Linear alkylbenzene sulfonate (LAS), a widely used anionic surfactant, is present in wastewater and can be discharged, causing environmental damage. When biodegradation is negligible, adsorption and desorption reactions play an important role, depending on the media characteristics (organic matter and clays) and hydrodynamic parameters. Previously published laboratory column data are modelled with PHREEQC (version 2.18) in three scenarios of LAS input: spill (LAS pulse), continuous discharge (LAS adsorption step) and remediation (LAS desorption step). The distribution coefficients (0.1-4.9 x 10-3 L/g) in the sand columns are lower than those determined in this paper from batch tests and in columns of 25% and 50% agricultural soil mixtures (1-70 x 10-3 L/g). Considering the Freundlich constant parameters from the modelling, the results are similar to the distribution coefficients, but the linear isotherms are more consistent throughout. The mass transfer coefficient from the sand columns is lower than the agricultural soil columns (20-40 h-1), indicating longer elution times for the heavier homologues and a higher percentage of agricultural soil. For lighter homologues, fast migration could cause contamination of aquifers. The great persistence of LAS in the environment necessitates the development of mitigation strategies using reactive transport models, which predict longer times for the remediation of LAS homologues.

Little was known about the leaching behavior of potentially toxic elements (PTEs) from soils under the interaction between freeze-thaw (F-T) cycle and the solutions of varying pH values. In this study, PTEs leachability from soils before and after F-T tests was evaluated using toxicity characteristics leaching procedure (TCLP) test. The microstructure and mineralogical evolution of soil mineral particles were conducted using pores (particles) and cracks analysis system (PCAS) and PHREEQC. The results indicated that during 30 F-T cycles, the maximum leaching concentrations of PTEs were 0.22 mg/L for As, 0.61 mg/L for Cd, 2.46 mg/L for Cu, 3.08 mg/L for Mn, 29.36 mg/L for Pb and 8.07 mg/L for Zn, respectively. Under the coupled effects of F-T cycle and acidification, the porosity of soil particles increased by 4.79%, as confirmed by the microstructure damage caused by the evolution of pores and cracks. The anisotropy of soil particles increased under F-T effects, whereas that decreased under the coupled effects of F-T cycle and acidification. The results from SEM-EDS, PCAS quantification and PHREEQC modeling indicated that the release mechanism of PTEs was not only associated with the microstructure change in mineral particles, but also affected by protonation, as well as the dissolution and precipitation of minerals. Overall, these results would provide an important reference for soil remediation assessments in seasonal frozen areas.