Hematite solubilization

In a modification the conversion process, the jarosite residue is hydrothermaHy decomposed to hematite by autoclaving at 220—250°C. This solubilizes zinc and other metal values and the hematite has a potential for iron recovery. Hematite stockpiles are less of a problem than jarosite because hematite is denser and holds up less of the soluble metals. 

Figure 3. Photochemical and thermal solubilization of hematite in deoxygenated hematite suspensions containing S(IV). (Reproduced from Ref. 42. Copyright 1985, American Chemical Society.)...

The noncrystalline hydrated iron oxide, ferrihydrite, is indicative of young deposits of Fe oxides in soils, forming by the fast hydrolysis of Fe " salts or rapid oxidation of Fe solubilized by reduction reactions. It is more reddish than goethite, but less reddish than hematite. It is stabilized relative to the more crystalline oxides by adsorbed cations and anions, notably silicate. There is some uncertainty about its structure, but it is composed of tiny (30-70 A) spherical particles that may have short-range hematitelike or goethitelike order. Ferrihydrite is probably a precursor of more crystalline oxides such as hematite. 

Much of the iron present in most condensates exists as finely divided suspended iron oxide particles. Since most operators of high pressiure boiler plants are concerned with the total concentration of iron in the various water cycles, solubilizing the suspended iron (usually hematite) is a necessary part of any procedure for this determination. Tetlow and Wilson (5) have shown that the suspended iron oxide is not completely... 

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