Heavy metal pollution in soils threatens food safety and human health. Calcium sulfate and ferric oxide are commonly used to immobilize heavy metals in soils. However, the spatial and temporal variations of the heavy metals’ bioavailability in soils regulated by a combined material of calcium sulfate and ferric oxide (CSF) remain unclear. In this work, two soil column experiments were conducted to investigate the spatial and temporal variations of CSF immobilized Cd, Pb, and As. In the horizontal soil column, the results showed that CSF’s immobilization range for Cd increased over time, and adding CSF in the center of the soil column decreased the concentrations of bioavailable Cd significantly, up to 8 cm away by day 100. The CSF immobilization effect on Pb and As only existed in the center of the soil column. The CSF’s immobilization depths for Cd and Pb in the vertical soil column increased over time and extended to 20 cm deep by day 100. However, the CSF’s immobilization depths for As only extended to between 5 and 10 cm deep after 100 days of incubation. Overall, the results from this study can serve as a guide to determine the CSF application frequency and spacing distance for the in-situ immobilization of heavy metals in soils.

The disposal and remediation of heavy metal (HM)-contaminated soil has become a difficult problem, and the high-temperature roasting process of ceramsite preparation was proposed to be an effective method to solve the problem. Ceramsite can be used as a multifunctional material in different scenarios. However, there are few research reports on the potential environmental risks of residual HMs in ceramsite produced from contaminated soil. In this study, two types of soil were calcined at temperatures of 200-1100ºC to prepare ceramsite. Special attention was paid to evaluating the stability of HMs in ceramsite. The results of the SPLP, TCLP, and DTPA tests showed that the HM leaching concentrations in ceramsite were more than 99% lower than those before roasting, which indicates that the environmental risk of HMs in ceramsite was significantly reduced. The HMs were solidified by high-temperature calcination, and this can be confirmed by chemical morphology, mineral morphology, and microscopic structure analysis. Long-term acid rain extraction experiments showed that the peak release of HMs in ceramsite occurs in the first three years and then decreases to an ideal level. This study is of great significance to assess the stability of HMs in ceramsite prepared using contaminated soil.

Natural attenuation is a potential way to reduce total petroleum hydrocarbons (TPH) contamination, but the microbial mechanisms that explain differences in attenuation performance between soil and groundwater remain unclear. In this study, field investigation and metagenomic analysis were conducted at a decommissioned refinery site with more than 20 years of operation. Over a four-year period, the average TPH degradation rate in the soil attenuation zone reached 307.7 ± 135.2 mg kg⁻¹ year⁻¹, whereas the groundwater attenuation group showed an average degradation rate of 5.2 ± 3.6 mg L⁻¹ year⁻¹. Metagenomic results showed that TPH attenuation in soil and groundwater was associated with two different microbial consortia adapted to local conditions. In soil, the attenuation zone was characterized by a possibly sessile and cooperative consortium dominated by Pseudomonadota and Actinomycetota, with Sphingomonas and Nocardioides as representative genera. The consortium showed broader amino acid metabolic potential (e.g., ko00250, ko00260, and ko00310) and a higher abundance of functions related to biofilm formation and quorum sensing, which may promote stable and surface-attached growth. In groundwater, the attenuation zone was characterized by a possibly motile and more specialized consortium dominated by Pseudomonadota, including Novosphingobium, Sphingorhabdus, and Tabrizicola. The consortium possessed a less complex catabolic network for TPHs and intermediates (e.g., ko01220/ko00621/ko00624; nahAc/catE/fadA/pcaD/atoB), coupled with stronger potential for motility and secretion. In both soil and groundwater, attenuation was associated with lower eukaryotic activity and enrichment of prokaryotic functions related to oxidative stress defenses and high-yield respiration. These results showed that natural attenuation of TPHs in soil and groundwater involved different microbial features, which could improve the evaluation of natural attenuation in heterogeneous environments.

In this work, three sulfur-iron materials (sulfide-modified nanoscale zerovalent iron (S-nZVI), ferrous sulfide (FeS), and pyrite (FeS₂)) were employed to enhance the Fenton process for naphthalene (NAP) degradation. The enhancement performance and mechanisms of S-nZVI, FeS, and FeS₂ were investigated and compared. The results showed that NAP removal was enhanced from 56.4% in the H₂O₂/Fe(II) system to 88.6%, 83.0%, and 89.1% with the addition of S-nZVI, FeS, and FeS₂, respectively. Three sulfur-iron materials could all reduce Fe(III) produced in aqueous solution, regenerate Fe(II), and slow down the precipitation of dissolved iron. In addition, the addition of sulfur-iron materials could promote the generation of hydroxyl radical (HO•), thus intensifying the degradation of NAP. The results of scavenging tests indicated that HO• was the dominant reactive oxygen species (ROS) for NAP removal, while superoxide radical (O₂⁻•) also participated. The effect of complex water matrices on NAP degradation was evaluated, showing that sulfur-iron material-enhanced techniques had a wide pH application range and had great tolerance to inorganic ions and humic acid. Moreover, NAP degradation intermediates and their toxicity were elucidated. Finally, the obvious removal of various pollutants in sulfur-iron material-enhanced systems demonstrated that these technologies could be used to remediate organic-polluted groundwater.

Rapid and rough economic development in southeastern China has led brownfields come to be big problems. In this study, heavy metal contaminated soil and sludge were used as raw materials for ceramsites making in a simulated calcination system. Different recipes of raw materials for ceramites making were estimated by physical properties, heavy metal releasing risk. The results suggested lightweight ceramsites obtained under the recipe of "30% municipal waste sludge and 70% contaminated soil" and "30% chemical sludge and 70% contaminated soil". Leaching amount of heavy metals decrease more than 80% after calcinated. However, releasing risk of heavy metal still exist both in the flue gas and ceramites.