Hydrolysis of Ferric Sulfate in the Presence of Zinc Sulfate at 200 °C:  Precipitation Kinetics and Product Characterization

The hydrolysis of ferric sulfate was studied in a batch reactor at 200 °C with the initial Fe(III) concentration ranging from 0.10 to 0.80 M in the presence/absence of zinc sulfate (1.2 M ZnSO4) with 3 h retention time. Regardless of the presence or not of ZnSO4, the hydrolytic precipitation kinetics at 200 °C was determined to be first-order with respect to Fe(III), and expressed by the following rate equation, rhyd = khyd(CFe(III) − CFe(III),eq), where the apparent kinetic constant, khyd, was determined to be 10-2 min-1. Two reaction stoichiometries were established: one leading to the formation of kinetically favored basic ferric sulfate at CFe(III),initial ≥ 0.4 M in the absence of ZnSO4 or at CFe(III),initial ≥ 0.7 M in the presence of ZnSO4, while the other led to the production of hematite. The hydrothermally produced hematite material possessed very high specific surface area (50−80 m2/g) and contained around 1% S (as SO4 via chemisorption), 0.2% Zn (when ZnSO4 was present), and about 4.5% H2O/OH....