Monoclinic Sr-celsian by thermal treatment of Sr-exchanged zeolite A, LTA-type framework

An unconventional method for preparing monoclinic Sr-feldspar starting from a synthetic Na-A zeolite is presented. Accordingly, samples of Sr2+-exchanged zeolite A (Sr-A), containing a residual 5% content of Na+, were thermally treated at temperatures up to 1150 °C for times up to 24 h. Sr-A zeolitic structure breakdown, occurred at about 900 °C and followed by the crystallization of the hexagonal formof Sr-feldspar (Sr-hexacelsian) at about 950 °C, resulted in the final conversion, in 1 h at 1150 °C, of the original zeolitic material into a monoclinic polymorph of Sr-feldspar. Increasing the duration of the thermal treatment up to about 5 h gave rise to the crystallization of monoclinic Sr-celsian at only 1000 °C.