Characterization of smectites synthesized from zeolites and mechanism of smectite synthesis.

Smectites were synthesized hydrothermally from zeolites in an Mg-rich brine at 300oC under a confining P of 30 MPa and characterized by XRD using the Greene-Kelley Li-saturation test and the K⁺-saturation/glycolation test. The synthetic smectites were found to be dioctahedral with only tetrahedral negative layer charge; the layer charge was also deduced to be low and they are classified as beidellites. The mechanism of formation includes H⁺ saturation of zeolites by the hydrolysis of Mg²⁺ under hydrothermal conditions, followed by decomposition of the zeolites and recrystallization to beidellites. These results show that solution chemistry is an important factor affecting stability of zeolites under hydrothermal conditions. (Authors' abstract) -D.J.M.