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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

Schematic drawings of a clay aggregate in a face-to-edge (F/E) orientation that is ubiquitous in unconsolidated fine-grained sediments. A typical sedimentary clay colloid is composed of several layers of clay unit cells that have sheet-like morphology. (It appears as a stack of rods in this schematic 2D cross section.) Each colloid has large, negatively-charged basal planes (i.e., faces) and less negatively (or positively) charged edges.
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Figure 2: Schematic drawings of a clay aggregate in a face-to-edge (F/E) orientation that is ubiquitous in unconsolidated fine-grained sediments. A typical sedimentary clay colloid is composed of several layers of clay unit cells that have sheet-like morphology. (It appears as a stack of rods in this schematic 2D cross section.) Each colloid has large, negatively-charged basal planes (i.e., faces) and less negatively (or positively) charged edges.

Mentions: The term "physicochemical flocs" has been used in the past to describe the initial formation of clay aggregates within water columns and in the immediate vicinity of sediment-water interface [4,8-10]. A similar physicochemical aggregation behavior has been also observed for iron oxides [11,12]. The previous clay studies argue that the open, typically "face-to-edge" association of clay colloids and particles in recent, unconsolidated fine-grained sediments (Figure 2) arises from the electrostatic attraction between negatively charged faces and positively, or at least less negatively, charged edges. The net surface charge of clay mineral particles is a result of two different types of surface charges: (i) permanently negative charge on the basal plane (i.e., "face") due to isomorphic substitution of Si by Al in Si-O4 tetrahedral sheets; and (ii) pH-dependent charge at the "edge" surfaces due to the reversible protonation and deprotonation of the surface hydroxyl groups [13]. The former is independent of pH and represents > 90% of the surface charge in the case of montmorillonite due to the platy morphology [14], whereas the latter is pH dependent. In low pH (i.e., high proton activity), the latter becomes less negative or even positive according to the reversible protonation and deprotonation reactions of silanol (Si-OH) and aluminol (Al-OH) surface groups. The edge surface charges of montmorillonite and kaolinite have been estimated from potentiometric titration to be very close to zero at circumneutral pH [15,16].


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)

Schematic drawings of a clay aggregate in a face-to-edge (F/E) orientation that is ubiquitous in unconsolidated fine-grained sediments. A typical sedimentary clay colloid is composed of several layers of clay unit cells that have sheet-like morphology. (It appears as a stack of rods in this schematic 2D cross section.) Each colloid has large, negatively-charged basal planes (i.e., faces) and less negatively (or positively) charged edges.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Schematic drawings of a clay aggregate in a face-to-edge (F/E) orientation that is ubiquitous in unconsolidated fine-grained sediments. A typical sedimentary clay colloid is composed of several layers of clay unit cells that have sheet-like morphology. (It appears as a stack of rods in this schematic 2D cross section.) Each colloid has large, negatively-charged basal planes (i.e., faces) and less negatively (or positively) charged edges.
Mentions: The term "physicochemical flocs" has been used in the past to describe the initial formation of clay aggregates within water columns and in the immediate vicinity of sediment-water interface [4,8-10]. A similar physicochemical aggregation behavior has been also observed for iron oxides [11,12]. The previous clay studies argue that the open, typically "face-to-edge" association of clay colloids and particles in recent, unconsolidated fine-grained sediments (Figure 2) arises from the electrostatic attraction between negatively charged faces and positively, or at least less negatively, charged edges. The net surface charge of clay mineral particles is a result of two different types of surface charges: (i) permanently negative charge on the basal plane (i.e., "face") due to isomorphic substitution of Si by Al in Si-O4 tetrahedral sheets; and (ii) pH-dependent charge at the "edge" surfaces due to the reversible protonation and deprotonation of the surface hydroxyl groups [13]. The former is independent of pH and represents > 90% of the surface charge in the case of montmorillonite due to the platy morphology [14], whereas the latter is pH dependent. In low pH (i.e., high proton activity), the latter becomes less negative or even positive according to the reversible protonation and deprotonation reactions of silanol (Si-OH) and aluminol (Al-OH) surface groups. The edge surface charges of montmorillonite and kaolinite have been estimated from potentiometric titration to be very close to zero at circumneutral pH [15,16].

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