Experimental synthesis of chlorite from smectite at 300°C in the presence of metallic Fe

The alteration and transformation behaviour of montmorillonite (bentonite from Wyoming, MX-80) in low-salinity solutions (NaCl, CaCl2) in the presence of metallic Fe (powder and 8 x 4 x 1 mm plate) and magnetite powder was studied in batch experiments at 300degreesC to simulate the mineralogical and chemical reactions of clays in contact with steel in a nuclear waste repository. The evolutions of pH and solution concentrations were measured over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, Transmission Mossbauer Spectroscopy and TEM (EDS, HR imaging and EELS). Dissolution of the di-octahedral smectite of the starting bentonite was observed, in favour of newly formed clays (chlorite and saponite), quartz, feldspars and zeolite. The formation of Fe-chlorite was triggered by contact with the metallic Fe plate and Fe-Mg-chlorite at distance from the Fe plate (>2 mm).