Interesting colors testing by SnCl2

[Renaldas]

Processed a little batch of old high power soviet transistors with crystal, placed on gold plated disk inside the transistor. Here you see the transistor after electrolysis to weaken its corpus for easy opening. Gold plated disks are welded to the copper corpus, and could be easily removed by heating. Here you see the disk after AR treatment for a long time. I dont know the material of the disk itself, it is reacting very slowly, have a quite high specific gravity, and is very stiff. Some chemists tell me this could me molybdenum.

The initial solution is yellow to orange, there is a lot of white precipitate (I think, this is welding material).

I tested AR solution of several these gold plated disks with SnCl2, you can see interesting colors.

Immediatly after SnCl2

http://www.youtube.com/watch?v=Hf0EGErkVBs

After 2 minutes, added one more SnCl2 drop

http://www.youtube.com/watch?v=Y1AyAdqhLxE

After 5 minutes, one more drop of SnCl2

http://www.youtube.com/watch?v=iOk_NrssVd0

After 10 minutes, rinsed with water

http://www.youtube.com/watch?v=TYE3FT4sCiY

You definitely see purple color, but there is some remaining quite dark blue at the corner. If I hadnt rinsed the paper, it would be very difficult to detect purple.

What do you think about all this?

 

[eeTHr]

Renaldas;

First of all, I'm not an expert. But I'll take an initial stab at it, and hope some of the pros will comment later.

The first thing unusual that I noticed is the bubbling, in the first video. I've never had this happen on a stannous test. I'm guessing that it is bubbling because you didn't evaporate the nitric out of the AR.

However, with too much nitric in the AR, the stannous test can fail to give a color even when there is Au present, because it will re-dissolve the purple-colored colloid Au that the stannous precipitates, and that results in no color at all; which I have had happen to me.

My thought is that with so much nitric left that it actually bubbles, there must be a very high concentration of Au to actually drop some out of that solution, and more so with such a dark color.

If that happened to me, I would first be sure that all the nitric was out, and neutralizing that much nitric, with Urea, would result an awful lot of unnecessary additional components to your solution. So evaporation would be the best remedy.

If you want to test for other PMs besides Au, the next thing would be to use ferrous sulfate, FeSO4, in a small test quantity of a couple of drops, and that will precipitate the Au to "normal" elemental gold and it will drop to the bottom, leaving your test solution the same color as it originally was, to enable you to test the solution which remains for other PMs, like platinum group metals (I don't know about molybdenum testing).

 

[Renaldas]

Renaldas;

First of all, I'm not an expert. But I'll take an initial stab at it, and hope some of the pros will comment later.

The first thing unusual that I noticed is the bubbling, in the first video. I've never had this happen on a stannous test. I'm guessing that it is bubbling because you didn't evaporate the nitric out of the AR.

However, with too much nitric in the AR, the stannous test can fail to give a color even when there is Au present, because it will re-dissolve the purple-colored colloid Au that the stannous precipitates, and that results in no color at all; which I have had happen to me.

My thought is that with so much nitric left that it actually bubbles, there must be a very high concentration of Au to actually drop some out of that solution, and more so with such a dark color.

If that happened to me, I would first be sure that all the nitric was out, and neutralizing that much nitric, with Urea, would result an awful lot of unnecessary additional components to your solution. So evaporation would be the best remedy.

If you want to test for other PMs besides Au, the next thing would be to use ferrous sulfate, FeSO4, in a small test quantity of a couple of drops, and that will precipitate the Au to "normal" elemental gold and it will drop to the bottom, leaving your test solution the same color as it originally was, to enable you to test the solution which remains for other PMs, like platinum group metals (I don't know about molybdenum testing).

Yes, you are right, there could be some nitric left. But where do the other colors come from?

 

[eeTHr]

Renaldas;

In a stannous test, Au will produce a darker color when there is a higher percentage of it in a solution. It will go from very light purple all the way to black.

Platinum will show as tan, orange, or coffee colored.

Paladium will produce blue-green.

These vary when other metals are also present in the solution. There are also specific tests for Platinum and Paladium, using other chemicals. You will find those if you use the search feature on this forum. Droping the Au out with the FeSO4 helps identify these with stannous, though.

 

[eeTHr]

Renaldas;

P.S. You can make FeSO4 by placing some nails into Sulfuric Acid, H2SO4. If you heat it, the nails will dissolve faster. Let it settle, then draw off the solution while it is still warm (coffee filters will dissolve in sulfuric). When it cools, it will form light green crystals of FeSO4.

If you start with fresh battery acid, which is about 33% Sulfuric, the water in it will evaporate while you have it heated, and will approach or become Concentrated Sulfuric, which is very dangerous (especially when hot) due to its water-seeking properties (like your skin and innards), so wear skin and, especially, eye protection (a full face shield is best).

If you don't heat it, you can just use the (saturated) solution with a dropper.

If you make or have crystals, just use a drop-sized crystal or two in your test.

 

[Renaldas]

Renaldas;

P.S. You can make FeSO4 by placing some nails into Sulfuric Acid, H2SO4. If you heat it, the nails will dissolve faster. Let it settle, then draw off the solution while it is still warm (coffee filters will dissolve in sulfuric). When it cools, it will form light green crystals of FeSO4.

If you start with fresh battery acid, which is about 33% Sulfuric, the water in it will evaporate while you have it heated, and will approach or become Concentrated Sulfuric, which is very dangerous (especially when hot) due to its water-seeking properties (like your skin and innards), so wear skin and, especially, eye protection (a full face shield is best).

If you don't heat it, you can just use the (saturated) solution with a dropper.

If you make or have crystals, just use a drop-sized crystal or two in your test.

Thank you for information!
I'm sure there is gold, the aim of this thread was to know what substances are responsible for such a color change?
I have FeSO4, i used it as a precipitant a year ago, I know it selectively drops gold. I never discard the solution even if stannous test is negative, I pour it into a large vessel, where is several copper wires. After a long time I found a tiny amount of dark powder on the bottom of this vessel, and this powder seems to be a mixture of precious metals. Only after this step I discard the soultion.

 

[eeTHr]

You definitely see purple color, but there is some remaining quite dark blue at the corner.

I'm sure there is gold, the aim of this thread was to know what substances are responsible for such a color change?

Renaldas;

I looked at your videos again. The far right end of your test strip has no color in the first or second video. In the third, the stannous seems to wash some blackish Au over the blank right end, then it floats to each side of the end, leaving the middle of the end part clear again.

In the forth video, the water dilutes the color, and you can see collodial gold running in the excess water on the plate. The right end gets diluted to a blue (as seen in the color representation of the video, anyway). My guess would be some palladium and gold mixed?

The best way to sort it out with stannous would be to put 5 or ten drops of your AR solution in a white plastic spoon, then put a crystal of the FeSO4 in it and stir it a little until all the Au drops to the bottom of the spoon. Then wet another test strip with the remaining solution, and perform another stannous test and post the results.

It would probably help to heat a small amount of your AR solution in a test tube first, to get rid of excess nitric. Then do as above.

Also try diluting your test drops to be able to differentiate resultant colors better.

 

[Barren Realms 007]

Looks like gold.