The Dehydration of Hemimorphite.
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The thermal dehydration of natural hemimorphite, obtained from Jinding Pb-Zn deposits in Yunnan, has been studied using wet chemical analysis, XRD, DTA and TG. Based on the analysis of DTA and TG, the hemimorphite has been heated to 600, 700, 800, 900, 1300℃ respectively for 3 hours. Infrared spectra and XRD of the heated hemimorphite have been analysised. The hemimorphite for study has the similar formular with Zn4Si2O7 (OH)2·H2O according to the results of chemical analysis. At about 500℃, molecular water is lost. At about 600℃, there is only slight change in the rest of the structure and the dimension turns a little smaller than the natural. At the same time, structure water still exists as zeolita water through the examination of the infrared spectra and the structure water is zeolita water. At this temperature, Zn4Si2O7(OH)2·H2O has turned into Zn4Si2O7(OH)2 but not γ-Zn2SiO4. At about 700℃, the structure water is lost and the calcined hemimorphite has the same XRD with "β-Zn2SiO4" studied by Taylor.β-Zn2SiO4 is a mixture with the same structure mainly of Zn-olivine, hemimorphite without molecular water and willemite through XRD. At about 800℃, hemimorphite has turned into willimite. And at about 900 and 1300℃, willimite does not change any more. It seemed that $$$$$$-Zn2SiO4 does not to be formed and disintegrate into ZnO and SiO2.