Surface-specific measurements of olivine dissolution by phase-shift interferometry

Abstract

Natural olivine dissolution and replacement often occurs preferentially along specific crystallographic planes. Thus, olivine reactivity at specific surfaces was examined in situ using phase-shift interferometry, which has a detection limit <10 -5 nm/s, by dissolving two smoothed olivine crystal faces and a third sample corresponding to a surface that was generated by preferential dissolution along structural defects. The experiments were conducted at 22 °C and ambient pressure in 0.1 M NaCl solutions that were acidified to pHs between 1 and 4 using 0.1 M HCl. These experiments show that olivine dissolution can vary from one surface to another as well as in different areas of the same surface that have similar characteristics. The fastest vertical retreat occurred at the surfaces related to defects. However, only vertical advancement was observed at pH 1 on this surface consistent with the observation of isolated islands on the surface during atomic force microscopy investigations after the experiment. Raman analysis of the precipitated phase showed that it was not one of the thermodynamically stable phases expected from PHREEQC modeling. However, the correlation between the siloxane ring peak of amorphous silica with a similar peak in the precipitate spectrum, in conjunction with previous experimental and natural observations, indicates that the precipitate was a Si-enriched amorphous phase. Therefore, precipitation can facilitate the further dissolution of olivine on this surface as long as it does not completely armor the surface. Precipitate formation on surfaces associated with outcropping defects supports the natural observations of preferential dissolution and serpentinization along these defects implying that the fast dissolution of these surfaces will play a critical role during olivine replacement. In addition, comparison with flow-through experiments indicates that outflow fluid chemistry may provide an incomplete picture of processes occurring during olivine dissolution.

A spatially resolved surface kinetic model for forsterite dissolution

“…Inspection of TEM images of larger areas (at lower zoom levels) and from two crosssections from two different mineral grains from sample 19R indicated the uniformity of the surface layer (not shown). Although the lattice spacing suggests different forsterite crystal faces are present, we do not see a strong relationship between the thickness of the surface layer and the particular orientation of the surface layer, in contrast with previous work for both olivine (King et al, 2014) and diopside . These results suggest that images we present are broadly representative of features associated In the unreacted sample, lattice fringes extend to the mineral surface, indicating the absence of an amorphous surface layer.…”

“…The entire sequence of alteration is consistent with both the development of a non-stoichiometric ''leached layer" (e.g., Luce et al, 1972;Schott et al, 1981;Chou and Wollast, 1984;Casey et al, 1988;Casey and Bunker, 1990;Stillings and Brantley, 1995;Hellmann, 1997;Pokrovsky and Schott, 2000a,b;Schott et al, 2012), and a process of interfacial dissolution-reprecipitation (Putnis, 2009;King et al, 2010;Hellmann et al, 2012;King et al, 2014;Ruiz-Agudo et al, 2014). However, given the stratigraphy evident in the alteration layer, including a sharp transition between amorphous and crystalline material and distinct compositional differences indicated by the Mg/Si profiles, we subdivide the altered layer into the zones defined above and in Fig.…”

“…Given the high reactivity of olivine, the surface chemistry and dissolution kinetics have been studied under a broad range of experimental conditions, including closedsystem (Giammar et al, 2005;King et al, 2010;Daval et al, 2011) and well-mixed flow-through dissolution experiments on powdered olivine samples (Pokrovsky and Schott, 2000b;Oelkers, 2001), as well as single crystals (Jarvis et al, 2009;Saldi et al, 2013). Characterization of the reaction products has also included a range of techniques, such as X-ray photoelectron spectroscopy (Pokrovsky and Schott, 2000a;Zakaznova-Herzog et al, 2008;Olsson et al, 2012), infrared spectroscopy (Pokrovsky and Schott, 2000a;Giammar et al, 2005;Loring et al, 2011), transmission electron microscopy (Bearat et al, 2006;Daval et al, 2011) and atomic force microscopy (King et al, 2014). Despite the range of studies focused on olivine reactivity in the presence of aqueous solutions, predictive models for olivine dissolution are subject to large uncertainties (Daval et al, 2011;Rimstidt et al, 2012).…”

Olivine dissolution rates: A critical review

“…Such interest has led to a large number of studies aimed at characterizing forsterite dissolution behavior and rates at various fluid compositions and temperatures (e.g. Luce et al, 1972;Sanemasa et al, 1972;Baily, 1974;Grandstaff, 1978Grandstaff, , 1986Eriksson, 1982;Helgeson, 1987, 1989;Blum and Lasaga, 1988;van Herk et al, 1989;Banfield et al, 1990;Walther, 1991, 1992;Casey and Westrich, 1992;Seyama et al, 1996;Awad et al, 2000;Chen and Brantley, 2000;Rosso and Rimstidt, 2000;Schott, 2000a, 2000b;Oelkers, 2001b;Giammar et al, 2005;Golubev et al, 2005;Hänchen et al, 2006;Olsen and Rimstidt, 2008;Davis et al, 2009;Beinlich and Austrheim, 2012;Rimstidt et al, 2012;Olsson et al, 2012;Plümper et al, 2012;Wang and Giammar, 2012;Declercq et al, 2013;Garcia et al, 2013;Saldi et al, 2013;van Noort et al, 2013;Bundeleva et al, 2014;Johnson et al, 2014;King et al, 2011King et al, , 2014Martinez et al, 2014;Torres et al, 2014;Agrawal and Mehra, 2016). Further studies have defined the spa...…”

Effect of pCO 2 on direct flue gas mineral carbonation at pilot scale

“…The decrease of Mg leaching can be explained by incongruent dissolution known to happen at ambient temperature (Daval et al, 2009). In addition, several studies also mentioned the development of Si rich layer through the leaching/precipitation process, which hindered the Mg disponibilty (Daval et al, 2011;King et al, 2014;Park et al, 2003;Pokrovsky and Schott, 2000;Teir et al, 2007). The passivating layer thickness grows as the Mg is removed from the solid lattice (Pokrovsky and Schott, 2004).…”