The application of persulfate (PS) for the remediation of petroleum hydrocarbon contamination is among the most widely employed in situ chemical oxidation (ISCO) techniques, and it has received widespread attention due to its limited impact on soil integrity. This study employed a FeSO4-activated PS oxidation method to investigate the feasibility of remediating soil contaminated with total petroleum hydrocarbons (TPHs). The factors tested included the TPH concentration, different PS:FeSO4 ratios, the reaction time for remediation, soil physical and chemical property changes before and after remediation, and the effect of soil before and after remediation on soybean growth. The TPH degradation rate in soil was highest for high-, medium-, and low-TPHs soils-81.5%, 81.4%, and 72.9%, respectively, with minimal disruption to the soil's physicochemical properties-when PS:FeSO4 = 1:1. The remediation verification results indicated that the condition of the soybeans was optimal when PS:FeSO4 = 1:1. Under this condition, the net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate all remained high. Therefore, the best remediation effect was achieved with PS:FeSO4 = 1:1, which also minimized the damage to the soil and the effects on crop growth.

To investigate the efficacy and strength properties of Fe2+-activated persulfate remediation for 1,2-dichlorobenzene-contaminated soil with varying persulfate concentrations, we conducted degradation, microscopic, particle size, liquid-plastic limit, unconfined compressive strength (UCS), and undrained shear tests. The results indicate that adding 15.0% Fe2+-activated persulfate achieves a 92.59% removal rate of 1,2-dichlorobenzene. Furthermore, the reaction produces sodium sulfate, calcium sulfate, and ferric hydroxide. Small amounts of sodium sulfate and calcium sulfate fill the pores between soil particles, leading to a denser soil structure. However, the expansive effect of excessive sodium sulfate crystals weakens the inter-particle cohesion, leading to soil loosening. After remediation, the clay content increases, while the silt and sand content decreases. The liquid limit, the plastic capacity and the plastic index increase, while the plastic limit decreases with the increase of the persulfate dosage. The UCS and the maximum shear stress decrease with the increase of the persulfate dosage. The UCS of the soil treated by 10.0% persulfate is 310.75 kPa, 20.34% higher than the strength of untreated soil. The maximum deviator stress at shear failure is 142.73 kPa.

In-situ chemical oxidation is an important approach to remediate soils contaminated with persistent organic pollutants, e.g., polycyclic aromatic hydrocarbons (PAHs). However, massive oxidants are added into soils without an explicit model for predicting the redox potential (Eh) during soil remediation, and overdosed oxidants would pose secondary damage by disturbing soil organic matter and acidity. Here, a soil redox potential (Eh) model was first established to quantify the relationship among oxidation parameters, crucial soil properties, and pollutant elimination. The impacts of oxidant types and doses, soil pH, and soil organic carbon contents on soil Eh were systematically clarified in four commonly used oxidation systems (i.e., KMnO4, H2O2, fenton, and persulfate). The relative error of preliminary Eh model was increased from 48-62% to 4-16% after being modified with the soil texture and dissolved organic carbon, and this high accuracy was verified by 12 actual PAHs contaminated soils. Combining the discovered critical oxidation potential (COP) of PAHs, the moderate oxidation process could be regulated by the guidance of the soil Eh model in different soil conditions. Moreover, the product analysis revealed that the hydroxylation of PAHs occurred most frequently when the soil Eh reached their COP, providing a foundation for further microorganism remediation. These results provide a feasible strategy for selecting oxidants and controlling their doses toward moderate oxidation of contaminated soils, which will reduce the consumption of soil organic matter and protect the main structure and function of soil for future utilization. Environmental implications: This study provides a novel insight into the moderate chemical oxidation by the Eh model and largely reduces the secondary risks of excessive oxidation and oxidant residual in ISCO. The moderate oxidation of PAHs could be a first step to decrease their toxicity and increase their bioaccessibility, favoring the microbial degradation of PAHs. Controlling the soil Eh with the established model here could be a promising approach to couple moderate oxidation of organic contaminants with microbial degradation. Such an effective and green soil remediation will largely preserve the soil's functional structure and favor the subsequent utilization of remediated soil.

The study of the mechanical properties of frozen saline soil is one of the key issues in addressing the design of infrastructure in cold regions. This research focuses on the supersulfated saline soil of the Ningxia Yellow River Irrigation Area in China, conducting triaxial tests under negative temperatures (-5, -10, -15 degrees C, and - 20 degrees C) with varying water contents (12%, 16%, 20%). Based on fractional calculus theory and incorporating an exponential decay factor, this study proposes a novel fractional-order constitutive model for a unified description of the softening and hardening behaviors in frozen saline soil. The model treats frozen saline soil as a composite blend of ideal solids and ideal fluids in varying proportions, taking into account the material's inherent timedependency and non-linear stress-strain relationships. Finally, the validity of the model is verified by the calculated values of the model and the triaxial tests. The results indicate that, based on preliminary judgment, due to the presence of salt solutes, a large amount of liquid water remains in the supersulfated saline soil at temperatures ranging from 0 to -10 degrees C, forming an unstable state called warm frozen saline soil. The mechanical properties of frozen saline soil depend on the relative content of unfrozen water, ice crystals, and salt crystals and the formation of ice and salt crystals significantly enhances the strength of frozen saline soil. The computational results of the improved fractional constitutive model align well with experimental results, effectively describing the stress-strain relationship of frozen supersulfate saline soil. In the model, the parameter functions analogously to an elastic modulus and exhibits a linear relationship with temperature, and the parameter alpha characterizes the strain hardening of saline soil, while beta describes its softening behavior. The proposed fractional constitutive model, with only three parameters having clear physical significance, is convenient for practical engineering applications.

The nanoscale zerovalent iron (nZVI) was successfully modified with sulfidation and loaded by kaolin (K@SnZVI) for enhanced persulfate (PS) activation. K@S-nZVI was characterized by SEM-EDS, TEM, XPS, BET and XRD. The better degradation performance of BDE209 was in the following order: K@S-nZVI/PS> S-nZVI/PS> nZVI/PS> > systems without PS activation. The maximum removal of BDE209 was 88.32% under PS concentration of 0.2 mol/L, soil-water ratio of 1:2.5 and the molar ratio of K@S-nZVI/PS of 2:1. The reactive oxygen species in the K@S-nZVI/PS system were identified by EPR and quenching experiments as SO4- & sdot;,& sdot;OH,& sdot;O(2)(- )and the nonracial of 1 O2. SO4-& sdot; and & sdot;O-2(-) dominated the degradation of BDE209 and & sdot;OH and 1 O2 were involved. According to gas chromatography-mass spectrometer (GC-MS) and density functional theory (DFT) calculations, BDE209 could be degraded to BDE7 by gradual debromination and further degraded into Br- and short-chain acids by ring opening reaction of benzene ring. The coexistence of SO42-, Cl- , CO32-, NO3- and HA reduced the degradation of BDE209. The soil pH did not change significantly during the remediation process. At the beginning of remediation process, soil catalase activities were enhanced while phosphatase and urease activities were weakened but they all recovered finally, exhibiting less damage to microbial cells. The K@S-nZVI/PS system is expected to be practically applied to the remediation of BDE209 contaminated soil.