Surfactant Modification of Mineral Surfaces for Environmental Applications

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Surfactant Modification of Mineral Surfaces for
Environmental Applications

• Rob Bowman
• HYD/PETR 552
• Spring 2004

Dept of Earth and Environmental Science
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Outline

• Overview of Zeolite Properties
• Review of HDTMA properties
• Mechanisms of HDTMA Sorption to Zeolite
• Counterion Effects
• Contaminant Sorption by SMZ
• Clay-Surfactant Interactions
• Contaminant Sorption by Surfactant-Modified Clays

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Properties of Natural Zeolites

• Hydrated aluminosilicates,
• e.g., Clinoptilolite (Cp),
• (Ca,Na2,K2)(Al6Si30O72)24H2O

• Variable particle size
• High cation exchange capacity
• High internal and external surface area

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St. Cloud Clinoptilolite
New Mexico
Albuquerque
St. Cloud Deposit
Cost 0.10/kg (sized to specifications)
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Properties of St. Cloud Cp (0.4- to 1.4-mm size)

• Cation exchange capacity
• Total 900 meq/kg
• External 100 meq/kg
• External surface area (BET) 14 m2/g
• Permeability 10-3 m/sec (equivalent to sand)

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SEM of St. Cloud Clinoptilolite
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Properties of Surfactants

• Water-soluble organic compounds
• Have polar and nonpolar portions
• For example, hexadecyltrimethylammonium
  (HDTMA, or CTA), CH3(CH2)15N(CH3)3

• Form micelles in solution
• Form admicelles and hemimicelles on surfaces

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HDTMA Sorption by St. Cloud Clinoptilolite
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Clinoptilolite Charge versus HDTMA Loading
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Properties of Hexadecyltrimethylammonium Chloride
(HDTMA-Cl, CTA-Cl)
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Sorption isotherms for TEA (24 hours), HDTMA
monomers (7 days), and HDTMA micelles (7 days) on
clinoptilolite. The ECEC equals 90 meq/kg.
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Sorbed amount of bromide counterion versus sorbed
amount of surfactant for HDTMA monomers, HDTMA
micelles, and TEA.
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Total meq desorbed cations (Mg2, Ca2, and Na)
versus sorbed amount of HDTMA monomers, HDTMA
micelles, and TEA.
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Ln(sorbed conc./soln. conc.) versus sorbed
surfactant concentration (symbols) and linear
regression of the data (solid lines).
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Model fits based on Equation 10 (solid lines) to
plotted ln Kideal data (symbols) for sorbed HDTMA
monomers, HDTMA micelles, and TEA. Ln Kideal
values for data below the ECEC were calculated
with Equation 6 and incorporate cation exchange
effects (K6). Ln Kideal values for data above
the ECEC were calculated with Equation 9 (K9).
Model fits were extrapolated to 0 to obtain
the value of ln K for each system.
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Enthalpy of sorption (per meq of surfactant
sorbed) versus surfactant sorbed, for HDTMA
monomers, HDTMA micelles, and TEA. Sorption
equilibration times for all systems were 2 hours.
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Conceptual model of entropic changes due to water
destructuring caused by sorption of TEA and HDTMA
to natural clinoptilolite. Sorption of TEA (A)
electrostatic interactions and weak water
destructuring. Sorption of HDMTA monomers (B)
electrostatic and weak water destructuring (C)
electrostatic and moderate water destructuring
(D) electrostatic and strong water destructuring
(E) electrostatic and strong water
destructuring. Sorption of HDTMA micelles (F)
electrostatic and moderate water structuring
(G) electrostatic and weak to moderate water
destructuring.
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Effect of counterion on HDTMA sorption to
zeolite. Solid lines are Langmuir fits to the
observed data using the parameters in Table 1.
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Sorption of HDTMA and counterions as a function
of initial Br- (Br- Cl-) ratio. The lines are
trend fits of observed data. Initial
HDTMA-counterion concentration was 0.033 M.
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Anion Exchange by SMZ
SO42-
CrO42-
SMZ
SeO42-
Untreated Clinoptilolite
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Equilibrium sorption data for monomer (ltCMC) and
micelle (gtCMC) HDTMA sorption to clinoptilolite
zeolite, with Br- counterion data for the initial
sorption step. Sorbed CrO42- and Br-
concentrations are also shown for the subsequent
CrO42- spike step.
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Effect of counterion on chromate sorption by
HDTMA-treated zeolite. Solid lines are Langmuir
fits to the observed data using the parameters in
Table 4.
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Counterion (Br- or Cl-) release as a function of
chromate sorption on HDTMA-treated zeolite.
Zeolite was initially treated with a 5050
mixture of HDTMA-Br HDTMA-Cl (abscissa value of
0.50 on Fig. 3). All the data points ware
corrected for Br- and Cl- desorption at zero
chromate concentration.
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Organic Sorption from Water by SMZ
1000
K
305 L/kg
oc

800
toluene
1120 L/kg
K
600
oc
Solute Sorbed (mg/kg)
p-xylene
400
K
136 L/kg
oc

benzene
200
0
0
20
40
60
80
Equilibrium Solution Concentration (mg/L)
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Koc/Kow Relationship for Organics Sorbed by SMZ
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Contaminant Sorption from Water by SMZ
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AFM Images of HDTMA on Clinoptilolite
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Perchloroethene Sorption versus HDTMA Loading
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FT-Raman higher-frequency spectra for (A) an
HDTMA micelle solution and HDTMA sorbed on
clinoptilolite zeolite for a series of treatment
levels (B) 310 ECEC, (C) 230 ECEC, (D) 160
ECEC, (E) 80 ECEC, and (F) 60 ECEC.
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Two-dimensional schematic of HDTMA sorbed as
micelles or monomers on the zeolite surface,
describing the effects of sorption on tail group
disorder. Although not illustrated, the third
dimension of the surfactant structure, surface
roughness, and time also affect the amount of
disorder in the surfactant tail groups.
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Monolayer vs. Bilayer HDTMA Sorption








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Zeolite surface
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Zeolite surface
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Jaynes and Boyd, Soil Sci. Soc. Am. J. 5543-48,
1991
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Jaynes and Boyd, Soil Sci. Soc. Am. J. 5543-48,
1991
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Jaynes and Boyd, Soil Sci. Soc. Am. J. 5543-48,
1991