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

Furukawa Y, Watkins JL, Kim J, Curry KJ, Bennett RH - Geochem. Trans. (2009)

Bottom Line: When montmorillonite is combined with humic acid or chitin, the aggregation of montmorillonite was effectively inhibited.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Naval Research Laboratory, Seafloor Sciences Branch, Stennis Space Center, Mississippi, USA. yoko.furukawa@nrlssc.navy.mil

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.

No MeSH data available.


Related in: MedlinePlus

The estimated range for the magnitude of repulsive forces operating in the montmorillonite-HA suspensions is indicated by the black band.
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Figure 12: The estimated range for the magnitude of repulsive forces operating in the montmorillonite-HA suspensions is indicated by the black band.

Mentions: The magnitude of steric repulsion can be estimated by comparing the values of VTOTAL (= VEL + VLW) at S = 3.6 and 7.2 psu. At S = 3.6 psu, the steric repulsion was at least as significant as the negative values of VTOTAL in order to keep the colloids dispersed. On the other hand, at S = 7.2 psu, the steric repulsion was exceeded by the negative values of VTOTAL. It should be noted that the range estimation is conducted under the assumption that the steric repulsion is independent of salinity; thus the range is a rough estimate. In reality, the hydrodynamic diameters of polymers are greater in higher salinity solution due to the polymer unfolding, and thus the steric repulsive forces may be greater in higher salinity solutions [49]. Figure 12 shows the estimated ranges for the magnitude of the additional repulsion (i.e., steric repulsion) VST for the montmorillonite-HA suspensions determined by bracketing with VTOTAL at S = 3.6 and VTOTAL at S = 7.2 psu. The estimate for montmorillonite-chitin suspensions is not shown but very similar. The VST values are quantitatively significant, as their values, even though rough estimates, are in the same order of magnitudes as the van der Waals attraction.


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

Furukawa Y, Watkins JL, Kim J, Curry KJ, Bennett RH - Geochem. Trans. (2009)

The estimated range for the magnitude of repulsive forces operating in the montmorillonite-HA suspensions is indicated by the black band.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2654465&req=5

Figure 12: The estimated range for the magnitude of repulsive forces operating in the montmorillonite-HA suspensions is indicated by the black band.
Mentions: The magnitude of steric repulsion can be estimated by comparing the values of VTOTAL (= VEL + VLW) at S = 3.6 and 7.2 psu. At S = 3.6 psu, the steric repulsion was at least as significant as the negative values of VTOTAL in order to keep the colloids dispersed. On the other hand, at S = 7.2 psu, the steric repulsion was exceeded by the negative values of VTOTAL. It should be noted that the range estimation is conducted under the assumption that the steric repulsion is independent of salinity; thus the range is a rough estimate. In reality, the hydrodynamic diameters of polymers are greater in higher salinity solution due to the polymer unfolding, and thus the steric repulsive forces may be greater in higher salinity solutions [49]. Figure 12 shows the estimated ranges for the magnitude of the additional repulsion (i.e., steric repulsion) VST for the montmorillonite-HA suspensions determined by bracketing with VTOTAL at S = 3.6 and VTOTAL at S = 7.2 psu. The estimate for montmorillonite-chitin suspensions is not shown but very similar. The VST values are quantitatively significant, as their values, even though rough estimates, are in the same order of magnitudes as the van der Waals attraction.

Bottom Line: When montmorillonite is combined with humic acid or chitin, the aggregation of montmorillonite was effectively inhibited.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Naval Research Laboratory, Seafloor Sciences Branch, Stennis Space Center, Mississippi, USA. yoko.furukawa@nrlssc.navy.mil

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.

No MeSH data available.


Related in: MedlinePlus