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=5400However, 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?