Thermogravimetric behaviour of Taranakite from Pollera cave (Liguria, Italy)

Taranakite (K3Al5(PO3OH)6(PO4)2·18H2O, trigonal, R3 ̅c) is a phosphate with a layered structure, in which water separates K3Al5(PO3OH)6(PO4)2·12H2O units [1]. Its formation can occur naturally as microcrystalline powdery aggregates after the interaction of bat or bird guano with clay minerals, as well as a reaction product between soil minerals and phosphate-rich fertilizers [2]. Frost et al. [3] reported the possibility for the ammonium ion (NH4+) to replace the K+ into the crystalline structure and a protocol for the low temperature synthesis of ammonium taranakite was reported by Schwieger [4]. The thermal behaviour of K-Taranakite has been investigated as well [5]. In this study, we explore the thermogravimetric behaviour of a Taranakite collected in the Pollera cave (Liguria, Italy). The thermogravimetric analysis (TGA) was coupled with a Fourier Transform Infrared (FTIR) spectroscopy to investigate the nature of the mass losses and confirm the presence of NH4+ ions in the structure.