My GF Watch Scrap Process needs advice...

[bgwatch]

I have managed to get through this to the precipitaton stage without a problem, but then I get what looks like fine salt contaminating the precipitant. From reading the posts on the forum it might be silver chloride.

Here's what I did:
1. Mixed 3 parts HCL(36%) with 1 part nitric acid (70%)
2. Waited 30 mins.
3. Added old gf watch cases, which reduced and disappeared overnight. Lots of brown smoke. Eventually solution was emerald green, dark but clear.
4. Added urea in solution to neutralize nitric. Some large clear crystals appeared in solution several hours later. I heated the solution and the crystals disappeared.
5. Added Sodium bisulfite solution to precipitate. Immediately fine white crystals precipitated along with some brown.

I have tried diluting with water, boiling and adding HCL but the white does not reduce. How do I get rid of it?

Thanks,

Mark

 

[qst42know]

You may be looking at silver chloride from the karat gold filled alloy.

Did you chill and dilute the solution before trying to precipitate gold to remove any silver?

 

[bgwatch]

Did you chill and dilute the solution to remove any silver?

No I didn't.

I think you are exactly right. These are old watch cases and probably do contain silver. I should have done as you said, but I missed that step. So now how do I get the silver chloride out?

Thanks for the quick reply!!

 

[qst42know]

Sodium bisulfate

Was this a spelling error? You should have used bisulfite

AR the solids again to redisolve the gold, a touch of sulfuric for possible lead, chill and dilute, and then filter it out.

 

[goldenchild]

I noticed you said bisulfAte and not bisolfIte. Did you use bisulfAte?

 

[bgwatch]

I noticed you said bisulfAte and not bisolfIte. Did you use bisulfAte?

Sorry, I used sodium bisulfite, I know in chemistry, spelling counts!!

 

[bgwatch]

AR the solids again to redisolve the gold, a touch of sulfuric for possible lead, chill and dilute, and then filter it out.

Awesome, I will do that with the next batch of gf parts. I don't have sulfuric so it will have to wait a few days.

Do I chill and dilute before adding the urea, or after?

 

[qst42know]

Add the nitric in increments so you don't need any.

But if needed I would try it before you dilute and chill.

 

[nickvc]

If when you redissolve the powder you add the hydrochloric acid first, a little more than you need will do no harm, then add the nitric slowly and in small increments only adding more as the reaction stops you shouldn't need urea apart from maybe using a few prills to check if there is too much nitric still in your solution, if so just heat the solution to evaporate the nitric adding small additions of hydrochloric until the brown fumes stop evolving.

 

[Palladium]

If it is silver chloride a wash in warm ammonium hydroxide will remove it.

 

[bgwatch]

I used your advice and spent more time reading the forums on this site. This is a great resource.

My second try was a success. This time I used sulphuric after neutralizing with urea. I know you say I don't need to (use urea) but I used about 40mL in solution just until the fizzing stops. I chilled with 6 ice cubes for about 10 hrs. This is the right time of year for chilling outdoors in Canada 8)
When I added the sodium bisulfite (about 50 g total) in solution, the gold precipitated right away and was just the right golden brown colour, so I knew things had gone well.

There was quite a lot of precipitate, but I only used the SB until no more appeared. I didn't want to precipitate any copper out of solution. I followed the washing advice given here http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=1900 and all went well.

After drying I ended up with 38.2 g of the good stuff.
Thanks to everyone who gave me such good advice.
Cheers!

 

[philddreamer]

Good job Mark! 8)

Phil

 

[bgwatch]

Thanks everyone!

 

[Geo]

did you test your solution to make sure you had precipitated all the gold out? it sounds like you tried to cut the process short to stop from precipitating copper. base metals will "drag down" if you are working with contaminated solution.

 

[qst42know]

Nice batch.

Do you intend to refine a second time?

 

[goldenchild]

38 grams for a first timer is a good amount! Congrats. Can I guess that you digested about 2 -2.5 pounds of watch cases?

 

[glondor]

Super Job. I would give a small bit of advise. please do not dry your powder on your stovetop. At first you are driving off the water, but soon you are volatilizing the acids and other chemicals. Not a lot of fumes but very bad ones none the less. Safety First!. Once again, super job!

 

[bgwatch]

Yes I did test with stannous, and it was negative. To be sure, I reserved the solution and added some more SB and let it sit longer. There was a small amount of solid at the bottom the next morning, it looks brown like gold, probably 0.5 g. I have saved it along with any other solids that I saved during the process. This will all go into another refining later.

Do I need to re-refine? I'm not sure, but I don't know how to test for purity. My goal was to get the gold out of the cases since they are practically worthless as they are and I get them for free anyway. I have no use for the gold so I was going to save it until I'm finished and sell it as-is. Is there a benefit to making it ultra-pure?

I have a hot plate in the garage where I do all of the heating. I used the stove in my basement kitchen for the final heating with distilled. You're right though, I did get a whiff of HCL as the final clumps broke down. I'll do it all in the garage from now on.

The material I used was about 1 kg of g.f. cases (2.2 lbs). Some of the metal was possibly solid 10k.

 

[Harold_V]

Do I need to re-refine? I'm not sure, but I don't know how to test for purity.

If your purpose is to market your gold to a reseller, no need to refine again. It will most likely end up in the hands of a refiner, where it will be processed again. If you were providing gold to a manufacturing jeweler, it's a good idea, to ensure it contains no harmful substances (for example, traces of lead destroy gold's ductility). When gold is precipitated from a dirty solution, it will be contaminated, if for no other reason, drag-down. It does not always wash out fully, just as all of the acid is never removed by water rinses.

While molten, the surface should be shiny. If you witness a scum that emanates from the center of the button and is absorbed by the flux in the dish at the edges, it is not pure. When cool, it should be free of oxides and have a shiny surface. A frosted surface is generally the result of contamination, as is discoloration.

Harold