Baffled with series of events processing transistors...

[AuggieDog]

I have a fairly decent amount of experience processing older tophat transistors. I do these directly in AR, and always have to deal with dirty solutions. Processing E-waste is very unpredictable and nothing ever goes "by the book" so I have a lot of experience figuring things out when they appear to go sideways. Not today, I need some suggestions...
Today I processed a lot of transistors for an estimated 20-30 grams. After everything was dissolved into solution, I added Sulfamic Acid when the solution was still hot/warm and used it until it stopped reacting...as always. I then added ice, filtered, and 17 grams SMB dissolved in water was added to one beaker containing half the total solution (5000ml). Gold dropped and could be seen but decanting it was a serious issue because the precipitate was about as fine as baby powder. In fact, decanting was impossible without disturbing the gold and it just poured into the decant vessel along with everything else. This is common. My usual fix is adding a bit of sulphuric and heating the solution. I also added a bit more Sulfamic acid thinking there was possibly re-dissolution of my gold going on. I then began to heat the solution and the gold dropped again. The photo below shows the precipitated gold which was looking pretty good. I left the solution on the heat for about 20 minutes, but noticed it was bubbling (effervescently, like soda). I then turned off the heat. I was doing something else but noticed (barely) a vigorous foaming starting...when all of the sudden it erupted out of the flask. About a third of it got way . I have a catch basin and NO precipitated gold was found in either the beaker or the basin!?! Where did it go? I am fairly certain it is back in solution as my Stannous test indicates. After and hour or two I added a pinch of sulfamic acid just to see if any thing would happen. Nothing. I added SMB again and the solution foamed pretty vigorously and was giving off NOX fumes...WTH??? Wouldn't that mean there is still free nitric in my solution??? Just to be clear BOTH vessels have done exactly the same thing...! Fool me twice...
My total solution was 3750ml of HCL and 1250ml of nitric. That consumed quite of bit of base metals and gold on high heat.

 

[Yggdrasil]

I have a fairly decent amount of experience processing older tophat transistors. I do these directly in AR, and always have to deal with dirty solutions. Processing E-waste is very unpredictable and nothing ever goes "by the book" so I have a lot of experience figuring things out when they appear to go sideways. Not today, I need some suggestions...
Today I processed a lot of transistors for an estimated 20-30 grams. After everything was dissolved into solution, I added Sulfamic Acid when the solution was still hot/warm and used it until it stopped reacting...as always. I then added ice, filtered, and 17 grams SMB dissolved in water was added to one beaker containing half the total solution (5000ml). Gold dropped and could be seen but decanting it was a serious issue because the precipitate was about as fine as baby powder. In fact, decanting was impossible without disturbing the gold and it just poured into the decant vessel along with everything else. This is common. My usual fix is adding a bit of sulphuric and heating the solution. I also added a bit more Sulfamic acid thinking there was possibly re-dissolution of my gold going on. I then began to heat the solution and the gold dropped again. The photo below shows the precipitated gold which was looking pretty good. I left the solution on the heat for about 20 minutes, but noticed it was bubbling (effervescently, like soda). I then turned off the heat. I was doing something else but noticed (barely) a vigorous foaming starting...when all of the sudden it erupted out of the flask. About a third of it got way . I have a catch basin and NO precipitated gold was found in either the beaker or the basin!?! Where did it go? I am fairly certain it is back in solution as my Stannous test indicates. After and hour or two I added a pinch of sulfamic acid just to see if any thing would happen. Nothing. I added SMB again and the solution foamed pretty vigorously and was giving off NOX fumes...WTH??? Wouldn't that mean there is still free nitric in my solution??? Just to be clear BOTH vessels have done exactly the same thing...! Fool me twice...
My total solution was 3750ml of HCL and 1250ml of nitric. That consumed quite of bit of base metals and gold on high heat.

You definitely have excess Nitric.
These reactions are best done in beakers and then with plenty of headroom to alleviate these runaway reactions.
Most likely the solution has not been hot enough for the Sulfamic, which should be foaming with these amounts of Nitric.
If you plan to run these the same way, it might be better to cement the values on Copper the first time. Then refine the powders with a minimum of AR or a HCl/Peroxide or similar solution.

 

[Shark]

Try ferrous sulfate for the drop. Seems to work better for me on dirty drops over smb.

 

[AuggieDog]

Try ferrous sulfate for the drop. Seems to work better for me on dirty drops over smb.

Making some now.

 

[AuggieDog]

You definitely have excess Nitric.
These reactions are best done in beakers and then with plenty of headroom to alleviate these runaway reactions.
Most likely the solution has not been hot enough for the Sulfamic, which should be foaming with these amounts of Nitric.
If you plan to run these the same way, it might be better to cement the values on Copper the first time. Then refine the powders with a minimum of AR or a HCl/Peroxide or similar solution.

It seems impossible that I would have excess nitric, but yes I think you must correct. Now, Yggdrasil, I have already added sulfamic and SMB (an EXCESS of BOTH if you ask me), do you think I should re-heat the solution, add sulfamic again and use SMB again...?

​

 

[Yggdrasil]

It seems impossible that I would have excess nitric, but yes I think you must correct. Now, Yggdrasil, I have already added sulfamic and SMB (an EXCESS of BOTH if you ask me), do you think I should re-heat the solution, add sulfamic again and use SMB again...?

​

No, cement it on Copper.

 

[FrugalRefiner]

You didn't necessarily have an excess of free nitric in your solution, but since it was a dirty solution, you may have had an abundance of multi-valent base metals.

Think about the copper chloride leach (aka AP). It works because copper is a multi-valent element, which can move easily from a +1 to a +2 state and back. Copper in the +2 state oxidizes metallic copper (which is at a 0 state), creating two ions of copper at the +1 state. The oxygen in the solution oxidizes them back to the +2 state, and the cycle continues.

In AR, the copper and some other base metals can similarly be oxidized to the higher states. You can eliminate any free nitric acid, but still run into your gold redissolving because as it drops, it can be reoxidized by the base metals.

This is common in dirty solutions like yours because there is a lot of highly oxidized base metal in there.

You can cement the values, then redissolve them in a much cleaner solution.

Dave

 

[Shark]

In AR, the copper and some other base metals can similarly be oxidized to the higher states. You can eliminate any free nitric acid, but still run into your gold redissolving because as it drops, it can be reoxidized by the base metals.

This is common in dirty solutions like yours because there is a lot of highly oxidized base metal in there.

That is the key. There was recent discussion on the use of urea where this was explained. From that I am now curious if the use of urea along with sulfamic might be a means to stop this. Sulfamic to neutralize the actual nitric, and urea to stop the NOx from becoming the oxidizer, thereby stopping the redesolving of the gold.
Edit for clarity.

 

[orvi]

It seems impossible that I would have excess nitric, but yes I think you must correct. Now, Yggdrasil, I have already added sulfamic and SMB (an EXCESS of BOTH if you ask me), do you think I should re-heat the solution, add sulfamic again and use SMB again...?

​

Eruptions of NOx gasses from AR solutions are common. There are many possibilities on what is happening, but many times nitric residues seems to coordinate with dissolved metals and form nitroso complexes. These are more known from PGM chemistry, but they can also form with base metals - like nickel, iron, or maybe copper. But definitely with iron and nickel. I observed this behaviour with transistors processing numerous times, but not quite like you did. Also, de-NOxing the predominantly nickel and iron solutions with sulfamic is very tedious and hardly ever going to completion in sane time, even with the juice boiling.
Usually, denoxing goes like crazy with first spoon or two and then rapidly slows down. It usually dies down, no matter how much of sulfamic you spoon in, even if you simmer the solution. But try to immerse some copper bar or thick wire into this solution and you will see how much NOx-es will come out of it

In your case, addition of SMB can be the culprit. With unreacted nitric in solution, putting in SMB is dangerous from this point (sometimes)- as reduction of nitric with SMB is dependent not only on temperature, but also on concentration. This happened to us back in the day with bad consequences.
---
We were doing classic AR dissolution of all kinds of mixed plated/ceramic/transistor stuff on 10kg scale. My refining partner was used to add just enough nitric to do the job, which took some time to properly react, but worked. Unreacted nitric in solution after the operation was always low - and this was the cause of our "unfortunate event". After we finished, gold was dropped with sodium sulfite as usual, settled and decanted. The barren liquid was siphoned into plastic canisters and placed behind the doors to the hallway to be taken out for treatment. As second canister was taken out, only thing I noticed that it inflated in matter of second and started spewing the spent AR through the screw-cap (obviously not tight) seal. I immediately ran away to the safe distance and watched greenish brown liquid spraying around, accompanied with brown cloud of NOx... I laugh at this story nowadays, but back then, I almost crapped my pants.
---
In cases we dealt with problematic material (lots of cavities, tight places for the acid, plating under large silicon dies etc.) that needed to be "pushed" with more aggressive oxidizing AR, we overshoot the nitric intentionally from the start. When it did the job, we heated the solution near boiling point and brute-force de-NOx/drop gold with sodium sulfite. In these conditions, there weren´t any delayed runaway reactions, as we always had plenty of unreacted nitric in solution and also it was done hot. This treatment isn´t nice, it is violent, eruptive, stinky and messy... But it does the job. Not recommending it tho

 

[anarxi]

Russian refiners, in videos on YouTube that I sometimes watch, usually process transistors with metal hats, first with a mixture of nitric and sulfuric acid (proportion 1/2).
or even electrolyte from batteries + ammonium nitrate..
then the solution is drained through a fabric filter and only then the sediment and what remains on the filter (washed with water) are poured with a solution of aqua regia..

 

[anachronism]

That is the key. There was recent discussion on the use of urea where this was explained. From that I am now curious if the use of urea along with sulfamic might be a means to stop this. Sulfamic to neutralize the actual nitric, and urea to stop the NOx from becoming the oxidizer, thereby stopping the redesolving of the gold.
Edit for clarity.

Shark I think Dean mentioned that that the Urea acts to lower the oxidation state of the base metals thereby preventing this happening by that mechanism.

 

[Shark]

I knew I had read it some place. Here is a link to Deano’s post. It also explains some of the problems I have ran across using nitrate salts at times.

https://goldrefiningforum.com/threads/urea-question.34282/post-369519

 

[anachronism]

I knew I had read it some place. Here is a link to Deano’s post. It also explains some of the problems I have ran across using nitrate salts at times.

https://goldrefiningforum.com/threads/urea-question.34282/post-369519

Brilliant thanks Shark. It's really good that there are discussions on this level because it improves the knowledge base well beyond the basics.

 

[Shark]

Brilliant thanks Shark. It's really good that there are discussions on this level because it improves the knowledge base well beyond the basics.

Yes, sometimes seemingly simple things can solve a whole series of problems. I have had issues from the beginning with some solutions constantly redisolving over and over. Deano’s post struck home but left me paying more attention to what was said and not enough to who said. Your comment reminded of where to look for the post. Thanks.

 

[AuggieDog]

Russian refiners, in videos on YouTube that I sometimes watch, usually process transistors with metal hats, first with a mixture of nitric and sulfuric acid (proportion 1/2).
or even electrolyte from batteries + ammonium nitrate..
then the solution is drained through a fabric filter and only then the sediment and what remains on the filter (washed with water) are poured with a solution of aqua regia..

I have done this in the past (nitro-sulphuric) and found it is not necessary, IN MOST CASES,...Yet, as we see here, sometimes things just go sideways for no apparent reason. I find the Nitro-Sulphuric process is tedious and messy (so is AR) but it is an unnecessary step.

 

[AuggieDog]

I was able to solve the problem by using FeSO4. I heated the solution, treated with Sulfamic (AGAIN) and added Iron Sulphate. Very strange coagulation afterwards of the gold. After decanting I saw just some of my gold in at the bottom of the vessel, but adding water was literally like a magic trick and gold just appeared to double afterwards. In any case, I was not happy with the yield so I am now cementing with copper.

 

[AuggieDog]

WHEN IS FeSO4 actually usable? Does it need to be crystalline? Or can it be used directly after synthesis?

 

[orvi]

I was able to solve the problem by using FeSO4. I heated the solution, treated with Sulfamic (AGAIN) and added Iron Sulphate. Very strange coagulation afterwards of the gold. After decanting I saw just some of my gold in at the bottom of the vessel, but adding water was literally like a magic trick and gold just appeared to double afterwards. In any case, I was not happy with the yield so I am now cementing with copper.

https://goldrefiningforum.com/threads/15lbs-of-gold-plated-pins.34142/page-2#post-373811

Here I nutshelled AR processing in way which I prefected to work the best for myself. I found sulfite/SMB drops from crude heavy base metal content solutions simply too unreliable and abandoned this approach for good.
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De-NOx-ing with sulfamic of heavy nickel solutions is very very tedious and hardly ever going into completion in sane time. That is why you seen more gold by diluting the juice - you lowered redox potential of the solution, shifting the equilibrium to the right.
In many YT videos, folks are showcasing use of urea as de-NOxing agent. It does not work with nitric acid (generally nitrogen (V) species), but they pair it with high dilution of solutions. This enable to drop the gold with SMB or sulfite, rendering the ORP too low to actually attack the gold in appreciable amounts.
---
My advice is to use copper paired with sulfamic for simultaneous drop and cementing. On production scale, this saved me a ton of time. Of course, you will generate little more waste as copper will be dissolved into solution, but this always beaten my time saved financially.

 

[orvi]

WHEN IS FeSO4 actually usable? Does it need to be crystalline? Or can it be used directly after synthesis?

There need to be active species, which are Fe(II) ions. Ferrous choride should also work. Keep it out of the air as much as you can and use as is. No need to evaporate to crystals or anything. You will just add respective volume to your juice, which will be then part of your waste stream - little more liquid to process. So keeping it concentrated can help in overall process.

 

[ólom]

I also process electronic waste and only use urea. I always let it settle for a day and the stannous chloride test is negative. Last time, it was in the acid for 3 days because it didn't want to settle and the stannous chloride test was negative even then.