Group IIA sulphates

The solid product, BaO, was apparently amorphous and porous. Decomposition rate measurements were made between the phase transformation at 1422 K and 1550 K (the salt melts at 1620 K). The enthalpy and entropy of activation at 1500 K (575 13 kJ mole-1 and 200 8 J K 1 mole-1) are very similar to the standard enthalpy and entropy of decomposition at the same temperature (588 7 kJ and 257 5 J K-1, respectively, referred to 1 mole of BaS04). The simplest mechanistic explanation of the observations is that all steps in the reaction are in equilibrium except for desorption of the gaseous products, S02 and 02. Desorption occurs over an area equivalent to about 1.4% of the total exposed crystal surface. Other possible models are discussed. 

Kinetic data available for the reactions of other metal sulphates refer to reaction conditions closer to those of actual pyrometallurgical processes [790]. 

Decomposition of BeS04 (either reagent grade or freeze-dried) yielded BeO [771] and kinetic analyses based on the contracting area equation [eqn. (7), n = 2] for 875—990 K gave values of E from 213 to 226 kJ mole-1. Under non-isothermal conditions, the values of E varied between 

Selected kinetic characteristics for the decomposition of metal sulphates 

Reactant Solid product Temperature E decomp.298K a Remarks Ref. 

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