Chemical studies on the reactions of synthetic 1.13-nm-tobermorite with alkali metal hydroxides at room temperature

摘要

The reaction of alkali metal hydroxides (MOH; M = Li, Na, K; c = 0.02-1.0 M) with synthetic 1.13-nm-tobermorite (Ca5Si6H2O18. 4H(2)O) at 25+/-2 degrees C was studied. The results obtained indicate that the reactivity highly depends on pH and cation field strength and to lesser degree on the ionic radius of M. MOH has negative effects on the crystallinity of the concerned phase in the following order: KOH > NaOH > LIOH. Furthermore, the hydroxides cause swelling of crystals, attributable to the creation of new cavities due to partial hydrolysis of tetrahedral SiO2(OH)(2) chains in the lattice. Hydrolysis via cleavage of Si-O-Si bonds facilitates the cation exchange process Ca2+ reversible arrow M+ which probably proceeds by a nucleophilic substitution reaction (S(N)2). The observed different affinities of 1.13-nm-tobermorite towards MOH could be used for the separation of these cations.