Pyrohydrolysis of ammonium fluoroferrates

The interaction of nonstoichiometric ammonium fluoroferrates (NH 4 ) x Fe(OH) 3 - x F 2 x (2.6 ≤ x ≤ 3) (I) and NH 4 H 2 x FeO x F 3 (0.2 ≤ x ≤ 0.4) (II) with steam in the isothermal mode from 165 to 400°C was studied. The earlystages of the process involve thermolysis of the starting complexes to yield intermediate ammonium fluoroferrates in the case of compound I and FeF 2 in the case of compound II. The pyrohydrolysis of ammonium fluoroferrate(II) is complicated by iron(II) oxidation. The ultimate product of both reactions is α-Fe 2 O 3 . The rates were calculated and the apparent activation energies were determined for the processes in the range of the specified temperatures.