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 degreesC 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 degreesC 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),C-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),C-initial greater than or equal to 0.4 M in the absence of ZnSO4 or at C-Fe(III),C-initial greater than or equal to 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 m(2)/g) and contained around 1% S (as SO4 via chemisorption), 0.2% Zn (when ZnSO4 was present), and about 4.5% H2O/OH. After excluding the SO4 and Zn content, the following stoichiometric formula for hematite was determined: Fe2O3-x(OH)(2x).yH(2)O where x = 0.08 and y = 0.29.