The oxidation of FeS - parabolic to linear rate law transition

Laboratory studies of some important industrial reactions 275 

Oxidation of complex sulphide ores — competitive oxidation of cations 

The difference in stability between FeO and NiO is not as large as that between iron and copper oxides, and so the preferential oxidation of iron is not so marked in pentlandite. Furthermore, the nickel and iron monoxides form a continuous series of solid solutions, and so a small amount of nickel is always removed into die oxide phase (Table 9.2). 

The kinetics of the processes of oxidation of these complex sulphides have not been established quantitively, but the rate of advance of the oxides into sulphide particles of inegular shapes were always linear. This suggests tlrat the oxide films were rupmred during growth thus permitting the gas phase to have relatively unimpeded access to tire sulphide-oxide interface in all cases. 

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