The precipitation of hematite from ferric chloride media at atmospheric pressure

The precipitation of hematite from ferric chloride media at temperatures <1 00 degrees C and at ambient pressure was studied as part of a program to re cover a marketable iron product from metallurgical processing streams or ef fluents. Hematite (Fe2O3) can be formed in preference to ferric oxyhydroxid es (e.g., beta-FeO . OH) at temperatures as low as 60 degrees C by controll ing the precipitation conditions, especially seeding. The hematite product typically contains >66 pet Fe and <1 pet Cl, and its composition does not c hange appreciably on repeated recycling. The amount of product formed incre ases significantly with increasing FeCl3 concentrations to similar to 0.2 M FeCl3, but nearly constant product yields are obtained thereafter; the pre cipitates consist only of hematite, provided that an adequate amount of see d is present. The contamination with Zn, Ca, and Na is <0.1 pet, even for h igh concentrations of dissolved ZnCl2, CaCl2, or NaCl. The extent of the pr ecipitation reaction depends principally on the temperature and the free-ac id concentration; accordingly, the controlled addition of a base allows the nearly complete elimination of the iron from metallurgical processing stre ams or effluents, as readily filterable Fe2O3.