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Compositional depth profiles in the leached layer of feldspar surfaces are usually interpreted by using analytical solutions
which introduce oversimplifying assumptions. Here we present a general multicomponent interdiffusion numerical model for simulating
cation release from a preferentially leached layer on feldspar surfaces in acid solutions. The numerical model takes into
account interdiffusion, dissolution of the solid phase (represented by a moving boundary problem), and adsorption in the leached
layer. Effective diffusion coefficients of ions vary with concentration along the leached layer. Governing equations of ions
diffusion in the leached layer are solved numerically with a finite element method implemented in a multicomponent reactive
transport code, CORE3D, previously verified against analytical solutions of compositional depth profiles. The numerical model is tested with published
X-ray photoelectron spectroscopy (XPS) data on early development of compositional profiles of labradorite leached in pH 2
HCl solutions. Model parameters are estimated by fitting depth profiles of Ca and Al measured at 12, 26, 48, 72, and 143 h.
The best fit is achieved with tracer diffusion coefficients of 4 × 10−18, 8 × 10−17, 3.4 × 10−17, and 7 × 10−18 cm2/s for H, Na, Ca, and Al, respectively, which fall within the range of values reported in the literature. Our estimate of
the retreat velocity corresponding to the dissolution rate is 3 × 10−13 cm/s. Results of sensitivity runs show that computed compositional profiles are sensitive to most model parameters. 相似文献
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CORE2D V4 is a finite element code for modeling partly or fully saturated water flow, heat transport, and multicomponent reactive
solute transport under both local chemical equilibrium and kinetic conditions. It can handle coupled microbial processes and
geochemical reactions such as acid–base, aqueous complexation, redox, mineral dissolution/precipitation, gas dissolution/exsolution,
ion exchange, sorption via linear and nonlinear isotherms, and sorption via surface complexation. Hydraulic parameters may
change due to mineral precipitation/dissolution reactions. Coupled transport and chemical equations are solved by using sequential
iterative approaches. A sequential partly iterative approach (SPIA) is presented which improves the accuracy of the traditional
sequential non-iterative approach (SNIA) and is more efficient than the general sequential iterative approach (SIA). While
SNIA leads to a substantial saving of computing time, it introduces numerical errors which are especially large for cation
exchange reactions. SPIA improves the efficiency of SIA because the iteration between transport and chemical equations is
only performed in nodes with a large mass transfer between solid and liquid phases. The efficiency and accuracy of SPIA are
compared to those of SIA and SNIA using synthetic examples and a case study of reactive transport through the Llobregat Delta
aquitard in Spain. SPIA is found to be as accurate as SIA while requiring significantly less CPU time. In addition, SPIA is
much more accurate than SNIA with only a minor increase in computing time. A further enhancement of the efficiency of SPIA
is achieved by improving the efficiency of the Newton–Raphson method used for solving chemical equations. Such an improvement
is obtained by working with increments of log concentrations and ignoring the terms of the Jacobian matrix containing derivatives
of activity coefficients. A proof is given for the symmetry and non-singularity of the Jacobian matrix. Numerical analyses
performed with synthetic examples confirm that these modifications improve the efficiency and convergence of the iterative
algorithm.
Changbing Yang is now at The University of Texas at Austin, USA. 相似文献
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讨论了如何将SOPC技术用于大天区多目标光纤光谱天文望远镜(LAMOST)项目的低分辨率光谱仪IP控制核的设计,并在NIOSⅡ软核基础上设计实现了光谱仪IP控制核。整个IP控制核主要分为底层电机控制单元和通信单元两部分。通过工业以太网,远程控制计算机可以方便地控制低分辨率光谱仪,使其完成指定动作。也可以从本地控制计算机上实行控制。设计中采用将步进电机控制器封装成IP再复用的方法,大大缩短了研发时间,减少错误的发生。通信控制中串口通信和以太网可以互为冗余,保证了通信的顺利进行。 相似文献
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