Pitch black solution - need help

[Wingedcloud]

Hello everyone,

I started a new batch on last wednesday, that consisted on applying the AR process to the material on the next picture.


The back part (where the solder is) had an IC, that I removed with an heat gun.

After removing those IC, I prepared a container with HCl and a bit of water, which I heated before i started small aditions of HNO3, to dissolve the metals in the pins.


The reaction was going smoothly (good color in the picture). When the reaction was almost done (i kept checking if the pins were already dissolved), I made one last addition of nitric (24 mL in total, if I recall correctly), and, since I had to leave, I removed the container from the hot plate and left it under the fume hood to finish the reaction for when I came back the next morning.
The next morning, my solution had cooled down and was very dark black, as I've never seen an AR before(and I have seen plenty). I made my usual procedure: prepared a new container with some ice to which I poured the AR solution, washed the residue with the wash bottle, and added a small amount of H2SO4 to precipitate any lead, as I always do.
I then proceed to filter the solution. After filtering, in my filter I had a dark powder (i can put a picture of it tomorrow) and some undissolved gold particles from the pins.
The AR solution remained very dark black (my phone lantern wont go throuhg it at all). I kept going forward and added SMB to precipitate the gold in the solution. No color change.
As I am writing this, i left the solution to decant the gold powder that would come out with the SMB addition, waiting to be filtered tomorrow. However, I'm feeling that I won't have much gold at the bottom of my container tomorrow, because I regularly checked for a deposit during today and couldnt see any.

I searched for a while in the forum for a similar problem, and came up with this idea: is it possible that the tin I initially had on the back of my starting material had produced colloidal gold, which is darkening my solution, and that some of it got on my filter?

I have 0 experience with colloidal gold, don't know much about it (how it forms and what causes this) and have never come across a similar situation. I too read that solutions with colloidal gold are usually red colored, and not dark as my solution is now.

I'll filter my solution tomorrow to check if any gold came out with the SMB, and keep the filtered solution until I know what happened. Meanwhile, if anyone can help me figuring this out, would be much appreciated.

Best regards,
Winged

 

[butcher]

With tin in your solution you can have colloidal gold. Good reason to pre-treat your scrap. If there are traces under a solder mask, or in layers of the fiberglass (where acid have a hard time leaching into (because of reaction bubbles trying to escape those hidden areas or pockets, the gold can also cement out of plate the copper in those areas.

 

[UncleBenBen]

I'm thinking all the nitric was consumed before the base metals were. That would allow gold to cement out as that dark powder in the filter and explain why you still had visible gold flakes in it. That would probably mean that you have gold cemented in the substrate on the copper traces.

The bases would go back into fresh AR to try and free that gold. The powder/flakes would be incinerated and reprocessed.

By the way what does stannous show on the black solution?

 

[Wingedcloud]

I'm thinking all the nitric was consumed before the base metals were. That would allow gold to cement out as that dark powder in the filter and explain why you still had visible gold flakes in it. That would probably mean that you have gold cemented in the substrate on the copper traces.

The bases would go back into fresh AR to try and free that gold. The powder/flakes would be incinerated and reprocessed.

By the way what does stannous show on the black solution?

Stannous test showed no gold in solution.
I can gather the bases that remained after the first AR treatment and put them along with the filter in a new AR batch. But what about the 1st AR, now treated with SMB solution? There's gotta be some gold in that one too right ? Some idea on how to get it back?

Winged

 

[UncleBenBen]

Stannous test showed no gold in solution.
I can gather the bases that remained after the first AR treatment and put them along with the filter in a new AR batch. But what about the 1st AR, now treated with SMB solution? There's gotta be some gold in that one too right ? Some idea on how to get it back?

Winged

As long as your stannous is working, it won't lie to you. If it was negative, and no precipitate from SMB, then it's pretty safe to say there is no gold in solution.

I think it's also pretty safe to say that all dissolved gold was reduced by copper when the nitric ran out. Most of it was caught in your filter with the visible gold, but some will also be wherever there was copper left, like in the layers of the fiber base.

At least this is what I've found in my own small scale tests with nitrates lately. If wrong I hope someone will chime in.

 

[Topher_osAUrus]

Stannous test showed no gold in solution.
I can gather the bases that remained after the first AR treatment and put them along with the filter in a new AR batch. But what about the 1st AR, now treated with SMB solution? There's gotta be some gold in that one too right ? Some idea on how to get it back?

Winged

As long as your stannous is working, it won't lie to you. If it was negative, and no precipitate from SMB, then it's pretty safe to say there is no gold in solution.

I think it's also pretty safe to say that all dissolved gold was reduced by copper when the nitric ran out. Most of it was caught in your filter with the visible gold, but some will also be wherever there was copper left, like in the layers of the fiber base.

At least this is what I've found in my own small scale tests with nitrates lately. If wrong I hope someone will chime in.

Im going to chime in.. But, not because you are wrong.. But to "second" your post.

No more nitric + Cu +Au = Au cementing on to any base metal it can.

But, your test of the solution that has smb in it, may yield a false positive.

So be careful on that test... I believe its only an issue if there is ALOT of extra smb... But, how much is too much?..is the answer to that "any" whenever there is no gold in solution? -i do not know-

 

[Barren Realms 007]

If copperas was used on the first drop it would not have the chance of reading a false positive from using SMB. It make life so much easier with a lot less headaches.

 

[Topher_osAUrus]

If copperas was used on the first drop it would not have the chance of reading a false positive from using SMB. It make life so much easier with a lot less headaches.

Very true.

And it doesnt produce CuCl like smb does if dropping in a copper fouled solution.

I dont know why more people don't use it?
Wonder if its more the 1lb copperas to 50 dwt gold compared to 1:1 smb/gold..

Or if they just dont like the iron mess in the waste stream.

I like to use it first, smb second

 

[UncleBenBen]

But, your test of the solution that has smb in it, may yield a false positive.

So be careful on that test... I believe its only an issue if there is ALOT of extra smb... But, how much is too much?..is the answer to that "any" whenever there is no gold in solution? -i do not know-

I've noticed that if you use so much SMB that you can smell SO₂ after the drop, then that's enough to start showing a false positive with stannous.

But a very light brown false positive can be just as misleading as a very dark one. That's why I love my little spot plate. It gives a lot more options for testing and helps eliminate any doubts.

 

[Wingedcloud]

Hello all,

Thank you very much for all your replies, which on planning my next procedure after the results I had yesterday.
After reading all your thoughts on what might have happened, first thing in the morning I did was take this picture of the black solution I ended up having after the first AR bath.

When I first analised the container I noticed that I could have gotten some sediment during the night. I proceded to filter the dark solution in the same filter I had the remains of gold from the first filtration. I got little to no additional powder in the filter than that I already had. I then kept the still dark solution for further investigation on what's in there.

Next step, I gathered my bases again and put all them together with the filter in a new AR bath, hoping that I could get some gold that cemented in the bases, as most of you outlined, plus some of the gold that was in the filter.

After the process was over, I cooled the solution and filtered it, and had this.

Not the worst solution to have after an AR bath

I then added SMB to this solution, and after some time, I think I may be getting some sediment to filter when I resume my work tomorrow morning (I hope it's gold ^^ )
As I am writing, I have got these 2 solutions.

Regarding the black solution, I have mixed feelings about it: for one, I feel like throwing it away (to my stock pot), and don't think about it anymore. On the other side, I really liked to know if there is a way to get the gold in there, if in fact there is something to recover from that. If someone can guide through a procedure to possibly get any gold from that dark solution (as I said, if there is a possibility to get any gold from that), would be much appreciated.

Kind regards,
Winged

 

[Topher_osAUrus]

Copperas

Or cementing on copper, which is pretty much step 1 of the stock pot.

Edit to add: stannous test, if barren, treat for waste, dont bother looking for gold where there is none.

 

[UncleBenBen]

Winged, if there is any gold in that original black solution it would have to be colloidal. I really don't think that's going to be the case, but I wouldn't mind being proven wrong.

If it is trapped as a colloid, there are several ways I've read about to deal with it. One of the easiest I can think of is to add a small amount of oxidizer. That can some times break the colloidal bonds. Then the solution can be retested with stannous.

Another would be to try and filter and incinerate. If it is colloidal and that dark I would think there would be a LOT of gold bound up that would take a long time to filter.

I think you may be chasing your tail any way you go. One of the things Hoke stressed about testing was learning to have faith in the tests, and your ability to perform them. If nothing else, evaporate to dryness and reprocess.

 

[Wingedcloud]

Winged, if there is any gold in that original black solution it would have to be colloidal. I really don't think that's going to be the case, but I wouldn't mind being proven wrong.

If it is trapped as a colloid, there are several ways I've read about to deal with it. One of the easiest I can think of is to add a small amount of oxidizer. That can some times break the colloidal bonds. Then the solution can be retested with stannous.

Another would be to try and filter and incinerate. If it is colloidal and that dark I would think there would be a LOT of gold bound up that would take a long time to filter.

I think you may be chasing your tail any way you go. One of the things Hoke stressed about testing was learning to have faith in the tests, and your ability to perform them. If nothing else, evaporate to dryness and reprocess.

Thank tou UncleBenBen for your reply.
I don't think i am ready to give up on that dark solution yet. Even if I end up getting nothing from there, one things remains for sure: knowledge and learning
As for you advice: i've read too that adding a little oxidizer (in my case nitric) might get the gold back in solution. But the gold won't get dissolves without something to keep him there. So isnt it important to add a little receptor (ex: HCl) to grab the dissolved gold, in case there isnt enough already in the dark solution? Too much receptor neer hurts as far as I've read about the AR reaction process.
One thing I've noticed is that my dark solution is very similar to a stressed abd saturared AP solution. It has that dark brown color given be Cu+ ions in solution. Maube that's the whole reason behind the dark colour, but i am not willing so accept that idea as true just yet.
I'll check back with more developments later.

Winged

 

[jason_recliner]

This advice from Butcher may be suitable to your situation:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=20995&p=216657&hilit=break+colloid+sulfuric+strong+heat+volatile#p216295
Edit: Warning, it's a solid reading and comprehending session.

 

[UncleBenBen]

That's a great link to have saved Jason_. Got to love a good Butcher post!

Winged I completely understand the need to learn it first hand. That's the reason I stay busy with my test tubes and tiny beakers! Good luck with it and be safe. Let us know what you find.

Ben

 

[jason_recliner]

Actually Ben, I didn't save it. But I read it and re-read it so many times that even after 2 years I still remember the keywords to find that post.

To be honest, much of it made very little sense back then. But as one progresses and keeps determinedly reading, slowly, hopefully, one becomes a little more 'edumacated'. Quitting school after Year 8, I feel I shall surely never reach Mr Butcher's comprehension of chemistry, despite how fascinating I find it. Though if I remember correctly, he too was a late entrant to the field. Which means hope for the rest of us.

I guess the bottom line is: One can be good enough at anything in which one is truly interested. Or, put another way, I can do science, me. :lol:

 

[Topher_osAUrus]

I'm not trying to be a negative Nancy or anything..
..but i have had a couple thoughts come to me over night on this.

-does tin in solution of ar, tend to become metastannic or stannous?
--i have no idea, but, i would think it would be the former...i try to keep tin/solder out of solution w gold as often ss humanly possible.. Just kickin' the idea out.


-does the black necessarily mean that its colloidal gold?
--i have a black solution here that i know definitively has no gold in solution whatsoever- it is black from dissolving kovar, from pins, that looked EXACTLY like your pins/Processors(apple i think?-idk, im an apple hate-monger)
Pic attached of my black solution

I would love to be able to tell you that there is gold in it (not really, then itd be a chore to get it out)...but, colloidal gold, is purple or shades there of... Have you dipped in a piece of paper and just let it dry in the sun? To see if there was any shade of purple of cassius? Not the best "test" but, bettwr than reducing solution to dryness and finding out it had all cemented out previously..
I would try a small sample first before doing the whole beaker, should you choose to break the colloid, that may only be hypothetical.

What yield are you expecting?
What yield did your yellow/green solution give?

Yea, i want there to be gold there for you..but
A famous philosopher once said "you cant always get what you want"

-topher

 

[UncleBenBen]

-does the black necessarily mean that its colloidal gold?

My understanding is a colloidal gold solution can range from a light red to black(or really just a very dark purple), depending on concentration. Just like the colors of the colliod produced when testing a gold solution with stannous.

I'd have to agree it looks like a saturated base metal solution. But I kind of hope I'm wrong. I've got a bucket with old black waste solution I'd have to take another look at before treating as waste! :mrgreen:

.. Have you dipped in a piece of paper and just let it dry in the sun? To see if there was any shade of purple of cassius? Not the best "test" but,

That is a really good idea there Topher! I'm going to have to remember that one. It does make sense that it would show like that if it was colloidal.

 

[UncleBenBen]

Actually Ben, I didn't save it. But I read it and re-read it so many times that even after 2 years I still remember the keywords to find that post.

To be honest, much of it made very little sense back then. But as one progresses and keeps determinedly reading, slowly, hopefully, one becomes a little more 'edumacated'. Quitting school after Year 8, I feel I shall surely never reach Mr Butcher's comprehension of chemistry, despite how fascinating I find it. Though if I remember correctly, he too was a late entrant to the field. Which means hope for the rest of us.

I guess the bottom line is: One can be good enough at anything in which one is truly interested. Or, put another way, I can do science, me. :lol:

Haha! I hear you. A year ago most of this stuff might as well have been hieroglyphics. You're right, if one sticks with it and is stubborn, I mean determined, enough it finally starts making a lot of sense!

 

[Wingedcloud]

Hello all,

As promised, I've got some news.
Yesterday I left my green solution container settling. So today, I had a nice brown powder on the bottom of it, which gave me this after filtering.

It's very very fine powder. Not much, but it looks as gold is supposed to look. Don't know how much it weighs. Will post it when I know

As for the dark solution, I read the Butcher post jason pointed, but to be honest it seemed to much work to a not so sure gold bearing solution. Didn't want to have that much "trouble" to end up having nothing in the end. Thanks anyway jason
So I opted to add a little nitric and HCl to it, heat it up and wait a while, doing a stannous test to detect some gold in solution. The test came out negative, and plus the heated solution revelead to be very dark green, giving reason to the base metals saturation hypothesis. So I threw away any gold wishes on that and put it all on the stock pot. Maybe one day that well hidden gold will come right into my hand

Answering topher: these cpu's where actually a model of Altera MAX.
I didn't remember to test the pins with a magnet, otherwise I could have known it was kovar underneath the gold plating.

When I first started this batch, I had the intention of document it as best as I could, share my info in a new thread in the forum, so people processing this type of material could have some basis to work on and compare results. However, since I've run into a little of setbacks, I was the one who had to search for help
Will anyway post the weight of my melt when I have it. Don't think my weight will represent the total yield of those pins, but it's something

Thank you all very much for all your replies and suggestions. You made me feel supported, and I guess that's what the forum is all about :mrgreen:

Best regards,
Winged