## 3 Results and Discussion
### Batch Tests  
#### 3.2.1 Adsorption Kinetics  
The amount of TNT or aniline absorbed on per unit mass of the loess (q\({}_{t}\), mg/g) can be calculated by the formula q\({}_{t}\) = (C\({}_{0}\) - C\({}_{t}\))\(\cdot\)V/m, where C\({}_{0}\) is the initial concentration of TNT or aniline (mg/L), C\({}_{t}\) is the concentration of TNT or aniline at a reaction time (mg/L), V is the solution volume (L), and m is the mass of the loess (g), respectively. The adsorption kinetic test data (Figure S2a) show the TNT amount adsorbed on the loess (q\({}_{t}\)) during the reaction time at TNT initial concentration (C\({}_{0}\)) from 25.0 to 100.0 mg/L at an interval of 25.0 mg/L under 25 \(\pm\) 2 \({}^{\circ}\)C, and their maximum adsorption amounts were 118.78, 239.15, 299.60 and 359.61 mg/kg, respectively, suggesting that the adsorption capacity increases with an increasing initial concentration. The higher the TNT initial concentration, the greater the driving force between the loess and water, and the loess adsorption ability is enhanced. This phenomenon was also reported by [PERSON] et al. (2017) [24]. TNT adsorption on the loess has two stages: a fast adsorption stage and a slow adsorption stage (Figure S2). The fast stage occurred within 4 hours, when almost 80% of the adsorption was completed in this stage, and then was followed by slow stage until reaching a steady state. The equilibrium times were 10, 9.5, 8 and 7 hours for TNT initial concentrations of 25.0, 50.0, 75.0 and 100.0 mg/L, respectively. This illustrates that the adsorption equilibrium time was shortened as the TNT initial concentration increased, as a great concentration difference between loess and water enhanced the initial adsorption rate. The equilibrium time was close to that of raw soil with 3.03% SOM reported by [PERSON] et al. (2018) [25], and much shorter than that of soil studied by [PERSON] et al. (2006) [26] because SOM was richer than the current loess used. The equilibrium time was approximately 18 h in 2% and 5% fulvic acid (FA) soil, and even reached 20 h in 10% FA soil [25]. Similarly, [PERSON] et al. (2004) [8] reported that the equilibrium time of TNT bound to dissolvedorganic matter (DOM) extended to about 1 day. These results further confirm that TNT is fixed on the loess via adsorption rather than the partition of SOM. The kinetic data were analyzed using four kinetic equations, including the pseudo-first order kinetic (PFOK) (Equation (S1)), the pseudo-second order kinetic (PSOK) (Equation (S2)), the Weber-Morris intraparticle diffusion model (WMIDM) (Equation (S3)) and the Elovich equation (EE) (Equation (S4)) [27; 28; 29], and the results are provided (Table S1). The four kinetic models fit well to describe TNT adsorption (Table S1), and the coefficient values (R\({}^{2}\)) were in the order PSOK \(>\) PFOK \(>\) WMIDM \(>\) EE in all the tests. The ranges of R\({}^{2}\) for PSOK are from 0.998 to 0.999, so are close to 1.0, and the theoretical adsorption amounts are 40.98, 115.06, 252.49 and 375.94 mg/kg, calculated based on the equation, and are consistent with the experimental values of 43.12, 127.56, 239.15 and 359.61 mg/kg. The results suggest that TNT adsorption on the studied loess perfectly complies with PSOK. [PERSON] et al. (2018) [25] also found a similar phenomenon, indicating that TNT adsorption on loess particles was a controlled physical and chemical process involving complexation and diffusion to surface active sites within the loess soil matrix [30; 31], and the adsorption was considered to be a complex mass transfer process depending on liquid film diffusion, surface adsorption and intraparticle diffusion [32]. The initial adsorption rate (h) (mg/(kg\(\cdot\)min)) can be determined by the formula \(\mathrm{h=}\mathrm{k_{2}\cdot q_{e}^{2}}\) for TNT adsorption on the loess [33]. The values of h increased with TNT concentration, increasing from 10.0 to 100.0 mg/L (Table S1).