Aggregation kinetics of humic acids in the presence of calcium ions

Effect of alginate on the aggregation kinetics of copper oxide nanoparticles (CuO NPs): bridging interaction and hetero-aggregation induced by Ca2+

“…Besides, significant coagulation of the alginate molecules was observed in solutions of high Ca 2+ concentrations, suggesting a heterocoagulation mechanism between the alginate-covered CuO NPs and the unabsorbed alginate under high concentration of Ca(NO 3 ) 2 . The results presented in this study suggested that not only the presence of NOM but also the ratio between NP and NOM should be taken into consideration in studying the NP stability in aqueous systems, due to the interaction between the multivalent cations and the ubiquitous organic matter (Kloster et al 2013;Wang et al 2013). More studies should be conducted to extend to more complex and environmentally relevant conditions in the future.…”

Effects of molecular weight-dependent physicochemical heterogeneity of natural organic matter on the aggregation of fullerene nanoparticles in mono- and di-valent electrolyte solutions

“…Electrolytes and pH can govern the surface charge and spectroscopic/photochemical properties of NOM in solutions (Her et al, 2003;Christl and Kretzschmar 2001). Furthermore, for di-and multivalent cations, in addition to the electrostatic interaction, interactions such as complexation/cation-bridging effects between functional groups in/among NOM and them, could result in significantly changes of NOM structures as well (Baalousha et al, 2006;Wang et al, 2013;Kloster et al, 2013). It is therefore of environmental significance to understand how the heterogeneous properties of NOM in environmental relevant conditions impact their physicochemical interactions with exogenous substances, especially the engineered nanoparticles (ENPs).…”

Enhanced performance of calcium-enriched coal ash for the removal of humic acids from aqueous solution

“…This inference is supported by the finding that the amount of Ca 2+ cations released from DT s (36.88 mg/L) in deionized water is nearly 14 times greater than that released from DT r (2.68 mg/L) at a given ash dosage of 10 mg/L ( Table 2). Other researchers also reported that the presence of Ca 2+ in solution dramatically increases the removal of humic substances [28][29][30].…”

“…The possible mechanism has been proposed to explain the effect of calcium on the removal of HA [28][29][30]: (1) Ca 2+ cations are capable of neutralizing some negatively charged groups of HA, such as the carboxyl, phenolic and aliphatic hydroxyl groups, to form bidentate complexes, which decrease the net negative charge and the electrostatic repulsion among HA molecules, thus promoting aggregation; (2) Ca 2+ cations can act as bridges between the functional groups of two adjacent HA molecules, increasing the attractive forces between them and contributing to the decreasing solubility in water; and (3) Ca 2+ cations can also promote intramolecular associations by simultaneously coordinating two carboxylic groups of the same HA molecule; this coordination results in a calcium-HA complex with a reduced negative charge, thus allowing such complexes to approach each other and interact via hydrogen bonds. Both aggregation and association of HA can increase the size of the HA network and thereby transfer it from the dissolved phase into the particulate one, which can be removed from the aqueous solution through filtration.…”