A Study of the Synhesis of Hectorite

Abstract

Hectorite, a trioctahedral magnesium montmorillonite, has been synthesized a t atmospheric pressure and reflux temperature. The reaction mixture was the system SiOz/MgO/LizO (or L3)/NazO in a large excess of water. The starting ratios were based on the following formula for the mineral [(LizMg~-z)SisOso(OH)4]z-.xNa+.Li+ has been found to accelerate the crystallization, and reasons for this effect are considered. Lowering of the p H of the reaction mixture by the use of alkali metal fluorides rather than hydroxides, resulting in an increase in the solubility of Mg(OH)z, also caused the crystallization of hectorite to proceed more rapidly. The products containing Li+ and F-proxying for Mg2+ and OH-, respectively, were %und 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 Mgz+, OH-and SiOz, 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 001 spacings in the current product. These earlier workars made a point of the lack of 001 reflections. I N T R O D U C T I O NThe Research Project a t Mellon Institute sponsored by Baroid Division National Lead Co. has been directed of late toward the variation of the physical properties of clay minerals as a function of the nature and extent of isomorphous substitution. As a consequence, considerable effort has been expended in the development of techniques for the synthesis of the clay minerals, with emphasis on hectorite.The clay mineral occurring a t Hector, California, was studied by Boshag and Woodford (1936) and by Nagelschmidt (1938). No11 (1936) studied the synthesis (using high-pressure techniques) of magnesium-containing montmorillonite and extended his work to the magnesium end member of the series. Strese and Hofmann (1941) also conducted extensive synthetic work in this area and included a study of the products obtained from an atmospheric pressure approach. A careful x-ray study of the Hector, California, clay is included in their paper. Their approach will be described in a later section of this paper. Incidentally, Strese and Hofmann discount the presence of Li+ in the structure and attribute it to accessory mineral.I n their classification of the montmorillonite minerals, Ross and Hendricks (1945) MacEwan (1951) in his discussion of the montmoriuonite minerals includes hectorite, and establishes the criterion that the 06 spacing for the trioctahedral montmorillonite should be slightly greater than 1.5 A, and slightly less than this value for the dioctahedral series. Pinally, Eitel (1952) describes compounds prepared by solid state reactions, which he terms " hectorites ", and gives the following formula Li2Mg6A12Si6020F4 nLiF, where the LiF is contained between...

The transformation of synthetic hectorite in the presence of Cu(II)

“…Moreover, in such a case, the presence of Cu(II) triggers the formation of Mg-F richterite. Since this phase can also be a conversion product of hectorite in the absence of Cu(II), but with a concentration of F which is five times greater than in the present experiment http://doc.rero.ch (Granquist and Pollack, 1959), Cu(II) probably influences either the distribution or the thermal stability of F in the sample. In the first case the simultaneous enrichment of Cu(II) and F would lead to broadening of the Cu(II) EPR signal due to dipole-dipole interactions, which was not observed.…”

Synthesis of Smectite Clay Minerals: A Critical Review

“…The resulting silicometallic precipitate contained small smectite nuclei, the crystallinity of which improved upon aging in the aqueous suspension at temperatures below 100~ In contrast to the method of Harder (1972Harder ( , 1977, this procedure allows better control of the homogeneity of the smectites, is easily reproducible, and can produce large quantities of material. Granquist and Pollack (1960) synthesized hectorite by hydrothermal treatment of an aqueous slurry containing -10% freshly precipitated Mg(OH)2, silica gel, and various amounts of NaOH, LiOH, and LiE The synthesis conditions used ranged from reflux temperature and atmospheric pressure to 300~ and --83 bars. Use of LiF accelerated the crystallization of hectorite.…”

Li-Bearing Stevensite from Moldova Nouǎ, Romania

“…ence may have been due to the high degree of crystallinity of Li-bearing smectite or to the lack ofoctahedral fluorine (see Granquist and Pollack, 1960). The differential thermal analysis curve of hectorite from Hector, California, had a low-temperature peak at 118 ~ 128~ and a dehydroxylation endotherm at 670~ Mackenzie (1957) and Deer et al (1962) reported a dehydroxylation temperature of 800~ for this hectorite.…”