Inglezakis V J, Fyrillas M M
The Environment & Resource Efficiency Cluster (EREC), Nazarbayev University, Astana, Kazakhstan.
Environmental Science & Technology Group (ESTg), Chemical & Materials Engineering Department, School of Engineering, Nazarbayev University, Astana, Kazakhstan.
Heliyon. 2019 Jul 27;5(7):e02143. doi: 10.1016/j.heliyon.2019.e02143. eCollection 2019 Jul.
Surface diffusivity in adsorption and ion exchange processes is probably the most important property studied expensively in the literature but some aspects, especially its dependence on solid phase concentration, is still an open subject to discussion. In this study a new concentration-dependent surface diffusion model, equipped with a flexible double selectivity equilibrium relationship is applied on the removal of Pb, Cr, Fe and Cu from aqueous solutions using a natural zeolite. The model incorporates the Chen-Yang surface diffusivity correlation able to deal with positive and negative dependence with surface coverage. The double selectivity equilibrium relationship successfully represents the experimental equilibrium data, which follow Langmurian isotherm type for Pb, sigmoidal for Cr and Fe and linear for Cu. The concentration-dependent surface diffusion model was compared with the constant diffusivity surface diffusion model and found to be moderately more accurate but considerably more useful as it provides more insights into the diffusion mechanism. The application of the model resulted in an average deviation of 8.56 ± 6.74% from the experimental data and an average solid phase diffusion coefficients between 10 and 10 cm/s. The results showed that the diffusion of metal ions in the zeolite structure is unhindered following the surface diffusion mass transfer mechanism.
吸附和离子交换过程中的表面扩散率可能是文献中研究成本最高的重要性质，但某些方面，尤其是其对固相浓度的依赖性，仍是一个有待讨论的开放性课题。在本研究中，一种配备灵活双选择性平衡关系的新的浓度依赖性表面扩散模型被应用于使用天然沸石从水溶液中去除铅、铬、铁和铜。该模型纳入了能够处理与表面覆盖率呈正相关和负相关的陈-杨表面扩散率关联式。双选择性平衡关系成功地表示了实验平衡数据，其中铅的数据符合朗缪尔等温线类型，铬和铁的数据呈S形，铜的数据呈线性。将浓度依赖性表面扩散模型与恒定扩散率表面扩散模型进行比较，发现前者适度更精确且相当更有用，因为它能更深入地洞察扩散机制。该模型的应用导致与实验数据的平均偏差为8.56±6.74%，平均固相扩散系数在10 和10 cm/s之间。结果表明，遵循表面扩散传质机制，金属离子在沸石结构中的扩散不受阻碍。
