Sciencemadness Discussion Board - Best Way to Dehydrate a Bunch of CaSO4

Best Way to Dehydrate a Bunch of CaSO4

VeritasC&E - 3-9-2022 at 12:57

What is the best way (as most energy efficient + fastest / most convenient) way to dehydrate (not completely but hemihydrate state, thus with sufficient temperature control) a bunch of CaSO4 (~10Kg)?

Is microwave a suitable method?

Can microwave form arcs with CaSO4 (or with metal salts)?

If I skip temperature control and dehydrate it completely, can I just leave it stored in a closed container with adequate amounts of H2O thrown in hoping that it will homogenise to produce a uniform mass or hemihydrate after a few weeks/months?

__

[Edited on 3-9-2022 by VeritasC&E]

Sulaiman - 3-9-2022 at 18:02

There are a couple of things to consider when heating gypsum (dihydrate) to plaster (hemihydrate),

Gypsum and plaster are poor thermal conductors - spread thinly on a tray/hot surface

micro-pockets of steam burst, emitting very fine dust - disposable oven/kiln or a big clean up

Water added to bulk anhydrate or hemihydrate forms a solid lump of dihydrate.
Keeping moisture OUT is required.

PS probably the cheapest and easiest way to get small quantities of the hemihydrate is to buy plaster

('plaster of Paris' is the purest type - I believe)

[Edited on 4-9-2022 by Sulaiman]

VeritasC&E - 31-1-2023 at 12:20

Quote: Originally posted by Sulaiman

There are a couple of things to consider when heating gypsum (dihydrate) to plaster (hemihydrate),

Gypsum and plaster are poor thermal conductors - spread thinly on a tray/hot surface

micro-pockets of steam burst, emitting very fine dust - disposable oven/kiln or a big clean up

Water added to bulk anhydrate or hemihydrate forms a solid lump of dihydrate.
Keeping moisture OUT is required.

PS probably the cheapest and easiest way to get small quantities of the hemihydrate is to buy plaster

('plaster of Paris' is the purest type - I believe)

[Edited on 4-9-2022 by Sulaiman]

Thank you Sulaiman!

What about the microwave: Can I use a microwave to dehydrate it? Up to what approximate amount could I process at a time in w microwave? And what would be the approximate dehydration time in the microwave per batch?

SplendidAcylation - 1-2-2023 at 05:27

Quote: Originally posted by VeritasC&E

If I skip temperature control and dehydrate it completely, can I just leave it stored in a closed container with adequate amounts of H2O thrown in hoping that it will homogenise to produce a uniform mass or hemihydrate after a few weeks/months?

__

[Edited on 3-9-2022 by VeritasC&E]

Herr Haber - 1-2-2023 at 08:19

Quote: Originally posted by Sulaiman

PS probably the cheapest and easiest way to get small quantities of the hemihydrate is to buy plaster

('plaster of Paris' is the purest type - I believe)

[Edited on 4-9-2022 by Sulaiman]

I'd agree with that !
But the old way certainly did give an inconsistent product.
Ground gypsum used to be heated by ovens under the hill of Montmartre.
The hill was pierced by two entries from which Paris inhabitants could see the smoke rising and red glow in the night. Quite the Hellish view !
In the morning, quarry workers collected the homeless who had slipped in to find a warm place for the night and suffocated because of CO2.

Anyway, you'll want to look specifically for plaster of Paris or plain plaster.
There are other plasters: White of Meudon, White of Spain (maybe translated Spanish White etc. Those for example contain clay, so if you are looking for a chemically pure product you'll want to read the label.

yobbo II - 3-2-2023 at 14:04

"If I skip temperature control and dehydrate it completely, ..."

Why do you want the hemihydrate as opposed to the anydrous?
I am asking because I simply don't know if the end result of adding water gives the same result.

Would putting it under a vacuum do the job?

"n the morning, quarry workers collected the homeless who had slipped in to find a warm place for the night and suffocated because of CO2."

Something similar would happen in a 'lime kiln' used to convert limestone into CaO except it was CO that did the killing.

Yob