Fresh and aged iron particle attachment onto model mineral surfaces was studied using atomic force microscopy based – force spectroscopy (AFM) in different water chemistries as well as in the presence of surface modifiers for the particles (carboxymethyl cellulose polymer). The forces of interactions measured with AFM were explained in terms of classical DLVO forces (electrostatic, Born and van der Waals forces) as well as hydration, steric and magnetic forces, which are not accounted for by classical models. Theoretical interpretation of the results was thus performed using extended models, in which such interactions were considered. In the absence of surface modifiers, iron particle attachment onto silicates and iron oxides appeared favorable in pure water and salt solutions at pH 4 and 5.5, but was hindered in water amended with humic acids. Attachment of bare CIP was also unfavourable at pH 8, except in the presence of CaCl2 salt at 100 mM concentrations. Attachment between iron particles and iron oxides was favorable even in the presence of polymeric coatings. Conversely, in all solutions such coatings contributed to electro-steric repulsion between particles and silicates, which dominated over attractive van der Waals forces, albeit to a lesser extent in the presence of salts. To best assess the role of polymeric coatings in particle attachment, polymer sorption onto the model mineral surfaces considered was investigated using a Quartz Crystal Microbalance with Dissipation Monitoring. The results obtained confirmed the AFM findings, and furnished insights regarding the role of salts on polymer sorption onto substrates. Finally, the effect of aging on attachment was probed both by AFM and by analyzing cementation phenomena of iron aggregates using scanning electron microscopy, as well as by probing changes in particle compositional properties with various spectroscopy tools. The major effect of aging was to promote the formation of large cemented aggregates, which did not appear prone to disruption or remobilization.

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