stanous chloride crystals

[arthur kierski]

does stanous chloride crystals exposed to air and light,loses the capacity to detect pms? i ask this because my test for gold gives a brown collor instead of violet, and the gold precipitates with smb----
thanks for help
Arthur

 

[butcher]

Arthur,

I do not think light affects stannous chloride that bad.

But stannous chloride is easily degraded by oxygen or air, by being less acidic, and if there is no free tin in solution, or diluting with water stannous chloride will form an hydroxide of tin.

Excess HCl acid, excess tin metal, and the solution keeping oxygen free, will help the stannous chloride stay fresh and last longer, where it does not breakdown into another tin salt.

Because of the oxygen, when I make my stannous chloride, I make enough to fill my small bottle, this way I am not leaving my stannous chloride sitting with mostly oxygen in the bottle, as opposed to if I only had a small amount of liquid in the bottle.

Excess tin and a little extra HCl to keep the solution fresh.
I do sit my stannous in the dark cool shed, many chemicals can change in sunlight, stannous chloride may but I have not heard of it doing so. I have seen commercial tin chloride dried salts (stannous chloride) in clear plastic, chemicals that are affected by light like nitric acid, H2O2 and so on are normally stored in amber or other glass or plastic where light will not decompose the chemical, this also gives me reason to believe stannous chloride is not affected by light to any great extent.

If your stannous chloride in a test is converting a solution to brown this makes me believe a reaction is occurring, and the stannous chloride is reducing something in solution, but this something does not have to be valuable metals, stannous chloride can also reduce many base metals, most of these other base metals do not color the solution in our tests (lucky for us), although some will like copper.

If I was concerned with whether the stannous was working I would test the stannous with a known solution.

Sometimes several metals in solution together, gold and PGM can make it hard to judge from the colors, this is where a spot plate and using some of the methods Harold or Hoke's speaks of, like using copperas to test for and precipitate the gold in one well of the spot plate, and moving the remaining gold barren solution from that test to another well, and testing with another test, like SnCl2 or DMG...
Basically (testing for) and separating out one metal from the solution to be tested, so then you can test for other metals in solution.

Arthur,
I know I am probably not saying anything you that you already do not know but I thought I would try to say it anyway.

 

[moose7802]

Good description Richard! I have been told that a brown color in a stannous test could be Cu or Fe. Correct me if I'm wrong.

Tyler

 

[butcher]

That is what I believe at this point, these metals being reduced by stannous chloride can give a color to the test.

Hokes speaks about testing, she tells how ammonia at certain stages when added to PGM solutions can form complexes, making it hard or impossible to test for the metal in solution.

She also talks of the problems with organics in solution giving a similar problem of not being able to test for values in the solution with the stannous chloride tests.


To overcome the problem above she talks of evaporating to dryness and incinerating before putting values back into solution before the test will work.
Same as we use for the problem below.

As we know this can also be a problem with tin in solution, reducing the gold in solution to colloidal gold that we cannot test for.

Hokes also speaks of how if there is too much iron or copper salts in solution it can make the stannous chloride (purple reaction) difficult to appear, we may have to keep adding a lot more of stannous chloride to even see the result, (it may be the gold Cassius of purple does not show up) until after the base metals are reduced, and excess stannous chloride is needed then to reduce the gold, but if there is a lot of other base metal coloring the tested solution we may have trouble even seeing a bit of purple in the stain sample.

just adding to the many reasons of why having cleaner, or base metal free solution is of such importance.

 

[arthur kierski]

thanks Butcher for another lesson---- i concluded that the brown collor comes from a mix of pd,au,and base metals being reduced -
regards
Arthur

 

[naporex]

Hello and Merry Xmas for everyone.
I'm doing my pin recovey lately but pins are with soft solder so I' did HCL wash, HNO3 dissolving then filter (what I could because of metastannic presence) and then incinerated in stainless deep dish. Next step was HCL treatment for dissolving Sn ->SnCl2. Been boiled for about half an hous or so then I took a stannous test the result is right side on photo left side stain I made another test same liquid but today after some SnCL2 crystals shows up. As You can see there is stronk pink/purple stain from yesterday's test. I read tghis post and I saw that presence of iron can create same colour effect with stannous test. When I saw that colour yesterday I thought that some nitric left and dissolves some gold to solution but hey it was an ash. I'm filtering it now and thinking what to do next to not make any stupid mistake.

 

[moose7802]

Fe will not cause a purple/black result when tested with stannouss, it will be brown. If you have purple that means you have Au in solution, meaning your Au is dissolving. There must still have been nitric that you did not incinerate off before you added hcl.

Tyler