## 3 Results and Discussion
### Batch Tests
#### 3.2.4 Interaction between TNT and Aniline Adsorption on the Saturated Loess  
The effect of TNT on aniline adsorption on the loess is shown in Figure 1, under initial aniline concentrations of 10.0 and 25.0 mg/L. Aniline adsorption rates decreased gradually from 80.62 and 66.19 to 73.96% and 62.03%, with TNT concentration increasing from 0 mg/L (control) to 25.0 mg/L, and the decreased percentage was 6.66 and 4.16% at the initial aniline concentrations of 10.0 mg/L and 25.0 mg/L (Figure 1), respectively, showing that TNT and aniline compete in their adsorption on the loess and that TNT has an inhibitory potential for aniline adsorption. The inhibition increases with TNT concentration increase, which is supported by other reports [1,41]. The inhibition of TNT on aniline adsorption is ascribed to its similar adsorption sites and driving forces, including Van der Waals, etc. Moreover, the statistical analysis of the tests shows that there is a linear relationship between initial TNT concentration (C) and aniline adsorption rate (\(\eta\) %), and Equations (1) and (2) were obtained, indicating that  
\[\eta=-0.2637\;\mathrm{C}+80.68\;\mathrm{(aniline\;concentration10.0\;mg/L)} \tag{1}\]  
\[\eta=-0.1709\mathrm{C}+66.31\;\mathrm{(aniline\;concentration25.0\;mg/L)} \tag{2}\]  
Figure 1: Effect of TNT on aniline adsorption on Chinese loess. (**a**) 10.0 mg/L aniline concentration; (**b**) 25.0 mg/L aniline concentration. where the inhibition effect is more obvious with the aniline concentration of 10.0 mg/L compared to that of 25.0 mg/L, as the slope of the former straight line is higher than the latter. Figure 2 shows the effect of aniline on TNT adsorption on the loess. The adsorption rate of TNT decreases as the aniline concentration increases, which means that aniline inhibits TNT adsorption, as TNT does to aniline adsorption. With an aniline concentration increase from 0 (control) to 25.0 mg/L, TNT adsorption rates are drawn from 48.11 and 38.56% to 6.23 and 28.15%, and the decline ranges are 21.88 and 10.41% with 50.0 and 100.0 mg/L TNT concentration. Obviously, compared with the effect of TNT on aniline (Figure 1), the decline of aniline on TNT adsorption is far greater than that of TNT on aniline, indicating that aniline has a stronger influence on TNT adsorption on the loess than that for its adsorption affected by TNT. However, when aniline concentration is lower than 10.0 mg/L, aniline has hardly any influence on TNT adsorption on the loess under the experimental conditions, and this is a significant difference from the influence of TNT on aniline adsorption. This phenomenon can be ascribed to the molecular polar force being larger than the surface force driving aniline adsorption on the loess preferentially over TNT. More coincidently, TNT adsorption on the loess is mainly via surface physical adsorption, so aniline at low initial concentrations is directly adsorbed by the loess rather than being in competition with TNT [41]. However, when the aniline concentration is high, surplus aniline molecules compete with TNT adsorption on the loess, and the influence becomes obvious and strong. Thus, there is also a linear relationship between aniline and its influence on TNT adsorption, as that for TNT done on aniline, and then the relationship can be described as in Equations (3) and (4), with initial TNT concentrations of 50.0 and 100.0 mg/L, respectively. \[\eta=-0.2185\;\mathrm{C}\;+46.811\;\mathrm{(TNT\;concentration\;50.0\; mg/L)} \tag{3}\]  
\[\eta=-0.0677\mathrm{C}+34.545\;\mathrm{(TNT\;concentration100.0\; mg/L)} \tag{4}\]  
Obviously, the inhibition of aniline on TNT adsorption has a significant relationship to initial TNT concentration, and decreases with increases in its concentration (Equations (3) and (4)). The slopes of these two lines are 0.2185 and 0.0677, which are very close to the 0.2637 and 0.1709 obtained by TNT influence on aniline adsorption on the loess (Equations (1) and (2)).