White/Silvery Crystalline Power Beneath Gold AFTER drop with SMB...?

[AuggieDog]

I processed a bunch of small black plastic/epoxy transistors with gold legs by going directly with AR. I have done this before with top hats, and aside from dealing with dirty solutions and long wait times for settling, it has gone very well and without any issues. This is the first time I did this type of transistor; an example is shown below. Normally I process top hat transistors based on ORVI's method found in a thread from just a few months ago. Dissolving the legs from these plastic types was very fast, maybe 2 hours total time for 2.2lbs in a 5 liter beaker. I did everything as I normally would. Using sulfamic for excess HN03, filtering, cooling and then adding SMB to drop gold from the solution for recovery...usually a re-refining follows.
This time I got this white crystalline powder (it is silvery in bright light) which is beneath the gold in my picture below in the first reply. It is more granular than powdery and seems to mix with the gold powder quite readily when moved around. But, as can be seen it has actually settled below the gold in the flask in the picture below. I am unsure what this is and thought maybe AgCl...?
Also, I guess I should ask...how do I proceed to solve this problem?
Thank you!

 

[AuggieDog]

This shows substance beneath gold

 

[Yggdrasil]

I processed a bunch of small black plastic/epoxy transistors with gold legs by going directly with AR. I have done this before with top hats, and aside from dealing with dirty solutions and long wait times for settling, it has gone very well and without any issues. This is the first time I did this type of transistor; an example is shown below. Normally I process top hat transistors based on ORVI's method found in a thread from just a few months ago. Dissolving the legs from these plastic types was very fast, maybe 2 hours total time for 2.2lbs in a 5 liter beaker. I did everything as I normally would. Using sulfamic for excess HN03, filtering, cooling and then adding SMB to drop gold from the solution for recovery...usually a re-refining follows.
This time I got this white crystalline powder (it is silvery in bright light) which is beneath the gold in my picture below in the first reply. It is more granular than powdery and seems to mix with the gold powder quite readily when moved around. But, as can be seen it has actually settled below the gold in the flask in the picture below. I am unsure what this is and thought maybe AgCl...?

If you used AR it can't be Silver.
Did it only appear after SMB?

 

[AuggieDog]

Thanks Yggdrasil, I thought the same thing about silver! Yes, this occurred after the drop with SMB. Is it possible that because I used a super saturated pre-mixed solution of H2O and SMB that the SMB drop out of solution?

 

[AuggieDog]

Well, I took half of this solution and put it back into AR. These are definitely silvery particles that do not seem to dissolve in aqua Regia.

 

[Yggdrasil]

Thanks Yggdrasil, I thought the same thing about silver! Yes, this occurred after the drop with SMB. Is it possible that because I used a super saturated pre-mixed solution of H2O and SMB that the SMB drop out of solution?

It is very murky, have you filtered it properly before precipitation?
The solution is supposed to be crystal clear,in the meaning no turbidity before adding the SMB.
And if you have too much salts in it it may drop when to solution get saturated.
Try adding some water and heat it.

 

[Yggdrasil]

Well, I took half of this solution and put it back into AR. These are definitely silvery particles that do not seem to dissolve in aqua Regia.

Silver Chloride is white and fluffy.

 

[AuggieDog]

Thank you for all your help.
So, as I stated above, I process these in directly in AR only doing a fast filtration before dropping with SMB. The solutions are always very dirty this way and usually I get a fairly normal gold drop, then decant, wash and re-refine. I am positive for Palladium & gold...odd because during my first test I did not see and orange color. Do you see these metallic particles in that AR...WTH?

 

[Yggdrasil]

Thank you for all your help.
So, as I stated above, I process these in directly in AR only doing a fast filtration before dropping with SMB. The solutions are always very dirty this way and usually I get a fairly normal gold drop, then decant, wash and re-refine. I am positive for Palladium & gold...odd because during my first test I did not see and orange color. Do you see these metallic particles in that AR...WTH?

Orange is Pt not Pd.
There might be Rhodium plating inside, and that is not very soluble in AR.
Most likely it is something else though.
Have you crushed any of these and checked how they look inside?
This is how the stannous look like

 

[AuggieDog]

Orange is Pt not Pd.

Have you crushed any of these and checked how they look inside?

Absolutely correct of course, platinum. Are asking if I crushed the transistors...? No did not. They are very tiny, actually smaller than the ones I showed so I did not bother with the tiny amount inside of them and sought only to extract the gold from the plated legs. What do you think of the metallic bits floating in solution? I am laughing and crying at the same time here, unsure what went wrong.

 

[Marcel]

The use of Platinum in general-purpose transistors like the ED1402B model is extremely rare. In typical low-cost, all-purpose transistor applications, Platinum is not necessary and does not make sense.

The use of Platinum in electronic components is generally infrequent. The only application that comes to mind is the use of thermoelements that precisely switch or control a temperature range. In such applications, a thin Platinum wire is used as a specialized temperature-sensitive resistor.

What is unique about these gold-plated legged transistors is that sometimes the wire of the leg is made from a "nasty" Nickel alloy (I forgot the name, sorry) that contains Nickel and some other non-metallic elements. This material impedes the normal Aqua Regia procedure, leading to the formation of unwanted compounds.

Therefore, I strongly suggest that you check for the presence of Platinum once more, perhaps by processing some of the legs alone to determine whether they contain Platinum or not, and try to avoid dissolving the base material beneath the Gold plating in future runs.

Edit: To check whether it is a Nickel alloy or not you can use a strong magnet.

 

[AuggieDog]

Well, I freed the gold from this mess. The problem was TOO much SMB and the solution was too dilute. After settling for 36 hours there was multiple layers of sediment forming so I filtered off as much of the top of the liquid as I could without disturbing the sediment at the bottom. It was very fine and easily disturbed and swirled around.

I then heated the remaining solution, about 1 liter, to near boiling and added some HCL. After that the gold dropped much quicker and cleaner. This was about 5 grams.

It took several filter changes for the 4 liters of top layer of liquid with suspended particles, and there was all sorts of goop in the filters. My first plan was to incinerate but I instead decided to drop the filters in hot AR. The solution was very dirty but cleared considerably after filtration. The color was like anti-freeze. There is also the question of the very strange metallic silvery particles that were in that sediment ??? that were not dissolved by AR...

I dropped 3 more grams that was trapped in the filters. This really taught me to STOP when there's a problem and shop this awesome forum for answers. In truth, it was something ORVI talked about in an old thread and at least several other comments by members that gave me a plan of action that worked in the end.

Thanks everyone! And newcomers should always realize that gold in solution that isn't doing what it should is always there somewhere, but you may have to pause to find it.

 

[g_axelsson]

A bit late but....

A strong solution of copper II chloride might be reduced down to Cu I chloride by excess SMB. The Cu I chloride precipitates as a white solid and small white crystals. It will dissolve in concentrated HCl.

Excess SMB in acidic solution decomposes into SO2 and will give a brown (or dull orange) reaction with stannous.

I've run into similar situations a couple of times. Every time it cleared up with a HCl wash.

I haven't run any similar transistors yet so I don't have any experience with this type. My memory tells me that it contains a ceramic base and epoxy covering the die and bond wires. If it is so then I would start the process by incinerating before going to aqua regia. I like to get all the gold I can.

Göran