[calciteandmagnesiumoxide]

Gravity separation? I don't know if that'd work..

This is for my M.Sc in engineering.

Also, if anyone knows anything about metakaolin I have a question about that too. But I don't there's many clay/concrete people here...

[Corribus]

Ask your clay question. I work a lot with clays recently, though admittedly not with concrete.

[calciteandmagnesiumoxide]

Yay, a fellow clay-scientist.

So, I'm trying to synthesize hydrotalcite (an anionic clay). From what I understand, hydrotalcite will precipitate when there's Mg2+ and Al3+ (in a 3:1 molar ratio), as well as some anion (typically carbonate) and a pH of around 10 (typically titrations are done with NaOH or Na2CO3).

Most researchers use Mg or Al salts (e.g. MgCl2/AlCl3). I can't do that because I'm trying to make this process cheaper. Instead, I was going to use MgO as my magnesium source, and for my aluminum source I'm trying to use metakaolin. Metakaolin (calcined kaolinite) consists of amorphous alumina and silica. I'm wondering what the behavior of metakaolin is when it is mixed in an MgO solution. The pH of an MgO solution is around 10.5...

Here's a paper where they do what I just described: http://www.scirp.org/journal/PaperDownload.aspx?paperID=5400

However, for the life of me I don't understand what's going on with the alumina and the silica in the metakaolin. At pH 10l.5, is Al3+ liberated from the metakaolin...? How...? Any idea?

[Corribus]

Yay, a fellow clay-scientist.

Lol, I totally wouldn't go that far. I'm fairly new to it. I don't do any of the kind of modifications you describe. We disperse it into polymers. Right now I'm trying to learn about clay spectroscopy, very complicated.

I don't know the answer to your question. I can tell you that we do see aluminum coming off of montmorillonite clays in both acidic (~pH 4) and aqueous (pH 7) solution. I have not tried an alkaline solution, but we do see a fair degree less coming off in water than acid. But available hydroxide will etch silica so I assume it will also etch alumina surface of clay as well. Particularly if the clay platelets are well-exfoliated, where there is ample surface area for reaction.

[calciteandmagnesiumoxide]

Cool, so you're working on organoclays/nanoclays?? I did some research on that (based on a really stupid original thesis idea my supervisor came with, ugh, glad I changed topics).

Hmm thanks for sharing your experience with montmorillonite.