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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

Average hydrodynamic diameters (dH) of montmorillonite-only suspensions (8 mg/L) in constantly stirred solutions were measured as a function of time after mixing with artificial seawater (ASW) using dynamic light spectroscopy. The pH was circumneutral. The results show a lack of aggregation in the zero salinity suspension. On the other hand, at elevated salinity values, (S = 1.8 – 7.2 psu), the colloidal particles rapidly aggregate during the initial ~15 minutes following the ASW mixing. In the S = 1.8 psu suspension, the aggregates reach the steady state average size of dH ≈ 600 nm after 20 minutes. In the S = 3.6 and S = 7.2 psu suspensions, the aggregates become larger (dH ≈ 1,100 nm) after the initial rapid aggregation.
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Figure 4: Average hydrodynamic diameters (dH) of montmorillonite-only suspensions (8 mg/L) in constantly stirred solutions were measured as a function of time after mixing with artificial seawater (ASW) using dynamic light spectroscopy. The pH was circumneutral. The results show a lack of aggregation in the zero salinity suspension. On the other hand, at elevated salinity values, (S = 1.8 – 7.2 psu), the colloidal particles rapidly aggregate during the initial ~15 minutes following the ASW mixing. In the S = 1.8 psu suspension, the aggregates reach the steady state average size of dH ≈ 600 nm after 20 minutes. In the S = 3.6 and S = 7.2 psu suspensions, the aggregates become larger (dH ≈ 1,100 nm) after the initial rapid aggregation.

Mentions: Montmorillonite colloids in montmorillonite-only suspension form aggregates in constantly stirred solutions with elevated salinity (Figure 4). In zero salinity solutions, the value of dH remains at approximately 200 nm throughout the first 60 minutes after mixing with ASW. In systems with ASW (i.e., S = 1.8, 3.6, and 7.2 psu), the DLS analysis detected increase in the value of the average hydrodynamic diameter (dH) which indicates the formation of aggregates. This result agrees with the previous studies of laboratory kaolinite and montmorillonite aggregation in which the dispersion-aggregation properties of pure clay suspensions were found to be primarily determined by the solution ionic strengths (See Figure 3, also [29,45]). This is the behavior expected from suspensions whose dispersion-aggregation behaviors are primarily governed by the DLVO behaviors of competing electrostatic repulsion and 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)

Average hydrodynamic diameters (dH) of montmorillonite-only suspensions (8 mg/L) in constantly stirred solutions were measured as a function of time after mixing with artificial seawater (ASW) using dynamic light spectroscopy. The pH was circumneutral. The results show a lack of aggregation in the zero salinity suspension. On the other hand, at elevated salinity values, (S = 1.8 – 7.2 psu), the colloidal particles rapidly aggregate during the initial ~15 minutes following the ASW mixing. In the S = 1.8 psu suspension, the aggregates reach the steady state average size of dH ≈ 600 nm after 20 minutes. In the S = 3.6 and S = 7.2 psu suspensions, the aggregates become larger (dH ≈ 1,100 nm) after the initial rapid aggregation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Average hydrodynamic diameters (dH) of montmorillonite-only suspensions (8 mg/L) in constantly stirred solutions were measured as a function of time after mixing with artificial seawater (ASW) using dynamic light spectroscopy. The pH was circumneutral. The results show a lack of aggregation in the zero salinity suspension. On the other hand, at elevated salinity values, (S = 1.8 – 7.2 psu), the colloidal particles rapidly aggregate during the initial ~15 minutes following the ASW mixing. In the S = 1.8 psu suspension, the aggregates reach the steady state average size of dH ≈ 600 nm after 20 minutes. In the S = 3.6 and S = 7.2 psu suspensions, the aggregates become larger (dH ≈ 1,100 nm) after the initial rapid aggregation.
Mentions: Montmorillonite colloids in montmorillonite-only suspension form aggregates in constantly stirred solutions with elevated salinity (Figure 4). In zero salinity solutions, the value of dH remains at approximately 200 nm throughout the first 60 minutes after mixing with ASW. In systems with ASW (i.e., S = 1.8, 3.6, and 7.2 psu), the DLS analysis detected increase in the value of the average hydrodynamic diameter (dH) which indicates the formation of aggregates. This result agrees with the previous studies of laboratory kaolinite and montmorillonite aggregation in which the dispersion-aggregation properties of pure clay suspensions were found to be primarily determined by the solution ionic strengths (See Figure 3, also [29,45]). This is the behavior expected from suspensions whose dispersion-aggregation behaviors are primarily governed by the DLVO behaviors of competing electrostatic repulsion and 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