The application of high-temperature X-ray diffraction and infrared emission spectroscopy to the thermal decomposition of krohnkite.

Abstract

High-temperature X-ray diffraction and infrared emission spectroscopy have been applied to measure the thermal stability of the sulphate mineral kro¨hnkite Na2Cu(SO4)2 2H2O. Kro¨hnkite shows a low thermal stability. The mineral decomposes into a complex mixture of sulphates below 500 C and sulphides below 650 C, before melting. Broad emission infrared bands at 3350 and 3105 cm-1 are assigned to the stretching vibration of the water units. The intensity of these two bands decreases as the temperature is raised. The intensity of these bands is lost by 250 C. The sharp IES band at 992 cm-1 is assigned to the m1 SO4 2- symmetric stretching vibration. Intensity in this band is lost by 200 C. New IES bands are noted. The important aspect of this work is the use of hightemperature X-ray diffraction to determine the thermal decomposition of a mineral, in this case krohnkite.