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Schematic diagrams of laboratory and in situ column experiments. Schematic diagrams of laboratory and in situ column experiments.
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Hydrothermally altered rocks generated from underground/tunnel projects often produce acidic leachate and release heavy metals and toxic metalloids, such as arsenic (As). The adsorption layer and immobilization methods using natural adsorbents or immobilizer as reasonable countermeasures have been proposed. In this study, two sets of column experim...
Contexts in source publication
Context 1
... larger diameter of the columns was used in the in situ conditions to collect natural rainfall more effectively. The schematics of the two columns are illustrated in Figure 1. Crushed mudstone and the RS were packed in eight columns, four in the laboratory and four in situ. ...
Context 2
... on the comparison between the laboratory columns and the in situ columns, the oxidation of sulfide minerals in the rock samples, or weathering of the rock, is accelerated by the effects of higher temperature and lower water contents due to rainfall conditions. Figure 10 illustrates the relationship between As and SO 4 2− leaching concentrations in the leachate in cases of L-T1, I-T1, L-T2 and I-T2. Positive correlations were observed between As and SO 4 2− in I-T1 and I-T2. ...
Citations
... Specifically, K d is defined as the ratio of radionuclide concentration between two phases (rock barriers and groundwater) at equilibrium [25]. Investigating the transport behavior of radionuclides can be challenging due to various factors that affect adsorption performance, and experimental studies often require significant resources and effort [26]. Support vector regression (SVR) stands as a robust statistical learning method employed in data analysis and pattern recognition [27]. ...
A low- and intermediate-level radioactive waste repository contains various types of radionuclides and organic complexing agents. Their chemical interaction within the repository can lead to the formation of radionuclide-ligand complexes, influencing the limited retention behaviors of radionuclides. This study focuses on the sorption behavior of radionuclides on both engineered (concrete) and natural barriers (sedimentary rock and granite), as well as the prediction of sorption distribution coefficients (Kd) using support vector regression. Batch studies were conducted to determine the K d values for three radionuclides (99Tc, 137Cs, and 238U) under different conditions, including pH, temperature, and the presence of organic ligands (such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, and isosaccharinic acid). The K d values for 238U exhibited a sharp decrease with increasing concentrations of organic ligands. In contrast, the K d values for 99Tc showed only a slight reduction at higher organic ligand concentrations. Meanwhile, the K d values for 137Cs remained relatively unchanged, regardless of the type and initial concentration of organic ligands. This suggests a high level of retention for 137Cs in the rock samples. The support vector regression model with a radial basis kernel function proved effective in predicting the K d values under different experimental conditions. This enhancement in predicting accuracy contributes valuable insights into understanding the sorption processes involved in radionuclide behavior. Overall, this study advances our knowledge of radionuclide behavior on both engineered and natural barriers while providing a reliable prediction tool for estimating sorption distribution coefficients.
... The dissolution of sulfide minerals like pyrite could releases hazardous elements into the environment because this mineral is well-known to incorporate elements with similar chemical properties as Fe (e.g., Pb, Zn, Cd, Mn, and Cu) and S (e.g., As and Se) [27][28][29][30][31][32][33]. The AMD/ARD could be treated by neutralization reactions [34][35][36], sorption-precipitation [37][38][39][40], galvanic interactions [41][42][43], microbial and electrochemically mediated processes like ferrous oxidation to ferric ions [44][45][46] and metal-organic complexation reactions [47][48][49][50]. ...
“Affordable and clean energy” is enshrined in the UN Sustainable Development Goals (SDGs; #7) because of its importance in supporting the sustainable development of society. As an energy source, coal is widely used because it is abundant and its utilization for electricity and heat generation do not require complex infrastructures and technologies, which makes it ideal for the energy needs of low-income and developing countries. Coal is also essential in steel making (as coke) and cement production and will continue to be on high demand for the foreseeable future. However, coal is naturally found with impurities or gangue minerals like pyrite and quartz that could create by-products (e.g., ash) and various pollutants (e.g., CO2, NOX, SOX). To reduce the environmental impacts of coal during combustion, coal cleaning—a kind of pre-combustion clean coal technology—is essential. Gravity separation, a technique that separates particles based on their differences in density, is widely used in coal cleaning due to the simplicity of its operation, low cost, and high efficiency. In this paper, recent studies (from 2011 to 2020) related to gravity separation for coal cleaning were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 1864 articles were screened after removing duplicates, and after a thorough evaluation 189 articles were reviewed and summarized. Among of conventional separation techniques, dense medium separator (DMS), particularly dense medium cyclone (DMC), is the most popular technologies studied, which could be attributed to the growing challenges of cleaning/processing fine coal-bearing materials. In recent years, most of works focused on the development of dry-type gravity technologies for coal cleaning. Finally, gravity separation challenges and future applications to address problems in environmental pollution and mitigation, waste recycling and reprocessing, circular economy, and mineral processing are discussed.
... From an environmental perspective, the tailings are highly polluted and hazardous because they contain Cu and Zn at values higher than those found in soils (Cu: 0.3-395 mg/kg; Zn: 2.8-1396 mg/kg) and sedimentary rocks (Cu: 20-200 mg/kg; Zn: 34-1500 mg/kg) (Reimann et al., 2018;Tabelin et al., 2018). The tailings also contain Pb (22-48 mg/kg) and As (10-65 mg/kg) (Fig. 2c), but both elements were within soil background levels (As: 0.19-666 mg/kg; Pb: 1.6-1309 mg/kg) despite the presence of pyrite-a mineral well-documented to incorporate Pb and As within its crystal structure-in the tailings (Abraitis et al., 2004;Arima et al., 2021;Reimann et al., 2018). ...
Historical tailings storage facilities (TSFs) are either abandoned or sparsely rehabilitated promoting acid mine drainage (AMD) formation and heavy metal release. To sustainably manage these sites, a geochemical audit coupled with numerical simulation to predict AMD flow paths and heavy metal migration are valuable. In this study, a 40-year-old TSF in Hokkaido, Japan was investigated. Tailings in this historical TSF contain pyrite (FeS2) while its copper (Cu) and zinc (Zn) contents were 1400-6440 mg/kg and 2800-22,300 mg/kg, respectively. Copper and Zn were also easily released in leaching tests because they are partitioned with the exchangeable phase (29% of Zn; 15% of Cu) and oxidizable fraction (25% of Zn; 33% of Cu). Kinetic modeling results attributed AMD formation to the interactions of pyrite and soluble phases in the tailings with oxygenated groundwater, which is supported by the sequential extraction and leaching results. Calibrations of groundwater/AMD flow and solute transport in the 2D reactive transport model were successfully done using hydraulic heads measured on-site and leaching results, respectively. The model forecasted the quality of AMD to deteriorate with time and AMD formation to continue for 1000 years. It also predicted ~24% AMD flux reduction, including lower Zn release with time when recharge reduction interventions are implemented on-site.
... In 2019, almost 4.5 billion tons of CG was discharged in China. Waste CG occupies tremendous land and is also harmful to the environment [15][16][17]. A similar scenario is encountered in other countries [18,19]. ...
The main aim of this investigation is to develop backfill concrete including coal gangue and metakaolin to reduce solid waste. For this purpose, a total of 30 concrete mixtures were designed by the inclusion of 0%, 25%, 50%, 75% and 100% coal gangue as coarse aggregates and 0%, 10% and 20% metakaolin as binder at 0.55 and 0.45 water to cement ratios. The compressive strength was tested after 3, 7 and 28 days for a total of 90 samples. Meanwhile, the influences of coal gangue and metakaolin on the elastic modulus, ultrasonic pulse velocity, rebound number and open porosity were explored. Then, the relationship between physical and mechanical properties was revealed by design code expressions and empirical models. Furthermore, an extreme learning machine was developed to predict compressive strength by concrete mixtures. The results show that the inclusion of coal gangue results in a poor performance in physical and mechanical properties of concrete. However, the drawbacks of concrete containing coal gangue can be compensated by metakaolin. The predicted results of design code expressions and empirical models are closed to the experiment results, with a 10% error. In addition, the findings reveal that the extreme learning machine offers significant potential to predict the compressive strength of concrete with high precision.
An extensive volume of acid mine drainage (AMD) generated throughout the mining process has been widely regarded as one of the most catastrophic environmental problems. Surface water and groundwater impacted by pollution exhibit extreme low pH values and elevated sulfate and metal/metalloid concentrations, posing a serious threat to the production efficiency of enterprises, domestic water safety, and the ecological health of the basin. Over the recent years, a plethora of techniques has been developed to address the issue of AMD, encompassing nanofiltration membranes, lime neutralization, and carrier-microencapsulation. Nonetheless, these approaches often come with substantial financial implications and exhibit restricted long-term sustainability. Among the array of choices, the permeable reactive barrier (PRB) system emerges as a noteworthy passive remediation method for AMD. Distinguished by its modest construction expenses and enduring stability, this approach proves particularly well-suited for addressing the environmental challenges posed by abandoned mines. This study undertook a comprehensive evaluation of the PRB systems utilized in the remediation of AMD. Furthermore, it introduced the concept of low permeability barrier, derived from the realm of site-contaminated groundwater management. The strategies pertaining to the selection of materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, as well as the challenges and prospects inherent in barrier technology, are elaborated upon in this discourse.
