Yaoguo Wu

To ascertain the effects of conventional hydrochemical components on the presence of endogenous fine loess particles (EFLPs) in groundwater over loess regions, Na⁺, NO₃⁻ and Cu²⁺, as conventional hydrochemical components, were employed in batch tests with EFLPs from a typical loess as aquifer media in Guanzhong Plain, China. The results showed that EFLPs had high zeta potential (ζ) and remained suspended over 40 h, indicating their good dispersity and potential to be suspended in groundwater. ζ was employed to replace electrostatic repulsion in the DLVO equation to determine the critical coagulation concentrations for Cu(NO₃)₂ and NaF as 0.1 mmol/L and 50 mmol/L for 1.1 µm D₅₀ EFLPs, which were almost consistent with the batch test results and greater than those in the groundwater, respectively, further implying that EFLPs are likely to be suspended in groundwater. The multi-factor tests showed that the key factors including particle size, hydro-chemical component and concentration interacted with each other and their relative magnitudes varied in the test processes, where the effects of concentration strengthened while those of the component weakened. So, hydrogeochemical conditions were beneficial to the suspension of EFLPs and the benefit got strong along the groundwater flow path, which is conducive to the cotransport of EFLPs with pollutants in groundwater over loess regions.

Adsorption performances of one pollutant on different adsorbents likely depend on the adsorbent microstructures heavily. Hereon, zeolite, diatomite and kaolinite particles were selected as inexpensive adsorbents in this study with 2,4,6-trinitrotoluene (TNT) as an organic pollutant for the batch test to verify the effect of adsorbent microstructure on TNT adsorption performance. The results of kinetic, adsorption isothermic, and thermodynamic analyses indicated that the adsorption process of TNT on three particles is controlled by chemisorption, and that both are non-spontaneous entropic endothermic reactions, although they have their own specific adsorption capacities, equilibration times, and kinetic rates. Comprehensively analyzing the characterization data and adsorption performances of the particles shows that, the pore physical properties including the pore diameter distribution and volume obviously control the adsorption capacities, and well the pore surface chemical properties such as the functional groups affect the adsorption kinetics; the microstructure affects the performances through the synergistic effect of physical and chemical pathways and results in the special performances. Briefly, a particle has its special microstructure and then determinedly unique performance. The finding provides insights into the role of the microstructure of the particles in their performances, and significances for selecting and utilizing the adsorbents in water treatment.

To determine the interactions between TNT and aniline adsorptions and the potential to enhance their transports in saturated Chinese loess, batch and column tests were conducted. The batch tests show that their adsorptions inhibit each other when they coexist, and their inhibitions depend on their concentrations, implying that their coexistence has the potential to enhance their transports of each other in the saturated loess. The column tests confirm this speculation, while aniline enhances TNT transport more obviously than TNT does. These findings are ascribed to TNT adsorption being primarily through surface adsorption, while aniline adsorption mainly takes place via electrostatic adsorption and inner pore diffusion adsorption, as well as surface adsorption. There is a certain competitive relationship in their adsorptions on the loess because they have same and different adsorption sites; in particular, electrostatic force is greater than surface force. Therefore, these inhibitions on adsorption are conducive to the existences of TNT and aniline in the water rather than being fixed on the loess, thus enhancing their transports in the saturated loess, indicating that their coexistence can increase the risk of soil and even groundwater pollution.