Thermogravimetry combined with mass spectrometry
has been used to study the thermal decomposition of a synthetic ammonium jarosite.
Five mass loss steps are observed at 120, 260, 389, 510 and 541°C. Mass
spectrometry through evolved gases confirms these steps as loss of water,
dehydroxylation, loss of ammonia and loss of sulphate in two steps. Changes
in the molecular structure of the ammonium jarosite were followed by infrared
emission spectroscopy (IES). This technique allows the infrared spectrum at
the elevated temperatures to be obtained. IES confirms the dehydroxylation
to have taken place by 300°C and the ammonia loss by 450°C. Loss of
the sulphate is observed by changes in band position and intensity after 500°C.