ACID DISSOLUTION OF HEMATITES OF DIFFERENT MORPHOLOGIES

Dissolution in HCl of hematite particles with different morphologies l ed to sigmoidal dissolution vs. time curves. The rate of dissolution w as directly proportional to the sample surface area and independent of crystal morphology. Hematites produced by heating goethite at 600 or 800-degrees-C dissolved more rapidly per unit area than did hematites grown from solution. TEM showed that some platy crystals developed cen tral holes after prolonged acid attack; the hole formation was attribu ted to enhanced dissolution at screw dislocations present on the (001) faces of the crystals. Except where particularly susceptible regions involving strained areas or dislocations were present, there appeared to be no preferential acid attack at any particular crystal face. The original morphology was usually maintained during the reaction.