Diffusivity of dissolved silica in rock pore water at 25°C as characterized by through-diffusion experiments

Yokoyama, Tadashi

doi:10.1002/2013wr013794

Cited by 10 publications

(4 citation statements)

References 38 publications

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“…m is one of the fitting parameters in our calculations. Moreover, given that D SiO2(aq) has only been determined for limited P-T conditions [16,[54][55][56], and not for the P-T conditions of the present experiment, D SiO2(aq) is also one of the fitting parameters in our calculations. Consequently, we considered a one-dimensional model for SiO 2(aq) involving diffusion and surface reactions in the olivine region, as follows:…”

Section: Reaction Numbermentioning

confidence: 85%

Multiple Kinetic Parameterization in a Reactive Transport Model Using the Exchange Monte Carlo Method

2018

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Water-rock interaction in surface and subsurface environments occurs in complex multicomponent systems and involves several reactions, including element transfer. Such kinetic information is obtained by fitting a forward model into the temporal evolution of solution chemistry or the spatial pattern recorded in the rock samples, although geochemical and petrological data are essentially sparse and noisy. Therefore, the optimization of kinetic parameters sometimes fails to converge toward the global minimum due to being trapped in a local minimum. In this study, we simultaneously present a novel framework to estimate multiple reaction-rate constants and the diffusivity of aqueous species from the mineral distribution pattern in a rock by using the reactive transport model coupled with the exchange Monte Carlo method. Our approach can estimate both the maximum likelihood and error of each parameter. We applied the method to the synthetic data, which were produced using a model for silica metasomatism and hydration in the olivine-quartz-H 2 O system. We tested the robustness and accuracy of our method over a wide range of noise intensities. This methodology can be widely applied to kinetic analyses of various kinds of water-rock interactions.2 of 15 happen simultaneously. Even for monomineralic systems, such as feldspar-water or olivine-water systems in batch experiments, coupled reactions could occur, marked by the dissolution of the primary mineral and the formation of a secondary mineral [9,[20][21][22][23]. Accordingly, an effective methodology is required to simultaneously estimate the reaction-rate constants of several minerals and/or diffusivity of elements from complex water-rock systems.However, multiple parameterizations from a coupled transport and reaction system, pertaining to the dissolution and precipitation of many minerals and the transport of aqueous species (ions and complexes), raise a difficult geochemical inverse problem due to computational difficulties. This is especially true when multiple parameters are to be estimated; estimation sometimes fails to converge to the global minima due to convergence to the local minima through error minimization [24,25]. Moreover, the data used for parameterization may be "noisy" due to analytical uncertainties, and therefore, the fitted parameters would also contain errors. Such errors on rate constants are typically ignored to avoid the complex computations required to handle error propagation. Therefore, it would be ideal to develop a versatile method that can extract multiple kinetic parameters and associated errors from noisy laboratory datasets without becoming trapped in local minima.In this study, we present a novel method to estimate not only multiple reaction-rate constants, but also the diffusivity of aqueous species using only the dataset of spatial mineral distribution, and by combining the reactive transport model and the exchange Monte Carlo (EMC) method [26][27][28]. The latter is well-known as an improvement on Markov chain Monte Carlo (MCMC) ...

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Section: Reaction Numbermentioning

confidence: 85%

Multiple Kinetic Parameterization in a Reactive Transport Model Using the Exchange Monte Carlo Method

2018

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“…The pH of the effluent solution was measured using a pH meter (LAQUAtwin, Horiba). The concentrations of Ca, Mg, K, and Al were determined by inductively coupled plasma optical emission spectrometry (ICP-OES, SPECTROBLUE, SPECTRO), and that of Si was by a molybdenum blue method using a liquid chromatograph apparatus (ICA2000, TOA-DKK) with a post column reaction system (the measurement procedure was the same with Yokoyama except for the use of 600 nm wavelength instead of 530 nm). The determination limits were approximately 0.2 μM for Ca, 0.002 μM for Mg, 0.1 μM for K, and 0.01 μM for Al, and 0.04 μM for Si.…”

Section: Experimental Methodsmentioning

confidence: 99%

Dissolution of Minerals Driven by the Wetting Film in Rock Pores: Comparison of Silicates and Carbonates

Yokoyama

Nishiyama

2020

ACS Earth Space Chem.

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To evaluate how the presence of air in pores affects mineral dissolution, flow-through dissolution experiments were conducted using Berea sandstone, composed mainly of quartz, K-feldspar, Ca-Mg-Fe carbonates, and clays. Water was passed through a core both under the water-saturated condition and the dry-start condition, and the amounts of dissolved elements were compared. In the dry-start condition, after the onset of water flow, the volume fraction of air in pores initially became 38% and gradually decreased to 0% (fully saturated with water) over ∼9 days. As the air decreased, the bulk release rate of Ca in the dry-start condition approached those in the water-saturated condition, but the rates of the two conditions did not coincide until pores were fully filled with water. On the other hand, the bulk release rate of Si in the dry-start condition coincided with those in the water-saturated condition even though air was remaining in pores. Thus, the reduction of the amount of dissolution due to the presence of air was greater for carbonate than for silicates. Dissolution of a mineral exposed to the air in the pore is driven by a thin water film wetting the mineral surface. It is inferred that due to slow dissolution of quartz, dissolved Si was sufficiently flushed by diffusion in the water film and dissolution proceeded effectively even under the presence of air. In contrast, due to fast dissolution of carbonate, the flushing of Ca on the carbonate surface was insufficient and dissolution was significantly retarded due to the proximity to equilibrium in the film.

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“…Dissolution rate constants of silicate minerals, ranging from ～10 -14 to 10 -9 mol m -2 s -1 under 1 Ω (2) r 0 は溶解速度定数(mol m -2 s -1 ) ，n 1 と n 2 は鉱物の溶解実験から求まる係数，Ω は飽和指数 (0 ～ 1 の値で，濃度が平衡濃度に近いほど 1 に近くなる)である。石英の溶解を扱う場合，c は溶存 Si の濃度であり，Ω ＝ c/c eq (c eq は平衡濃度) ，n 1 ＝ n 2 ＝ 1 となる (Schott et al, 2009) ( 図 2d) がよく行われる (Skagius and Neretnieks, 1986;喜多ほか, 1989;Yokoyama, 2013b (Skagius and Neretnieks, 1986) 。図 2e の例では，c 1 ＝ 1.68 mmol L -1 ，s ＝ 10.29 cm 2 ，l ＝ 0.50 cm，V 2 ＝ 0.10 L より，D e ＝ 3.83´10…”

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Reactive Transport Processes from Outcrop Scale to Nano Scale

Yokoyama

Nishiyama

2017

Journal of Geography(Chigaku Zasshi)

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Water⊖rock interactions proceed as a result of reaction and transport occurring at an outcrop scale and in pores at a millimeter to nanometer scale. To quantitatively evaluate these processes, various parameters including porosity, dissolution rate, fluid flow rate, effective diffusion coefficient, and surface area are required. Focusing on rock weathering, some examples are presented of how these parameters are determined, and a brief review is provided of the nature of the parameters. Hydraulic conductivities, a measure of fluid flow rate, ranging from < 10 -13 to 1 m s -1 , largely depend on pore radius or fracture opening size and porosity. Effective diffusion coefficients, ranging from ～10 -15 to 10 -9 m 2 s -1 , are known to be a power law function of porosity.Dissolution rate constants of silicate minerals, ranging from ～10 -14 to 10 -9 mol m -2 s -1 under ambient conditions, are affected by the connectedness of the SiO 4 tetrahedra. Using those values, some simple examples are presented of calculations of the profiles of concentration and reaction rate at an outcrop scale and at a pore scale, as well as some recent advances in pore scale geochemical processes.

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Diffusivity of dissolved silica in rock pore water at 25°C as characterized by through-diffusion experiments

Cited by 10 publications

References 38 publications

Multiple Kinetic Parameterization in a Reactive Transport Model Using the Exchange Monte Carlo Method

Multiple Kinetic Parameterization in a Reactive Transport Model Using the Exchange Monte Carlo Method

Dissolution of Minerals Driven by the Wetting Film in Rock Pores: Comparison of Silicates and Carbonates

Reactive Transport Processes from Outcrop Scale to Nano Scale

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