Application of X-ray diffractometry and scanning electron microscopy to study the transformation of carnallite and thenardite to schoenite at 25 °C.

Autor: Hai, Qingyu, Cheng, Huaide, Ma, Haizhou, Li, Jun, Qin, Xiwei
Předmět:
Zdroj: Chemical Engineering Communications; 2020, Vol. 207 Issue 2, p161-176, 16p, 3 Diagrams, 7 Charts, 10 Graphs
Abstrakt: An experimental study was carried out on the preparation of schoenite from carnallite and thenardite by the double-decomposition method. According to the metastable phase diagram for the quinary system, Na+, K+, Mg2+//Cl–, and SO42−-H2O at 25 °C, three theoretical models were established for the double-decomposition processes. The mineralogy and morphology of schoenite, sylvite, epsomite/hexahydrite, and halite were studied by X-ray powder diffractometry and scanning electron microscopy during the double-decomposition processes. It is confirmed the preparation of schoenite via carnallite and thenardite is feasible. The double-decomposition reactions processes were described by three model equations. First, sylvite was obtained by carnallite decomposition in aqueous solution; second, epsomite/hexahydrite was obtained by a conversion reaction via thenardite and an MgCl2-rich mother liquor; third, schoenite was obtained via sylvite and epsomite/hexahydrite. The results suggest that (1) sylvite exists in the primary reaction time, epsomite/hexahydrite form simultaneously, and their contents decrease as the reaction time increase. (2) The terminal product of the double-decomposition is schoenite, and its formation results from conversion via sylvite and epsomite/hexahydrite. (3) A tendency for the X-ray diffraction intensity of sylvite and epsomite/hexahydrite to weaken increases visibly with reaction time, and its change agrees well with the third model. (4) Scanning electron microscopy images of the halite, sylvite, epsomite/hexahydrite, and schoenite are clear and integrated, and their formation results from the precipitation of the three model conversion reactions. Results showed that a good agreement exists between the experimental and theoretical models. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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