Source identification and migration fate of metal(loid)s in soil and groundwater from an abandoned Pb/Zn mine.

Understanding the spatial distribution, source identification, and migration fate of toxic metals is crucial for managing the potential risks associated with metal(loid)s in abandoned Pb/Zn mines. This study provides a comprehensive analysis of the heterogeneous characteristics, contamination sources, and migration fate of metal(loid)s in both mine soil and groundwater. The results reveal that the abandoned mine soil is primarily contaminated with As and Pb, whereas groundwater in the mining and smelting area is mainly contaminated with Pb. The concentrations of As and Pb in the soil reached a maximum of 37.5 mg/kg and 289 mg/kg, respectively, significantly exceeding the local background values of 13.6 mg/kg for As and 29 mg/kg for Pb. The sources of soil contamination were attributed to historical smelting activities (31.4 %) for As, Cd, Hg, and Sb, while Pb and Mn were primarily derived from the ore-deposited belt (21.5 %). Machine learning predictions indicate that the migration of As in the soil can extend up to six meters or more, predominantly influenced by the presence of grit and silt. As a significant source of groundwater contamination, both soil As and Cd can infiltrate the groundwater through convection or diffusion processes. In conclusion, it is imperative to address the long-term release of heterogeneous metal ores in the soil of abandoned mine sites, as this can severely deteriorate the quality of both soil and groundwater.

Pollution Risk Prediction for Cadmium in Soil from an Abandoned Mine Based on Random Forest Model.

It is highly uncertain as to the potential risk of toxic metal(loid)s in abandoned mine soil. In this study, random forest was used to predict the risk of cadmium pollution in the soils of an abandoned lead/zinc mine. The results showed that the random forest model is stable and precise for the pollution risk prediction of toxic metal(loid)s. The mean of Cd, Cu, Tl, Zn, and Pb was 6.02, 1.30, 1.18, 2.03, and 2.08 times higher than the soil background values of China, respectively, and their coefficients of variation were above 30%. As a case study, cadmium in the mine soil had "slope" hazard characteristics while the ore sorting area was the major source area of cadmium. The theoretical values of the random forest model are similar to the practical values for the ore sorting area, metallogenic belt, riparian zone, smelting area, hazardous waste landfill, and mining area. The potential risk of soil Cd in the ore sorting area, metallogenic belt, and riparian zone are extremely high. The tendency of pollution risk migrates significantly both from the ore sorting area to the smelting area and the mining area, and to the hazardous waste landfill. The correlation of soil pollution risk is significant between the mining area, the smelting area, and the riparian zone. The results suggested that the random forest model can effectively evaluate and predict the potential risk of the spatial heterogeneity of toxic metal(loid)s in abandoned mine soils.

Immobilization of Cd in the soil of mining areas by FeMn oxidizing bacteria.

Microorganisms are widely used in large-scale pollution remediation due to their rapid reproduction and low cost. In this study, bioremediation batch experiments and characterization methods were adopted to investigate the mechanism of FeMn oxidizing bacteria on the immobilization of Cd in mining soil. The results showed that the FeMn oxidizing bacteria successfully reduced 36.84 % of the extractable Cd in the soil. The exchangeable forms, carbonate-bound forms, and organic-bound forms of Cd in the soil decreased by 11.4 %, 8 %, and 7.4 %, respectively, due to the addition of FeMn oxidizing bacteria, while FeMn oxides-bound and residual forms of Cd increased by 19.3 % and 7.5 %, as compared to the control treatments. The bacteria promotes the formation of amorphous FeMn precipitates such as lepidocrocite and goethite, which have high adsorption capacity on soil Cd. The oxidation rates of Fe and Mn in the soil treated with the oxidizing bacteria reached 70.32 % and 63.15 %, respectively. Meanwhile, the FeMn oxidizing bacteria increased soil pH and decreased soil organic matter content, further decreasing the extractable Cd in the soil. The FeMn oxidizing bacteria have the potential to be used in large mining areas to assist in the immobilization of heavy metals.

The South China Sea is not a mini-Atlantic: plate-edge rifting vs intra-plate rifting.

The South China Sea, as 'a non-volcanic passive margin basin' in the Pacific, has often been considered as a small-scale analogue of the Atlantic. The recent ocean drilling in the northern South China Sea margin found, however, that the Iberian model of non-volcanic rifted margin from the Atlantic does not apply to the South China Sea. In this paper, we review a variety of rifted basins and propose to discriminate two types of rifting basins: plate-edge type such as the South China Sea and intra-plate type like the Atlantic. They not only differ from each other in structure, formation process, lifespan and geographic size, but also occur at different stages of the Wilson cycle. The intra-plate rifting occurred in the Mesozoic and gave rise to large oceans, whereas the plate-edge rifting took place mainly in the mid-Cenozoic, with three-quarters of the basins concentrated in the Western Pacific. As a member of the Western Pacific system of marginal seas, the South China Sea should be studied not in isolation on its origin and evolution, but in a systematic context to include also its neighboring counterparts.

Potential role of strike-slip faults in opening up the South China Sea.

Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea (SCS). We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian continent. Results of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the east. The hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore-offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early Cenozoic. It was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene (33/34 Ma). The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 Ma. The plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene.