Adsorption illite

Mahoney JJ, Langmuir D (1991) Adsorption of Sr on kaolinite, illite, and montmorillonite at high ionic strengths. Radiochim Acta 54 139-144... 

Fig. 4.18 shows the result of Cd2+ adsorption on illite in presence of Ca2+ (Comans, 1987). The data are fitted by Freundlich isotherms after an equilibration time of 54 days. It was shown in the experiments leading to these isotherms that adsorption approaches equilibrium faster than desorption. Comans has also used 109Cd to assess the isotope exchange he showed that at equilibrium (7-8 weeks equilibration time) the isotopic exchangeabilities are approximately 100 % i.e., all adsorbed Cd2+ is apparently in kinetic equilibrium with the solution. The available data do not allow a definite conclusion on the specific sorption mechanism. 

Adsorption-desorption equilibrium for Cd(II) on illite after 54 days of equilibration. The solution contains HCO3, 2 x 10 3 M Ca2+ and has a pH = 7.8. Freundlich isotherms based on separate adsorption ( ) and desorption (O) data are given from Comans (1987). 

In a similar study (Comans et al., 1990), the reversibility of Cs+ sorption on illite was studied by examining the hysteresis between adsorption and desorption isotherms and the isotopic exchangeability of sorbed Cs+. Apparent reversibility was found to be influenced by slow sorption kinetics and by the nature of the competing cation. Cs+ migrates slowly to energetically favorable interlayer sites from which it is not easily released. 

The Adsorption of Cs+on Clays - an ion with a simple solution chemistry (no hydrolysis, no complex formation) - can be remarkably complex. Grutter et al. (1990) have studied adsorption and desorption of Cs+ on glaciofluvial deposits and have shown that the isotherms for sorption and exchange on these materials are nonlinear. Part of this non-linearity can be accounted for by the collaps of the c-spacing of certain clays (vermiculite, chlorite). As illustrated in Fig. 4.23 the Cs+ sorption on illite and chlorite is characterized by non-linearity. 

Notwithstanding the exceedingly high selectivities, the process occurring at trace loading is not an irreversible fixation but a reversible ion exchange reaction, as can be deduced from the internal consistency of +the trace Cs and trace Rb adsorption equilibria in Na - and K -illite shown in fig. 6. 

Extremely high selectivities are frequently interpreted as "ion fixation", which suggests an irreversible phenomenon. This is the case for exchanges of Cs, Rb and K in illite clay minerals (95-96) as well as for Cu(NHj) exchange in fluorhectorite (66). However, reversibility was verified from the Hess law for adsorption of Cs, Rb and K on the high affinity sites in illite (91) and modified montmorillonites (101) as well as for the exchange of transition metal complexes (29, 75). 

The assessment of surface area may sometimes present difficulties, e.g. with smectites N2 adsorption measurements grossly underestimate the area that is exposed in solution when the layers are fully expanded. In an attempt to overcome this problem a simple theoretical model has recently been developed (j4) for deriving double-layer potentials for the clay-solution interface from co-ion exclusion measurements. The results of this work suggest that the surfaces of montmorlllonlte and illite have constant potentials and do not behave like constant-charge surfaces as is generally assumed. 

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. 

Abstract The aim of this work was to study the simultaneous effect of amount of clay, activation temperature, contact time, pH, and size of the adsorbent on the retention of oil-grease thermally activated illite by adsorption. The values obtained for the percentage of oil-grease removed ranged from 93.87% for 110°C up to 66.73% for 900°C. The adsorption experiment showed surface that the stronger heat treatment the most effective adsorption of oil-grease. 

The studies relating the effect of temperature on adsorption was carried out at eight different temperatures (natural illite clay, 110°C, 200°C, 350°C, 450°C, 550°C, 750°C, 900°C) with a oil-grease concentration of 1,000 mg L and 5 g of illite clay sample, keeping the other parameters constants. Figure 20.2 shows oil-grease adsorption as a function of temperature. 

Fig. 20.2 Effect of temperature on percentage adsorption of oil at natural and thermal activate illite clay minerals...

Table 20.3 Effect of particle size on adsorption of oil thermal activated illite mineral...

Adsorption of oil- grease for seven different particle sizes on thermally activated illite clay (>710 pm 710-600 pm 600-425 pm 425-355 pm 355-150 pm 150-75 pm <75 pm) was studied keeping the other parameters as constant. The result of variation of this particle sizes on oil-grease adsorption show in Table 20.3. 

Figure 20.5 shows the effect of contact time and percentage adsorption oil-grease on the removal by thermally activated illite. 

The adsorption capacity of thermal activated illite is increased as 5.5% according to natural illite mineral. It has seen that there is on significant loss of adsorption capacity of illite at about 550°C. The capacity of oil - grease adsorption is... 

The CEC of clay minerals is partly the result of adsorption in the interlayer space between repeating layer units. This effect is greatest in the three-layer clays. In the case of montmorillonite, the interlayer space can expand to accommodate a variety of cations and water. This causes montmorillonite to have a very high CEC and to swell when wetted. This process is reversible the removal of the water molecules causes these clays to contract. In illite, some exchangeable potassium is present in the interlayer space. Because the interlayer potassium ions are rather tightly held, the CEC of this illite is similar to that of kaolinite, which has no interlayer space. Chlorite s CEC is similar to that of kaolinite and illite because the brucite layer restricts adsorption between the three-layer sandwiches. 

A recent paper by Lairdinvestigated the efficacy of HPAM flocculation of kaolinite, illite and quartz by carrying out visible absorption experiments. He concluded that HPAM more effectively flocculates kaolinite than quartz or illite. This was also the conclusion of previous work by Allen et al. who studied the adsorption of HPAM onto kaolinite, quartz and feldspar at various HPAM concentrations and solution pH by X-ray photoelectron spectroscopy (XPS). Much of the previous work on polyacrylamide adsorption onto aluminosilicates monitored the adsorbed amount by viscometry, carbon analysis and radiotracer techniques. These methods rely on following adsorption by subtraction from that detected in solution. 

Note that this Kid value is significantly smaller than the Kjd obtained in the linear part of the isotherm (i.e., at low 1,4-DNB concentrations). Furthermore, as can be seen from Fig. 2, the Freundlich equation overestimates C(S (and thus Kid) at both the low and the high end of the concentration range considered. In fact, inspection of Fig. 2 reveals that at very high concentrations, the K+-illite surface seems to become saturated with 1,4-DNB, which is not surprising considering that only limited adsorption sites are available. In such a case, the sorption isotherm can also be approximated by a Langmuir equation (Eq. 9-3). 

The retardation of subsurface transport of TNT arises from this compound s absorption into NOM and adsorption onto mineral siloxane surfaces covered with weakly hydrated cations like potassium (but not sodium and calcium). While components of feldspars exhibit some siloxane surfaces, here we anticipate that most of the silox-anes occur in the aluminosilicate clay minerals (e.g., illite) because these particles have such high specific surface areas (Table 11.3). Hence, the total for TNT may be found at this site ... 

Adsorption to the K+-covered siloxane surfaces of the clay, illite, can be estimated using Eq. 11-20. A tnt.eda is 300,000 L mol-1 and the surface area factor, /saf, for illite is 6 (Table 11.2). Since the ground water contains so much calcium relative to potassium (30 1), only a very small fraction of the cation exchange sites on the illite are covered with weakly hydrated potassium ions you assume/K+clay is about 0.01. Thus, you estimate ... 

In natural soils which commonly contain illite and smectite, there can be a significant charge imbalance between Si4+ and Al3+ in the structures of these clay minerals. This results in a net negative charge on the clay mineral surfaces, resulting in more adsorption of mobile cations. When an acid front encounters these adsorbed mobile cations, they are very easily displaced by the H ion, which by virtue of its small size is strongly adsorbed to the clay surface. As a result, the measured CEC of such clay-bearing soils is predicted to increase, as we have observed in our experiments. 

Terce, M. and R. Calvet (1978). Adsorption of several herbicides by montmorillonite, kaolinite and illite clays. Chemosphere, 4 365-370. 

Rates of ion exchange on kaolinite, smectite, and illite are usually quite rapid. Sawhney (1966) found that sorption of cesium on illite and smectite was rapid, while on vermiculite, sorption had not reached an equilibrium even after 500 h (Fig. 5.5). Sparks and Jardine (1984) found that potassium adsorption rates on kaolinite and montmorillonite were rapid, with an apparent equilibrium being reached in 40 and 120 min, respectively. However, the rate of potassium adsorption on vermiculite was very slow. Malcom and Kennedy (1969) studied Ba-K exchange rates on kaolinite, illite, and montmorillonite using a potassium ion-specific electrode to monitor the kinetics. They found >75% of the exchange occurred in 3 s, which represented the response time of the electrode. The rate of Ba-K exchange on vermiculite was characterized by a rapid and slow rate of exchange. 

Figure 5.5. Adsorption of cesium (Cs) by Ca-saturated clay minerals with time.Ill, illite Mt. montmorillonite Vr, vermiculite. [From Sawhney (1966), with permission.]...

The most common type of mixed-layer clay is composed of expanded, waterbearing layers and contracted, non-water-bearing layers (i.e., illite-montmorillonite, chlorite-vermiculite, chloritc-montmorillonite). Most of these clays form by the partial leaching of K or Mg (OH)2 from between illite or chlorite layers and by the incomplete adsorption of K or Mg(OH)2 on montmorillonite- or vermiculite-like layers. They most commonly form during weathering or after burial but are frequently of hydro-thermal origin. 

This was shown, for example, by electrokinetic measurements of Kavanagh and Quirk177) in the system Fe203-illite at pH 2.5. Electrophoretic and cation-exchange data indicated that the net charge of clay surface became strongly positive at low pH values as a result of adsorption of polycations Fe3+. Further examples of metal ion hydrolysis in oxide and silicate flotation systems were published by Fuerstenau178) and Stumm et al.62). 

ATR-FTIR and the HF/3-21G(d,p) level of theory [103], it was predicted that salicylic acid is adsorbed strongly onto illite. Salicylate forms surface complexes predominantly with the Al3+ octahedra located on the edges of the illite grains. The authors of DFT studies [104, 105] show that the ordering for the best sorption of dioxine and furane on the surface of smectites follows the order Mg2+ > Fe2+ > Fe3+ > Li+, which was obtained also in the case of adsorption of nitrogen heterocyclics on smectites [106]. 

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