Quartz constitutes approximately 20% of the crustal rocks exposed to weathering. As for other major rock-forming minerals, the reactivity of quartz influences a plethora of geochemical processes, such as dissolution/deposition and adsorption/desorption phenomena. In turn, these processes affect the mobility and availability of nutrient ions and contaminants in aqueous environments. So far, studies on the quartz reactivity have been conducted mainly using fine-sized or colloidal particles. However, many of the reactive properties including the surface charge, dissolution rate, and their dependence on the chemical and physical conditions of the system (e.g. pH, temperature) could be anisotropic with respect to the crystallographic orientation of a particular face. Here we present new X-ray Reflectivity and Resonant Anomalous X-ray Reflectivity results to demonstrate differences in sorptive properties of quartz (101) and (100) surfaces for mono- and di-valent cations under alkaline conditions. The results show that monovalent Rb+ adsorbs on the (101) surface at pH =10, and is distributed broadly without forming any discrete inner-sphere or outer-sphere complex. On the other hand, preliminary results show that adsorption of divalent Ba2+ occurs at higher pH (>12), and adsorbed Ba2+ mostly forms discrete layers near the surface. A similar structure was observed for Ba2+ adsorbed at the (100) surface, while the metal uptake occurred at lower pH (<12), implying a difference in the surface charge and elemental selectivity.

Differences in adsorption behavior of mono- and di-valent cations onto the quartz (101) and (100) crystallographic surfaces

247th National Meeting (2014)

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