# Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption
## 3 Results and Discussion  
### Characterisation of Bentonite and Modified Bentonite  
#### 3.1.1 XRF and CEC Analysis  
Table 1 shows the effects of acid and heat treatment on the chemical and CEC properties of the adsorbents. Acid treatment has a significant effect on chemical composition. The weight percentage of oxide metal of Na\({}^{+}\), Mg\({}^{2+}\), K\({}^{+}\), Ca\({}^{2+}\), Fe\({}^{3+}\), and of Al\({}^{3+}\) decreases significantly during treatment with acid in both single- and two-step modified samples, such as BA\({}_{0.5}\), BC\({}_{500}\)A\({}_{0.5}\), and BA\({}_{0.5}\)C\({}_{500}\) resulting from the effects of acid leaching. When comparing the SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratios of BC\({}_{500}\)A\({}_{0.5}\) and BA\({}_{0.5}\)C\({}_{500}\), it shows that BA\({}_{0.5}\)C\({}_{500}\), treated with acid prior to heat treatment has a higher SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratio (see Table 1), probably due to the calcined sample (BC\({}_{500}\)) with larger mean particle sizes than unmodified bentonite before further treatment with acid (as mentioned in Topic 3.1.8). There are various methods available to determine CEC. Most approaches involve the complete exchange of naturally occurring cations in a clay mineral with a cationic species such as ammonium ion, followed by the removal of excess substitution ion and the determination of the amount retained in the clay interlayer [15]. It was found that CEC values for acid and heat-treated samples are lower than those for bentonite (see Table 1).  
The decrease in CEC value with acid treatment results from cationic leaching, while low CEC values resulting from heat treatment may be explained by a charge reduction as the result of the migration of small radii cations into vacant octahedral sites and the formation of covalent bonds after heating [31]. Another explanation is that the cation becomes more strongly bound to the surface during calcination, so the exchange by NH\({}_{4}\)\({}^{+}\) becomes more difficult. However, the extent of charge reduction depends on the nature of the cation and the heating temperature.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{8}{c}{**Chemical (\%Weigh)**} & \multicolumn{2}{c}{**SiO\({}_{J}\)**} & \multicolumn{2}{c}{**CEC**} \\  & **Na\({}_{2}\)O** & **MgO** & **Al\({}_{3}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **P\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **CaO** & **TiO\({}_{2}\)** & **MnO** & **Fe\({}_{2}\)O\({}_{3}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **(emol kg\({}^{-1}\))** \\ \hline Bentonite & & & & & & & & & & & & \\ (Na,Ca)\({}_{3}\)(Al,Al,Mg,Si,O,O,OH)\({}_{2}\),nH\({}_{2}\)O & 0.079 & 0.607 & 9.472 & 78.543 & 1.347 & 1.703 & 2.813 & 0.788 & 0.045 & 4.239 & 8.29 & 67.62 & 13.04 \\ BC\({}_{500}\) & 0.058 & 0.760 & 9.426 & 78.914 & 1.308 & 1.693 & 2.750 & 0.805 & 0.044 & 4.021 & 8.37 & 47.21 & 4.98 \\ BC\({}_{500}\)A\({}_{55}\) & ND & 0.664 & 8.982 & 83.010 & 1.301 & 0.963 & 0.825 & 0.758 & 0.024 & 3.342 & 9.24 & 44.15 & 8.69 \\ BA\({}_{0.5}\) & ND & 0.505 & 7.705 & 85.236 & 1.279 & 0.838 & 0.530 & 0.740 & ND & 2.997 & 11.06 & 43.45 & 9.43 \\ BA\({}_{0.5}\)C\({}_{500}\) & ND & 0.642 & 7.355 & 85.001 & 1.274 & 0.832 & 0.558 & 0.740 & 0.020 & 2.687 & 11.56 & 19.11 & 4.29 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition and CEC values for bentonite and modified bentonite samples.