Process for synthesizing compositions containing smectite-type clays and gellants produced thereby

Abstract

This invention provides a process for synthesizing compositions containing trioctahedral smectite-type clays which contain fluorine within their layer lattices. In particular, the invention provides a process for synthesizing compositions having mole ratios of Li, Na, Mg and Si, expressed as oxides, and F of: aLi.sub.2 O : bNa.sub.2 O : cMgO : dF : 8SiO.sub.2 (I) where 0.ltoreq.a<1.2, 0.ltoreq.b<0.6, 4.75.ltoreq.c<7, 0<d<4, o.ltoreq.a+b<1.4, and 5.5<a+b+c<8, and where c.gtoreq.6 when a+ b= 0. The process comprises: (a) forming an aqueous suspension containing from 12% to 35% solids by weight, the solids having the chemical composition represented by formula I, by (i) combining and mixing hydrofluoric acid, magnesia, water, and a base selected from the group consisting of lithium hydroxide, sodium hydroxide, and mixtures thereof, until the base is dissolved; and (ii) adding a silica sol; (b) agitating and heating the suspension until a viscous slurry is obtained; (c) allowing the slurry to gel; (d) hydrothermally reacting the gel under autogenous pressure at a temperature in the range from about 85.degree. C to about 250.degree. C for a period of time sufficient to form a well crystallized trioctahedral smectite-type clay; and (e) drying the product to form the composition. Gellants having a cation exchange capacity within the range from about 70 to 100 milliequivalents per 100 grams, a Bingham Yield Value of at least 50 dynes/cm.sup.2 as a 2% dispersion in water, and the ability to disperse in deionized water at a concentration of 2% by weight to produce a thixotropic gel having a Bingham Yield Value greater than about 20 dynes/cm.sup.2, the gel having a Bingham Yield Value above 50 dynes/cm.sup.2 upon aging are provided by the process when: 0.25.ltoreq.a<1.1, 0<b<0.60, 5.85.ltoreq.c<7.0, 0.5<d.ltoreq.3.5, 0.5.ltoreq.a+b<1.3, and 6.5<a+b+c<8.0.

Dependencies are inferred from the claim text.