Thermal Decomposition of Ammonium Jarosite (NH4)Fe3(SO4)2(OH)6

Abstract

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 degrees Celsius. 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 degrees Celsius and the ammonia loss by 450 degrees Celsius. Loss of the sulphate is observed by changes in band position and intensity after 500 degrees Celsius