The dissolution of biotite and chlorite at 25°C in the near-neutral pH region
ABSTRACT We studied the dissolution of biotite and chlorite in laboratory systems with flow-through and batch reactors. The initial dissolution of biotite in the near-neutral pH region, under N2(g) atmosphere is highly non-stoichiometric. A slow linear release of iron during a period of weeks indicates a surface-chemical-reaction-controlled mechanism of release for iron. The release of potassium is much faster than that of iron. A parabolic dependence of accumulated release with time suggests a diffusion-controlled mechanism of potassium release. The rates of magnesium, aluminium and silicon release are between those for potassium and iron and approach that of iron with time. There is no significant influence of (bi)carbonate or pH on biotite dissolution rate or stoichiometry in the pH region 7 < pH < 8.5. The release rates of elements from chlorite are close to stoichiometric and similar to the iron release rate from biotite. In closed batch reactors at near-basic pH the composition of test solutions in contact with biotite is apparently controlled by gibbsite (Al), kaolinite (Si) and Fe(III)-(hydr)oxide. We estimated a turn-over time (101−102 yr) for molecular oxygen and a time scale (10 months) to develop characteristic Fe(II) concentrations for a granitic groundwater.
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- "(i) fall within the range of rates reported for hornblende; (ii) are similar to those reported for anthophyllite by Mast and Drever (1987); and (iii) are over one order of magnitude higher than the anthophyllite dissolution rates measured by Chen and Brantley (1998). The dissolution rates of chlorites have been reported by Ross (1967), Kodama and Schnitzer (1973), Sverdrup (1990), May et al. (1995), Malmström et al. (1996), Rochelle et al. (1994) "
ABSTRACT: The dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25 °C and 2 < pH < 12 in mixed flow reactors. At pH 2.0 and 3.2, chlorite rates are 3 and 5 times faster, respectively, than corresponding actinolite rates, whereas the Si release rates from metabasalt are intermediate between chlorite and actinolite rates. In contrast, at pH 7.2 and 12.0, chlorite, actinolite and the metabasalt release Si at the same rates within analytical uncertainties. At pH 6.3, it was only possible to obtain the chlorite dissolution rate; at this pH the measured chlorite dissolution rate is 10− 11.86 mol/m2/s. Mineral dissolution rates obtained in this study are within the range of corresponding values reported in the literature. This observation suggests that the dissolution rates of major-constituent minerals in a multi-phase rock are not affected by the presence of the other minerals. This conclusion validates the common assumption that the dissolution rate of an individual mineral is equal to that of the same mineral in a dissolving multi-mineralogic rock, at least for major constituents.Chemical Geology 10/2014; 390:100-108. DOI:10.1016/j.chemgeo.2014.10.013 · 3.48 Impact Factor
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- "The reactive surface areas used are also reasonably consistent with those from geometric estimates based on microfracture spacings and apertures (Spiessl et al., 2007). The reactive surface area for chlorite is computed by multiplying a physical surface area for the fracture of 10 m 2 L − 1 H 2 O (Andersson et al., 1989; Malmström et al., 1996) by a chlorite surface area fraction of 0.2. This results in a reactive surface area of 2 m "
ABSTRACT: In the crystalline rocks of the Canadian Shield, geochemical conditions are currently reducing at depths of 500-1000 m. However, during future glacial periods, altered hydrologic conditions could potentially result in enhanced recharge of glacial melt water containing a relatively high concentration of dissolved oxygen (O2). It is therefore of interest to investigate the physical and geochemical processes, including naturally-occurring redox reactions, that may control O2 ingress. In this study, the reactive transport code MIN3P is used in combination with 2k factorial analyses to identify the most important parameters controlling oxygen migration and attenuation in fractured crystalline rocks. Scenarios considered are based on simplified conceptual models that include a single vertical fracture, or a fracture zone, contained within a rock matrix that extends from the ground surface to a depth of 500 m. Consistent with field observations, Fe(II)-bearing minerals are present in the fractures (i.e. chlorite) and the rock matrix (biotite and small quantities of pyrite). For the parameter ranges investigated, results indicate that for the single fracture case, the most influential factors controlling dissolved O2 ingress are flow velocity in the fracture, fracture aperture, and the biotite reaction rate in the rock matrix. The most important parameters for the fracture zone simulations are flow velocity in the individual fractures, pO2 in the recharge water, biotite reaction rate, and to a lesser degree the abundance and reactivity of chlorite in the fracture zone, and the fracture zone width. These parameters should therefore receive increased consideration during site characterization, and in the formulation of site-specific models intended to predict O2 behavior in crystalline rocks.Journal of Contaminant Hydrology 02/2008; 95(3-4):141-53. DOI:10.1016/j.jconhyd.2007.09.002 · 2.70 Impact Factor
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- " s [ 2004 , 2005 ] were performed 19 ( but before the KCl ones ) , revealed that the biotite grains had been altered . It is well 20 known during weathering alteration , biotite is chloritized by potassium release [ e . g . , 21 Mitchell and Taka ; 1984 , and references herein ] and that this reaction is quite rapid 22 [ Craw , 1981 ; Pal , 1985 ; Malmström et al . , 1996 ] ."
ABSTRACT: We measured the self-potential (SP) response to advective transport of KCl concentration fronts through two laboratory-scale sand-bodies with different mineralogical composition. In pure quartz sand, the amplitude and polarity of the SP signals agreed with a previously published model. In sand containing 3% potassic feldspars and 1% micas and clays, the shape of the SP response differed significantly: the amplitude was much larger than the model prediction and a change in polarity occurred after the passage of the front. Furthermore, the KCl concentration in the effluent was strongly reduced. We suggest that the minor mineral phases reacted with the K+ ions, trapping them during the front passage and releasing them later. Even though the reactions involved are not fully identified to date, this study demonstrates that even small amounts of chemically active mineral phases, such as micas or clays, can significantly influence the SP signals.Geophysical Research Letters 12/2006; 332(24). DOI:10.1029/2006GL028048 · 4.46 Impact Factor