## 3 Results and Discussion
### Batch Tests
#### 3.2.2 Adsorption Isotherms  
The adsorption isotherm could describe the distribution of TNT and aniline between aqueous and loess, and then the isotherm data were simulated by three mathematical equations--the Langmuir (Equation (S5)), [PERSON] (Equation (S6)) and Redlich Peterson models (Equation (S7)) [28,36] and the results were obtained (Table S2). It was found that (Table S2) the adsorption of TNT was well-fitted to the three adsorption isotherm models, with correlation coefficients R\({}^{2}\)>0.90, and the order of R\({}^{2}\) value was Freundlich> Langmuir> Redlich-Peterson model. Obviously, the test data were more consistent with the Freundlich model, indicating that physical interaction is the main mechanism of adsorption. The predicted parameter K\({}_{\text{F}}\) in the Freundlich model presents an increasing trend, i.e., 11.69, 16.18, 25.16, 37.32 and 48.15 ((mg/kg)\(\cdot\)(L/mg)\({}^{1/n}\)), with the temperature increasing from 278 to 318 K, implying that the process of TNT being adsorbed by the loess is an exothermic reaction. The parameter n is 1.69, 1.58, 1.59, 1.68 and 1.77 at 278, 288, 298, 308 and 318 K, respectively, and these values are much greater than 1.0. These results suggest that the Freundlich equation can also describe the adsorption behavior of TNT on the loess well. Combining the results observed by [PERSON] et al. (2013) [15], TNT adsorption on the loess is mainly monolayer adsorption [37] and the loess surface heterogeneity and anisotropy have few influences on the adsorption [32]. These further prove that TNT adsorption on the loess is mainly physical adsorption supplemented with chemical adsorption. Similarly, the R\({}^{2}\) values of the Langmuir model are more than 0.94, also illustrating that TNT adsorption on the loess is more like monolayer adsorption. The predicted parameter q\({}_{\text{m}}\) in the Langmuir model shows an increasing trend, i.e., 230.42, 390.63, 529.10, 609.06 and 786.32 mg/kg with temperature increasing from 278 to 318 K, illustrating that TNT adsorption is sensitive to temperature, and this is consistent with the results of the Freundlich isotherm analysis. The R\({}^{2}\) values of the Redlich-Peterson model were greater than 0.91, showing that TNT adsorption on the loess involves monolayer and multilayer adsorption simultaneously [32]. The exponent g reflects the heterogeneity of the adsorbent, and when g values are equal to 0 and 1, the Redlich-Peterson model converges to Henry and Langmuir isotherms, respectively. The present study shows that g is in the range of 0.53-0.54, revealing the loess is heterogenous [37], which is in agreement with the SEM results (Figure S1). The values of the predicted parameter B in the Redlich-Peterson model are less than 1.0, further proving that the adsorption has a characteristic of the Langmuir adsorption model, where the adsorption mainly occurs on the surface of the loess and is dominated by monolayer adsorption accompanied by multilayer adsorption [20]. By comparing their adsorption behaviors (Table S2), aniline adsorption has similar characteristics to TNT adsorption regarding the loess, and also has some differences. Firstly, the values of the parameter n in the Freundlich model for aniline adsorption are 4.25, 4.52, 4.67, 5.15 and 5.17, which are much greater than those for TNT adsorption, demonstrating that aniline is subject to nonlinear adsorption rather than linear adsorption. Meanwhile, the values of K\({}_{1}\) obtained for aniline (from 4.23 to 5.21 L/mg) are greater than the values for TNT (from 2.09 to 2.60 L/mg), indicating a high energy for aniline adsorption [18]. Secondly, from the results of the Redlich-Peterson model, both g and B values for aniline adsorption (0.68, 0.70, 0.53, 0.62, 0.63 and 143.26, 114.84, 93.21, 71.53, 68.32) are greater than those for TNT adsorption (0.58, 0.53, 0.53, 0.54, 0.55 and 0.37, 0.39, 0.41, 0.42, 0.46), illustrating that the isothermal adsorption tends towards a Freundlich model.