Evaluation of mineral reactive surface area estimates for prediction of reactivity of a multi-mineral sediment

Abstract

Our limited understanding of mineral reactive surface area contributes to significant uncertainties in quantitative simulations of reactive chemical transport in subsurface processes. Continuum formulations for reactive transport typically use a number of different approximations for reactive surface area, including geometric, specific, and effective surface area. In this study, reactive surface area estimates are developed and evaluated for their ability to predict dissolution rates in a well-stirred flow-through reactor experiment using disaggregated samples from the Nagaoka pilot CO 2 injection site (Japan). The disaggregated samples are reacted with CO 2 acidified synthetic brine under conditions approximating the field conditions and the evolution of solute concentrations in the reactor effluent is tracked over time. The experiments, carried out in fluid-dominated conditions at a pH of 3.2 for 650 hours, resulted in substantial dissolution of the sample and release of a disproportionately large fraction of the divalent cations. Traditional reactive surface area estimation methods, including an adjusted geometric surface area and a BET-based surface area, are compared to a newly developed image-based method. Continuum reactive transport modeling is used to determine which of the reactive surface area models provides the best match with the effluent chemistry from the well-stirred reactor. The modeling incorporates laboratory derived mineral dissolution rates reported in the literature and the initial modal mineralogy of the Nagaoka sediment was determined from scanning electron microscopy (SEM) characterization. The closest match with the observed steady-state effluent concentrations was obtained using specific surface area estimates from the image-based approach supplemented by literature-derived BET measurements. To capture the evolving effluent chemistry, particularly over the first 300 hours of the experiment, it was also necessary to account for the grain size distribution in the sediment and the presence of a highly reactive volcanic glass phase that shows preferential cation leaching.

Permeability, porosity, and mineral surface area changes in basalt cores induced by reactive transport of CO2‐rich brine

“…Recently, Beckingham et al . [] used many reactive surface area models to identify the one that was best able to reproduce experimental results in CrunchFlow [ Steefel et al ., ] simulations, which also required the incorporation of a highly reactive volcanic glass phase and a specified grain‐size distribution. Still, research opportunities remain to more fully constrain the intricacies of reactive transport.…”

Evaluation of the Potential for Dissolved Oxygen Ingress into Deep Sedimentary Basins during a Glaciation Event

“…Similarly, the specific surface area for chlorite ranges between 3.4 and 4.4 m 2 g −1 for grain sizes from 125 to 300 m and 75 to 125 m, respectively [41]. Beckingham et al [42] report specific surface areas for biotite (0.5-4.7 m 2 g −1 , grain size range from 10 to 420 m), chlorite (2.8-7.6 m 2 g −1 , 10-250 m), and pyrite (0.03-1.1 m 2 g −1 , 10-250 m). Although surface area is strongly dependent on mineral morphology and grain size, it can be concluded that the reactive surface areas considered for the base case are typically around three orders of magnitude lower than literature values for specific surface areas, implying that the base case mineral reactivities to limit O 2 -ingress to 200 m are highly conservative, even taking into account the often large discrepancies between laboratory-measured specific surface areas and reactive surface areas in the field.…”

“…In comparison to literature data for oxidative mineral dissolution rates and SOM oxidation, effective rates on the order of 10 −15 to 10 −13 mol dm −3 bulk s −1 , as used for the base case, are very low. For example, utilizing rate data, mineral abundances, and effective surface areas reported by Beckingham et al [42], effective dissolution rates for pyrite, biotite, and chlorite in a volcanic sandstone are determined as 2.3 × 10 −9 , 2.1 × 10 −10 , and 2.7 × 10 −10 mol dm −3 bulk s −1 for pyrite, biotite, and chlorite, respectively. Mineral volume fractions associated with these calculations are 0.4, 2.6, and 1.2 dm 3 mineral dm −3 bulk for pyrite, biotite, and chlorite, respectively, within a factor of 5 of the volumetric fractions of the present study.…”

Impact of grain size and rock composition on simulated rock weathering

“…Beckingham et al (2016) showed that the presence of a highly reactive volcanic glass phase indeed enhanced the chemical weathering rate of a volcanogenic sandstone. Deng et al (2017) indicated that preferential dissolution of highreactivity phases enhances fracture evolution in carbonaterich shales.…”