Thermodynamic studies of zeolites; natrolite, mesolite and scolecite Journal Article uri icon

DCO ID 11121/3382-9877-6570-7595-CC

year of publication

  • 1983

abstract

  • Calorimetric measurements have been carried out on specimens of natrolite, mesolite, and scolecite in order to assess the thermodynamic properties of a zeolite series having the same alumino-silicate framework. Low-temperature  heat  capacity and high-temperature enthalpy increments of natrolite and scolecite were  measured by adiabatic and drop­ calorimetric techniques. Standard enthalpies of formation at 298.15 K of all three zeolites were determined by solution calorimetry. Thermodynamic functions have been calculated for natrolite to 660 K and for scolecite to 470 K. The heat capacity and standard entropy at 298.15 K have  been  estimated for mesolite. The  following  values  at T = 298.15 K and a pressure of 1 bar have been obtained:

    (Table abbrev'd.)

    With reference to zeolitic water, it is concluded that the entropy of water molecules in both natrolite and scolecite is similar to that in ice. A consideration of the X-ray results  for the present  specimen of  natrolite leads  to  the  conclusion that  a  contribution of  about  9.2 J/(mol·K) to the  standard entropy is made by the Al-Si disorder in the alumino-silicate framework. The new results allow calculations to be made by which  the pressure and temperature effect can be deduced for such equilibria as:

    natrolite  + SiO2(aq)  = 2 analcime

    and

    natrolite + Ca2+(aq)  + H2O = mesolite + 2Na+(aq).

    Results are consistent with observed parageneses in natural occurrences.

description

  • Work performed under the auspices of the Division of Engineering, Mathematical and Geosciences, Office of Basic Energy Sciences, of the U.S. Department of Energy.

publication date

  • 1983

volume

  • 68