K and Ca exchange behavior of zeolite A

Powdered samples of zeolite-A ([Na11.8Al11.8Si12.2O48 · 26H2O]8, LTA, Na-A) were completely Ca and K exchanged. Several compositions between the end members Na-, Ca-, and K-zeolite A were produced. Combined results from X-ray powder diffraction including lattice parameter refinements in space group F m  3‾c, energy dispersive X-ray spectroscopy, and thermal gravimetric analyses are presented. Rietveld refinements are performed for the three Na-rich samples in the Ca exchange series. The linear dependence of the lattice parameter a on the Ca and K contents is described as well as the relationship between water, Ca and K content. The lattice parameter a decreases with increasing Ca and K content, ranging from 24.62 to 24.46 Å for the Ca-exchanged forms and from 24.63 to 24.58 Å for the K-exchanged forms. Higher Ca content results in a higher amount of water incorporated in the zeolite, ranging from 25 (Na-A) to 28 (Ca-A) molecules per formula unit (m.p.f.u.) whereas the water content in the K-exchanged forms varies about 23.5 ± 1.0 m.p.f.u. not directly correlated with the K contents but significantly lower than the 26 m.p.f.u. of the Na-A starting material. The Ca and K contents can be estimated from lattice parameter a by linear regression.

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► Two exchange series with end members zeolite Na-A and zeolites Ca-A and K-A.
► Ca-exchange: linear dependence of lattice parameter a on Ca content.
► K-exchange: linear dependence of lattice parameter a on K content.
► Ca and K content can be calculated from lattice parameter a.