What would be possibilities for a black precipitate sulfate? 1

[condrj]

I am a chemist and one of my wastewater treatment laboratories obtains a black precipitate upon required sulfuric acid preservation with sulfuric acid. He is required to preserve this effluent sample when he analyzes ammonia effluent by ammonia ISE. Has anyone had this experience before? Can you give me some information on your experience?

Thank you.

 

[bimr]

Bacterial action has converted some of the sulfate to sulfide. The ferrous sulfide is extremely finely divided, and it only takes a very small quantity to blacken the water.

You probably need to reduce the sampling handling time.