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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

Surface interaction energy calculated from electrostatic interaction (VEL) (i.e., Equation 1) and Lifshitz-van der Waals interaction (VLW)(i.e., Equation 5). The VEL and VLW values are shown individually in the upper figures, whereas the net energy values are shown in the lower figures. The net sum of VEL and VLW remains negative throughout the experimental conditions used to derive the z-potential (i.e., circumneutral pH at salinity values indicated on figure) except for the interaction between face and HA-covered edge at very low salinity (S = 0.4 psu). Net negative surface interaction energy would induce aggregation, whereas our observations yielded very little aggregation for S = 3.6 psu and below. On the other hand, aggregation was observed at S = 7.2 psu.
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Figure 11: Surface interaction energy calculated from electrostatic interaction (VEL) (i.e., Equation 1) and Lifshitz-van der Waals interaction (VLW)(i.e., Equation 5). The VEL and VLW values are shown individually in the upper figures, whereas the net energy values are shown in the lower figures. The net sum of VEL and VLW remains negative throughout the experimental conditions used to derive the z-potential (i.e., circumneutral pH at salinity values indicated on figure) except for the interaction between face and HA-covered edge at very low salinity (S = 0.4 psu). Net negative surface interaction energy would induce aggregation, whereas our observations yielded very little aggregation for S = 3.6 psu and below. On the other hand, aggregation was observed at S = 7.2 psu.

Mentions: The values of and , as well as + were calculated for certain discrete salinity values (i.e., S = 0.3, 1, 3.6, and 7.2 psu) using the ζ-potential values experimentally determined and interpolated at circumneutral pH (Figure 10), and shown in Figure 11. These results show that the sum of electrostatic and Lifshitz-van der Waals forces is constantly negative under the experimental conditions we considered, except for the HA system with very low salinity (S = 0.4 psu). This negative interaction energy would cause particles to approach each other and aggregate. However, montmorillonite did not aggregate in the HA-containing systems at S < 3.6 psu. Meanwhile, aggregation was observed at S = 7.2. Consequently, it is clear that other repulsive forces, such as steric repulsion, are quantitatively important in these systems in order to keep particles well dispersed in suspensions with S = 3.6 psu or less.


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)

Surface interaction energy calculated from electrostatic interaction (VEL) (i.e., Equation 1) and Lifshitz-van der Waals interaction (VLW)(i.e., Equation 5). The VEL and VLW values are shown individually in the upper figures, whereas the net energy values are shown in the lower figures. The net sum of VEL and VLW remains negative throughout the experimental conditions used to derive the z-potential (i.e., circumneutral pH at salinity values indicated on figure) except for the interaction between face and HA-covered edge at very low salinity (S = 0.4 psu). Net negative surface interaction energy would induce aggregation, whereas our observations yielded very little aggregation for S = 3.6 psu and below. On the other hand, aggregation was observed at S = 7.2 psu.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 11: Surface interaction energy calculated from electrostatic interaction (VEL) (i.e., Equation 1) and Lifshitz-van der Waals interaction (VLW)(i.e., Equation 5). The VEL and VLW values are shown individually in the upper figures, whereas the net energy values are shown in the lower figures. The net sum of VEL and VLW remains negative throughout the experimental conditions used to derive the z-potential (i.e., circumneutral pH at salinity values indicated on figure) except for the interaction between face and HA-covered edge at very low salinity (S = 0.4 psu). Net negative surface interaction energy would induce aggregation, whereas our observations yielded very little aggregation for S = 3.6 psu and below. On the other hand, aggregation was observed at S = 7.2 psu.
Mentions: The values of and , as well as + were calculated for certain discrete salinity values (i.e., S = 0.3, 1, 3.6, and 7.2 psu) using the ζ-potential values experimentally determined and interpolated at circumneutral pH (Figure 10), and shown in Figure 11. These results show that the sum of electrostatic and Lifshitz-van der Waals forces is constantly negative under the experimental conditions we considered, except for the HA system with very low salinity (S = 0.4 psu). This negative interaction energy would cause particles to approach each other and aggregate. However, montmorillonite did not aggregate in the HA-containing systems at S < 3.6 psu. Meanwhile, aggregation was observed at S = 7.2. Consequently, it is clear that other repulsive forces, such as steric repulsion, are quantitatively important in these systems in order to keep particles well dispersed in suspensions with S = 3.6 psu or less.

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