foils were washed several times prior to the AR stage and as far as I am awhere, no base metals made it through.

Thanks in advance for your insite on this material!

Don
 
Yes, I added sulfuric during at the end of the AR reaction incase any lead was present. The strange thing is the amount of this material that is present. Volume wise it is basically the same volume as the gold. The amount of gold should be around 20 grams.
 
Don, 20g of gold is the yield you expected? If so, how much have you dried & recovered?
If its less than 20g, then the fine black powder could be the rest of your gold.

How much GF material you started with, 1 or 2#'s?

Just a wondering.

Phil
 
May very well be copper (I) chloride, but it usually manifest it self as dark grayish color.

Also, contaminated gold solution tend to drop the last remaining gold along with some copper, which create a fine black ppt.

In any case, a proper wash cycle will take care of that.
I usually run this kind of ppt once again in AR.
 
donl001 said:
Gentlemen,

Once again I would like to ask for assistance from the experts.

I processed a batch of gold filled jewelry using the process outlined on Lasersteve's DVD.

On the last two batches, when it came time to percip. the gold out of solution using SMB, I ended up with gold and approx. an equal quantity of a black silty material. The unknown material is significantly less dense than the gold, but, is an extremely fine powder. The powder is light, but, is mechanically carried along with the gold. I can post photos if needed, but, any guesses of what the material my be?

The gold foils were washed several times prior to the AR stage and as far as I am awhere, no base metals made it through.

Thanks in advance for your insite on this material!

Don
Click to expand...

Was this after the first pass with AR?

All the gold filled I have ever processed reported far too dark on the first drop.

Was any of the gold filled, White gold filled?

I should have saved the white gold items to run separately and had to deal with some palladium when I didn't.
 
P.S. (to my previous post)

Very tiny gold particles will be black. These will sometimes seem to be suspended in the solution, but will settle to the bottom eventually. They may also contain some drag-down of either base metals or PGMs.

Since these almost suspend in the solution, it would seem like they are lighter. Also it would be reasonable to assume that upon swirling of the solution, they would rise up into the solution easier than larger particles of gold, and thus seem to be "lighter" in weight, but still actually be gold or drag-down PGMs.
 
Gentlemen,

Sorry for the delay in my response, but, thank you for all who provided insite to this situation!

I believe that the black material was indeed copper chloride. After washing I have 18.3g of gold remaining. My only real question is that my guestimate of 20g gold in the lot was only slightly high, so I didn't overshoot the SMB by much. That being said, how did I drop that much copper chloride?

Anyway, thank you for your assistance!!

Don
 
Well, assuming that you used the cell, maybe the solution got a bit too hot & you had a fair amount of copper dissolved & mixed with the black gold powder. After the washing ,you ended up with 18.3g of gold.
I understand you started with 1100g of GF material. Keeping in mind that you might have had a mixeture of GF, GP, GE, gold tone & so on. So, worst case scenario it was 1/20th 10k material your yield is close. I would have calculated this way, .05 x .375(9k) x 1100g = 20.6g 24k, if my math is right. :roll:
18.3g is pretty close. At today's spot you have $1022.00. That would be good or bad depending on how much you paid for the material.

My .02 centavos! :mrgreen:

Phil
 
Phil,

No cell was used, just simple precipatation with SMB. That is why I was so concerned with the amount of the "extra" stuff. I expected around 20g gold and added 20g SMB to precip. ....I did add an extra 2 - 3 grams of SMB as I always do to assure no remaining gold in solution.

I have processed several batches using this same methodology, but, never experienced or expected that much crap to fall from solution.

Even more strange to me is that this batch was almost fully dissolved in nitric. The batch was practically all purple mud and with fewer "clean" foils than I normally experience with a GF Jewelry batch. I washed the gold with several rinses of distilled water just to minimize any silver chloride due to the amount of chlorine in my "city" water before the AR stage. So, I really did not expect any contamination let alone the amount that I experienced.

Again, thanks for your assistance!

Don
 
Your batch may have had a different alloy amongst it than you normally encounter, perhaps some plated junk. This is the place to use incineration after the original nitric digestion and then a hydrochloric acid wash before the dissolution in AR, easy said after the event, been there done that!
Sounds as if you ended up with some colloidal gold so check for any sediment in your waste nitric solutions.
 
I have had 3 grams of black percipate drop before when using poormans ar and ceramic cpu's.I thought it might be the resin from the cpu's but I melted it in my crucible and it melted right into gold.And it was pure black not brown.
 
Gold, tellurium, selenium, lead, silver, barium, bismuth The first is reduced to metal, the next two are reduced to semi-metals, the last four come down as sulfites when SMB or SO2 gas is added to an impure gold chloride solution. Cold precipitants of gold often are black and have colloidal gold remaining in the liquid. Apparently there wasn't enough gold to exothermically heat the reaction. A possibility of pewter (bismuth, tin, antimony) from cheap gold plated jewelry.
:| Dr. Poe
 

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