E3S Web Conf.
Volume 98, 201916th International Symposium on Water-Rock Interaction (WRI-16) and 13th International Symposium on Applied Isotope Geochemistry (1st IAGC International Conference)
|Number of page(s)||5|
|Section||Thermodynamics and Kinetics of Water-Rock Interaction, Experimental Geochemistry|
|Published online||07 June 2019|
Absence of solid solution between Fe(II) and Mg(II) hydroxides and consequences on formation of fougerite and smectites
Académie d'Agriculture de France, 75007 Paris, France
2 INRA-UAPV, UMR 1114 Emmah, 84914 Avignon, France
3 UPMC, IMPMC, 75006 Paris, France
* Corresponding author: firstname.lastname@example.org
As there exists extended solid solutions between ferrous and magnesian silicates, experiments were conducted to check if ferrous and magnesian hydroxides can co-precipitate in a solid solution. Results show that no solid solution forms and instead Fe(II) and Mg(II) hydroxides precipitate separately with the same solubilities as pure components. However, in fougerite, F(III), Fe(II) and Mg(II) coexist in a brucitic type hydroxide, with an extended solid solution. This implies that fougerite formation results from Fe(III) precipitation, Fe(III) being surrounded by divalent Fe(II) and Mg(II) to comply with the exclusion rule: Fe(III) ions cannot be direct neighbours. Consequently, Fe(III) - Fe(II) - Mg(II) smectites cannot form by oxidation of a ferrous magnesian brucitic layer, but by silication of fougerite. The impossibility of formation of a solid solution between Fe(II) hydroxide and Mg(II) hydroxide, while their electric charge and ionic radii are identical can be explained by the differences of electronegativities of the elements. Fe(II) and Mg(II) can dimerize separately in aqueous solution, but an heterodimer cannot form.
© The Authors, published by EDP Sciences, 2019
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