What causes precipitation when concentrated sulfuric acid is diluted?
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Our company has invested in a copper smelting production line in Zambia; the raw material, concentrated sulfuric acid, is purchased from South Africa, and sulfuric acid is produced by burning sulfur. The concentrated sulfuric acid purchased is colorless, but when diluted with water, a white, flocculent, viscous substance appears; after removing this flocculent substance and burning it in a crucible, a white (slightly gray) solid is obtained. I would like to ask the experts: what could be this white precipitate that is soluble in concentrated sulfuric acid but not in dilute sulfuric acid? I am extremely grateful.
It might be certain salts; could it be mercury sulfate?
Why not conduct a qualitative analysis on this dried flocculent substance? I think it’s very likely to be calcium sulfate, as calcium sulfate can dissolve in concentrated sulfuric acid. The precipitate is ground fine, then dissolved in concentrated sodium carbonate and left to soak for a while; after that, the precipitate is separated again, washed thoroughly with pure water, hydrochloric acid is added, and it is fully dissolved – at this point, calcium ions can be detected. A positive reaction indicates that the precipitate is calcium sulfate (gypsum).
Thank you, thank you! Too few samples have been brought back from Africa, and the exact components within them are unknown; therefore, there isn’t enough material for testing at laboratories. Conducting tests without a clear target also results in very high costs.