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Published online 6 January 2006
Published in Soil Sci Soc Am J 70:297-304 (2006)
DOI: 10.2136/sssaj2005.0200
© 2006 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Soil Mineralogy

Adsorption of Polyacrylamide on Smectite, Illite, and Kaolinite

Youjun Dengb,*, Joe B. Dixona and G. Norman Whitea

a Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843-2474
b current address: Dep. of Crop and Soil Sciences, Washington State Univ., Pullman, WA 99164-6420

* Corresponding author (yjdeng{at}mail.wsu.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Interactions between polyacrylamides (PAMs) and clay minerals are the primary reactions in most applications of the water-soluble polymers. Our main objectives were to study (i) the effects of charge of PAM on the flocculation/dispersion of clay suspensions and on the adsorption of the polymers on clays, and (ii) the surface properties of PAM-clay complexes. Three PAMs—an anionic PAM 836A, a nonionic PAM 903N, and a cationic PAM 494C—were used to react with three common clay minerals—smectite, kaolinite, and illite. In the polymer concentration range tested (0–1.2 g L–1), the anionic PAM 836A increased the dispersion of the clay suspensions but the cationic PAM 494C promoted the flocculation. The strong flocculation function of cationic PAM 494C made trapped clay particles inaccessible for adsorption despite its highest affinity for clay surfaces. The adsorption of the polymers was irreversible. Nonionic PAM 903N and cationic PAM 494C intercalated smectite but anionic PAM 836A did not. The adsorbed polymer moderately altered the charge properties: the cation exchange capacity (CEC) and the abilities to remove heavy metal Cu and Cr had the following order: anionic PAM 836A-clay > nonionic PAM 903N-clay {approx} clay > cationic PAM 494C-clay. The PAM-clay complexes did not show distinct adsorption for hydrophobic chlorophenols, indicating that the adsorbed polymers did not increase the hydrophobicity of the clay surfaces.

Abbreviations: CEC, cation exchange capacity • PAM, polyacrylamide


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
POLYACRYLAMIDE and its copolymers, loosely referred to as polyacrylamides, are the most important commercial water-soluble polymers (Bikales, 1973). They are commonly used in soil erosion control, soil conditioning (Nadler et al., 1996; Zhang and Miller, 1996), irrigation control (Sojka et al., 1998), water treatment (Letterman and Pero, 1990), oil recovery (Stutzmann and Siffert, 1977; Pefferkorn, 1999), and many other industrial applications. In most of the applications, the polymers react mainly with clay minerals that occur in soils or sediments, or as suspended particles in water treatment. It is important to know how the polymers are adsorbed on the minerals, and how the adsorption alters the surface properties of the minerals. These reactions and surface changes influence the reaction and fate of other compounds, such as nutrients, heavy metals, and organic compounds in the polymer-reacted minerals, soils, or sediments. They also determine the disposal and reuse of the polymer-clay sludge from water treatments.

The reactions between PAM and clays minerals are not well understood. For example, the molecular conformation of the adsorbed polymers, the reaction sites, the roles of exchangeable cations in the adsorption, and surface properties of PAM-clay composites have not been systematically investigated. A general model of "train," "loop," and "tail" conformations (Theng, 1979; Deng and Dixon, 2002) can only be used for polymers adsorbed on external surfaces of minerals. For smectite and other expandable minerals, the polymers might access the interlayer gallery. There were controversial reports whether the intercalation can occur. It has been observed that the adsorption of PAM occurred exclusively on the external surfaces of soil aggregates (Ben-Hur et al., 1992; Nadler and Letey, 1989) and clay particles (Stutzmann and Siffert, 1977); implying PAM cannot intercalate smectite. Yet Hwang and Dixon (2000) pointed out two cationic PAMs intercalated a smectite. If the intercalation can occur, the interlayer polymers may have different conformations from those adsorbed on the external surfaces. The interlayer surface properties of smectite could be altered. Charge type and charge density on polymer chains are expected to have significant effect on the amount of adsorption and the conformation of the adsorbed polymers.

Our objectives were to investigate (i) the effects of charge of PAM on the flocculation/dispersion of clay suspensions and on the adsorption of the polymers on clays; (ii) if PAM can access the interlayer of smectite; (iii) stability of adsorbed polymers, and (iv) the effect of adsorbed PAM on the surface charge and hydrophobicity of the clay minerals.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Clay Minerals
We tested three most common clay minerals—smectite, kaolinite, and illite—in this study. They were a Texas smectite (the Southern Clay Products Inc., Gonzales, TX); a Georgia kaolinite (J.M. Huber Corp., Macon, GA); and an illite from Rochester, NY (Ward's Natural Science Establishment Inc.). The greenish illite shale was ground to pass a 0.25-mm (60 mesh) sieve and then was treated with dithionite-citrate-bicarbonate (DCB) to remove iron oxides and with hydrogen peroxide to remove organic matter (Kunze and Dixon, 1986).

The clay fractions of the minerals were collected by dispersion and centrifugation. The collected clays were saturated with Ca by repeated washing with 0.5 M CaCl2 solutions and then with water. Each washing included adding 25 mL of solution or water to 10 g of clay in a centrifuge tube, shaking for 24 h, centrifuging, and replacing supernate with fresh solution or water. These clays are referred to as Ca-saturated clays and were used to synthesize PAM-clay complexes. Powder x-ray diffraction and Fourier transform infrared (FTIR) analyses (data not shown) revealed that the smectite and the kaolinite clay fractions were pure in mineral composition and that the illite sample contained illite, kaolinite, and quartz (Table 1). For the PAM adsorption and the flocculation/dispersion experiments, the clays were saturated with Na+ by three times of washing with 1 M NaClO4 solution and then with distilled water. The Na-clay suspensions were transferred to volumetric flasks to make 40 g L–1 stock suspensions.


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  		Table 1. Mineral composition and surface properties of clays.

 
Polyacrylamides
The trade names of three PAMs are Magnifloc 494C Flocculent (cationic), Magnifloc 903N Flocculent (nonionic), and Magnifloc 836A Flocculent (anionic), respectively. They were provided by Cytec Industries Inc. (West Paterson, NJ) and are referred to as cationic PAM 494C, nonionic PAM 903N, and anionic PAM 836A respectively (Table 2).


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  		Table 2. Structures and molecular weights of polyacrylamides (PAMs).

 
Flocculation/Dispersion of Clays in the Presence of Polyacrylamides
Polyacrylamide solutions were mixed with Na-clay suspensions in a set of 10 mL test tubes. The clay content in the initial mixtures was about 0.6 g L–1, and the polymer concentration was varied from 0 to 70 mg L–1 for PAM 494C and 0 to 160 mg L–1 for PAM 903N and PAM 836A. The tubes were hand shaken for 1 min. Three hours later, 3 mL of supernatant from each tube was taken at 3.0 cm deep and was transferred to a disposable cuvette. The content of suspended clay at a fixed depth in the cuvette was monitored by turbidity at 600 nm.

Adsorption of Polyacrylamides on Clays
Adsorption isotherms of PAMs were determined as follows: an aliquot of 5.00 mL of stock Na-clay suspension was mixed with a PAM solution in a 40-mL Nalgene centrifuge tube. The tube was capped and shaken for 22 h at 23 ± 0.5°C. The shaken time was based on equilibrium time reported in the literature (Kislenko and Verlinskaya, 1999; Bajpai and Bajpai, 1995; Volpert et al., 1998). After shaking, clay and supernates were separated by centrifugation (1.2 x 104 g, 0.5 or 1 h). Concentration of PAM in the supernates was determined by UV absorption at 190 nm with a Beckman, DU640B spectrophotometer (Beckman Coulter, Inc., Fullerton, CA). The amount of adsorbed PAM was calculated from the concentration difference of the initial and final solutions.

Freundlich and Langmuir equations were used to fit the adsorption isotherms. Freundlich equation is expressed as

[1]
where q is the amount of adsorbed polymer (mg g–1), C is the final concentration of polymer in solution (mg L–1), k and n are two constants. The Langmuir equation is expressed as

[2]
where b is maximum adsorption, k determines the initial slope of the isotherm.

The effect of pH on PAM adsorption was determined using similar procedures as those used for the adsorption isotherm. The pH of clay suspensions was adjusted with 0.1 or 0.7 M HClO4, or 0.1 M NaOH solutions before mixing the clays with the polymers. Only one concentration for each PAM—200 mg L–1 for anionic PAM 836A and 400 mg L–1 for nonionic PAM 903N and cationic PAM 494C—was tested in the pH effect experiment.

Resistance of Adsorbed Polymers to Water Washing
From the isotherm experiment, tubes that contained 400 mg L–1 PAM 494C, 400 mg L–1 PAM 903N, and 200 mg L–1 PAM 836 were selected to test the resistance. The clay-polymer sediments were washed four times with distilled water. In each washing, the sediments were mixed with 25 mL of fresh distilled water, shaken for 24 h, and centrifuged. The concentration of desorbed PAM was quantified by the UV absorption at 190 nm.

Synthesis and Characterization of Polyacrylamide-Clay Complexes
Ten grams of Ca-clays were dispersed in distilled water by sonication and then treated three times with 1 or 1.5 g L–1 PAM solutions. In each treatment, the clay-polymer suspensions were shaken for 24 h. Excess polymers were removed by washing with distilled water. Resulting PAM-clay complexes were freeze-dried.

Responses of Basal Spacings of Polyacrylamide-Smectite Complexes to Heating
To test if the polymer can access the interlayer of smectite, the PAM-smectite complexes were heated for 4 h at each sequentially increased temperature up to 550°C. The d(001) spacing of the heated complexes were analyzed with a Philips x-ray diffractometer (Philips Electronic Instruments, Mahwah, NJ).

Cation Exchange Capacity of Polyacrylamide-Clay Complexes
Cation exchange capacities of the clays and the complexes were quantified with Ca2+–Mg2+ exchange method (Dixon and White, 2000). The charge properties of the complexes were verified in removal of Cu2+ and Cr3+ from solution by a batch method (Deng et al., 2003). Two CEC equivalents of each cation was mixed with the complexes. The pH of Cu2+ solutions was 5.3 and of Cr3+ solutions was 3.9.

Effect of Polyacrylamides on Surface Hydrophobicity of Clays
The hydrophobicity of the clays and PAM-clay complexes was tested by sorbing 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol in a pH 4.9 buffer solution of sodium acetate (Deng et al., 2003). A smectite modified with a cationic surfactant benzyldimethyl-tetradecyl-ammonium (BDTA, Fluka Chemical Co., Buchs, St. Gallen, Switzerland) was used for comparison and this organo-clay is referred to as BDTA-smectite. To check if the hydrophobicity of the interlayer of PAM-intercalated smectite was changed, a 10% (v/v) glycerol aqueous solution was sprayed on air-dried PAM-smectite films on glass slides. The d(001) spacing of the glycerol treated PAM-smectite complexes was determined by XRD.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Flocculation/Dispersion of Clays in the Presence of Polyacrylamides
In the concentration range tested, the anionic PAM 836A was a stabilizer and the cationic PAM 494C was a strong flocculant for the Na-clay suspensions. The effect of nonionic PAM 903N fell between those of anionic PAM 836A and cationic PAM 494C. Presence of anionic PAM 836A increased stability of the clay suspensions. The suspended clay concentrations were not discernable in the first few hours (e.g., Fig. 1a and 2a ), but the stabilization effect of PAM 836 became more obvious after longer time. For example, after 1 mo settling, about 80% kaolinite, 20% smectite, and 20% illite still suspended in 160 mg L–1 PAM 836A solution, whereas only negligible clays suspended in distilled water (data not shown).



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  		Fig. 1. Settlement of smectite in the presence of (a) anionic PAM 836A, (b) nonionic PAM 903N, and (c) cationic PAM 494C. Six hours after mixing the polymers and clay suspension. Illite and kaolinite suspensions had similar responses to the polymer solutions as smectite suspension had.

 


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  		Fig. 2. Concentration of clay remained in suspension after settling for 6 h in the presence of (a) anionic PAM 836A, (b) nonionic PAM 903N, and (c) cationic PAM 494C.

 
Flocculation occurred immediately once cationic PAM 494C was added to the clay suspensions and the flocs settled quickly (Fig. 1c). More smectite and illite clays were flocculated and settled when the solution concentration of PAM 494C was increased (Fig. 2c). It appeared that 10 mg L–1 was the optimum concentration for PAM 494C to flocculate kaolinite. Settled flocs in PAM 494C solutions were loosely packed. After 3 yr of settling, the bulk density of the wet flocs was only about 0.003 g cm–3, which is three orders of magnitude lower than the density of the clays. The loose packing of the flocs is likely the result of the strong charge repulsion of the polymer chains (Theng, 1979) in the PAM-clay complexes. The flocs were hard to disperse by shaking or sonication.

The nonionic PAM 903N was also a flocculant for the clays, but with much less impact than the cationic PAM 494C (Fig. 1b and 2b). The flocs in PAM 903N solutions could be redispersed by sonication or extensive shaking. The results observed here suggest that the flocculation or dispersion role was largely determined by the charges of the polymer and the clays. Electrostatic repulsion between same charged PAM 836A and clays resulted in the stabilization role of PAM 836A whereas the electrostatic attraction between oppositely charged PAM 494C and the clays resulted in the flocculant role of PAM 494C.

Effect of pH on Polyacrylamide Adsorption
The three curves of anionic PAM 836A adsorption vs. pH on smectite, illite, and kaolinite nearly overlapped with each other (Fig. 3a ), suggesting that mineral differences did not strongly affect the adsorption. In the range of pH 4 to about 6.5, the adsorption of PAM 836A decreased abruptly with increasing pH; when pH is <4 or >6.5, the adsorption varied <10%. The adsorption of nonionic PAM 903N on the three clays similarly decreased with increasing pH (Fig. 3b), but the decreasing rates and magnitudes were smaller than those of anionic PAM 836A. Between pH 7 and 8.5, the adsorption of cationic PAM 494C increased rapidly with increasing pH; when pH is <7 or >8.5, the adsorption did not show large variation with pH (Fig. 3c).



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  		Fig. 3. Effect of pH on the adsorption of (a) anionic PAM 836A, (b) nonionic PAM 903N, and (c) cationic PAM 494C on smectite, illite, and kaolinite.

 
The responses of PAM adsorption to solution pH can be attributed to (1) the flocculation/dispersion effect of the polymers and (2) the pH dependant charges of the clays and polymers. At high pH, the acrylamate units on PAM 836A become negatively charged by acid dissociation reaction (-COOH ->-COO– + H+), and its repulsion to the clays was increased too. In addition, the amide groups on nonionic PAM units can hydrolyze and become carboxylate groups (-CONH2 ->-COOH ->-COO–). This is the main reason why the adsorption of anionic PAM 836A and nonionic PAM 903N decreased when pH was increased (Fig. 3a,b). Increasing pH increases dispersion of clays, and thus the accessibility of the clays, this contributed the increased adsorption of cationic PAM 494C at high pH (Fig. 3c).

Polyacrylamide Adsorption Isotherms
The adsorption isotherms of anionic PAM 836A and nonionic PAM 903N were L-type and could be fitted with Langmuir and Freundlich equations (most of the R2 > 0.9). The anionic PAM 836A had the lowest adsorption on the three clays (Fig. 4a ). The adsorption of PAM 836A on the three clays showed marginal differences. The adsorption of nonionic PAM 903N on smectite and illite steadily increased with increasing polymer concentration (Fig. 4b). The adsorption on clays was correlated to the surface areas of the clays: smectite > illite > kaolinite. The adsorption of cationic PAM 494C could not be described by either Langmuir equation or Freundlich equation (most of the R2 < 0.5). The adsorption isotherms had the steepest initial slopes, indicating the strongest affinity of PAM 494C for the clay surfaces. The adsorption of PAM 494C on smectite and illite decreased with increasing polymer concentration when the polymer concentration was >50 mg L–1 (Fig. 4c). The maximum adsorption of cationic PAM 494C was lower than those of nonionic PAM 903N.



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  		Fig. 4. Adsorption isotherms of (a) anionic PAM 836A, (b) nonionic PAM 903N, and (c) cationic PAM 494C on smectite, illite, and kaolinite.

 
The isotherms suggest that the adsorption of the polymers were determined not only by the charge properties of the polymers and the clays, but also by the flocculation/dispersion effects of the polymers. The strong flocculation effect of concentrated cationic PAM 494C hindered the accessibility of the trapped particles in the flocs and therefore, the adsorption of cationic PAM 494C on smectite and illite clays reduced with increasing polymer concentration in the high concentration range (Fig. 4).

There were other two mechanisms have been proposed for the decreased adsorption of cationic polymers at high concentration. (1) It has been explained that decrease was because neutralizing the CEC of the mineral required less polymer with a higher cationicity—the percentage of cationic repeating unit N,N,N-trimethylaminoethyl acrylate on the polymer chain (Breen, 1999; Denoyel et al., 1990). This reason cannot be used to explain our results. The maximum adsorption of PAM 494C on smectite was 30.5 mg g–1 or 6.9 cmol(c) kg–1 (Fig. 4c), implying that only 9% CEC of smectite was neutralized by the polymer. Similarly, only <9.8 cmol(c) kg–1 charge of illite was neutralized by adsorbed PAM 494C. (2) It has been proposed that at low concentration the polymers dissolve in water with fully extended conformations and therefore have more reaction points; at high concentration, the polymers dissolved with coiled or weak-extended conformations and thus the steric hindrance becomes an obstacle for their adsorption to the clays (Misra, 1996). This mechanism should be applicable to all of the three types of PAMs, but sorption decrease for anionic PAM 836A and nonionic PAM 903N at high concentration was not observed.

Resistance of Adsorbed Polymers to Water Washing
The adsorbed polymers were resistant to water washing. After four consecutive washing with water, an accumulative of <3% of the adsorbed polymer was removed from the clays (Fig. 5 ). The resistance of the adsorbed polymers to water washing was a result of combined electrostatic interaction, entropy effect (Theng, 1979, 1982), and kinetic factors. The latter two mechanisms contribute the most to the resistance of nonionic PAM 903N and anionic PAM 836A. In the anionic PAM 836A, about 80% of the repeating units are nonionic and the nonionic units contributed the most to the adsorption and resistance of the polymer.



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  		Fig. 5. Accumulative amount of desorbed polymers from clays by four consecutive water washing: (a) anionic PAM 836A, (b) nonionic PAM 903N, and (c) cationic PAM 494C.

 
Responses of Basal Spacings of Polyacrylamide-Smectite Complexes to Heating
The d(001) spacings of smectite and the three PAM-smectite complexes were about 1.5 nm at room temperature. When heated, the Ca-smectite began to collapse at 200°C, and completely collapsed to 1.0 nm at 250°C (Fig. 6a ). The anionic PAM 836A-smectite complex had lower d(001) spacing than Ca-smectite at same temperatures (Fig. 6b), suggesting that anionic PAM 836A did not intercalate smectite. There were two phases in both the cationic PAM 494C-smectite and the nonionic PAM 903N-smectite complexes. One phase maintained its d(001) spacing >1.4 nm at <300°C, and then gradually collapsed to 1.1 nm till the temperature was raised to 550°C (Fig. 6c,d); the other phase had essentially the same response as Ca-smectite, it collapsed to 1.0 nm at 250°C and higher temperatures. These results suggest that the nonionic PAM 903N and the cationic PAM 494C intercalated smectite. The incomplete intercalation of nonionic PAM 903N and cationic PAM 494C was also due to the flocculation effects. Trapped clay particles inside the flocs were inaccessible to the polymers. The d(001) spacing of the PAM-smectite was about 1.5 nm, indicating only one layer of the polymer entered the interlayer.



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  		Fig. 6. X-ray diffraction patterns of (a) Ca-smectite, (b) anionic PAM 836A-smectite, (c) nonionic PAM 903N-Smectite, and (d) cationic PAM 494C-smectite after 4-h heating at each sequentially increased temperature.

 
Effect of Adsorbed Polyacrylamide on Surface Properties of Clays
Remaining Charge on Polyacrylamide-Clay Complexes
The polymers modestly altered the CECs of the clays: the anionic PAM 836A slightly increased the CEC (about 2–3 cmol(c) kg–1) (Fig. 7 , black columns); the nonionic PAM 903N did not cause distinct changes; and the cationic PAM 494C modestly reduced the CEC, yet more than 77% of the CEC of smectite and illite remained, and it caused a 4 cmol(c) kg–1 reduction in the CEC of kaolinite. The small reductions of CEC caused by cationic PAM 494C suggest that the polymer only partially replaced the exchangeable cations in the minerals.



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  		Fig. 7. Cation exchange capacities of smectite, illite, kaolinite, and their PAM complexes; and the amount of adsorbed Cu and Cr on the clays and complexes.

 
The weak effect of PAM adsorption on surface charge sites was supported by the Cu2+ and Cr3+ sorption experiments (Fig. 7). The polymer-clay complexes' capacities of adsorbing the heavy metals were similar to those of the starting clays: the anionic PAM 836A increased the capacity about 10%, the nonionic PAM 903N slightly decreased the capacity, and cationic PAM 494C reduced about 20% or less of the capacity.

Surface Hydrophobicity of Polyacrylamide Adsorbed Clays
Even though the backbone (-CH2CH-) of the polymers is nonpolar and hydrophobic, sorption of the polymer on the clays did not increase the hydrophobicity of the clays. This is shown by the negligible adsorption of the complexes for hydrophobic chlorophenols: the adsorbed amounts of the three chlorophenols on Ca-smectite and the three PAM-smectite complexes were <4 µM g–1 whereas the amounts on a reference BDTDA-smectite were in the range 243–437 µM g–1. The surface of BDTA-smectite complexes was hydrophobic, the adsorption of the chlorophenols on this BDTA-smectite increased with hydrophobicity of the chlorophenols. The adsorption of the chlorophenols on illite, kaolinite, and their PAM complexes were also nearly zero (data not shown). The negligible adsorption and indiscernable differences among the clays and the PAM-clay complexes suggest that PAM did not distinctly increase the hydrophobicity of the mineral surfaces. When glycerol was added to smectite and the polymer-smectite complexes, the d(001) spacing was uniformly expanded to 1.8 nm (Fig. 8 ). The expansion by glycerol indicates that the interlayer spaces of PAM-smectite complexes could be accessed by polar solvents and therefore were still hydrophilic.



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  		Fig. 8. X-ray diffraction patterns of glycerol solvated (a) Ca-smectite, (b) anionic PAM 836A-smectite, (c) nonionic PAM 903N-smectite, and (d) cationic PAM 494C-smectite.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
In the concentration range tested (0–1.2 g L–1), the adsorption of PAMs on smectite, illite, and kaolinite was strongly affected by the flocculation/dispersion effects of the polymers to the clay suspensions. Cationic PAM 494C had the highest affinity for the clay minerals due to electrostatic attraction, yet had less adsorption than nonionic PAM 903N because of its strong flocculation that make trapped clay particles inside the flocs inaccessible to the polymer. Only a small fraction of the exchangeable cations were replaced by the cationic units on PAM 494C. Anionic PAM 836A had the lowest affinity for the clay surfaces due to charge repulsion and it served as a stabilizer for the clay suspensions. The affinity and the flocculation capacity of nonionic PAM fell between the cationic and anionic polymers, it had the highest adsorption to the clays.

Nonionic and cationic PAMs can access the interlayer of smectite and form one-layer complexes. The adsorption of PAMs was irreversible regardless of the charge type they had. Adsorption of PAM onto the clay minerals did not significantly modify the surface properties of the clays: the surfaces or the interlayer space of smectite were still hydrophilic, the CECs of the clays were only moderately modified. The weak modification of the polymers on the clay surface properties implies that the polymer would not dramatically change the chemical and physical reactions of the clays with other compounds such as nutrients, heavy metals, and organic compounds in soils and sediments.

Received for publication June 24, 2005.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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