Thermal decomposition of sabugalite– A controlled rate thermal analysis study

Abstract

The mineral sabugalite (HAl)0.5 [(UO2)2(PO4)]2•8H2O, has been studied using a combination of energy dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate thermal analysis techniques. X-ray diffraction shows that the starting material in the thermal decomposition is sabugalite and the product of the thermal treatment is a mixture of aluminium and uranyl phosphates. Four mass loss steps are observed for the dehydration of sabugalite at 48 degrees Celsius (temperature range 39 to 59 degrees Celsius), 84 degrees Celsius (temperature range 59 to 109 degrees Celsius), 127 degrees Celsius (temperature range 109 to 165 degrees Celsius) and around 270 degrees Celsius (temperature range 175 to 525 degrees Celsius) with mass losses of 2.8, 6.5, 2.3 and 4.4 % respectively, making a total mass loss of water of 16.0 %. In the CRTA experiment mass loss stages were found at 60, 97, 140 and 270 degrees Celsius which correspond to four dehydration steps involving the loss of 2, 6, 6 and 2 moles of water. These mass losses result in the formation of four phases namely meta(I)sabugalite, meta(II)sabugalite, meta(III)sabugalite and finally uranyl phosphate and alumina phosphates. The use of a combination of dynamic and controlled rate thermal analysis techniques enabled a definitive study of the thermal decomposition of sabugalite. While the temperature ranges and the mass losses vary due to the different experimental conditions, the results of the CRTA analysis should be considered as standard data due to the quasi-equilibrium nature of the thermal decomposition process.