The Precipitation of Hematite from Ferric Chloride Media at Atmospheric Pressure

The precipitation of hematite from ferric chloride media at temperatures <100 °C and at ambient pressure was studied as part of a program to recover a marketable iron product from metallurgical processing streams or effluents. Hematite (Fe2O3) can be formed in preference to ferric oxyhydroxicles (e.g.,(beta)-FeO-OH) at temperatures as low as 60 °C by controlling the precipitation conditions, especially seeding. The hematite product typically contains >66 pel Fe and <1 pct Cl, and its composition does not change appreciably on repeated recycling. The amount of product formed increases significantly with increasing FeCl(3) concentrations to ~0.2 M FeCl(3) but nearly constant product yields are obtained thereafter: the precipitates consist only of hematite, provided that an adequate amount of seed is present. The contamination with Zn, Ca, and Na is <0.1 pet, even for high concentrations of dissolved ZnCl(2), CaCl(2) or NaCI. The extent of the precipitation reaction depends principally on the temperature and the free-acid concentration: accordingly, the controlled addition of a base allows the nearly complete elimination of the iron from metallurgical processing streams or effluents, as readily filterable Fe(2)O(3).