## 3 Environmental Applications of Organoclays
### Soil Pollution
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Clay** & **Modifier** & **Methodology** & **Application** & **Efficiency** & **Reference** \\ \hline Montmorillonite (China) & Fe\({}_{3}\)O\({}_{4}\)-CuO & Coprecipitation & \begin{tabular}{c} Anthracene \\ Removal \\ \end{tabular} & 96.2\% & [29] \\ \hline Montmorillonite (China) & Tetramethylammonium (a) & & Heavy metal & (TCLP) Cr(VI) & \\ Hexadecyltrimethylammo (China) & Cation exchange & & removal & 16.4\% (a) & [30] \\  & nium (b) & & (Cr(VI)) & 3.5\% (b) & \\ \hline \multirow{4}{*}{Montmorillonite (China)} & trimethylstearylammonium bromide & & & & \\  & 3-meraptpropyltrime & Cation exchange & Heavy metal & & \\  & thyxylsilane & grafting & immobilization & 96.7\% (Hg) & [31] \\  & thiol group & & & & \\ \hline Montmorillonite (China) & humic acid & Cation exchange & Heavy metal & (TCLP) & \\  & & removal & 97.6\% (Cd) & [32] \\  & & & & 93\% (Hg) & \\ \hline Montmorillonite (China) & Magnesium & Cation exchange & Heavy metal & \begin{tabular}{c} Cu 53.8\% \\ Pb 76.4\% \\ Zn 32.2\% \\ Cd 38.2\% \\ \end{tabular} & [33] \\ \hline Ca-Montmorillonite (China) & \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles & Magnetic stirred & Pyrene & \\  & Cation exchange & Removal & 843.9 \(\mu\)g g\({}^{-1}\) & [34] \\ \hline Montmorillonite (China) & Fe(III) & Cation exchange & \begin{tabular}{c} As(III) \\ oxidation \\ Anthracene \\ \end{tabular} & 90\% & [35] \\ \hline Vermiculite- & & & & \\ Montmorillonite (China) & MnO\({}_{2}\) & Cation exchange & Heavy metal & 98.2\% (Hg) & [36] \\ \hline Montmorillonite (China) & Iron & Cation exchange & \begin{tabular}{c} Heavy metal \\ removal \\ \end{tabular} & 73\% (Hg) & [37] \\ \hline Montmorillonite (China) & \begin{tabular}{c} butane-1,4-bis(dodecyl \\ dimethyl ammonium bromide) \\ tetrachloroferrate (FeCl\({}_{4}\)-) \\ \end{tabular} & Cation exchange & \begin{tabular}{c} Heavy metal \\ immobilization \\ \end{tabular} & 96.04 \(\pm\) 0.12\% (Cr) & [38] \\ \hline Montmorillonite (China) & Humus-like substances & \begin{tabular}{c} polyphenol- \\ Maillard \\ reaction \\ \end{tabular} & Heavy metal & \begin{tabular}{c} TCLP reduced \\ 13.96\% (Pb) \\ 13.18\% (Zn) \\ \end{tabular} & [39] \\ \hline Montmorillonite (China) & goethite & co-precipitation & \begin{tabular}{c} Heavy metal \\ Removal \\ \end{tabular} & 50.61 mg g\({}^{-1}\) (Cd) & [40] \\  & & & 57.58 mg g\({}^{-1}\) (As) & [41] \\ \hline Montmorillonite (China) & Exopolysaccharideacrylides by & & Heavy metal & 256 mg g\({}^{-1}\) (Cs) & [41] \\  & Rhizobium tropici & Cation exchange & Removal & 90.9 mg g\({}^{-1}\) (Sr) & [42] \\ \hline Montmorillonite (China) & Ferrihydrite & Ultrasonic & \
\begin{tabular}{c} Heavy metal \\ removal \\ \end{tabular} &
\begin{tabular}{c} 86.28\% (Sb) \\ 94.60\% (Pb) \\ could not be \\ detected (As) \\ \end{tabular} & [42] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of the application of natural clay and its modified clay in the removal of soil pollutants and their efficiency. in anthracene was reported; most importantly, this Fe\({}_{3}\)O\({}_{4}\)-CuO-modified montmorillonite clay catalyst was successfully reused for eight cycles. [PERSON] et al. [30] synthesized montmorillonite clay modified with tetramethylammonium (TMA) and hexadecyltrimethylammonium (HDTMA) for Cr(VI) immobilization capacity and found that TMA-modified clay has a larger surface area and pore volume compared to HDTMA-modified clay. A modified toxicity characteristic leaching (TCLP) method was used to assess Cr(VI) immobilization capacity and it was found that both modified clays may have a higher Cr(VI) stabilization capacity. However, HDTMA has a higher capacity than TMA. [PERSON] et al. [31] studied the grafting of thiol-functionalized onto organically modified montmorillonite used for Hg stabilization in soil contamination. The stabilization efficiency was over 90% after grafting the thiol group onto the modified clay. This graft increased the stability efficiency to 96.7%, which is 82.4% higher than regular organically modified clay.