ACID D ISSOLUTION OF HEMATITES OF D IFFERENT MORPHOLOGIES

ABSTRACT: Dissolution in HCl of hematite particles with different morphologies led to sigmoidal dissolution vs. time curves. The rate of dissolution was directly proportional tothe sample surface area and independent of crystal morphology. Hematites produced by heating oethite at 600 or 800 ~ dissolved more rapidly per unit area than did hematites grown from solution. TEM showed that some platy crystals developed central holes after prolonged acid attack; the hole formation was attributed to enhanced dissolution at screw dislocations present on the (001) faces of the crystals. Except where particularly susceptible r gions involving strained areas or dislocations were present, there appeared to be no preferential cid attack at any particular crystal face. The original morphology was usually maintained during the reaction. Goethite (c~-FeOOH) and hematite (o~-Fe203) are two of the most widespread iron oxides in soils and sediments. Their dissolution behaviour is important because it can influence the availability of nutrients for plant growth and also helps regulate migration of pollutant ions in soils. An understanding of dissolution behaviour of these minerals may also assist in elucidation of weathering mechanisms. The dissolution behaviour of goethite and hematite has been investigated intensivel