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RE: [APD] diatoms

Hmmm. I stand corrected. But from what I have read the
baking is done to control the finess of filtering.  If not
calcined, it's about 10 microns or less and not too useful
for many filtering purposes because it clogs up too fast.
I've seen as many as 10 diff ratings for fineness of

Perhaps I'm using the wrong word or reading from the wrong
mineral suppliers?  

Scott H. 
--- Wright Huntley <whuntley at verizon_net> wrote:
>> a
>> particular kind of fine media.  Most often it is a
>> calcined
>> diatomaceous material.
> Naah. It is almost never really calcined as it is mostly
> SiO2 and has no 
> CO2 to drive off, or water of hydration as in limestone
> or many silicate 
> clays. It is dried out at elevated temps, because it is
> so good at 
> holding water in the micropores that it still acts like
> dust when as 
> much as 50% of the weight is H2O! Its microporosity is
> amazing, with 
> over 80% of volume being air.

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