Data Sheet 1_Comparison for colloidal stability and aggregation behavior of fulvic and humic acids: effects of cations and pH.docx

Fulvic acid (FA) and humic acid (HA) are organic materials that can form complexes with metal ions, playing a crucial role in predicting the behavior of organic colloids. The colloidal stability values of FA and HA vary with pH and specific cations, but this has rarely been comprehensively examined. This study systematically compared the aggregation kinetics and colloidal stability of FA and HA and the mechanisms behind their behavior based on particle interaction theory. The results showed that higher pH values stabilized FA and HA colloids by increased electrostatic repulsive energy. Additionally, increased electrolyte concentration destabilized FA and HA colloids by cationic polarization (chemical bond formation). The cation aggregation ability followed the order Ca2+ > Mg2+ > K+ > Na+, showing that the specific ion effects induced by non-classical polarization resulted from the strong electric field of the highly negatively charged FA and HA. With pH values ranging from 5 to 7 and 9, FA and HA were stabilized through raising the critical coagulation concentrations (CCCs) in NaCl and KCl. With increasing pH, the enhanced electrostatic repulsive energies in the Na+ and K+ systems resulted in weaker aggregation behaviors due to the deprotonation of the hydroxyl and carboxyl groups of colloids. Compared with HA, FA had a lower Hamaker constant, higher surface negative charges, larger CCCs, and stronger dispersion stability. This work will contribute to the understanding of organic colloidal aggregation mechanisms and act as a reference to predict their environmental behaviors.

黄腐酸（Fulvic acid, FA）与腐殖酸（Humic acid, HA）是一类可与金属离子形成络合物的有机物质，在预测有机胶体的行为中发挥着关键作用。FA与HA的胶体稳定性随pH值与特定阳离子种类发生变化，但目前针对该现象的系统性研究尚较为匮乏。本研究基于粒子相互作用理论，系统对比了FA与HA的聚集动力学、胶体稳定性及其背后的作用机制。研究结果表明，更高的pH值可通过提升静电排斥能稳定FA与HA胶体；而电解质浓度升高则会通过阳离子极化（化学键形成）作用使FA与HA胶体失稳。阳离子的凝聚能力遵循Ca²⁺ > Mg²⁺ > K⁺ > Na⁺的顺序，这表明由非经典极化诱导的离子特异性效应，源于带高负电荷的FA与HA所产生的强电场。当pH值处于5~7及9区间时，FA与HA在NaCl和KCl溶液中可通过提升临界凝聚浓度（critical coagulation concentrations, CCCs）实现胶体稳定。随着pH值升高，胶体表面羟基与羧基发生去质子化作用，使Na⁺与K⁺体系中的静电排斥能增强，进而削弱了聚集行为。相较于HA，FA具备更低的哈马克常数（Hamaker constant）、更高的表面负电荷量、更大的临界凝聚浓度以及更强的分散稳定性。本研究有助于深化对有机胶体聚集机制的理解，并可为预测其环境行为提供参考依据。