dissolving gold after using nitric

[glorycloud]

Greetings!

I have used nitric acid to dissolve the base metals from two batches of nice escrap.
One batch was some nice old IC's (the long rectangular ones with gold plates and legs)
and the other batch was of ceramic CPU's that had pins that were not all gold.
I used nitric to get at the non gold part of the pins.

Both batches seem to have turned out pretty well so far. (I did have to filter off and
re-do the cpu's again as I left the gold plates in with them and the underlying material
didn't quite get dissolved the first go around. oops!)

My question is what should I do now? Use poor mans AR to dissolve the gold or would HCL / clorox work
just as well? I have rinsed both batches really well in distilled water so far.

Thanks for the advice!!! 8)

 

[oldtimmer]

I much prefer to go the HCL CL route at this point as I dislike Nitric.

I have a batch that I ran this way and will be checking the results tonight as I dropped the gold with SMB just before going to work. There was a lot of nice brown gold precepitate just starting as I left.

Good luck

dave

 

[Oz]

This is a very good question if you choose not to incinerate to remove all nitric. Since I do not know the answer to having traces of nitric present and adding Cl2 I would personally go to AR if I was not going to incinerate first.

I would be interested in the chemists on the forum weighing in on the nitric/Cl2 combination.

Personally I prefer to rid a solution of free chlorine than nitric any day, but when in doubt triple evaporation is not that bad.

 

[markqf1]

Glorycloud,
I don't usually process electronic scrap but, a few months ago I tried a batch just as you described.
All of the remaining solids went right into the A/C.
A nice golden color and a good stannous test made me feel that this was a good choice.
However, when I tried to precipitate with SMB, I had problems.
From the moment I added it, I knew something was wrong.
The small amount of brown powder that dropped turned black and very fine overnight.
Adding more SMB did not help at all.
I thought my SMB had went (bad) but, I determined later that the SMB was fine.
I ended up using copper to get the rest of the gold out.
I wrote it off to contamination and have not tried this method again.
I felt sure it had been washed enough to remove any remaining nitric and I know there was no chlorine remaining in the solution.

I too, would be interested in hearing what the gurus have to say about this.

Mark

 

[glorycloud]

I tried the HCL / Cl last night and it seemed to dissolve the gold like it does when
I use it for dissolving the gold finger foils. Same nice yellow auric cloride is now
in the coffee pot ready for precipitation with SMB. I hope to have some details
soon about how it went.

I still have the bits of broken ceramic IC chips in the bucket that I will look over
today to see if all the gold was dissolved. I also have the other batch of ceramic chips
that I may also try the HCL / Cl on after I wash well with water.

I would like to learn how to incinerate but I am a chicken. I don't go out
of my way to play with fire. Using Steve's mini-furnace is a stretch for me. 8)
If some nice forum member would do a training video on incineration and put it
on a CD or make it available on the forum website, I know I would greatly appreciate
it as I am such a visual learner. :lol:

THANKS!!!!!!!!!!!!!!!!!!!!!!!!!

 

[glorycloud]

After diluting the auric cloride solution from the old rectanguler IC's with distilled water
before I added SMB, I had some white residue precipitate out. I have read GSP write
about silver cementing out when the solution is diluted 3:1 with water.

I was thinking about siphoning off the auric cloride and leaving the white residue
behind to play with later. Any thoughts out there amigos?

 

[butcher]

lead or silver, boiling water can seperate and help indicate which, in boiling hot water lead chloride slightly soluble, silver cloride is not. also Ag chloride usually will turn violet to dark in sun.

 

[glorycloud]

I am precipitating some batches of ceramic CPU's that were processed with
nitric acid, washed well with water and then HCL - Cl'd to dissolve the gold remaining
on the cpu's and floating around in the bucket. I seem to have to use more Clorox
to dissolve the gold then when I am using it on the finger foils which is to be expected
as the foils are way thinner from the fingers.

Both batches took a lot of SMB to drop the gold. One gave me the normal dark cloud
in the solution as the gold dropped out. The other one was different in that the gold
hasn't dropped out in cloud form but has seemed to have dropped out clumpier and
grainier straight to the bottom of the glass container. There seems to be a lot of yellow
color remaining in the solution as well. This batch I was unable to dilute as much with distilled
water as I did with the first batch due to volume restrictions in my container.

I was thinking of removing half of the volume of auric cloride into another container
and diluting them both again with distilled waterand then re-precipitating with SMB.

Any thoughts out there amigos??

Thanks! 8)

 

[goldsilverpro]

I would first make sure the yellow color in the solution is gold and not iron. Test with stannous chloride.

 

[glorycloud]

will do - I have to make a fresh batch of stannous. 8)

 

[glorycloud]

The yield on about one pound of the rectangular ceramic IC's was fairly disappointing.
Only .77 grams. :roll:

However, that did not include the little gold plates. I put them in with the others that
I have been collecting.

I do have some other ceramics processing in nitric and HCL-Cl. I will report back on
how I do on them. The first batches did precipitate out OK with SMB. I just seemed
to have to use a lot of SMB to get it to drop though. Stannous tests were positive for gold
and I have some powder almost washed and ready for the mini-furnace. 8)

 

[glorycloud]

Well I finally have re-refined all the gold powder that I have been collecting.
I used poor mans AR. Interesting process. Not as much brown fumes as when
I processed some ceramic CPU's, so that was nice.

I got a nice deep orange color after evaporating down and adding HCL three
times. After diluting with an equal amount of water and adding the SMB I got
and immediate chocolate brown cloud that I do enjoy seeing for some weird
reason. Maybe I didn't get enough Yoo-Hoo as a boy. :lol:

Anyway, is there a need to run the powder through AR again after this or should
it be ready for Steve's mini-furnace??

THANKS!!!!

 

[lazersteve]

Wash as per Harold's clean up routine (hot HCl, water, then optionally ammonia, water), then redissolve a second time for highest purity.

Steve

 

[glorycloud]

Cool - will do!

An observation though. It seemed like the two teaspoons of sodium nitrate called for
with poor mans AR recipe was going to be a lot for doing AR on the gold powder that
I wanted to re-refine. I only ended up using one teaspoon and even that seemed like
too much as there were really no very noticeable red vapors coming off.

Any thoughts on the amoint of sodium nitrate to use when re-refining
your gold powder???

Gracias amigos!!

 

[lazersteve]

The 'two teaspoons' was meant for processing when a larger (>greater that 1kg) batch of base metals are present.

For redissolving gold powder or foils I have found that approximately 15 grams of sodium nitrate are need for each ounce of gold to be dissolved. Always start with less than you calculate and use just enough to dissolve all the material is the main point with the modified Poorman's AR reaction. Near the end of the reaction, when the powder is nearly dissolved, only add small pellets of nitrate to dissolve the last traces of powder.

Be sure you heat and let all the tiny bubbles fully cease before adding more nitrate.

Fumes should just fill the covered reaction beaker and not be pouring out the spout. Just as with the HCl-Cl reaction, the more off gassing you see, the more reagent loss you have to the environment. Optimally, with this technique, you want a slight red cloud to fill the air space in the beaker. When the air space clears from red-brown to transparent and the tiny bubbles cease, the nitrate is nearly used up or you need more HCl.

Once the cloud inside the beaker clears and the tiny bubbles stop, always check for too little HCl before adding more nitrate. Do this by adding a few mL of HCl, if you get more brown fumes or fizzing you are short on HCl. If the addition of a small amount of HCl shows no reaction, the nitrate is used up.

Repeat these small additions until the metal is fully dissolved.

Steve