Hydrothermal treatment of okenite. Experimental studies on the genesis of stevensite (Part 5).

In order to investigate the genesis of stevensite experimentally, naturally occurring okenite was treated hydrothermally with 0.5 mol/l magnesium chloride solution and with basic magnesium carbonate for Mg (in basic magnesium carbonate)/Si (in okenite) molecular ratios ranging from 0.1 to 1.5. As a result, okenite was altered to “hydrated talc” by treatment with magnesium chloride solution. On the other hand, it was altered to stevensite (Mg/Si = 0.3-0.5), and “hydrated talc” and serpentine (Mg/Si = 0.75-1.5) by basic magnesium carbonate treatment. Furthermore, when sodium hydrogencarbonate was added to the reaction system, larger amount of stevensite (Mg/Si =0.1-1.0) and serpentine (Mg/Si = 1.5) were obtained. The mechanism of the conversion process was quite similar to other studies on calcium silicates as reported previously.