Hydrothermal reactivity of K-smectite at 300 degrees C and 100 bar: dissolution-crystallization process and non-expandable dehydrated smectite formation

The hydrothermal reactivity of a smectite saturated with K was studied expe rimentally at 300 degrees C and 100 bar in (Na,K) chloride solutions (Na/K = 0, 50 and 100, liquid/solid ratio = 10/1). X-ray diffraction, TEM and mic roprobe results show: (1) a partial to total dissolution of the initial sme ctite layers; and (2) the crystallization of newly-formed euhedral I-S. Ran dom I-S is formed after 7 days, but an ordered mixed-layer I-S containing < 30% expandable layers formed in the longest runs (112 days). The I-S is cha racterized by non-expandable layers of two distinct types: dehydrated smect ite and illite. The Si content is lower in the I-S than in the initial smec tite, thus creating a charge deficit, mostly compensated by the introductio n of Na to the interlayer space, and yielding a silica release to the solut ion and subsequent crystallization of quartz and cristobalite.