Iron-silica interactions: mobility of the crystalline iron compounds
AbstractA study of the behaviour of artificial and natural iron compounds in the presence of quartz during experimental leaching, led to the following conclusions: (i) iron compounds, during crystallization into oxides, are able to form a stable colloidal suspension in the presence of monomolecular silicic acid, Si(OH)4. The dispersed phase is principally constituted (X-ray diffraction and electron microscopy) of elementary oxide crystals, <0·l ?m; (ii) the electronegative charge of the suspended particles is explained by the existence of monomolecular silicic acid linked to hydrated ions on the iron oxide crystal surface and expulsion of protons which seems to be stimulated by the proximity of the electropositive field of the oxide crystal lattice. The ease of formation and the stability of the suspension, as well as the very fine size of suspended particles, allows the possibility of the existence in nature of the phenomena observed in the laboratory. The mobilization of crystallized iron compounds in colloidal suspension, is a purely geochemical mechanism, which could contribute to the understanding of large ferruginous accumulations without the intervention of exceptional climatic and biochemical cycles.