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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 (8 mg/L) + HA (4.8 mg/L) suspensions 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. In addition, no time-dependent aggregation was detected in suspensions with elevated salinity (i.e., S = 1.8 and 3.6 psu). At the highest salinity value investigated (S = 7.2 psu), the colloidal particles gradually aggregated during the ~60 minutes following the ASW mixing.
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Figure 6: Average hydrodynamic diameters (dH) of montmorillonite (8 mg/L) + HA (4.8 mg/L) suspensions 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. In addition, no time-dependent aggregation was detected in suspensions with elevated salinity (i.e., S = 1.8 and 3.6 psu). At the highest salinity value investigated (S = 7.2 psu), the colloidal particles gradually aggregated during the ~60 minutes following the ASW mixing.

Mentions: The colloidal suspensions in montmorillonite + HA systems did not aggregate as much as the montmorillonite-only suspensions upon mixing with ASW (Figures 5 and 6). With a small amount of HA (1.6 mg/L), the aggregation in S = 1.8 and 3.6 psu suspensions were trivial (Figure 5). With more HA (4.8 mg/L), no time-dependent aggregation was detected in S = 1.8 and 3.6 psu suspensions (Figure 6). With a higher salinity value (S = 7.2 psu), the mixed montmorillonite + HA suspensions went through some degree of time-dependent aggregation. However, the rate of aggregation was significantly slower than the rate of aggregation observed in the system with no HA (Figures 4, 5, 6). These results agree with the previous studies in which the salinity-induced aggregation of clays were hindered by the addition of HA [27]. It has been argued that the HA is adsorbed on the clay edge surfaces due to the surface complexation between clay aluminol and HA carboxyl groups [28,46]. This increases the dispersion by: (1) the increased negativity (or even charge reversal from positive to negative) at the clay edge surfaces (and thus increased electrostatic repulsion); and (2) steric repulsion due to polymeric components of HA [27,32,33].


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 (8 mg/L) + HA (4.8 mg/L) suspensions 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. In addition, no time-dependent aggregation was detected in suspensions with elevated salinity (i.e., S = 1.8 and 3.6 psu). At the highest salinity value investigated (S = 7.2 psu), the colloidal particles gradually aggregated during the ~60 minutes following the ASW mixing.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Average hydrodynamic diameters (dH) of montmorillonite (8 mg/L) + HA (4.8 mg/L) suspensions 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. In addition, no time-dependent aggregation was detected in suspensions with elevated salinity (i.e., S = 1.8 and 3.6 psu). At the highest salinity value investigated (S = 7.2 psu), the colloidal particles gradually aggregated during the ~60 minutes following the ASW mixing.
Mentions: The colloidal suspensions in montmorillonite + HA systems did not aggregate as much as the montmorillonite-only suspensions upon mixing with ASW (Figures 5 and 6). With a small amount of HA (1.6 mg/L), the aggregation in S = 1.8 and 3.6 psu suspensions were trivial (Figure 5). With more HA (4.8 mg/L), no time-dependent aggregation was detected in S = 1.8 and 3.6 psu suspensions (Figure 6). With a higher salinity value (S = 7.2 psu), the mixed montmorillonite + HA suspensions went through some degree of time-dependent aggregation. However, the rate of aggregation was significantly slower than the rate of aggregation observed in the system with no HA (Figures 4, 5, 6). These results agree with the previous studies in which the salinity-induced aggregation of clays were hindered by the addition of HA [27]. It has been argued that the HA is adsorbed on the clay edge surfaces due to the surface complexation between clay aluminol and HA carboxyl groups [28,46]. This increases the dispersion by: (1) the increased negativity (or even charge reversal from positive to negative) at the clay edge surfaces (and thus increased electrostatic repulsion); and (2) steric repulsion due to polymeric components of HA [27,32,33].

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