Evaluation of the stability of soil nanoparticles: the effect of natural organic matter in electrolyte solutions

Abstract

Nanoparticles are ubiquitous in soil, and their quantity and stability play important roles in the fate, transport and bioavailability of contaminants in the environment. In this research, four soil nanoparticles (SNPs) were extracted from typical soil of different regions in China. Three different kinds of natural organic matter (NOM) were subsequently added to suspensions of SNPs to determine the effects of NOM on the stability of SNPs. The critical coagulation concentration (CCC), one of the most important indicators of the stability of the colloidal suspension in electrolyte solutions, was measured. The increase in CCC values indicated that the stability of SNPs was enhanced by NOM; however, the stability varied with the different electrolytes, properties of SNPs and properties of NOM. A coating of NOM increased the negative charges on the surface of SNPs. Therefore, the electrostatic force had a greater effect on the stability of SNPs than the van der Waals force, which contributed to their stability. The effect of NOM on the stability of SNPs was more evident in electrolytes with a monovalent cation (Na+) than in those with a divalent (Ca2+) or trivalent cation (La3+). The NOM increased the stability of less stable SNPs in relation to the composition and properties of SNPs. Further research is required to understand better how the behaviour and fate of SNPs are affected by NOM in the environment.Highlights The effect of organic matter on the stability of soil nanoparticles is evaluated. Stability of soil nanoparticles was enhanced by a surface coating of organic matter. The electrostatic force contributed to the stability of soil nanoparticles with the addition of organic matter. Change in stability was also related to types and properties of soil nanoparticles and organic matter.