Selenium Sulphide Reaction?

Maybe you haven't achieved stoichiometry at lower concentrations.

Thanks Lyn,

I thought it might be something to do with the concentration rather than the pH as they are both at 13+.

Would you have any idea what is being formed?

SeS2 + NaOH= ?

The darkening from orange to brown then almost black could be light sensitive, I will investigate tomorrow to see if it is.

I was wondering if it could be selenium being released, but what is the other compound?

Thanks Sam

Selenium sulfides do not have well defined compositions. An almost infinite number of different combinations of S and Se atoms can be present. My guess is that you are changing the way they are combined when you increase the pH, hence the color change.

See these articles:

http://en.wikipedia.org/wiki/Selenium_disulfide

http://en.wikipedia.org/wiki/Selenium_hexasulfide

Thanks Mikerho,

I would prefer to know if the hydroxide could oxidise the selenium sulphide ring, possibly allowing the selenium to precipitate. I have taken a sample of the black slurry and washed it to remove the excess sodium hydroxide (which is now straw coloured not clear).

On closer inspection the black slurry is more green/black in suspension now, its nothing like the bright orange/yellow it once looked like.

Regards

Sam

Hi Sam,

The only way to really know is to do an elemental analysis before and after. Atomic absorption spectrometry would be the way I'd go. Do you have access to an analytical lab or services?

Mike

Sulfur exhibits allotropy more than any other element - more than 30 allotropes have been identified. The colors vary from yellow through to black. It occurs to me that you could be precipitating some sulfur, which then gradually undergoes changes in its crystalline form (and even to the amorphous form), yielding the color changes you observe. Your reaction with sodium hydroxide could be a far more complicated event than we can guess at.