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Effects of Temperature and Iron(III) Concentration on the Hydrolytic Formation of Iron(III) Oxyhydroxides and Oxides
Author(s) -
Wang Ming K.,
Hsu Pa Ho
Publication year - 1980
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1980.03615995004400050043x
Subject(s) - goethite , hematite , lepidocrocite , supersaturation , chemistry , hydrolysis , inorganic chemistry , mineralogy , organic chemistry , adsorption
Fe(ClO 4 ) 3 solutions, of concentration ranging from 0.01 M to 0.1 M , were hydrolyzed at different temperatures and periodically analyzed up to 14 months. The reaction products were very different in their appearance and stability. For a given iron(III) concentration, the sample appearance changed as the temperature of preparation changed. Beginning as true solutions at lower temperatures, the samples progressively appear as coarse precipitates, turbid suspensions and clear sols as the temperature of preparation increases. For a given temperature of preparation, the products showed the same sequence of changes with decreasing Fe(III) concentration. The products are largely goethite, with an occasional presence of lepidocrocite when prepared at 37°C or below, but are hematite and/or goethite when prepared at 55°C or above. The results suggest that the differences in appearance and stability merely reflect the distribution of particle size but not the mineralogical composition. The degree of supersaturation is suggested as the key factor governing the initial number of nuclei relative to the concentration of monomeric Fe(III) ions, which, in turn, governs the appearance and stability of hydrolyzed Fe(III) solutions. A change in temperature results in changes in the reaction rate as well as the equilibrium constant and, thus, the degree of supersaturation.