BRGM, French Geological Survey, Orléans, France.
BRGM, French Geological Survey, Orléans, France.
J Colloid Interface Sci. 2015 Aug 1;451:21-39. doi: 10.1016/j.jcis.2015.03.047. Epub 2015 Apr 3.
Clay minerals have remarkable adsorption properties because of their high specific surface area and surface charge density, which give rise to high electrochemical properties. These electrochemical properties cannot be directly measured, and models must be developed to estimate the electrostatic potential at the vicinity of clay mineral surfaces. In this context, an important model prediction is the zeta potential, which is thought to be representative of the electrostatic potential at the plane of shear. The zeta potential is usually deduced from electrophoretic measurements but for clay minerals, high surface conductivity decreases their mobility, thereby impeding straightforward interpretation of these measurements. By combining a surface complexation, conductivity and electrophoretic mobility model, we were able to reconcile zeta potential predictions with electrophoretic measurements on montmorillonite immersed in NaCl aqueous solutions. The electrochemical properties of the Stern and diffuse layers of the basal surfaces were computed by a triple-layer model. Computed zeta potentials have considerably higher amplitudes than measured zeta potentials calculated with the Smoluchowski equation. Our model successfully reproduced measured electrophoretic mobilities. This confirmed our assumptions that surface conductivity may be responsible for montmorillonite's low electrophoretic mobility and that the zeta potential may be located at the beginning of the diffuse layer.
粘土矿物具有显著的吸附性能，因为它们具有高比表面积和表面电荷密度，从而产生高的电化学性能。这些电化学性质不能直接测量，必须开发模型来估计粘土矿物表面附近的静电势。在这种情况下，一个重要的模型预测是zeta 电位，它被认为是剪切平面处静电势的代表。zeta 电位通常是从电泳测量中推断出来的，但对于粘土矿物，高表面电导率降低了它们的迁移率，从而阻碍了对这些测量的直接解释。通过结合表面络合、电导率和电泳迁移率模型，我们能够协调 zeta 电位预测与 montmorillonite 在 NaCl 水溶液中的电泳测量。Stern 和扩散层的电化学性质通过三层模型进行了计算。计算出的 zeta 电位的幅度明显高于用 Smoluchowski 方程计算出的测量 zeta 电位。我们的模型成功地复制了测量的电泳迁移率。这证实了我们的假设，即表面电导率可能是 montmorillonite 电泳迁移率低的原因，zeta 电位可能位于扩散层的起始处。
