Aggregation kinetics of humic acids in the presence of calcium ions
Aggregation kinetics of humic acids in the presence of calcium ions
复制标题
DOI：
10.1016/j.colsurfa.2013.03.030
复制
发表时间：
2013-06-20
影响因子：
5.2
通讯作者：
Avena, Marcelo
中科院分区：
文献类型：
--
作者：
Kloster, Nanci;Brigante, Maximiliano;Avena, Marcelo
研究了在pH值为5、7和9时，腐殖酸（HA）样品的聚集动力学随钙离子浓度的变化。采用紫外 - 可见光谱法定量分析聚集反应的进程，并利用电泳法评估腐殖酸分子的ζ电位。在所有研究的pH值下，随着钙离子浓度的增加，聚集速率显著提高，且在pH值为9时比在pH值为5和7时更高。提出了一种聚集机制，该机制至少包括两个步骤：钙离子与腐殖质分子的快速结合，随后是腐殖酸分子相互靠近并发生聚集的较慢过程。这种聚集之所以可能，是因为钙离子的结合使腐殖酸的ζ电位从 -37 mV降低到 -15 mV，并且能够在腐殖酸分子之间形成桥键。在聚集程度达到60%之前没有分子分级现象。超过该值时，腐殖酸聚集体中芳香性更强的腐殖酸分子含量增加。在钙离子存在的情况下腐殖酸的快速聚集意味着聚集体可能会在环境中暂时捕获、保护和运输污染物。（C）2013爱思唯尔有限公司。保留所有权利。
The aggregation kinetics of a humic acid (HA) sample as a function of Ca2+ concentration at pH 5, 7 and 9 was investigated. UV-VIS spectroscopy was employed to quantify the progress of the aggregation reaction, and electrophoresis was used to evaluate the zeta potential of the HA molecules. The aggregation rate increases significantly by increasing Ca2+ concentration at all investigated pH, being higher at pH 9 than at pH 5 and 7. An aggregation mechanism is proposed, which consists of at least two steps: a rapid binding of Ca2+ to humic molecules, followed by a slower process where HA molecules approach each other and become aggregated. This aggregation is possible because Ca2+ binding decreases the zeta potential of HA from -37 mV to -15 mV and because it is able to form bridges between HA molecules. There is no molecular fractionation up to 60% of aggregation. Above this value, HA aggregates become enriched with more aromatic HA molecules. The fast aggregation of HA in the presence of calcium ions implies that aggregates may temporarily trap, protect and transport pollutants in the environment. (C) 2013 Elsevier B.V. All rights reserved.