Magnesite dissolution rates at different spatial scales: The role of mineral spatial distribution and flow velocity

Salehikhoo, F.; Li, Li; Brantley, Susan L.

doi:10.1016/j.gca.2013.01.010

Cited by 92 publications

(141 citation statements)

References 113 publications

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“…The data that were given directly in terms of spatial variables are taken from Maher (2010) and Peng et al (2012). The data from Salehikhoo et al (2013) . Note the equivalence in scaling between immobilization, mobilization, and weathering.…”

Section: Resultsmentioning

confidence: 99%

“…As an upper limit, Molins et al (2012) assert that transport control is expected only for flow velocities less than 100 lm/s, about two orders of magnitude greater than the lower limit. A similar range of flow velocities under which chemical reaction rates are transport-controlled is given by Salehikhoo et al (2013). Fig.…”

Section: Natural Flow Ratesmentioning

confidence: 91%

“…Using the commonly assumed ratio of pore size to particle size of 0.3 gives a mean pore size of about 120 lm, which we take as the fundamental length scale. Salehikhoo et al (2013) demonstrated that data for different column lengths and flow velocities could be reasonably collapsed to a single curve when represented in terms of the Dammkohler number. We digitized their data and chose to represent the dependence of the reaction rate on system length, in accord with the observation above that for a constant flow velocity, the Dammkohler number is proportional to the system length.…”

Section: à3mentioning

confidence: 97%

“…However, in that comparison we scale the reaction rates from Maher to 10 À2.3 yr À1 , just as in the spatial comparison. Salehikhoo et al (2013) Column experiments on magnesite dissolution were performed in columns of length from 5 to 22 cm, and at various flow velocities. Results were reported in terms of the Dammkohler number, Da I ¼ x/(v 0 s R ), where s R is a reaction time and x the column length.…”

Section: à3mentioning

confidence: 99%

“…R 0 and x 0 for the data of Peng et al (2012) were simply chosen as the largest R and corresponding x 0 value, respectively. The choice of x 0 for Salehikhoo et al (2013) was also described in Materials and Methods. Note that use of the value of R 0 reported by Salehikhoo et al (2013) would not allow such outstanding correspondence between theory and experiment.…”

Section: Figmentioning

confidence: 99%

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Scaling of geochemical reaction rates via advective solute transport

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Chaos: An Interdisciplinary Journal of Nonlinear Science

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A new model for gas transport in fractal-like tight porous media J. Appl. Phys. 117, 174304 (2015) Transport in porous media is quite complex, and still yields occasional surprises. In geological porous media, the rate at which chemical reactions (e.g., weathering and dissolution) occur is found to diminish by orders of magnitude with increasing time or distance. The temporal rates of laboratory experiments and field observations differ, and extrapolating from laboratory experiments (in months) to field rates (in millions of years) can lead to order-of-magnitude errors.The reactions are transport-limited, but characterizing them using standard solute transport expressions can yield results in agreement with experiment only if spurious assumptions and parameters are introduced. We previously developed a theory of non-reactive solute transport based on applying critical path analysis to the cluster statistics of percolation. The fractal structure of the clusters can be used to generate solute distributions in both time and space. Solute velocities calculated from the temporal evolution of that distribution have the same time dependence as reaction-rate scaling in a wide range of field studies and laboratory experiments, covering some 10 decades in time. The present theory thus both explains a wide range of experiments, and also predicts changes in the scaling behavior in individual systems with increasing time and/or length scales. No other theory captures these variations in scaling by invoking a single physical mechanism. Because the successfully predicted chemical reactions include known results for silicate weathering rates, our theory provides a framework for understanding changes in the global carbon cycle, including its effects on extinctions, climate change, soil production, and denudation rates. It further provides a basis for understanding the fundamental time scales of hydrology and shallow geochemistry, as well as the basis of industrial agriculture. V C 2015 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4913257]Chemical reactions at the surfaces of porous media drive the weathering of silicate minerals in the earth's crust. This weathering affects surface denudation rates and the global carbon cycle, and thereby also climate change and extinctions through geologic time. But reactions within porous media exhibit non-trivial dependences on time, space, and measurement scales that cannot be interpreted as transport-limited in the context of Gaussian transport. Thus, the role of solute transport in controlling such reaction rates has been controversial. Because our transport theory, which is based on concepts from percolation theory, is the first theory that can actually predict nonGaussian solute transport in porous media, we are able to resolve the controversial aspects of chemical reaction rate scaling. In particular, we show that our calculated functional dependence of the solute velocity acts as a proxy for chemical reaction rates, proving that they are limited by transport. Importantly, the solute...

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Section: Resultsmentioning

confidence: 99%

Section: Natural Flow Ratesmentioning

confidence: 91%

Section: à3mentioning

confidence: 97%

Section: à3mentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

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Scaling of geochemical reaction rates via advective solute transport

Hunt

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Skinner

et al. 2015

Chaos: An Interdisciplinary Journal of Nonlinear Science

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Solute transport in low‐heterogeneity sandboxes: The role of correlation length and permeability variance

Heidari

2014

Water Resources Research

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This work examines how heterogeneity structure, in particular correlation length, controls flow and solute transport. We used two-dimensional (2D) sandboxes (21.9 cm 3 20.6 cm) and four modeling approaches, including 2D Advection-Dispersion Equation (ADE) with explicit heterogeneity structure, 1D ADE with average properties, and nonlocal Continuous Time Random Walk (CTRW) and fractional ADE (fADE). The goal is to answer two questions: (1) how and to what extent does correlation length control effective permeability and breakthrough curves (BTC)? (2) Which model can best reproduce data under what conditions? Sandboxes were packed with the same 20% (v/v) fine and 80% (v/v) coarse sands in three patterns that differ in correlation length. The Mixed cases contain uniformly distributed fine and coarse grains. The Four-zone and One-zone cases have four and one square fine zones, respectively. A total of seven experiments were carried out with permeability variance of 0.10 (LC), 0.22 (MC), and 0.43 (HC). Experimental data show that the BTC curves depend strongly on correlation length, especially in the HC cases. The HC One-zone (HCO) case shows distinct breakthrough steps arising from fast advection in the coarse zone, slow advection in the fine zone, and slow diffusion, while the LCO and MCO BTCs do not exhibit such behavior. With explicit representation of heterogeneity structure, 2D ADE reproduces BTCs well in all cases. CTRW reproduces temporal moments with smaller deviation from data than fADE in all cases except HCO, where fADE has the lowest deviation.

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Long‐term observation of permeability in sedimentary rocks under high‐temperature and stress conditions and its interpretation mediated by microstructural investigations

Yasuhara

Kinoshita

Ohfuji

et al. 2015

Water Resources Research

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In this study, a series of long-term, intermittent permeability experiments utilizing Berea sandstone and Horonobe mudstone samples, with and without a single artificial fracture, is conducted for more than 1000 days to examine the evolution of rock permeability under relatively high-temperature and confining pressure conditions. Effluent element concentrations are also measured throughout the experiments. Before and after flow-through experiments, rock samples are prepared for X-ray diffraction, X-ray fluorescence, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to examine the mineralogical changes between pre and postexperimental samples, and also for microfocus X-ray CT to evaluate the alteration of the microstructure. Although there are exceptions, the observed, qualitative evolution of permeability is found to be generally consistent in both the intact and the fractured rock samples-the permeability in the intact rock samples increases with time after experiencing no significant changes in permeability for the first several hundred days, while that in the fractured rock samples decreases with time. An evaluation of the Damkohler number and of the net dissolution, using the measured element concentrations, reveals that the increase in permeability can most likely be attributed to the relative dominance of the mineral dissolution in the pore spaces, while the decrease can most likely be attributed to the mineral dissolution/crushing at the propping asperities within the fracture. Taking supplemental observations by microfocus X-ray CT and using the intact sandstone samples, a slight increase in relatively large pore spaces is seen. This supports the increase in permeability observed in the flow-through experiments.

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Magnesite dissolution rates at different spatial scales: The role of mineral spatial distribution and flow velocity

Cited by 92 publications

References 113 publications

Scaling of geochemical reaction rates via advective solute transport

Scaling of geochemical reaction rates via advective solute transport

Solute transport in low‐heterogeneity sandboxes: The role of correlation length and permeability variance

Long‐term observation of permeability in sedimentary rocks under high‐temperature and stress conditions and its interpretation mediated by microstructural investigations

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