Schulthess Cristian P, Ndu Udonna
Department of Plant Science and Landscape Architecture, University of Connecticut, Storrs, Connecticut, United States of America.
Civil and Environmental Engineering Department, Duke University, Durham, North Carolina, United States of America.
PLoS One. 2017 May 2;12(5):e0176743. doi: 10.1371/journal.pone.0176743. eCollection 2017.
Simultaneous adsorption modeling of four ions was predicted with a strict net charge-neutral ion-exchange theory and its corresponding equilibrium and mass balance equations. An important key to the success of this approach was the proper collection of all the data, particularly the proton adsorption data, and the inclusion of variable concentrations of conjugate ions from the experimental pH adjustments. Using IExFit software, the ion-exchange model used here predicted the competitive retention of several ions on goethite by assuming that the co-adsorption or desorption of all ions occurred in the correct stoichiometries needed to maintain electroneutrality. This approach also revealed that the retention strength of Cl- ions on goethite increases in the presence of phthalate ions. That is, an anion-anion enhancement effect was observed. The retention of Cl- ions was much weaker than phthalate ions, and this also resulted in a higher sensitivity of the Cl- ions toward minor variations in the surface reactivity. The proposed model uses four goethite surface sites. The drop in retention of phthalate ions at low pH was fully described here as resulting from competitive Cl- reactions, which were introduced in increasing concentrations into the matrix as the conjugate base to the acid added to lower the pH.
采用严格的净电荷中性离子交换理论及其相应的平衡和质量平衡方程，对四种离子的同时吸附模型进行了预测。该方法成功的一个重要关键是正确收集所有数据，特别是质子吸附数据，并纳入实验pH调节中可变浓度的共轭离子。使用IExFit软件，这里使用的离子交换模型通过假设所有离子的共吸附或解吸以维持电中性所需的正确化学计量比发生，预测了几种离子在针铁矿上的竞争保留。该方法还表明，在邻苯二甲酸根离子存在下，Cl-离子在针铁矿上的保留强度增加。也就是说，观察到了阴离子-阴离子增强效应。Cl-离子的保留比邻苯二甲酸根离子弱得多，这也导致Cl-离子对表面反应性的微小变化具有更高的敏感性。所提出的模型使用四个针铁矿表面位点。本文充分描述了低pH下邻苯二甲酸根离子保留率的下降是由竞争性Cl-反应引起的，随着添加酸以降低pH值的共轭碱，Cl-反应以增加的浓度引入到基质中。
