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 ZnSO 4 ) with 3 h retention time. Regardless of the presence or not of ZnSO 4, 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, r hyd = k hyd ( C Fe(III) − C Fe(III),eq ), where the apparent kinetic constant, k hyd, 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 C Fe(III),initial ≥ 0.4 M in the absence of ZnSO 4 or at C Fe(III),initial ≥ 0.7 M in the presence of ZnSO 4, while the other led to the production of hematite. The hydrothermally produced hematite material possessed very high specific surface area (50−80 m 2 /g) and contained around 1% S (as SO 4 via chemisorption), 0.2% Zn (when ZnSO 4 was present), and about 4.5% H 2 O/OH. After excluding the SO 4 and Zn content, the following stoichiometric formula for hematite was determined: Fe 2 O 3 - x (OH) 2 x · y H 2 O where x = 0.08 and y = 0.29.