A method of estimateng the Gibbs free energies of formation of hydrated and dehydrated clay minerals
A method of estimateng the Gibbs free energies of formation of hydrated and dehydrated clay minerals
复制标题
估算水合和脱水粘土矿物形成吉布斯自由能的方法
DOI：
10.1016/0016-7037(92)90287-s
复制
发表时间：
1992
影响因子：
5
通讯作者：
J. Duplay
中科院分区：
文献类型：
--
作者：
Y. Tardy;J. Duplay
粘土矿物通常是水合的，水分子附着在两个不同的层间和颗粒间水合位点上。当干燥的粘土骨料与水接触时或当湿且膨胀的骨料被放置在干燥的大气中时，这两个位点都会产生水合能。吸附水的量以及水合能随着颗粒聚集体所处的水的活性而变化。对不同成分的粘土矿物的不同样品建立的脱水等温线的积分用于评估不同水化阶段（即从水饱和阶段到干燥状态）的水合吉布斯自由能。所提出的估计吉布斯自由能的模型基于以下步骤和假设：1.（1）水合和脱水粘土矿物是理想的固溶体，如 Tardy 和 Fritz 提出的(1981)2.(2) 在每一个系列的层状硅酸盐（滑石、云母和青瓷石）中，水合、脱水和结晶良好的氧化物生成吉布斯自由能线性依赖于参数ΔOMz+2−与八面体位置的阳离子Mz+的电负性相关3。(3) 在每个矿物系列中，水合能与层电荷； 4.（4）在相同电荷和相同层间阳离子的每个矿物系列中，水化能也与ΔOMz+2−成正比。模型的主要结果是1.（1）给定化学成分的结晶不良但水合的粘土矿物2.（2）结晶不良的脱水粘土矿物3.（3）化学成分相同的干燥的、大尺寸的、结晶良好的层状硅酸盐，所有这些在它们的化学成分上有很大差异自然条件下的吉布斯形成自由能及其稳定场。此外，这些矿物质的溶解度积和相应的阳离子交换常数取决于发生平衡反应的水的活性。这些参数还取决于四面体、八面体或总层间电荷，最后取决于位于八面体层中的阳离子的性质（即 Mg2+、Fe2+、A13+ 或 Fe3+）。还提出，对于给定的层间阳离子（Li+、Na+、K+、Mg2+ 或 Ca2+）和给定的八面体组成（Mg2+、Fe2+、A13+ 或 Fe3+），水合能通常随着层电荷的增加而增加，因此大多数高电荷矿物是亲水性的，应该在水中自发水合。然而，K+ 交换的绿脱石 (Fe3+) 和贝得石 (A13+)（均为双八面体）的水合能随着层电荷的增加而降低，因此伊利石和海绿石、白云母和铁白云母可能表现为疏水性，当与水接触时不应自发水合。
Clay minerals are commonly hydrated, and water molecules are attached in two different interlayer and interparticle hydration sites. Both sites contribute to the hydration energy involved when a dry clay aggregate is placed in contact with water or when a wet and swollen aggregate is placed in a dry atmosphere. The amounts of adsorbed water, and the hydration energy as well, vary as functions of the activity of water in which particle aggregates are placed. Integration of dehydration isotherms, established for different samples of various compositions of clay minerals, was used to evaluate the Gibbs free energies of hydration at different hydration stages, i.e., from the water-saturated phases to the dry states.The proposed model of estimating Gibbs free energies is based on the following steps and assumptions:1.(1) Hydrated and dehydrated clay minerals are ideal solid solutions, as presented by Tardy and Fritz (1981)2.(2) In each of the series of phyllosilicates (talc, mica, and celadonites), hydrated, dehydrated, and wellcrystallized Gibbs free energies of formation from the oxides are linearly dependent on the parametersΔOMz+2−related to the electronegativity of the cationMz+in the octahedral position3.(3) In each of the mineral series, hydration energies are proportional to the layer charge; and4.(4) In each of the mineral series of the same charge and same interlayer cation, the hydration energy is also proportional toΔOMz+2−.The principal results of the model are1.(1) poorly crystallized but hydrated clay minerals of a given chemical composition2.(2) poorly crystallized, dehydrated clay minerals3.(3) dry, largely sized, wellcrystallized phyllosilicates of the same chemical composition, all of which differ largely in their Gibbs free energies of formation and in their stability fields in natural conditions. Furthermore, the solubility products and the corresponding cation exchange constants of these minerals are dependent on the activity of water in which the equilibrium reactions take place. These parameters also depend on the tetrahedral, octahedral, or total interlayer charge, and finally on the nature of the cation located in the octahedral layer (i.e., Mg2+, Fe2+, A13+, or Fe3+). It is also proposed that for a given interlayer cation (Li+, Na+, K+, Mg2+, or Ca2+) and for a given octahedral composition (Mg2+, Fe2+, A13+, or Fe3+), the hydration energy generally increases with the layer charge so that most of the minerals of high charge are hydrophylic and should hydrate spontaneously in water. However, the hydration energy of K+-exchanged nontronites (Fe3+) and beidellites (A13+), both dioctahedral, decreases with the layer charge so that illite and glauconite, muscovite, and ferrimuscovite presumably appear as hydrophobic and should not hydrate spontaneously when placed in contact with water.