STABILIZATION OF SWELLING CLAYS BY MG(OH)(2) - CHANGES IN CLAY PROPERTIES AFTER ADDITION OF MG-HYDROXIDE

Stabilization of the swelling clay structure is attempted by intercala tion of Mg(OH)(2) and the development of a brucite interlayer between the clay layers. The properties of the product obtained by applying th e technique, formulated as described in a previous work, are considere d here. The materials used were Wyoming bentonite (USA), Fuller's Eart h (UK), kaolinite, illite, lignite, and silica gels. The Mg(OH)(2)-cla y products were examined by the methylene blue dye test, X-ray diffrac tion analysis (XRD), differential thermal analysis (DTA), and derivati ve thermogravimetry analysis (DTGA). From the results obtained it is c oncluded that: the Mg-hydroxide is adsorbed by swelling clays both on their external and internal surface, whereas it is adsorbed on the ext ernal surface by non-swelling clays. The internally adsorbed phase of Mg-hydroxide forms an ill-defined interlayer of brucite, retarding swe lling, whereas the external phase covers the particles modifying drast ically their surface properties, like the adsorption of the MB dye. Th e material produced after precipitation of Mg-hydroxide on swelling cl ays (smectites) did not re-expand on wetting or after glycolation. The adsorption of MB dye was also reduced by some 80-90%, due to coating effect, preventing the measurements of the external surface area of th e clay by polar molecules. The principal forces involved in the proces s are believed to be physical adsorption on the external surface, alon g with chemisorption and some chemical bonding, mostly in the internal surface. Cementation due to crystallization and, in the long term, so me pozzolanic reactions take also place. Internal adsorption of the Mg -hydroxide is postulated to be in the form of positively charged mono- and/or small polymers and it is, chiefly, diffusion controlled. Since Mg-hydroxide is internally adsorbed by swelling clays, whereas Ca-hyd roxide(lime) is not, and the (Mg, Ca)-clay aggregates are more stable than the Ca-clay of the Mg-one, the combination of the two hydroxides could give better results in soil stabilization than each hydroxide al one.