Quartz precipitation kinetics at 180°C in NaCl solutions—Implications for the usability of the principle of detailed balancing
Quartz precipitation kinetics at 180°C in NaCl solutions—Implications for the usability of the principle of detailed balancing
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DOI：
10.1016/j.gca.2004.09.026
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发表时间：
2005-04
影响因子：
5
通讯作者：
J. Ganor;T. Huston;L. M. Walter
中科院分区：
文献类型：
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作者：
J. Ganor;T. Huston;L. M. Walter
在180°C和pH接近4的条件下测定了非均相石英沉淀的动力学，其为过饱和度和溶解NaCl浓度的函数。使用搅拌间歇式反应器，并使用H4SiO4浓度随时间的变化来模拟反应速率。由于分批实验中的浓度变化在所有采样间隔期间与时间不是线性的，因此通过将实验观察值拟合到正向模型来检索沉淀率，即，使用规定的速率定律并将结果与实验进行比较的模型。石英沉淀通过整体反应发生，因此不能预先假定过渡态理论（TST）预测的适用性。因此，在正演模型中检查了描述速率对偏离平衡的依赖性的不同函数。无论使用何种函数，所得沉淀率均在误差范围内。将TST预测值代入正演模型，（在180°C，pH 4和0.1M的离子强度下）与平衡的偏差被发现在误差范围内，该观察到的速率与石英沉淀速率的预测一致，该预测是使用详细平衡原理计算的，与Dove（1994）的平衡石英溶解速率和Kharaka等人（1988）的平衡常数相差甚远。使用BCF（Burton Cabrera和Frank）晶体生长理论（Burton等人，1951年）。相反，TST和BCF，一个更一般的形式的偏离平衡的速率依赖性未能预测所观察到的降水率。基于详细平衡原理在180°C和pH 4条件下石英溶解和沉淀过程中得到验证的观察结果，我们认为详细平衡原理可以有效地应用于石英溶解速率的庞大数据库，以及适当的热力学数据，用于模拟自然条件下的石英沉淀过程。
The kinetics of heterogeneous quartz precipitation were determined at 180°C and a pH near 4 as a function of the degree of super saturation and dissolved NaCl concentrations. Stirred batch reactors were used and the changes in H4SiO4concentrations over time were used to model the reaction rates. As the change in concentration in the batch experiment is not linear with time during all sampling intervals, the precipitation rates were retrieved by fitting the experimental observations to a forward model, i.e., a model that uses a prescribed rate law and compares the results with the experiments. Quartz precipitation occurs via an overall reaction, and therefore one can not presuppose the applicability of the predictions of Transition State Theory (TST). Therefore, different functions describing the dependence of the rate on deviation from equilibrium were examined in the forward model. The obtained precipitation rates were within error the same, regardless of the function that was used. By substituting the prediction of TST into the forward model, the change of quartz precipitation rate (at 180°C, pH 4 and ionic strength of 0.1M) with deviation from equilibrium was found to be Within error, this observed rate agreed with predictions of quartz precipitation rates, which were calculated using the principle of detailed balancing, far from equilibrium quartz dissolution rates of Dove (1994) and equilibrium constant from Kharaka et al. (1988). Similar agreement between observations and predictions was obtained using the BCF (Burton Cabrera and Frank) crystal growth theory (Burton et al., 1951). In contrast to TST and BCF, a more general form of the rate dependence of deviation from equilibrium failed to predict the observed precipitation rates. Based on the observation that the principle of detailed balancing was verified for quartz dissolution and precipitation at 180°C and pH 4, we suggest that the principle of detailed balancing could be fruitfully applied to the huge database of quartz dissolution rates, together with appropriate thermodynamic data, for modeling quartz precipitation under natural conditions.