HYDROTHERMAL TRANSFORMATION OF SEPIOLITE TO STEVENSITE AND THE EFFECT OF ADDED CHLORIDES AND HYDROXIDES

Hydrothermal reactions in the system sepiolite/H//2O have been examined between 149 degree and 316 degree C. Approximately 10-20% of the starting sepiolite was converted to a smectite (stevensite) at 204 degree C within 24 hr. Similar results were obtained when CaCl//2, NaOH, Ca(OH)//2, or Mg(OH)//2 was added to the system. In the presence of NaCl, about 60% of the sepiolite was converted to stevensite, whereas, only 5% stevensite formed in the presence of MgCl//2. Greater amounts of stevensite formed at 260 degree C in these systems. Above 316 degree C, 60-80% of the sepiolite was converted to stevensite in 24 hr, regardless of the presence or absence of salts. Within the experimental conditions used, temperature is the most important factor in the sepiolite-to-stevensite conversion. Refs.