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Re: calcined montmorillonite clay

On Sun, 6 Dec 1998, David Brooks wrote:

[snip interesting discussion made long by inclusion of both plain text and

> And for clarification are phosphates sequestered just by iron containing =
> clays or would CEC alone play a role.=20

Phosphate is sequestered by iron and/or aluminum hydroxides and
oxyhydroxides.  Those are contained in abundance in laterite.  The ability
of the hydroxide to sequester phosphorus depends a lot on the density and
texture of the stuff.  Phosphate is a positively charged ion (anion); CEC
- cation exchange capacity - effects negatively charged ions (cations) and
so has no direct effect on phosphate.

Some clays contain coatings of iron hydroxides -- it's probably the
coatings that give red art clay it's red color.  Iron is generally not a
major part of pure clay.  The hydroxide coatings can give the clay some
anion exchange capacity and the capacity to sequester phosphate but the
clays themselves don't have that ability.

What that means is that any clay product is likely to be highly variable
in its ability to sequester phosphate.  Very qualitatively, I expect its
ability to range from none to moderate.

Does anyone know if the "Akadama ceramics" shown in the first volume of
"Nature Aquarium World" are calcined clay?

Roger Miller