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The thermal decomposition of syngenite, K2Ca(SO4)2·H2O, formed during the treatment of liquid manure has been studied by thermal gravimetric analysis, differential scanning calorimetry, high temperature X-ray diffraction (XRD) and infrared emission spectroscopy (IES). Gypsum was found as a minor impurity resulting in a minor weight loss due to dehydration around 100 °C. The main endothermic dehydration and decomposition stage of syngenite to crystalline K2Ca2(SO4)3 and amorphous K2SO4 is observed around 200 °C. The reaction involves a solid-state re-crystallisation, while water and the K2SO4 diffuse out of the existing lattice. The additional weight loss steps around 250 and 350 °C are probably due to presence of larger syngenite particles, which exhibit slower decomposition due to the slower diffusion of water and K2SO4 out of the crystal lattice. A minor endothermic sulphate loss around 450 °C is not due to the decomposition of syngenite or its products or of the gypsum impurity. The origin of this sulphate is not clear. [Copyright &y& Elsevier]

FTIR and Infrared emission spectroscopy (IES) has been used to characterise the Uley (Australian) and Garfield nontronites. These clay minerals are characterised by a strong emission band at 3570 cm−1 attributed to the FeFeOH unit. Dehydroxylation is followed by the loss of intensity of this band as a function of temperature. Dehydroxylation is also followed by the loss of intensity of the FeFeOH deformation vibration at 843 cm−1. IES shows that the dehydroxylation occurs as a continuous process in comparison to DTA/TGA studies where the dehydroxylation occurs abruptly at 425 °C. Water in these high iron bearing smectites have been observed through the stretching mode at 3430 cm−1 and the bending mode at 1630 cm−1. Different types of water are identified in the nontronite structure by the analysis of the band profile in the 1590–1680 cm−1 region. Low frequency vibrations show that the Uley green nontronite is similar to the Garfield nontronite. The brown Uley nontronite is closer to the Hohen–Hagen nontronite. The Uley nontronites may, therefore, be used spectroscopically to replace other nontronites as a reference clay mineral. [ABSTRACT FROM AUTHOR]

The presence of arsenate compounds in soils and mineral dump leachates is common. One potential method for the removal of the arsenates from soils is through thermal treatment. High-resolution thermogravimetric analysis has been used to follow this thermal decomposition of selected vivianite arsenates. This decomposition occurs as a series of steps. The first two steps involve dehydration with 6 mol of water lost in the first step and two in the second. The third major weight loss step occurs in the 750–800 °C temperature range with de-arsenation. The application of infrared emission spectroscopy confirms the loss of water by around 250 °C and the loss of arsenic as arsenic pentoxide is observed by the loss of AsO stretching bands at around 826 cm−1. Thermal activation of arsenic contaminated soils may provide a method of decontamination. [Copyright &y& Elsevier]

Thermal analyses of synthetic and natural vivianite (Fe2+)3(PO4)2·8H2O) were determined using a high-resolution thermal analyser coupled to a mass spectrometer.Five dehydration weight loss steps were observed for the natural vivianite at 105, 138, 203, 272 and 437 °C. The first weight loss step involves the reaction (Fe2+)3(PO4)2·8H2O→(Fe2+)3(PO4)2·3H2O+5H2O. The TGA/MS for the synthetic vivianite gave similar results to that of the natural sample. Mass spectrometry shows that water is lost up to 450 °C and after this temperature oxygen is lost. Changes in the structure of vivianite were followed using infrared emission spectroscopy. A model is proposed for the dehydration of vivianite. [Copyright &y& Elsevier]