THE PRECIPITATION OF HEMATITE FROM FERRIC-CHLORIDE MEDIA

The precipitation of hematite from ferric chloride media was systemati cally investigated in a series of autoclave experiments. The minimum t emperature to form hematite in the absence of hematite seed is similar to 125 degrees C; akaganeite, beta-FeO . OH, is precipitated at lower temperatures for the < 6 h reaction times used. In the presence of he matite seed, Fe2O3 is precipitated at temperatures as low as 100 degre es C. The amount of iron precipitated and the concentration of co-gene rated HCl increase systematically as the initial concentration of ferr ic chloride increases from 0.025 to 0.3 M FeCl3. Further increases in the FeCl3 concentration have a negligible effect on the quantity of Fe 2O3 precipitated or on the concentration of HCl generated. Increasing initial HCl concentrations, however, sharply reduce the amount of hema tite precipitated. In contrast, pre-neutralization of the solution sig nificantly increases the extent of hematite precipitation. The presenc e of soluble species such as FeCl2, NaCl, CaCl2, ZnCl2 and PbCl2 somet imes decreases the extent of iron precipitation but has only a minor e ffect on the purity of the hematite product; the precipitates typicall y contain > 65% Fe, < 0.5% Cl and less than 0.1% of Na, Ca, Zn or Pb. The precipitated hematite is very fine, but its filterability is great ly improved by the presence of hematite seed.