Help interpreting a stannous test

[glondor]

I am trying to drop some gold from some tophat transistors dissolved in poor mans nitric. Added some prills of urea to kill nitric and minimal reaction. Only a few prills needed.

Added smb last night, some gold precipitated overnight but not as much as expected. Solution did not change colour, still green. Tested with Stannous and this is the result. I do not know what it means. With the addition of Stannous, the colour change is almost instant. What metal am I looking at? I will answer any questions you may have. Thanks.

Photos shot under fluorescent light with flash. Same solution on filter and spot plate.

 

[eeTHr]

glondor---

At first I thought you were saying that you just had a nitric solution, and added urea to that. My mistake in reading too fast, I guess.

So, you dissolved the base metals out of these transistors, and then put the remaining gold in AR, and used urea to neutralize any remaining nitric.

It would be good to show a photo of the solution. From the sound of it, there shouldn't be lots of base metals left over to be dissolved in the AR solution, which could hamper precipitation. I don't like using urea, because it's just more stuff that could slow down the dropping of your gold.

Did you dilute your AR solution between three and five times with water, after all the Au was dissolved?

There is a "sweet spot" with gold solutions, where there is little contamination of any kind, and a certain range of dilution, in which there are no problems dropping the gold very nicely. The amount that you vary from that sweet spot, will result in that degree of non-optimum results. Sometimes it will take quite awhile for it all to drop, and other odd things can happen, if you are too far off with the solution.

 

[Harold_V]

I see you use a spot plate. Good for you. I highly endorse their use.

You, above most others (because you use a spot plate) have a test that others do not have. After you have reacted with stannous chloride, assuming you have a dark response (similar to the one shown), you can eliminate gold as the source by allowing the spot to remain a minute or two, then pouring out the cavity. If you have gold present, you generally end up with a purple stain where the solution sat. Only gold yields the stain, so this is a valid way to discern the presence of gold when you are testing a solution that yields questionable results.

As has been mentioned, I'd suggest you avoid the use of urea. To me, it is akin to painting over rust. There are better ways to achieve the same end.

Harold

 

[Palladium]

Great tip Harold !

I use cheap plastic spoons for the same effect. I use spoons so i can write different batch or sample numbers on the handles and I can do multiple and separate test at one time.
I love the color purple. 8)

 

[glondor]

Thanks for the input. Some great teaching here.
To answer the questions, I Diluted the solution ALMOST 3 times by volume. I was limited by the container size. I did transfer to a larger container and tomorrow I will add more water. When I transfered the solution, I noticed a odd thing with the colour. In the semi-transparent bucket the solution looks light green, but as I poured it to a larger green pail, the solution appeared orange as I poured it. Now it is in a green pail I don't know what colour it is.

I used a minimum amount of urea just to test to make sure there was no free nitric in the solution. Normally I use a gold button but I did not have one with me at the time. I will continue to use a gold button as first choice.

I have noticed the purple stain in the spot plate several times, Thanks Harold for the insight in to this indicator, It solves the issue of diluting the test very well. I too love to see that colour purple in the spot.

I will work on this some more tomorrow. Thanks.