Migration Of Heavy Metals Research Articles

Effect of Polystyrene Microplastics on Pb(II) Adsorption onto a Loessial Soil (Sierozem) and Its Mechanism.

Microplastics (MPs) have received significant attention recently. However, their influence on soil heavy metal adsorption remains unclear. The effect of polystyrene (PS) MPs on the adsorption of Pb(II) onto a loessial soil (sierozem) was studied by batch experiments in single soil (S), soil with 1 mm PS (S-PS1), and soil with 100 μm PS (S-PS100) systems. The mechanisms of Pb(II) adsorption reduction were investigated. The adsorption of Pb(II) reached equilibrium within 12 h, and the pseudo-second-order model fitted the adsorption processes best. The Langmuir adsorption model provided a better fit to the isotherms, compared to the Freundlich one. The presence of PS decreased the level of adsorption of Pb(II). Larger PS particle size, dose, and fulvic acid (FA) concentration inhibited Pb(II) adsorption onto the soil. The solution pH value showed a positive correlation with the adsorption amount. The adsorption amounts (q e) of Pb(II) in binary metal systems (Cu-Pb and Cd-Pb) were lower than those in single Pb systems, indicating the competitive adsorption among the ions. The adsorption amount presented a trend of S > S-PS100 > S-PS1. The primary mechanism on which PS reduced the adsorption of Pb(II) was the "dilution effect" of MPs. Conclusively, the presence of MPs might elevate the availability of heavy metals by reducing the soil's adsorption capacity for them and then amplifying the risk of heavy metal contamination and migration.

The heterogeneous distribution of heavy metal(loid)s at a smelting site and its potential implication on groundwater

The downward migration of soil heavy metal(loid)s (HMs) at smelting sites poses a significant risk to groundwater. Therefore, it is requisite for pollution control to determine the pollution characteristics of soil HMs and their migration risks to groundwater. 198 soil samples collected from a Pb-Zn smelting site were classified into 6 clusters by self-organizing map (SOM) and K-means clustering. Cd, Zn, As, and Pb were identified as the characteristic contaminants of the site. The driving factors for the heterogeneous distribution of HMs have been validated through the implementation of K-means clustering and multiple-hits calculation. Using ultrafiltration extraction and microscopic analysis, the soil colloids were identified as crucial carriers facilitating the migration of HMs. Specifically, the colloidal fractions of Cd, Zn, and As, Pb in deep soil (3–4 m) accounted for 91 %, 78 %, 88 %, and 82 %, respectively, consistently surpassing those found in topsoil (0–0.5 m). It was primarily attributed to the strong affinity of HMs toward soil colloids (franklinite, PbS, and kaolinite) and dissolved organic matter (humic acids and protein). The research findings highlight the potential risk of colloidal HMs to groundwater contamination, providing valuable insights for the development of targeted management and remediation strategies.

The spatial distribution and source of heavy metals in soil-plant-atmosphere system in a large coal mining area

Due to the lack coupling analysis of heavy metals in soil-plant-atmosphere system, the migration and transformation of heavy metals remains unclear. In this study, 240 surface (0–20 cm) soil samples, 365 plant samples and 168 atmospheric dust samples were collected in a large coal mining area, in which selected heavy metals arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), plumbum (Pb), zinc (Zn) were analyzed, to elucidate the spatial distribution and source of heavy metals and their bioavailability. According to the results of ArcGIS mapping analysis, the distribution patterns of Cd, Cu, Pb, and Zn in the three media are similar, while the distribution characteristics of Cr and Ni are highly consistent. The factors contributing to these spatial distribution characteristics of heavy metals could be associated with human activities and the characteristics of the elements. Compared with the background value, Zn, Cr, Pb in soil, Zn, Cr, Cu in plants and Zn, Pb, Cu in atmospheric dust apparently accumulated. The geological accumulation pollution index (Igeo) shows that there exist mild to moderate levels of Cr and Cd pollution in soil, and mild to moderate levels of Cd, Cr, Pb, and Zn pollution in the air. The evaluation of potential risks of heavy metals showed moderate ecological hazards in soil and strong ecological hazards in atmospheric dust. The sources of heavy metals were assessed using principal component analysis (PCA), land use type, and spatial analysis. Anthropogenic factors are the main sources of heavy metal content. Coal-related industrial processes related to coal, sewage irrigation, the use of agricultural chemicals, and vehicle emissions may be anthropogenic sources of heavy metals.

Plant litter as a heavy metal migration strategy following application of sewage sludge to subtropical forest soils

The environmental risks of migration of heavy metals (HMs) following applications of sewage sludge (SS) to forest soils are garnering increased attention. Plant litter at the forest floor may modify HM migration pathways through impacts on soil aggregates and water/soil erosion; however, HM migration responses to plant litter are poorly understood. The aim of this study was to determine the effects of plant litter cover on HMs migration, and water and soil erosion following the application of SS to subtropical forest soils. Effects of addition of SS along and SS plus plant litter at 0.75 or 1.5 kg m−2 on the migration of cadmium, chromium, copper, nickel, lead, and zinc in surface runoff, soil interflow, and sediments were quantified across nine simulated rainfall events in a laboratory experiment and following natural intense rain events in a field experiment. Addition of SS elevated HM concentrations in surface runoff by 38.7 to 98.5 %, in soil interflow by 48.3 to 312.5 %, and in sediment by 28.5 to 149.4 %, and increased the production of sediment aggregates <0.05 mm that led to greater cumulative migrations of HMs in surface runoff and sediment; sediment accounted for 89.5 % of HM migrations. Addition of plant litter reduced cumulative migration of HMs by 87.1–97.27 %; however, the higher rate of plant litter led to a decrease in surface runoff and sediment yield, and an increase in soil interflow. Addition of plant litter shifted the main pathway of HM migration from sediment to surface runoff and soil interflow. The potential ecological HM risk index was “low” for each treatment. We found consistency in HM concentrations and migrations via surface runoff between the field and laboratory experiments. Overall, the addition of plant litter with SS mitigated soil erosion and reduced total migration of HMs, resulting in a 88.7–97.3 % decrease in the ecological risk index of the six HMs. We conclude that the addition of plant litter may provide a management strategy for the mitigation of HM risks to environmental safety for the disposal of SS in subtropical forest systems.

Effect of pH, Temperature, and Salinity Levels on Heavy Metal Fraction in Lake Sediments.

Heavy metals (HMs) in aquatic environments are characterized by high toxicity, a propensity for bioaccumulation, and non-degradability, and pose significant risks to biological communities. Previous studies of HMs in lakes have shown that the physical and chemical characteristics of the lake water may control both the migration of HMs in the sediments and the concentration of heavy metals in the lake water. In fact, the change in aquatic environments changes the heavy metal fraction in the sediment, which controls the release of HMs. In this paper, we investigated the effects of the pH, temperature, and salinity levels of overlying water on the chemical fraction of Cu and Zn in Wuliangsuhai Lake surface sediments. The results show that lower water pH and higher water salinity and temperature could increase Cu and Zn release from the sediment. An increase in pH led to changes in the speciation of solid fractions of Zn, namely increases in the residual fraction and decreases in the organic matter and sulfide, whereas acid-extractable and Fe-Mn oxide fractions remained largely the same. Increases in temperature and salinity led to opposite changes in the speciation of solid fractions, namely decreases in the residual fraction and increases in the organic matter and sulfide and Fe-Mn oxide fractions, whereas acid-extractable fractions remained largely the same. The effect of pH, temperature, and salinity on Cu fractions in the solids was much smaller. According to the ratio of the secondary phase to the primary phase (RSP), acidic, high-temperature, and high-salt conditions increase the release risks of Zn. Changes in water temperature have the greatest influence on the risk of Zn and Cu release from sediments, followed by the influence of salinity changes.

Leaching characteristics and environmental impact of heavy metals in tailings under rainfall conditions: A case study of an ion-adsorption rare earth mining area

Following ion-adsorption rare earth mining, the residual tailings experience considerable heavy metal contamination and gradually evolve into a pollution source. Therefore, the leaching characteristics and environmental impact of heavy metals in ion-adsorption rare earth tailings require immediate and thorough investigation. This study adopted batch and column experiments to investigate the leaching behaviour of heavy metals in tailings and assess the impact of tailings on paddy soil, thereby providing a scientific basis for environmental protection in mining areas. The results showed that Mn, Zn, and Pb contents were 431.67, 155.05, and 264.33 mg·kg−1, respectively, which were several times higher than their respective background values, thereby indicating significant heavy metal contamination in the tailings. The batch leaching experiment indicated that Mn and Pb were priority control heavy metals. Heavy metals were divided into fast and slow leaching stages. The Mn and Pb leaching concentrations far exceeded environmental limits. The DoseResp model perfectly fitted the leaching of all heavy metals from the tailings (R2 > 0.99). In conjunction with the findings of the column experiment and correlation analysis, the chemical form, rainfall pH, ammonia nitrogen, and mineral properties were identified as the primary factors controlling heavy metal release from tailings. Rainfall primarily caused heavy metal migration in the acid-extraction form from the tailings. The tailing leachate not only introduced heavy metals into the paddy soil but also caused the transformation of the chemical form of heavy metals in the paddy soil, further exacerbating the environmental risk posed by heavy metals. The study findings are significant for environmental conservation in mining areas and implementing environmentally friendly practices in rare earth mining.

Effect of hydrothermal temperature on the optical properties of hydrochar-derived dissolved organic matter and their interactions with copper (II)

Hydrothermal carbonization (HTC) has been regarded as a promising technique for turning wet biomass into hydrochar due to its low energy consumption, low exhaust gas emissions, etc. In addition, hydrochar is an important source of dissolved organic matter (DOM), which plays a crucial part in the migration and destiny of pollutants in the environmental medium. However, there are limited studies that focus on the factors that influence the formation of DOM in hydrochar, such as hydrothermal temperature. Therefore, the current study comprehensively characterized the optical properties of DOM within hydrochar derived from sawdust (HDOM) under different hydrothermal temperatures (150–300 °C) by Ultraviolet–visible (UV–Vis) and fluorescence spectroscopy, as well as its complexation characteristic with Cu(II). The findings revealed that the organic carbon content of HDOM reached a peak of 37.3 mg L−1 when the temperature rose to 240 °C and then decreased as the temperature increased. UV–Vis spectroscopy analysis showed that the absorption capacity of HDOM at 275 nm increases with temperature and reaches a maximum value at 240 °C, indicating that high temperature promotes the formation of monocyclic aromatic compounds. High temperature enhances the aromaticity, hydrophobicity, and humification degree of HDOM, thus improving its stability and aromaticity. The E3/E4 ratios are all greater than 3.5, confirming that the main component of HDOM is fulvic acid, which corresponds to 3D-EEM and Pearson's correlation coefficient analysis. The humification index (HIX) of HDOM increased with the rise in hydrothermal temperature (150–240 °C), as observed by the three-dimensional excitation-emission matrix spectroscopy (3D-EEMs). After reaching its peak at 240 °C, the HIX value gradually dropped in line with the trend of the DOC change. Moreover, the bioavailability (BIX) value of DOM was all high and greater than 1, indicating all the HDOM are readily bioavailable. Two microbial humic substances (C1 and C4), a humic-like substance (C2), and a protein-like substance (C3) were discovered in DOM by integrating 3D-EEMs with parallel factor analysis (PARAFAC). Their fluorescence intensity decreases as the Cu(II) concentration increases, indicating the formation of complexes with Cu(II). As the temperature rises, the binding ability of DOM and Cu(II) changes significantly, reaching the optimum at 300 °C. Meanwhile, the substance C2 has the strongest binding ability with Cu(II). This research emphasizes the significance of spectroscopy analysis in determining the evolution of hydrochar-derived DOM, the potential for heavy metal binding and migration, and its characteristics and features.Graphical

Tracing the vertical migration of exogenous cadmium in soil by seasonal freeze-thaw event using rare earth elements

Environmental behaviors of heavy metal in soil are strongly influenced by seasonal freeze-thaw events at the mid-high altitudes. However, the potential impact mechanisms of freeze-thaw cycles on the vertical migration of heavy metal are still poor understood. This study aimed to explore how exogenous cadmium (Cd) migrated and remained in soil during the in-situ seasonal freeze-thaw action using rare earth elements (REEs) as tracers. As a comparison, soil which was incubated in the controlled laboratory (25 °C) was employed. Although there was no statistically significant difference in the Cd levels of different soil depths under different treatments, the original aggregate sources of Cd in the 5–10 cm and 10–15 cm soil layers differed. From the distributions of REEs in soil profile, it can be known that Cd in the subsurface of field incubated soil was mainly from the breakdown of >0.50 mm aggregates, while it was mainly from the <0.106 mm aggregates for the laboratory incubated soil. Furthermore, the dissolved and colloidal Cd concentrations were 0.47 μg L−1 and 0.62 μg L−1 in the leachates from field incubated soil than those from control soil (0.21 μg L−1 and 0.43 μg L−1). Additionally, the colloid-associated Cd in the leachate under field condition was mainly from the breakdown of >0.25 mm aggregates and the direct migration of <0.106 mm aggregates, while it was the breakdown of >0.50 mm and the direct migration of <0.106 mm aggregates for the soil under laboratory condition. Our results for the first time provided insights into the fate of exogenous contaminants in seasonal frozen regions using the rare earth element tracing method.

Environmental Implications of the Soil-to-Groundwater Migration of Heavy Metals in Mining Area Hotspots

Groundwater contamination was studied at several hotspot sites in the Majdanpek copper mining area (Serbia). These sites include a milling facility, a metallurgical wastewater treatment plant, a heavy vehicle service area, and a waste disposal site. In addition to Cu, high concentrations of As and heavy metals (Cd and Pb) were detected in groundwater and soil at the same sampling points. Mining operations and heavy vehicle transport activities have been identified as the main sources of pollution. The migration of metals from soil to groundwater, expressed as a concentration ratio, were the highest for Co and the lowest for Mn. The environmental implications of groundwater pollution were studied using the heavy metal pollution index (HPI), Nemerov pollution index (NPI), hazard index (HI), and incremental lifetime cancer risk (ILCR). HPI and NPI show the high potential of groundwater to have adverse environmental effects. HPI ranges in the following descending order of metals: Cd &gt; Pb &gt; As &gt; Mn &gt; Ni &gt; Cr &gt; Hg &gt; Cu &gt; Zn. NPI exceeds the threshold of 0.7 in 66.7% of the samples. Potential human exposure to the studied groundwater may cause severe health problems in adults, with HI ranging from 0.61 to 5.45 and ILCR from 1.72 × 10−4 to 1.27 × 10−3. Children were more susceptible to non-carcinogenic risk than adults, with HI ranging from 0.95 to 8.27. However, the results indicated that children were less prone to carcinogenic risks, with ILCR ranging from 5.35 × 10−5 to 3.98 × 10−4. Arsenic is the most contributing element to both risks. This research imposes the need for enhanced groundwater monitoring at hotspots in the mining area and the adoption of remediation plans and measures.

Material flow analysis of heavy metals in large-scale cattle farms and ecological risk assessment of cattle manure application to fields

This study bridges the knowledge gap pertaining to the pathways of heavy metal accumulation and migration within the industrial chain of large-scale cattle farms. Two such farms in Shaanxi serve as a basis for our exploration into Zn, Cu, Cr, Pb, As, and Cd dynamics. Employing material flow analysis complemented by predictive models, we evaluate the potential ecological risks of arable soil from heavy metal influx via manure application. Our findings indicate that Zn and Cu predominate the heavy metal export from these operations, composing up to 60.00%–95.67% of their total content. Predictive models based on 2021 data reveal a potential increase in Cd soil concentration by 0.08 mg/kg by 2035, insinuating a reduced safe usage period for cattle manure at less than 50 years. Conversely, projections from 2022 data point towards a gradual Cu rise in soil, reaching risk threshold levels after 126 years. These outcomes inform limitations in cattle manure utilisation strategies, underscoring Cu and Cd content as key barriers. The study underscores the criticality of continuous heavy metal surveillance within farm by products to ensure environmental protection and sustainable agricultural practices.

Geoenvironmetal assessment of different types of cryolithic soils in Western Yakutia under the conditions of diamond-mining operations

The problems of geoenvironmental consequences of mining operations are especially acute in the arctic and subarctic regions, where the spread of permafrost significantly reduces the buffering capacity of landscapes. The article presents data on the content of heavy metals in the soil cover of the transient zone between the middle taiga and north taiga landscapes of Western Yakutia under the conditions of mining operations and assesses the resistance of different types of soils to heavy metals pollution. Field and laboratory works were carried out in August 2022. The heavy metals content was determined by atomic absorption spectrometry. Specialized software was used for analysis, such as MS Excel 2013, Statistica 12.0, and QGis 3.26.1. Calculation of organic forms of heavy metals in soil solutions was performed using the NICA-Donnan model. In the course of studies, the structure of the soil cover in the Nakyn kimberlite field in the conditions of the mining industrial complex operation was determined and a sketch map of the soil cover of the territory was compiled. The geochemical series of the studied heavy metals is as follows according to the degree of concentration of heavy metals in cryolithic soils: Pb &gt; Zn &gt; Ni &gt; Cu &gt; Cd &gt; As &gt; Hg. Positive correlations between humus and Cd, Pb, Zn, as well as the occurrence of synergism in the Pb–Cd, Zn–Pb, Zn–Cu pairs were revealed. The soils organic matter enhances migration of heavy metals. The man-made input of Ni and Zn in cryolithic soils will lead to increase of mobile fraction. Cd is more mobile in pale-yellow carbonate and cryogenic soils. The regional background level of heavy metals for these types of soils was calculated, which can be used in future works when the intensity of mining operations increases.

Improving the performance of iron-rich calcium sulfoaluminate cement from municipal solid waste incineration fly ash through diverse pretreatment approaches

The utilization of municipal solid waste incineration fly ash (MSWI-FA) is environmentally significant. In this study, MSWI-FA was pretreated using organic acid solution and CO2 microbubble carbonation washing. The pretreated MSWI-FAs were then used to produce Iron-rich calcium sulfoaluminate (IR-CSA) cement at different substitution rates (CFA) for various raw materials. The evolution of iron phase distribution, mineral composition, and hydration of IR-CSA cement were investigated, alongside heavy metal migration. The results showed that the MSWI-FA-based IR-CSA clinker had suitable mineralogical phases. However, gehlenite in MSWI-FA reduced CaO availability in the clinker formation reaction, hindering the involvement of Fe2O3 in the ye'elimite formation reaction. The calcination temperature was increased to facilitate clinker and iron phase formation in the case of high CFA levels. CO2 microbubble carbonation washing pretreatment of MSWI-FA, with which the IR-CSA clinker achieved suitable pH values and alkali content, facilitated the early growth and chained evolution of ettringite, resulting in a denser microstructure and lower cumulative hydration heat. Consequently, the compressive strength of MSWI-FA-based IR-CSA cement increased, with a maximum gain of 43.65 MPa. Chromium content in the residual form increased, and heavy metal leaching was well below standard limits. This approach provides a new perspective for the purification treatment of MSWI-FA and its high-value, large-scale recycling in low-carbon cement.

Effects of woodland slope on heavy metal migration via surface runoff, interflow, and sediments in sewage sludge application

Sewage sludge (SS) application to forest plantation soils as a fertilizer and/or soil amendment is increasingly adopted in plantation forest management. However, the potential risks of SS-derived heavy metals (HMs) remain a concern. Many factors, including woodland slope may affect the risks, but the understanding of this issue is limited. This research evaluated the HMs migration via surface runoff, interflow, and sediments when SS was applied in woodlands of varying slopes. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. These results indciate that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤ 0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.

Energy recoveries and heavy metal migration behaviors of different oily sludges treated by pyrolysis versus solvent extraction

The pyrolysis and trace element mitigation characteristics are investigated by contrast to solvent extraction for four oily sludges, including storage tank bottom sediment (OS-1), scum from a wastewater separator (OS-2), white-clay-adsorbed waste oil (OS-3), and settlings from wastewater treatment (OS-4). Slow pyrolysis at 700 °C generated a single oil phase for OS-1 and separate oil and aqueous phases for OS-2, OS-3 and OS-4. Up to 73.0–88.3 % of the total energy were recovered from OS-1, OS-2 and OS-3 in the oil phase with 19.9–77.1 % oil yield; however, the oil phase from OS-4 accounted for only 13.3 % of the total energy, while the aqueous product accounted for 68.0 % of the total energy. Quantification of 16 trace elements revealed that OS-2 and OS-4 had much higher contents of Cu/Zn/As/Se/Cd/Pb and Ni/Cu/Zn/Se/Cd contents than the average crustal abundances, respectively. Correlations between evaporation and extraction rates indicated that the mitigation behaviors of trace elements were related to their occurrence modes in different oily sludges. Except for Cd, As and Se, all other trace elements were enriched in the pyrolysis residues of the oily sludges. Ni in the pyrolysis residue of OS-4 posed a moderate potential ecological risk.

Iron Plaque: A Shield against Soil Contamination and Key to Sustainable Agriculture.

Soils play a dominant role in supporting the survival and growth of crops and they are also extremely important for human health and food safety. At present, the contamination of soil by heavy metals remains a globally concerning environmental issue that needs to be resolved. In the environment, iron plaque, naturally occurring on the root surface of wetland plants, is found to be equipped with an excellent ability at blocking the migration of heavy metals from soils to plants, which can be further developed as an environmentally friendly strategy for soil remediation to ensure food security. Because of its large surface-to-volume porous structure, iron plaque exhibits high binding affinity to heavy metals. Moreover, iron plaque can be seen as a reservoir to store nutrients to support the growth of plants. In this review, the formation process of iron plaque, the ecological role that iron plaque plays in the environment and the interaction between iron plaque, plants and microbes, are summarized.

Comparative study of iron and aluminium coagulants in conditioning sludge: Sludge dewatering performance, physicochemical properties, and risk of heavy metal migration

Inorganic coagulants are essential agents that can facilitate the sludge deep dewatering, but comprehensive comparative research of commonly used coagulants is lacking. The systematic comparison of six coagulants, including Ferric Chloride (FeCl3), Polymeric Ferrous Sulfate (PFS), Ferrous Sulfate (Fe2(SO4)3), Aluminium Chloride (AlCl3), Aluminium Sulfate (Al2(SO4)3), and Polymeric Aluminium Chloride (PAC) regarding their performance in conditioning sludge dewatering, physicochemical properties, the risk of heavy metals migration in sludge cake and the mechanism of sludge dewatering, was investigated. Within a dosage range of 20% dry solids (DS), the PFS and FeCl3 showed a better dewatering effect among the six coagulants, and the water content (Wc) of the sludge cake decreased from 81.2%±1.1% to 57.7%±1.0% and 59.2%±1.6%, respectively. There was a correlation between the pH, zeta potential, viscosity, and bound water content of the sludge and the Wc of the sludge cake during dewatering conditioned by six coagulants. However, there was no correlation between sludge particle size and Wc of the sludge cake. The PFS and FeCl3 reduced the protein content of tightly bound extracellular polymeric substances (TB-EPS) by 66.1% and 62.6%, respectively. Moreover, the iron coagulants significantly reduced the content of As, Cu, Ni, and Zn in the sludge cake, where the risk levels of As and Ni were largely weakened. The economic analysis shows that iron coagulants were more valuable than aluminium coagulants for engineering applications. Meanwhile, the dewatering mechanisms of the two types of coagulants were revealed. This study provides significant insights into the application of coagulants in engineering practice.

Study on Plant-blanket to reduce heavy metal migration caused by precipitation and to improve the soil environment of pyritic tailings

The increasing demand for mineral resources due to industrial development has led to significant tailings pollution during the mineral extraction process. In the southwestern region of China, a large amount of pyritic tailings containing pyrite cinder easily leaches heavy metals and other pollutants when exposed to precipitation, resulting in widespread soil contamination. Effective remediation methods are urgently needed to address this issue. This study utilized naturally occurring Plant-blanket formed by the symbiosis of moss and herbaceous plants on pyritic tailings as restoration material. Through leaching experiments and staining tracer techniques, the study investigated the ability of Plant-blanket to reduce the migration of heavy metals from pyrite cinder to soil under the influence of precipitation and its role in improving the soil environment. The results showed that within 12 h, the Plant-blanket could absorb water equivalent to 206.9 % of its own weight and had good water retention ability. It reduced the stained area ratio of soil horizontal and vertical profiles after precipitation leaching by a maximum of 76.08 % and 46.41 %, respectively, and improved the pH, cation exchange capacity (CEC), bulk density, and water content of soil at different depths. In addition, after being covered by Plant-blanket, the migration of Cd and Cu was reduced by a maximum of 44.35 % and 55.77 % respectively, and it increased the diversity and abundance of bacterial communities, promoting the recovery of soil microbial ecological functions. These findings indicate that Plant-blanket can regulate water and improve soil environment, and has certain control ability on the migration of Cd and Cu produced by pyritic tailings. Meanwhile, Plant-blanket plays an important role in improving the soil environment in mining areas and promoting ecosystem restoration, providing valuable reference for further exploration of ecological restoration of tailings.

Pollutant Emissions and Heavy Metal Migration in Co-Combustion of Sewage Sludge and Coal

The treatment of sewage sludge has become a global concern. Large amounts of sewage sludge can be disposed of by burning coal-mixed sludge. Thermogravimetric analysis and lab-scale combustion experiments in a drop tube furnace were utilized to study the combustion characteristics, pollutant emissions, and heavy metal migration during the co-combustion of coal and sewage sludge. The results showed that the blended fuels with a sewage sludge content less than 10 weight percent exhibited coal-like combustion characteristics. Additionally, the additional sewage sludge favored the ignition performance of blended fuels. When sewage sludge was added, the SO2 emissions rose to 76 mg/Nm3 under the 10% sludge condition—nearly three times higher than that of coal alone. While NOx emissions stayed mostly unchanged, HCl and HF emissions were very low. Meanwhile, Cr, Cu, and Ni migrated to the bottom ash, and their concentrations were all reduced with an increase in sewage sludge. Pb, Cd, Cr, Cu, Ni, and Hg migrated to the flue gas, mostly in the form of gaseous components. The results provide crucial information in the co-combustion of sewage sludge and coal, with implications in the development and improvement of large-scale, harmless, and resource-recovering techniques for waste sludge.

Treatment of landfill leachate by black soldier fly (Hermetia illucens L.) larvae and the changes of intestinal microbial community

Black soldier fly larvae (BSFL) (Hermetia illucens) are commonly used to treat organic waste. This work aims to evaluate the transformation effect, heavy metal migration, and alterations in the gut microbiota of BSFL in addition to treating landfill leachate (LL) with BSFL. We found that BSFL may grow in various landfill leachate concentrations without obvious toxicity and growth inhibition. In addition, the results indicated a significant increase in the content of ammonia nitrogen and the activity of urease and β-glucosidase (β-GC) in LL, increased from 2570.17 mg/L to 5853.67 mg/L, 1859.17 mg/(g·d) to 517,177.98 mg/(g·d), 313.73 μg/(g·h) to 441.91 μg/(g·h) respectively. Conversely, the content of total nitrogen (TN) and total organic carbon (TOC) decreased in LL, decreasing by 31.24% and 29.45% respectively. Heavy metals are accumulated in the leachate by the BSFL to differing degrees, the descending sequence of accumulation is Cd > As > Cu > Cr. As dropped by 26.0%, Cd increased by 22.6%, Cu reduced by 5.23%, and Cr increased by 317.1% in the remaining matrix. The concentration of heavy metals satisfies the organic fertilizers' limit index (NY/T1978). The diversity of intestinal microorganisms in BSFL decreased, from 2819 OTUs to 2338 OTUs, with Providencia and Morganella emerging as the core flora. The gene abundance of nitrogen metabolism in the microbiota increased significantly. The TOC, β-GC, and Copper (Cu) content in BSFL correlated significantly with the gut microbiota. In Summary, this study revealed the treatment effect of BSFL on LL, the migration of heavy metals, and changes in the intestinal microorganisms of BSFL. The content of heavy metals in BSFL was found to be much lower than the upper limit of feed protein raw materials, demonstrating that BSFL is a sustainable method to treat LL.

Effect of aluminosilicates on the release and form transformation of semi-volatile heavy metals during the combustion of hyperaccumulator plants

With the development of phytoremediation of heavy metals contaminated soils, the harmless disposal of hyperaccumulator plants has been imminent. In this study, the effects of typical aluminosilicates on the heavy metal migration during the combustion of ryegrass were compared. The addition of kaolin, montmorillonite, and γ-Al2O3 were all effective in solidifying Pb and Zn. As the combustion temperature increased, the toxicity of remaining Pb and Zn decreased. Compared to montmorillonite, kaolin was more effective in capturing Pb and Zn at 600–825 °C, and the remaining Pb and Zn were mainly in acid-soluble form. The large amount of alkali/alkaline earth metals will react with the Si/Al components to form various potassium feldspars and calcium silicates, thus inhibiting the solidification of heavy/alkali metals. However, the Si in montmorillonite was more effective in converting Pb and Zn into residual form than kaolin when faced with the competition solidification of alkali/alkaline earth metals, at which time the percentage of Pb and Zn in the residual form increased from 13.27% and 6.00% to 39.21% and 9.84%, respectively. This work provided a research perspective based on the solidification of heavy metals by Si component, which enables a more comprehensive analysis of the differences in heavy metals solidification by Si/Al-based minerals.