**6.6. Adsorption of toxic heavy metals**

Results obtained for flexural strength, elasticity modulus, tensile strength, and thermal resistance on the applied dental adhesive, using montmorillonite as an additive, were encouraging. Adhesive produced with dimethacrylate copolymer and montmorillonite (0.2% concentration) showed significant performance as a dental adhesive. Improved performance obtained using 0.2% concentration of montmorillonite, indicated by X-ray diffraction (XRD) test results, was attributed to its exfoliated morphology. The resulting dental adhesive reduces the weakening of tooth structure. However, the highest concentration of 1.5% produced agglomerated clay

The use of montmorillonite as a filler may be possible in any of the following morphologies:

**ii.** Intercalated form, where a polymer or a substrate molecule can be between platelets.

**iii.** Exfoliated form where platelets are isotropically dispersed in polymer or substrate

Adsorption and swelling characteristics of montmorillonite are useful in drug delivery systems. An increased adsorption capacity provides improved drug entrapment and sustained release of pharmaceutical drugs. Solubility, dissolution rate, adsorption, and bioavailability of hydrophobic drugs are enhanced by montmorillonite. The effects of montmorillonite in

Effluent loading, from dyeing industries and textile-processing units, to natural environment is a serious concern. Technological solution is required to remove residual dye content from the used water. The application of montmorillonite as an adsorbent for cationic dye is an important effect. The removal of cationic dye, methylene blue, from water is achievable through adsorption process. Montmorillonite concentration used for the removal of cationic dye depends upon the initial dye concentration, contact time, solution pH, and temperature. Results obtained on dye adsorption demonstrated the equilibrium data follow the Langmuir isotherm equation [37]. Thermodynamic study of methylene blue adsorption on montmorillonite indicates that the process is endothermic revealed by the determination of enthalpy, entropy, and Gibb's free energy. Importantly, the results support the possibility of using montmorillonite as low-cost adsorbent for wastewater treatment containing cationic dyestuff. There is a large number of textile dyeing industries, in India, Pakistan, and China, that release used dye bath water containing cationic dyestuff. Adsorption system developed using montmorillonite can be useful

Possibly, montmorillonite can be used to influence the optical, chemical, and spectral characteristics of cationic dyes. The layer charge of montmorillonite can affect the cationic dye molecular aggregation. The subject was reviewed through the research literature discussing

**i.** Agglomerated particle comprising the particle with a joined layer structure. The surface

and no significant performance enhancement [35].

molecules.

**6.4. Drug delivery system**

**6.5. Adsorption of dyestuff**

for water recycling in dyeing industries.

dye reaction with clay minerals [38].

particle interacts with a polymer or a substrate.

14 Current Topics in the Utilization of Clay in Industrial and Medical Applications

improving the drug delivery system were reviewed [36].

An important application of adsorption properties of montmorillonite is seen in the removal of toxic heavy metals from aqueous solution. The adsorption studies using montmorillonite and kaolinite for the removal of toxic metals including As, Cd, Cr, Co, Cu, Fe, Pb, Mn, Ni, and Zn were reviewed [39].

Montmorillonite and its modified forms exhibited a significantly increased metal adsorption capacity relative to kaolinite and modified kaolinite. The modified clay mineral form was produced by pillaring montmorillonite or kaolinite by using polyoxy cations including Zn4+, Al3+, Si4+, Ti4+, Fe3+, Cr3+, or Ga3+. The modified form can also be produced using quaternary ammonium cations including tetramethylammonium-, tetramethylphosphonium-, and trimethylphosphonium-, N<sup>−</sup> -didodecyl-N, N<sup>−</sup> -tetramethylethanediammonium, etc.

Montmorillonite modified using sodium dodecylsulfate (SDS) can remove Cu2+ and Zn2+ by sorption from aqueous solutions. The study was conducted as a function of solution pH, solute concentration, and temperature (25–55°C). The thermodynamic parameters (Δ*H*<sup>o</sup> and Δ*S*<sup>o</sup> ) for Cu2+ and Zn2+ sorption on modified montmorillonite were evaluated. The study finds out that the kinetics for the sorption of Cu2+ and Zn2+ was assessed and the pseudo-first-order rate constant was evaluated [40].
