Montmorillonite Adsorption isotherms

As noted above, adsorption isotherms are largely derived empirically and give no information on the types of adsorption that may be involved. Scrivner and colleagues39 have developed an adsorption model for montmorillonite clay that can predict the exchange of binary and ternary ions in solution (two and three ions in the chemical system). This model would be more relevant for modeling the behavior of heavy metals that actively participate in ion-exchange reactions than for organics, in which physical adsorption is more important. 

Based on their molecular properties as well as the properties of the solvent, each inorganic or organic contaminant exhibits an adsorption isotherm that corresponds to one of the isotherm classifications just described. Figure 5.1 illustrates these isotherms for different organic contaminants, adsorbed either from water or hexane solution on kaolinite, attapulgite, montmorillonite, and a red Mediterranean soil (Yaron et al. 1996). These isotherms may be used to deduce the adsorption mechanism. 

Fig. 5.1 Examples of adsorption isotherms. S-type aldrin on oven dry kaolinite from aqueous solution. L-type parathion on oven-dry attapulgite from hexane solution. H-type methylene blue at pH = 6 on montmorillonite from aqueous solution. C-type parathion on clay soil from hexane solution (Yaron et al. 1996)...

The amount of adsorbed chemical is controlled by both properties of the chemical and of the clay material. The clay saturating cation is a major factor affecting the adsorption of the organophosphorus pesticide. The adsorption isotherm of parathion from an aqueous solution onto montmorillonite saturated with various cations (Fig. 8.32), shows that the sorption sequence (Al > Na > Ca ) is not in agreement with any of the ionic series based on ionic properties. This shows that, in parathion-montmoriUonite interactions in aqueous suspension, such factors as clay dispersion, steric effects, and hydration shells are dominant in the sorption process. In general, organophosphorus adsorption on clays is described by the Freundhch equation, and the values for parathion sorption are 3 for Ca +-kaoUnite, 125 for Ca -montmorillonite, and 145 for Ca -attapulgite. 

Figure 8.18. Adsorption isotherm of six. v-triazines on Na-montmorillonite. Order of solubility simetone > atratone > promatone > atrazine > trietazine > propazine (from Bailey et al., 1968, with permission).

FIGURE 2.5 Composite (upper), ion exchange, and adsorption isotherms (lower) of zinc ion/calcium-montmorillonite interfacial reaction. T = 20°C, pH 5.8. 

In the present work we examine the microporosity of a TSLS complex formed from synthetic imogolite and natural montmorillonite. Nitrogen adsorption and desorption isotherms are reported and analyzed in terms of microporous volume and surface area. Also, the adsorption isotherm for an organic adsorbate, m-xylene, is reported. Preliminary FTIR results for the chemisorption of pyridine and catalytic studies of the dealkylation of cumene suggest that TSLS complexes are promising microporous acids for shape selective chemical conversions. 

Adsorption isotherms were obtained for four amino acids in an investigation of their interaction with calcium montmorillonite and sodium and calcium illite. Linear isotherms were obtained in the study of their adsorption by the calcium clay. These isotherms were described in terms of a constant partition of solute between the solution and the adsorbent Stem layer. Free-energy values were calculated using the van t Hoff relation [16,27]. 

Figure 10.7. Adsorption isotherms for water on a Na-montmorillonite at three temperatures. (Adapted from P. L Hall and D. M. Astill. 1989. Adsorption of water by homoionic exchange forms of Wyoming montmorillonite. (SWy-1). Clays Clay Min. 37 355-363.)...

Two researches studied the adsorptive properties of montmorillonite clay modified by tetra-butyl ammonium (Akgay, 2004, 2005). The adsorption of p-chlorophenol in this clay was done in batch with 20 mL of pollutant solution to 0.1 g of clay, at 25°C for 16 h. The adsorption isotherms were adjusted according to the models of Freundlich and Dubinin-Radushkevich. The kinetic and thermodynamic parameters pointed to the application of organoclay as adsorbent effective of phenolic compounds in contaminated effluents. 

Reference (4) provides detailed information about the sorption of polar and nonpolar sorbates (both gases and liquids) on many different types of clays, current to 1978. Rutherford et al. reported adsorption isotherms as recently as 1997 of various ion-exchanged montmorillonites (45). They found that the lateral dimen-... 

FIGURE 6 N2 adsorption isotherms at 77 K obtained for montmorillonite pillared with different pillaring species (Al, Zr, Fe, Ti). (From Ref. 30.)... 

The unmodified and modified pillared clays, synthesized using amines or with mixed pillars, have an intermediate hydrophylic-hydrophobic character and thus have some potential for the removal of chlorinated hydrocarbons. In Figure 12, the adsorption isotherms of some hydrocarbons on different pillared clays are compared to the adsorption isotherm on Na-montmorillonite (79). In all cases, the adsorption capacity of the mixed Fe-/Zr-PILC is a factor 4 higher than that of the pure Fe-PILC. Besides the adsorption capacity, the isotherm type also changes. 

FIGURE 12 Adsorption isotherms at 273 K of chlorinated hydrocarbons (CCI4, CHCI3, CH2CI2, CH4) on different pillared clays and on the parent Na-montmorillonite. (From Ref. 79.)... 

Hensen EJM, Tambach TJ, Bliek A, Smit B (2001) Adsorption isotherms of water in Li-, Na- and K-montmorillonite by molecular simulation. J Chem Phys 115 3322-3329... 

Adsorption isotherms of NaDS on montmorillonite and HDP-montmorillonite are shown in Fig. 13. Adsorption of the anionic surfactant via electrostatic interactions can take place only at the broken edges of the clay plates with pH-dependent surface charge sites under appropriate pH conditions. In our experiments the pH of the suspension was not adjusted, but it can be supposed that the edge sites are partly positively (A/-OH) and pardy negatively (Si-OH) charged at neutral pH. The adsorption of DS may... 

Flocculation and deflocculation of montmorillonite (Veegum) suspensions by a non-ionic surfactants has been studied by Ohno et al. [21]. Adsorption isotherms of the surfactant on to the clay showed points of inflexion due to bimolecular adsorption. Maximum flocculation occurred when the surface was covered by a layer of surfactant oriented with the alkyl chain pointing out into the aqueous phase. The deflocculation which occurs on further addition of surfactant is due to the hydrophilization of the surface by the second layer of surfactant molecules. The viscosity of the clay suspension reaches a maximum at the point of maximum monolayer coverage and then falls on further addition of surfactant. Fig. 9.9... 

Roderick, G. L., D. Senich, and T. Demirel, 1969. X-ray diffraction and adsorption isotherm studies of the montmorillonite-water system. Proc. 3rd Int. Clay Conf, AIPEA (Tokyo) 1 659-668. 

Fig. 3.17 Isotherms on a natural sodium-rich montmorillonite. Circles denote adsorption, crosses desorption. (Courtesy Barrer.)...

Fig. 4.28 Isotherms for polar adsorbates on natural montmorillonite at 323 K. (Courtesy Barrer.) O, adsorption x, desorption.

Figure 2 shows us the N2 adsorption-desorption isotherm of Beta/montmorillonite composite. At low relative pressure a sharp adsorption of nitrogen indicates the existence of large amount of micropore. The hysteresis shown in figure 2 is ascribed to type H4 which usually can be observed on layered clay and other materials [2], It is obvious that part of the pore structure in montmorillonite is still preserved after calcination under high temperature and the following hydrothermal crystallization. 

Figure 2. N2 adsorption-desorption isotherm of Beta/montmorillonite composite...

Fluoride in minor concentrations is beneficial for animals and humans, bnt it becomes toxic when ingested in excessive amounts. Bar-Yosef et al. (1989) investigated adsorption kinetics and isotherms of K -montmorillonite and a series of soils (clay, 4-61% organic matter, 2-7%), as affected by solution pH. The flnoride... 

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