Lead ions on montmorillonite

FIGURE2.14 The equivalent fractions of lead ion on the surface of montmorillonite and the ratios of different lead-EDTA complexes in the solution at Pb EDTA =1 1. (Reprinted from Nagy and Konya 1998, with permission from Elsevier.)... 

Lead enrichments can be detected only when the system contains both lead ions and montmorillonite. However, they cannot be observed on mica flakes immersed... 

Nagy, N. M., J. Kdnya, and I. Kdnya. 1998b. Ion exchange processes of lead and cobalt ions on the surface of calcium-montmorillonite in the presence of complex forming agents. II. The effect of DTPA, tartaric acid and citric acid on the sorption of lead ion on calcium-montmorillonite. Coll. Surf. 137 243-252. 

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

The evidence for quasicrystal formation in suspensions of mono-valent-ion-saturated montmorillonites [23,58] indicates that wav for Na-montmorillonite should lie between 1.0 and 2.0. The viscosity data in Fig. 11 in fact lead to wav = 1.3 if the ratio of hD-values [from Eq. (30)] for Na-montmorillonite and Li-montmorillonite is equated to their ratio of av values, with av = 1.0 for Li-montmorillonite. Similarly, if the ratio of mp-values taken from Eq. (31) is equated to a ratio of av values (i.e., mp = wo wav, where wo is the mass of a unit-layer particle), then av = 1.4 0.3 on the basis of the data in Fig. 11, along with other published data on light transmission by dilute Li- and Na-montmorillonite suspensions [23]. 

Hachiya, K., M. Ashida, M. Sasaki, H. Kan, T. Inoue, and T. Yasunaga. 1979. Study of the kinetics of adsorption-desorption of lead(2+) ion on a gamma-aluminum oxide surface by means of relaxation techniques. J. Phys. Chem. 83 1866-1871. Heller-Kallai, L., and C. Mosser. 1995. Migration of Cu ions in Cu montmorillonite heated with and without alkali halides. Clays Clay Miner. 43 738-743. 

Mortland, Pinnavaia and their co-workers have found that the adsorption of certain aromatic molecules on montmorillonites whose exchangeable cations are saturated with transition metal ions leads to the formation of colored complex(2-4). The IR spectrum of benzene complex formed under a dry atmosphere Indicates the chemical state of the adsorbed benzene is remarkably different from that of liquid benzene (2,3), while adsorbed anisole is reported to dimerize to 4,4 -dimethoxy-biphenyl(5). The essential step in the formation of these colored complexes has been shown to involve an electron transfer from the adsorbed organic molecules to the interlayer transition-metal ion, notably by ESR(4,6). However, the detailed spectroscopic information concerning the structure of adsorbed species have not been sufficient. 

The structural parameters of cation-exchanged montmorillonites prepared from calcium-montmorillonite (Istenmezeje) are listed in Table 2.3. As seen in Table 2.3, the basal pacing of monovalent montmorillonite is approximately 1.25 nm, and the water content is approximately 1%. It means that there is one layer of water in the interlayer space. For bivalent montmorillonite, both basal spacing (>1.5 nm) and water content (>10%) are higher, showing two layers of water molecules in the interlayer space. The basal spacing of Pb-montmorillonite is 1.254 nm, which is similar to the value characteristic of monovalent montmorillonite (1.241 nm). However, it does not mean that lead is sorbed on the surface of montmorillonite as monovalent cation since the other parameters that are determined by the distance between the layers (hydration entropy, charge/ion radius value, water content in the interlayer space) lie between the values for bivalent and monovalent cations (Foldvari et al. 1998). 

Srivastava S.K., R, Tyagi, N. Pant, and N. Pal. 1989. Studies on the removal of some toxic metal ions. Part II. Removal of lead and cadmium by montmorillonite and kaolinite. Environ. Technol, Lett. 10 275-282. 

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