A Study of the Synhesis of Hectorite

Hectorite, a trioctahedral magnesium montmorillonite, has been synthesized at atmospheric pressure and reflux temperature. The reaction mixture was the system SiO₂/MgO/Li₂O (or LiF)/Na₂O in a large excess of water. The starting ratios were based on the following formula for the mineral [(LixMg6−x)Si8O20(OH)4]x−.xNa+.${\left[ {\left( {L{i_x}M{g_6}_{ - x}} \right)S{i_8}{O_{20}}{{\left( {OH} \right)}_4}} \right]^{x - }}^.xN{a^ + }.$ Li⁺ has been found to accelerate the crystallization, and reasons for this effect are considered. Lowering of the pH of the reaction mixture by the use of alkali metal fluorides rather than hydroxides, resulting in an increase in the solubility of Mg(OH)₂, also caused the crystallization of hectorite to proceed more rapidly. The products containing Li⁺ and F⁻ proxying for Mg²⁺ and OH⁻, respectively, were found to be most like natural hectorite.The time-dependent data obtained in this work were rationalized on the basis of a postulated appearance of hectorite embryos in the dilute aqueous solution of Mg²⁺, OH⁻ and SiO₂, followed by growth of this material to crystalline hectorite by transfer of components from solution to the solid phase.Strese and Hofmann (1941) also conducted synthesis work in this area. A comparison of the products resulting from the two techniques showed the main difference to be the presence of 00l spacings in the current product. These earlier workers made a point of the lack of 00l reflections.