Clays and Clay Minerals, Vol. 59, No. 2, 136–146, 2011.
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Authors
Salmimies, Riina
Mannila, Marju
Kallas, Juha
Hakkinen, Antti
Issue Date
2011
Type
Article
Language
Keywords
Periodicals , Geology , Dissolution , Iron Ore , Magnetite , Oxalic Acid , Nitric Acid , Sulfuric Acid , Particle Size , Temperature
Alternative Title
Acidic Dissolution Of Magnetite: Experimental Study On The effects Of Acid Concentration And Temperature
Abstract
Magnetite (Fe3O4) is a key economically valuable component in iron ore and is extracted by dissolution processes, but among the Fe (oxyhydr)oxides its solubility behavior is one of the least understood. The objective of this study was to improve understanding of magnetite dissolution mechanisms leading to thermodynamic equilibrium by comparing the dissolution of two solid samples, one synthetic and one industrial, using oxalic, sulfuric, and nitric acids at varying concentrations and temperatures. Of the three solid-liquid systems investigated, only the system consisting of magnetite and oxalic acid reached an equilibrium state within the duration of an individual experiment (6 h). In this system, increasing the acid concentration resulted in a significant increase in the equilibrium concentration of dissolved Fe. When dissolving synthetic and industrial magnetite, increasing the temperature not only increased the rate of reaction but also affected the concentration of dissolved Fe. Significant effects were observed when increasing the temperature from 15 to 35ºC, but only slight differences were seen on further increases in temperature. Observations regarding the equilibrium state of the sulfuric and nitric acid systems could not be made because equilibrium was not reached. The most important individual observation regarding the equilibrium state of the nitric- and sulfuric-acid systems seems to be that in future studies a much longer reaction time is necessary, due to slow kinetics of the dissolution mechanism. A proton-based mechanism has been hypothesized as the one governing the dissolution of magnetite by these two acids, but only the dissolution of the industrial sample yielded results that were similar for these two acids and consistent with that hypothesis.
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Citation
Clays and Clay Minerals, Vol. 59, No. 2, 136–146, 2011.
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