Crundwell Frank K
CM Solutions (Pty) Ltd., 89J Victoria Drive, London SW19 6PT, U.K.
ACS Omega. 2017 Aug 23;2(8):4845-4858. doi: 10.1021/acsomega.7b00344. eCollection 2017 Aug 31.
Although dissolution reactions are widespread and commonplace, our understanding of the factors affecting the rate of dissolution is incomplete and consequently the kinetics of these reactions appear complicated. The focus in this work is on the behavior of the rate as conditions approach equilibrium. The reverse reaction is often treated in terms of chemical affinity, or saturation state. However, the implementation of the chemical affinity model fails, requiring arbitrary empirical adjustments. In this study, a mechanism of dissolution is proposed that describes both the fractional orders of reaction with respect to H and OH and correctly describes the approach to equilibrium. The mechanism is based on the separate removal of anions and cations from the surface, which are coupled to one another through their contribution to and dependence on the potential difference across the interface. Charge on the surface, and hence potential difference across the interface, is caused by an excess of ions of one sign and is maintained at this stationary state by the rate of removal of cations and anions from the surface. The proposed model is tested using data for NaCl (halite), CaCO (calcite), ZnS (sphalerite), NaAlSiO (albite), and KAlSiO (K-feldspar). An important feature of the proposed model is the possibility of "partial equilibrium", which explains the difficulties in describing the approach to equilibrium of some minerals. This concept may also explain the difficulties experienced in matching rates of chemical weathering measured in laboratory and field situations.
尽管溶解反应广泛存在且司空见惯，但我们对影响溶解速率的因素的理解并不完整，因此这些反应的动力学显得复杂。这项工作的重点是在接近平衡的条件下速率的行为。逆反应通常根据化学亲和力或饱和状态来处理。然而，化学亲和力模型的应用并不成功，需要进行任意的经验调整。在本研究中，提出了一种溶解机制，该机制描述了相对于H和OH的反应分数阶，并正确描述了接近平衡的过程。该机制基于从表面分别去除阴离子和阳离子，它们通过对界面电位差的贡献和依赖相互耦合。表面电荷以及因此界面上的电位差是由一种符号的离子过量引起的，并通过从表面去除阳离子和阴离子的速率维持在这种稳定状态。使用NaCl（石盐）、CaCO（方解石）、ZnS（闪锌矿）、NaAlSiO（钠长石）和KAlSiO（钾长石）的数据对所提出的模型进行了测试。所提出模型的一个重要特征是“部分平衡”的可能性，这解释了描述某些矿物接近平衡时的困难。这个概念也可以解释在匹配实验室和野外情况下测量的化学风化速率时所遇到的困难。
