## 3 Environmental Applications of Organoclays
### Soil Pollution
[PERSON] et al. [32] used humic acid to modify montmorillonite for Cd- and Hg-contaminated soils. In total, 5 wt% of humic acid-modified clay reduced the Cd and Hg concentrations in TCLP leachates by 94.1% and 93.0%, respectively. In the long-term immobilization, a quantitative accelerated aging method was performed and the reliability of both metals in the modified clay was found to be over 0.95. [PERSON] et al. [33] used magnesium-based montmorillonite for heavy metals immobilized in contaminated soil and found lower TCLP extractability for Cu, Pb, Zn, and Cu heavy metals in soil. According to their proposed mechanism, heavy metals are first induced mainly through electrostatic attraction, then precipitation, and finally chelation with water-soluble organic carbon. [PERSON] et al. [34] prepared FeSO\({}_{4}\cdot\)7H\({}_{2}\)O-modified Ca-montmorillonite and applied it for pyrene removal and found a removal capacity of 843.9 \(\mu\)g g\({}^{-1}\). This higher removal rate efficiency was due to the formation of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles generated on the surface of the clay and at the edges of the clay. It was found that not only the efficiency but also the reusability is at five cycles. According to them, this \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)-modified montmorillonite is a green material for removing organic pollutants from soils and sediments. [PERSON] et al. [35] prepared Fe(III)-modified montmorillonite for the oxidation of As(III) to As(IV) and the degradation of anthracene. They found that Na montmorillonite without Fe(II) has a conversion rate of 60% for As and \(<\)30% for anthracene, which would be 90% and almost 100% converted after using Fe-modified montmorillonite with 15 days of incubation. [PERSON] et al. [36] used MnO\({}_{2}\) loading on vermiculite-montmorillonite to remove Hg in contaminated soils. They found that adding 15 g/kg of modified vermiculite-montmorillonite reduced the Hg concentration in the soil to 98.2%. In addition, the plant height and biomass of Brassica chinensis L also increased. Similar Hg removal work by [PERSON] et al. [37] involved modifying montmorillonite clay with Fe to control the release of Hg. After deployment, the root of Brassica pekinensis increased in Hg content but the leaf decreased in Hg content. This is because Fe-modified montmorillonite clay can adsorb Hg0 and decrease ionic Hg mobilization through surface adsorption, complexation, and in situ precipitation. [PERSON] et al. [38] studied montmorillonite clay modified with gemini cationic surfactant (butane-1,4-bis(dodecyl-dimethyl-ammonium bromide)) and tetrachloroferrate (FeCl\({}_{4}\)\({}^{-}\)) to study the retention performance of W and/or Cr in soil and found that W and Cr were immobilized in soil within 5 min. This is because modified clay along with FeCl\({}_{4}\)\({}^{-}\) turns exchangeable W and Cr to reducible fractions. [PERSON] et al. [39] studied the applicability of humus-like substances to modified montmorillonite for the remediation of Pb and Zn in contaminated soils. They found that the mobility, bioavailability, and leachability of Pb and Zn decreased significantly. They found that the TCLP of Pb and Zn decreased by 9.27-13.96% and 10.3-13.18%, respectively, after the introduction of modified clay. Recently, [PERSON] et al. [40] investigated montmorillonite clay loaded with goethite to assess the simultaneous adsorption of Cd(II) and As(III) in the water and soil system. They reported removal rates of 50.61 mg/g and 57.58 mg/g for Cd(II) and As(III) after the modified clay introduction. In another recent study, [PERSON] et al. [41] researched the modification of montmorillonite by exopolysaccharide and requested the removal of Sr and Cs heavy metals. They found that the adsorption capacity of montmorillonite clay increased by 53.8 and 54.5%, reaching adsorptions of 256 mg/g and 90.9 mg/g for Cs and Sr, respectively. [PERSON] et al. [42] synthesized amorphous ferrihydrite-modified montmorillonite clay for the removal of As, Sb, and Pb in soil.