Illite is a common layered silicate mineral in the Earth's crust.Ammonium illite can be formed when NH4+ is located in the interlayers of illite.The identification of ammonium illite mineralogical characteristics and the thermostability of interlayered NH4+ can provide an important basis for understanding the geochemical cycling of nitrogen.The mineralogical characteristics and thermal stability of ammonium illite collected from gangue in Xinjing coal mine of Yangquan city,Shanxi province,were comprehensively investigated with spectroscopic,electron microscopic,and thermal analyses,and using illite(its interlayered cation is K+)as a reference.The results show that the ratio of NH4+ to total interlayer cations in ammonium illite is about 0.86,and the basal spacing(10.344Å)of ammonium illite is significantly larger than that(9.973 Å)of illite;meanwhile,the intensity ratio of the(002)∶(003)diffraction peaks of ammonium illite is about 1∶1,whereas the corresponding ratio for illite is about 1∶3;in the tetrahedral sheets of ammonium illite,the isomorphous substitution of Al3+ for Si4+(Al3+ →Si4+)widely exists,leading to a layer charge density of approximately 0.85;the presence of interlayered NH4+ does not have a significant impact on the layered silicate framework of illite,but it can cause a blue shift in the structural hydroxyl groups;the interlayered NH4+ of ammonium illite exhibits good thermostability;at temperatures ranging from 400℃to 700℃,NH4+ gradually decomposes with the loss of structural hydroxyl groups;this suggests that interlayered NH4+ reacts with the structural hydroxyl groups during heating,resulting in the formation of NH3 and H2 O.These research results contribute to a deep understanding of the mineralogical characteristics and thermostability of ammonium illite.
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