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For sustainable geologic CO2sequestration(GCS), itis important to understand the effects of temperature and CO2pressure on mica’s dissolution and surface morphologicalchanges under saline hydrothermal conditions. Batch experiments wereconducted with biotite (Fe-end member mica) under conditions relevantto GCS sites (35–95 °C and 75–120 atm CO2), and 1 M NaCl solution was used to mimic the brine. With increasingtemperature, a transition from incongruent to congruent dissolutionof biotite was observed. The dissolution activation energy based onSi release was calculated to be 52 ± 5 kJ mol–1. By comparison with N2experiments, we showed that CO2injection greatly enhanced biotite’s dissolution andits surface morphology evolutions, such as crack formation and detachmentof newly formed fibrous illite. For biotite’s dissolution andmorphological evolutions, the pH effects of CO2were differentiatedfrom the effects of bicarbonate complexation and CO2intercalation.Bicarbonate complexation effects on ion release from biotite werefound to be minor under our experimental conditions. On the otherhand, the CO2molecules in brine could get into the biotiteinterlayer and cause enhanced swelling of the biotite interlayer andhence the observed promotion of biotite surface cracking. The crackingcreated more reactive surface area in contact with brine and thusenhanced the later ion release from biotite. These results providenew information for understanding CO2–brine–micainteractions in saline aquifers with varied temperatures and CO2pressures, which can be useful for GCS site selection andoperations. [ABSTRACT FROM AUTHOR]

The simultaneous homogeneous and heterogeneous precipitationofhydrous Fe(III) oxides was investigated in the presence of environmentallyubiquitous anions (nitrate, chloride, and sulfate). Experiments wereconducted with 10–4M Fe(III) at acidic pH (pH =3.7 ± 0.2), which often occurs at acid mine drainage sites orgeologic CO2storage aquifers near injection wells. Quartzwas used as a model substrate for heterogeneous precipitation. Smallangle X-ray scattering (SAXS) and grazing incidence SAXS (GISAXS),atomic force microscopy (AFM), and dynamic light scattering (DLS)measurements were conducted. In situ SAXS/GISAXS quantified the size,total particle volume, number, and surface area evolutions of theprimary nanoparticles formed in the nitrate and chloride systems.In both systems, the heterogeneously precipitated particles were smallerthan the homogeneously precipitated particles. Compared with chloride,the volume of heterogeneously precipitated hydrous Fe(III) oxideson the quartz surface was 10 times more in the nitrate system. Afterinitial fast heterogeneous nucleation in both nitrate and chloridesystems, nucleation, growth, and aggregation occurred in the nitratesystem, whereas Ostwald ripening was the dominant heterogeneous precipitationprocess in the chloride system. In the sulfate system, fast growthof the heterogeneously precipitated particles and fast aggregationof the homogeneously precipitated particles led to the formation ofparticles larger than the detection limit of GISAXS/SAXS. Thus, thesizes of the particles precipitated on quartz surface and in solutionwere analyzed with AFM and DLS, respectively. This study providesunique qualitative and quantitative information about the location(on quartz surfaces vs in solutions), size, volume, and number evolutionsof the newly formed hydrous iron oxide particles in the presence ofquartz substrate and ubiquitous anions, which can help in understandingthe fate and transport of pollutants in the environment. [ABSTRACT FROM AUTHOR]