亚稳平衡吸附态与亚稳平衡系数关系的热力学研究

在相同温度、压力、pH值和离子强度等条件下,同一种金属离子在无机矿物表面上发生的吸附反应可以形成能量不同的吸附状态(如Zn可以边-边和角-角两种方式吸附在水锰矿表面上),因而反应终了时吸附质可处于不同的亚稳平衡吸附态(MEA).应用MEA理论,针对吸附反应A+H₂O=xA₁+yA₂+H₂O,推导出实际吸附反应“平衡常数”(Kreal)与亚稳平衡系数(Kme)的热力学关系式,从理论上分析了吸附反应MEA状态的变化对实际吸附反应平衡性质的影响.分析结果表明,Kme值与两种MEA状态之间的能量差呈指数关系,通过影响吸附反应的MEA状态(包括能量和组成)的反应动力学因素可影响吸附平衡常数和吸附等温式(线)等吸附热力学性质.

A Thermodynamic Study on the Relationship Between Metastable Equilibrium Adsorption States and the Metastable-equilibrium Coefficient of Surface Adsorption Reactions

A given metal ion can form various adsorption states with different energies on inorganic mineral surfaces under the same conditions of temperature, pressure, pH and ionic strength. For example, hydrated zinc ions were adsorbed onto manganite surfaces in two different modes of corner-linkage and edge-linkage. Surface adsorption reactions were generally terminated in various metastable equilibrium adsorption (MEA) states rather than a unique ideal equilibrium state that was predicted from the classical adsorption thermodynamics. Based on the MEA inequality of the MEA theory, we deducted the thermodynamic relationships between the real equilibrium adsorption constant (K_ real) and the metastable-equilibrium coefficient (K_ me) . It showed that K_ me is exponentially related to the energy difference between different MEA states. By affecting MEA states, kinetic factors, such as reactant concentrations, can fundamentally influence the real equilibrium adsorption constants and other thermodynamic properties such as adsorption isotherms.