Research article

Aggregation of montmorillonite and organic matter in aqueous media containing artificial seawater

Yoko Furukawa¹ , Janet L Watkins¹ , Jinwook Kim² , Kenneth J Curry³ and Richard H Bennett⁴

¹  Naval Research Laboratory, Seafloor Sciences Branch, Stennis Space Center, Mississippi, USA

²  Yonsei University, Department of Earth System Sciences, Seoul, South Korea

³  University of Southern Mississippi, Department of Biological Sciences, Hattiesburg, Mississippi, USA

⁴  SEAPROBE, Inc., Picayune, Mississippi, USA

author email corresponding author email

Geochemical Transactions 2009, 10:2doi:10.1186/1467-4866-10-2

Published:	23 January 2009

Abstract

Background

The dispersion-aggregation behaviors of suspended colloids in rivers and estuaries are affected by the compositions of suspended materials (i.e., clay minerals vs. organic macromolecules) and salinity. Laboratory experiments were conducted to investigate the dispersion and aggregation mechanisms of suspended particles under simulated river and estuarine conditions. The average hydrodynamic diameters of suspended particles (representing degree of aggregation) and zeta potential (representing the electrokinetic properties of suspended colloids and aggregates) were determined for systems containing suspended montmorillonite, humic acid, and/or chitin at the circumneutral pH over a range of salinity (0 – 7.2 psu).

Results

The montmorillonite-only system increased the degree of aggregation with salinity increase, as would be expected for suspended colloids whose dispersion-aggregation behavior is largely controlled by the surface electrostatic properties and van der Waals forces. When montmorillonite is combined with humic acid or chitin, the aggregation of montmorillonite was effectively inhibited. The surface interaction energy model calculations reveal that the steric repulsion, rather than the increase in electronegativity, is the primary cause for the inhibition of aggregation by the addition of humic acid or chitin.

Conclusion

These results help explain the range of dispersion-aggregation behaviors observed in natural river and estuarine systems. It is postulated that the composition of suspended particles, specifically the availability of steric polymers such as those contained in humic acid, determine whether the river suspension is rapidly aggregated and settled or remains dispersed in suspension when it encounters increasingly saline environments of estuaries and oceans.