Influence of the synthesis medium on the saponite crystallisation:formation mechanism in acidic and basic media.

摘要

The present work is relative to the hydrothermal synthesis of saponite,a clay mineral having the following chemical formula per half unit cell :M_xMg3 (Si_(4-x)Al_x)O_(10)(OH,F)_2,0.2 < x < 1.20,where M is an hydrated exchangeable cation and x is the layer charge.Syntheses were performed in fluorine medium in the pH range 1 to 12.Two mechanisms can be proposed:in acidic medium,tetrahedral polysilicic acid incorporate Al~(3+) cations and,in basic medium,silica polycondensation occurs around a [Mg(OH)2] brucite-like layer.