Synthesized gellants containing smectite-type clay and process for producing same

A process for preparing a gellant consisting of a complex of a fluorine-containing trioctahedral smectite-type clay and an occluded amorphous phase selected from the group consisting of lithium hydroxide, sodium hydroxide, magnesium hydroxide, lithium oxide, sodium oxide, magnesium oxide, and mixtures thereof, said gellant containing 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 0.25 .ltoreq. a <
• 1.1, 0 .ltoreq. b <
• 0.60, 4.75 <
• c <
• 5.85, 0.5 <
• d .ltoreq. 3.5, 0.6 .ltoreq. a+b <
• 1.25, 6.0 <
• a+b+c <
• 6.65, and said gellant being characterized as having a cation exchange capacity within the range from about 0.7 to 1.2 milliequivalents per gram, a Bingham Yield Value of at least about 50 dynes/cm..sup.2 as a 2% dispersion in water, and the ability to disperse in deionized water within 15 minutes at a concentration of 2% by weight to produce a sol having a Bingham Yield Value less than 20 dynes/cm..sup.2, which sol is slowly converted to a thixotropic gel having a Bingham Yield Value above 50 dynes/cm..sup.2, said process comprising:
• 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 magnesium oxide, water, hydrofluoric acid, 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 from which no solids settle out;
• c. allowing the slurry to gel;
• d. hydrothermally reacting the gel under autogenous pressure at a temperature within the range from 85.degree. C. to about 250.degree. C. for a period of time sufficient to form said gellant;
• and
• e. drying the solid obtained.