Distribution and transport of contaminants in soil through mining processes and its environmental impact and health hazard assessment: A review of the prospective solutions

Fissure channeling caused anomalous uranium concentration in groundwater downstream of a uranium mine tailings impoundment site

Widespread uranium mining resulted in large amounts of radioactive wastes. While impoundment has been commonly used to store U-laden wastes, information has been lacking on the secondary contamination potential. We conducted a field-scale study at a prototype uranium mine tailings impoundment site in China to understand the abnormally high concentrations (0.90-36.7 μg/L) of uranium recently observed in the downstream groundwater. Based on on-site hydrogeological measurements and modeling analysis, fracture channels were identified in the aquifer. To consider the fissure channeling flow in the solute transport modeling, a modified discrete-continuum coupled modeling approach was established, which considers the flow dynamics within both the matrix domain and the preferential flow through the main fractures. The model was not only able to simulate the observed uranium concentrations at various locations, but also to reveal the U release rate from the impoundment. Moreover, the contaminant transport modeling supported that the abnormal uranium concentrations were attributed to the channeling flow in the aquifer fractures, which was confirmed through geological analysis. In addition to valuable field data, this work offered an effective modeling approach for assessing contaminant transport through fissure channeling and the associated environmental impact of waste disposal facilities in complex hydrogeological settings.

A nitrogen and phosphorus enriched inorganic-organic hybrid material for electrochemical detection of selenium(iv) ions

A heteroatom (nitrogen and phosphorus) enriched pyridinic bridged inorganic-organic hybrid material (HPHM) was synthesized by polycondensing phosphonitrilic chloride trimer (PNC) and 2,6-diaminopyridine in DMSO at 140 °C. The synthesized material was used as an efficient electrode material for the electrochemical detection of selenium(iv) ions [Se(iv)] in aqueous solution. The HPHM electrode (active mass loading of 4.1 mg cm-2) achieves a detection range of 5-50 ppb at a deposition potential of -1.2 V and a deposition time of 170 s with a lower limit of detection (LOD) of 2.18 ppb. This LOD is significantly below the World Health Organization's (WHO) recommended maximum level for selenium in drinking water. Moreover, the electrode material maintains high selectivity for Se(iv) ions in the presence of various interfering ions and high sensitivity over 200 cycles with only a minimal (∼6.83%) decline in current density response. The higher Se(iv) ion detection capability is attributed to the strategic incorporation of nitrogen and phosphorus heteroatoms, enhancing the material's electrochemical properties.

Hematite tailings to high-purity silica: Mechanistic studies and life cycle assessment analysis

This study aimed to recover high-purity silica from hematite tailings (HTs) using superconducting high-gradient magnetic separation (S-HGMS) technology. This process involved converting silica into a silicone-rich concentrate and subsequently employing a fluorine-free mixed acid to leach the silicon-rich concentrate to remove impurities and achieve refinement and purification. The optimization of the S-HGMS process was conducted using the "Box-Behnken Design" method, resulting in the following optimal conditions: a pulp concentration of 50 g/L, a magnetic velocity ratio of 0.076 T s/m, and a pulp velocity of 500 mL/min. These conditions yielded a silica grade range of 61.905% in the HTs to 91.818% in the silicon-rich concentrate, with corresponding recovery rates of 53.031%. Under the optimized leaching process, this resulted in an increase in the silica content from 91.818% in the silicon-rich concentrate to 99.938% in high-purity silica. Additionally, by analyzing the production process of 1 kg of high-purity silica from HTs using the process LCA method, environmental hotspots were identified, and corresponding solutions were proposed. This approach is vital for efficient utilization of HTs as a resource. This process has low energy consumption and is environmentally friendly, enabling the reduction of hematite tailings. It has a wide range of applications and offers substantial economic benefits, rendering it a promising candidate for industrial applications.

Critical steps in the restoration of coal mine soils: Microbial-accelerated soil reconstruction

Soil reconstruction is a critical step in the restoration of environments affected by mining activities. This paper provides a comprehensive review of the significant role that microbial processes play in expediting soil structure formation, particularly within the context of mining environment restoration. Coal gangue and flotation tailings, despite their low carbon content and large production volumes, present potential substrates for soil reclamation. These coal-based solid waste materials can be utilized as substrates to produce high-quality soil and serve as an essential carbon source to enhance poor soil conditions. However, extracting active organic carbon components from coal-based solid waste presents a significant challenge due to its complex mineral composition. This article offers a thorough review of the soilization process of coal-based solid waste under the influence of microorganisms. It begins by briefly introducing the primary role of in situ microbial remediation technology in the soilization process. It then elaborates on various improvements to soil structure under the influence of microorganisms, including the enhancement of soil aggregate structure and soil nutrients. The article concludes with future recommendations aimed at improving the efficiency of soil reconstruction and restoration, reducing environmental risks, and promoting its application in complex environments. This will provide both theoretical and practical support for more effective environmental restoration strategies.

Unearthing Earth's secrets: Exploring the environmental legacy of contaminants in soil, water, and sediments

The Earth's history is documented in human civilizations, soil layers, river movement, and quiet sediments throughout millennia. This investigation explores the significant legacy of environmental toxins in these key planet components. Understanding how ancient activity shaped the terrain is crucial as mankind faces environmental issues. This interdisciplinary study uses environmental science, archaeology, and geology to uncover Earth's mysteries. It illuminates the dynamic processes that have built our globe by studying pollutants and soil, water, and sediments. This research follows human actions, both intentional and unintentional, from ancient civilizations through contemporary industrialization and their far-reaching effects. Environmental destiny examines how contaminants affect ecosystems and human health. This study of past contamination helps solve modern problems including pollution cleanup, sustainable land management, and water conservation. This review studies reminds us that our previous activities still affect the ecosystem in a society facing rapid urbanisation and industrialization. It emphasises the importance of environmental stewardship and provides a framework for making educated choices to reduce toxins in soil, water, and sediments. Discovery of Earth's secrets is not only a historical curiosity; it's a necessary step towards a sustainable and peaceful cohabitation with our home planet.

Synthesis of high-crystallinity Zeolite A from rare earth tailings: Investigating adsorption performance on typical pollutants in rare earth mines

The ecological restoration of rare earth mines and the management of rare earth tailings have consistently posed global challenges, constraining the development of the rare earth industry. In this study, Zeolite A is efficiently prepared from the tailings of an ion-type rare earth mine in the southern Jiangxi Province of China. The resulting Zeolite A boasts exceptional qualities, including high crystallinity, a substantial specific surface area, and robust thermal stability. The optimum conditions for Zeolite synthesis are experimental determination and the adsorption properties of Zeolite A for typical pollutants (Cd2+, Cu2+, NH4+, PO43- and F-) in rare earth mines. The synthesised Zeolite A material is found to have strong adsorption properties. The adsorption mechanism is mainly cation exchange, and the priority of adsorption of pollutants is Cu2+> Cd2+ > NH4+ > PO43- > F-. Notably, the sodium Zeolite A material synthesized at room temperature can be effectively recycled multiple times. In summary, we propose a method to synthesise low cost and high adsorption zeolites using rare earth tailings. This will facilitate the reduction of rare earth tailings and the rehabilitation of rare earth mines. Our method has great potential as a rehabilitation technology for rare earth mines.

Assessment of heavy metal distribution and bioaccumulation in soil and plants near coal mining areas: implications for environmental pollution and health risks

Monitoring heavy metals (HMs) across source distance and depth distribution near coal mining sites is essential for preventing environmental pollution and health risks. This study investigated the distribution of selected HMs, cadmium (Cd2+), chromium (Cr2+), copper (Cu2+), manganese (Mn2+), nickel (Ni2+), lead (Pb2+), and zinc (Zn2+), in soil samples collected from ten sites (S-1-S-10) at two different depths (0-15 and 15-30 cm) and distances of 50, 100, and 200 m from a mining source. Additionally, three plant species, Prosopis spp., Justicia spp., and wheat, were collected to assess HM bioavailability and leaf accumulation. Coal mine activities' impact on soil properties and their HM associations were also explored. Results reveal HM concentrations except for Cr2+ exceeding World Health Organization (WHO) limits. In surface soil, Cd2+ (58%), Cu2+ (93%), Mn2+ (68%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (88%) surpassed permissible limits. Subsurface soil also exhibited elevated Cd2+ (53%), Cu2+ (83%), Mn2+ (60%), Ni2+ (80%), Pb2+ (35%), and Zn2+ (77%). Plant species displayed varying HM levels, exceeding permissible limits, with average concentrations of 1.4, 1.34, 1.42, 4.1, 2.74, 2.0, and 1.98 mg kg-1 for Cd2+, Pb2+, Cr2+, Cu2+, Mn2+, Ni2+, and Zn2+, respectively. Bioaccumulation factors were highest in wheat, Prosopis spp., and Justicia spp. Source distance and depth distribution significantly influenced soil pH, electrical conductivity (EC), and soil organic carbon (SOC). Soil pH and EC increased with an increase in soil depth, while SOC decreased. Pearson correlation analysis revealed varying relationships between soil properties and HMs, showing a considerably negative correlation. Concentrations of HMs decreased with increasing depth and distance from mining activities, validated by regression analysis. Findings suggest crops from these soils may pose health risks for consumption.