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首页> 外文期刊>Chemical geology >Pitfalls in the determination of empirical dissolution rate equations of minerals from experimental data and a way out: an iterative procedure to find valid rate equations, applied to Ca-carbonates and -sulphates
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Pitfalls in the determination of empirical dissolution rate equations of minerals from experimental data and a way out: an iterative procedure to find valid rate equations, applied to Ca-carbonates and -sulphates

机译：从实验数据确定矿物的经验溶出速率方程的陷阱和出路：应用于碳酸钙和硫酸盐的有效速率方程的迭代程序

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Empirical rate equations such as R = k(1 - c/c(eq))(n) in the dissolution of minerals are common in nature, e.g. limestone. The quantity c is the concentration of a major ion contained in the mineral, and c(eq) its concentration at equilibrium. If experimental data obey such a rate equation, by plotting log(R) versus log(1 - c/c(eq)) straight lines are found from which k and n can be determined. In many experiments, however, especially for natural minerals c,, is not known exactly. If one uses wrong values of ceq that deviate only a few percent from true equilibrium such plots are severely distorted and one may conclude that above some value c, the true order n changes to a new value, even when a rate equation as given above is valid. We present an iterative computational procedure, which allows to find the valid rate equation from experimental data, even when c(eq) is not known. The method is applied to limestone and synthetic calcite as well as to natural and synthetic gypsum. New experimental data are given for the dissolution rates of anhydrite (CaSO4). By use of our new method, we find that this mineral exhibits a surface controlled rate equation with k = 5.0 1.0 x 10(-6) mmol cm(-2) s(-1) n = 4.5 +/- 0.2 and c(eq) = 23.5 +/- 0.1 mmol/l at T = 10 degreesC. (C) 2002 Elsevier Science B.V All rights reserved. [References: 21]
机译：矿物溶解中的经验速率方程（例如R = k（1- c / c（eq））（n）在自然界很常见，例如石灰石。量c是矿物中所含主要离子的浓度，而c（eq）是平衡时的浓度。如果实验数据服从这样的速率方程，则通过绘制log（R）对log（1-c / c（eq））绘制直线，可以确定k和n。然而，在许多实验中，尤其是对于天然矿物质c，并不清楚。如果使用错误的ceq值偏离真实均衡仅几个百分点，则这些图将严重失真，并且可以得出结论，即使在上面给出的费率方程为有效。我们提出了一种迭代计算程序，即使c（eq）未知，也可以从实验数据中找到有效的速率方程。该方法适用于石灰石和合成方解石以及天然和合成石膏。给出了硬石膏（CaSO4）溶解速率的新实验数据。通过使用我们的新方法，我们发现这种矿物表现出具有k = 5.0 1.0 x 10（-6）mmol cm（-2）s（-1）n = 4.5 +/- 0.2和c（ eq）=在T = 10摄氏度时为23.5 +/- 0.1 mmol / l。 （C）2002 Elsevier Science B.V保留所有权利。 [参考：21]

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