Formation and stability of NOM-Mn(III) colloids in aquatic environments

Qianqian Li, Lin Xie, Yi Jiang, John D. Fortner, Kai Yu, Peng Liao, Chongxuan Liu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

23 Citations (Scopus)

Abstract

Soluble Mn(III) species stabilized by natural organic matter (NOM) plays a crucial role in a number of biogeochemical processes. To date, current understanding of these phenomena has been primarily concerned on the occurrence and chemistry of soluble NOM-Mn(III) complexes; much less is known regarding the formation and stability of NOM-Mn(III) colloids in the environment. This presents a critical knowledge gap with regard to biogeochemical cycling of manganese and associated carbon, and for predicting the fate and transport of colloid-associated contaminants, nutrients, and trace metals. In this work, we have characterized the chemical and physical properties of humic acid based (HA)-Mn(III) colloids formed over a range of environmentally relevant conditions and quantified their subsequent aggregation and stability behaviors. Results show that molar C/Mn ratios and HA types (Aldrich HA (AHA) and Pahokee peat soil HA (PPSHA)) are critical factors influencing HA-Mn(III) colloidal properties. Both the amount and the stability of HA-Mn(III) colloids increased with increasing initial molar C/Mn ratios, regardless of HA type. The correlation between the critical coagulation concentration (CCC) and zeta potential (R2 > 0.97) suggests that both Derjaguin-Landau-Verwey-Overbeek (DLVO) type and non-DLVO interactions are responsible for enhanced stability of HA-Mn(III) colloids. For a given C/Mn ratio, PPSHA-Mn(III) colloids are significantly more stable against aggregation than AHA-Mn(III) colloids, which is likely due to stronger electrostatic interactions, hydration interactions, and steric hindrance. Further examination in real-world waters indicates that the HA-Mn(III) colloids are highly stable in surface river water, but become unstable (i.e. extensive aggregation) in solutions representing a groundwater-seawater interaction zone. Overall, this study provides new insights into the formation and stability of NOM-Mn(III) colloids which are critical for understanding Mn-based colloidal behavior(s), and thus Mn cycling processes, in aquatic systems.

Original languageEnglish
Pages (from-to)190-201
Number of pages12
JournalWater Research
Volume149
DOIs
Publication statusPublished - 1 Feb 2019

Keywords

  • C/Mn ratios
  • Colloid formation
  • Colloid stability
  • HA types
  • NOM-Mn(III) colloids

ASJC Scopus subject areas

  • Ecological Modelling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution

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