Speciation of Fe(II) and Fe(III) effect on CaCO3 crystallization |
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Authors: | Wided Mejri,Ilhem Ben  Salah,Mohamed Mouldi Tlili |
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Abstract: | The present work was carried out to investigate separately the effect of Fe2+ and Fe3+ on the precipitation kinetics and the microstructure of CaCO3. For this an experimental procedure was proposed. Precipitation tests were made by using the dissolved‐CO2 degassing method. Both air and nitrogen were employed to strip the CO2 from a Ca(HCO3)2 solution initially rich in this gas. At anoxic medium, it was shown that iron (II) prolongs the nucleation step and decelerates the crystalline growth rate. X‐ray diffraction analysis shows that its presence inhibits calcite and promotes aragonite variety. By using air, the reaction medium is rich in oxygen and iron (II) is rapidly oxidized. Seeing the higher solution pH (> 6.5), iron hydroxide forms before the onset of CaCO3 precipitation and plays a role of seed permitting to initiate CaCO3 nucleation. So, contrary to the observed effect of iron (II), the presence of iron (III) accelerates the precipitation rate of CaCO3. As for iron (II), iron (III) inhibits calcite formation but favored the vaterite variety instead of the aragonite one. |
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Keywords: | Iron ions water calcium carbonate iron hydroxide precipitation |
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