In its natural form, tobermorite exhibits little or no exchange for alkali cations; synthetic tobermorites, however, exhibit reversible alkali cation exchange and selective caesium uptake upon a coupled substitution of (Al3+ + Na+) for Si4+. Substituted tobermorites were synthesized using aluminosilicate gels, NaOH and CaO, in Parr bombs at 175oC for 4 days. Unsubstituted tobermorite was synthesized using quartz and CaO in a Parr bomb at 175oC for 20 hr. Two (Al + Na)-substituted tobermorites showed c.e.c. of 77 and 71 me./100 g, whereas an unsubstituted tobermorite showed a c.e.c. of 12 me./100 g. The substituted tobermorites exhibited selective Cs exchange from either NaCl or CaCl2 solutions. For example, one substituted tobermorite showed a Cs-exchange coefficient (Kd) of 15 100, whereas unsubstituted tobermorite showed a Kd of only 90 from a 0.02 N CaCl2 solution containing 0.0002 moles/litre CsCl. Exchange isotherms for Na+ reverse= Cs+ showed that Cs+ is preferred over Na+ throughout the exchange in the (Al + Na)- substituted tobermorites. This group of cation exchangers is expected to find applications in radioactive waste disposal.-R.A.H.
ASJC Scopus subject areas
- Water Science and Technology
- Soil Science
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)