Leachate Composition Research Articles

Caesium and iodine release from spent mixed oxide fuels under repository relevant conditions: Initial leaching results

Autoclave leaching experiments are conducted on three well-characterised, irradiated, and cladded mixed oxide fuel-rod segments with burnups ranging from 29 GWd/tHM to 52 GWd/tHM to investigate the instant release fraction of fission gases and long-lived fission products and to assess the long-term fuel matrix corrosion. The segments are exposed to bicarbonate solutions as reference groundwater at neutral pH and a synthetic young cementitious water at pH 13.5 under reducing atmosphere (4 vol% H2 in Ar at 40 bar pressure), since 2018. The initial leaching results for the fission products caesium and iodine as representative elements of the instant release fraction were found to depend on the leachate composition as well as on the fuel burnup.Graphical abstract

Effect of solid waste landfill leachate contaminants on hydraulic conductivity of landfill liners.

Landfilling is one of the most widely used methods to reduce the impact on the environment and human health by ensuring the management of solid wastes. For the process in question to be called landfill, the landfill leachate must be controlled and liner impermeability conditions must be provided. For this reason, compacted clay liners (CCL) and geosynthetic clay liners (GCL) with very low hydraulic conductivity are often used as hydraulic barriers in landfills to prevent the risk of leachate mixing with groundwater. However, as a result of various interactions between leachate-clay liners, changes occur in the hydraulic conductivity of the liners. In this review, the change (increase/decrease) in the hydraulic conductivity of the landfill liners caused by the contaminants in the leachate composition and the mechanisms responsible for this change were examined. In addition, deficiencies in the literature on this subject were identified and directions for future studies were presented.

Evaluation of the phytotoxicity of landfill leachate treated with a Rotating Biological Reactor

ABSTRACT One of the major drawbacks of this final disposal technique is leachate production, which occurs due to the degradation of organic matter and rainwater percolation. The leachate composition is quite varied, with high organic load and various compounds that may be toxic to the environment. To reduce the polluting potential of the leachate, it must be subjected to an appropriate treatment. Biological treatments are widely used in the treatment of leachate, although these technologies have some drawbacks. As an alternative to conventional biological treatments, rotating biological reactors are used. The objective of this study was to determine the efficiency of a pilot scale rotating biological reactors in the removal of biochemical oxygen demand, chemical oxygen demand, and phosphorus from the landfill leachate. Effluent toxicity and rotating biological reactors's ability to remove this toxicity were also verified by calculating the germination index of lettuce (Lactuca sativa) and cucumber (Cucumis sativus) seeds. The reactor showed an average efficiency of 75.99% of biochemical oxygen demand removal, 33.53% of chemical oxygen demand removal, and 16.04% of phosphorus removal. In fact, the cucumber and lettuce seeds proved sensitive to the toxicity of the effluent. For crude leachate, the germination index values of lettuce and cucumber were 13.28 and 49.61%, respectively. In this study, rotating biological reactors obtained a good efficiency in the removal of toxicity from leachate. The germination index of the seeds for the treated effluent was 60.9% for lettuce and 82.49% for cucumber.

Exploratory analysis of the microbial community profile of the municipal solid waste leachate treatment system: A case study

Studies on the degradation dynamics of landfill leachate indicate that the microbial community profile is a valuable and sensitive tool for landfill monitoring programs. Although knowledge about the microbial community can improve the efficiency of leachate treatment systems, little is known about the microbial profile changes that occur throughout the leachate attenuation process. In the present work, an exploratory analysis of the microbial community profile of the MSW leachate treatment system in the municipality of Osório (Brazil) was conducted. In this way, a comprehensive analysis of chemical parameters, isotopic signature and microbial profile data were applied to monitor the changes in the structure of the microbial community throughout the leachate attenuation process and to describe the relationship between the microbial community structure and the attenuation of chemical and isotopic parameters. From data analysis, it was possible to assess the microbial community structure and relate it to the attenuation of chemical and isotopic parameters. Based on massive parallel 16S rRNA gene sequencing, it was possible to observe that each leachate treatment unit has a specific microbial consortium, reflecting the adaptation of different microorganisms to changes in leachate characteristics throughout treatment. From our results, we concluded that the structure of the microbial community is sensitive to the leachate composition and can be applied to study the municipal solid waste management system.

Temporal variation in leachate composition of a newly constructed landfill site in Lahore in context to environmental pollution and risks.

This study investigated the seasonal and temporal variations in the extent and source of physiochemical and toxic trace elements in the Lakhodair landfill site of Lahore, Pakistan. For this purpose, systematic composite samples were collected every month, consecutively for 1year, and analyzed for different physiochemical parameters and trace elements. The results of TDS, TSS, COD, NH3-N, BOD5, sulfate, sulfides, phenolic compounds, and oil and grease were higher than the national environmental quality standard (NEQs). The concentrations of trace elements, especially Mn (1.7mg/L) and Cd (0.05mg/L), were above the MPL, while Fe (14mg/L), Ni (1.6mg/L), and Zn (6.7mg/L) were also found higher than the NEQs in some samples. In Lakhodair leachates, the TDS, COD, NH3-N, BOD5, sulfides, and Cl- have high concentration coefficient (i.e., CC 3 to > 6), which falls in the category of considerable to high contamination and risk level, while the remaining parameters were in the category of low to moderate contamination (CC 1 to ≤ 3) and moderate risk. The lower BOD5/COD ratio (< 0.1) in spring and autumn seasons represents the active methanogenesis and anaerobic activities in the Lakhodair landfill site. The anaerobic and methanogenesis activities enhance the redox reaction as a result of CO2 emission, which increases the pH, TDS, COD, Cl-, BOD5, NH3-N, sulfides, and phenolic compounds in the leachate site. However, the lower concentrations of some trace elements in leachate may be because of an anaerobic process that may immobilize the trace elements. It is presumed that the trace elements in the Lakhodair landfill may be in a metastable state, which is difficult to leach out. It is hereby recommended that leachate produced in the Lakhodair landfill site should be handled carefully to limit the environmental and health implications.

A framework for identifying the host phases in Coal-derived fly ash

Harmful trace elements trapped in fly ash during coal combustion have the potential to be released to the environment. Characterizing the dominant host phases for environmentally important elements is necessary to control the impacts and develop sustainable industrial symbiosis. In this study, a synergistic framework including microcharacterization techniques and leaching tests was developed and assessed to identify the host phases in a pulverized coal fly ash. The Quantitative X-ray diffraction (QXRD) mainly identified the host phases for major elements (Al, Si, Ca, Fe), and characterized the glass phase oxide composition. Cluster analysis of elemental maps from scanning electron microscopy/ energy dispersive spectroscopy (SEM/EDS) was capable of effectively determining the host phases for trace elements (As, Mo, B, and Se). The results of column leaching tests detected the phases associated with surface (e.g., sodium- and potassium-sulfate salts) and those infused inside the glass matrix with delayed release. A geochemical model was built based on the QXRD and SEM/EDS results to analyze the leachate composition using minerals saturation indices and potential of sorption/desorption. A few host minerals for minor and trace elements such as carbonates for As and sulfide/organics for K were only detected by the sequential extraction method. By assessing the capabilities and limitations of selected techniques, the Integrating framework enabled identifying host phases for a wide range of major, minor, and trace elements in fly ash. Such methodology advances development of reactive transport models and predicting the long-term environmental impacts of combustion byproducts under various beneficial use scenarios.

Desorption and Migration Behavior of Beryllium from Contaminated Soils: Insights for Risk-Based Management.

Factors influencing the desorption, distribution, and vertical migration behavior of Be in contaminated soils are not fully understood. This study examined the desorption and migration of Be in a soil profile from a legacy radioactive waste disposal site using different batch leaching [monofilled waste extraction procedure (MWEP); synthetic precipitation leaching procedure (SPLP); simulated acid rain solution (SARS); and toxicity characteristic leaching procedure] and sequential leaching [community bureau of reference (BCR)] methods for insights relevant to the application of risk-based management. The results showed that Be desorption was higher in the presence of organic than the inorganic leachate composition (MWEP < SPLP < SARS < TCLP < BCR first-step). The desorption followed three diffusion control mechanisms, which resulted in three desorption rate constant estimates of 157, 87.1, and 40.4 Be/kg.h0.5, and the estimated desorption maximum was 556 μg/kg. The desorption process was, spontaneous (ΔG > 0), enthalpically and entropically influenced. Increasing the incubation period and heat treatment resulted in a decrease of Be desorption and migration. The soil clay content and pH were the primary factors influencing Be desorption, and the results suggested that Be was desorbed from metal oxyhydroxides and surfaces of silicates (e.g., reactive surfaces of clay minerals), organic matters, and soil pores. Because of high Kd values, the mobility of Be was limited, and no exceedances of ecological or human health risk index or guidelines were determined for the current contamination levels at the site. However, Be released from the waste trenches has the ongoing potential to increase Be concentration in the soil.

Vegetation changes as indicators of landfill leachate seepage locations: Case study

Landfills remain widely used for waste disposal, despite their negative impact on human health and environment. Adverse impact is mainly due to gas and leachate emissions. Leachates are liquids that are characterized by high variability in composition, high ammonia and chloride content, and presence of toxic and non-biodegradable compounds. In recent years there has been growing interest in issues related with the reactions of living organisms to pollution - biomonitoring. However, bioindicative methods are not fully used in landfill studies and are still rarely applied. The aim of this work is finding the relationship between the composition and leachate seepage points and determining the possibilities of their practical utilization for the assessment of the applied mineral sealing of landfill surfaces. Additionally, detailed analysis of leachate composition was made. The hypothesis is that some species indicating natural salinity will also indicate landfill sites with the occurrence of leachate seepage, which increase salinity. Physico-chemical analysis of the leachate were carried out. Moreover, vegetation assessment was conducted by phytocoenological relevés. The landfill has different habitats in places where leachate seepage is observed. The results indicate that the presence of leachates alters the plant species composition. The composition shows increasing representation of species tolerant to salinization and a decreasing share of glycophytes in leachate seepage points. Based on the relation of glycophytes to plant species tolerant to salinization, a work procedure and index of leachate vegetation were created, which provide a fast identification of leachate seepage points. The presented results confirm the diagnostic potential of plants for the assessment and location of leachate seepage points. The results may be applied in the reclamation works on landfills.

Sequential leaching of silicified Archaean carbonates: A Rb-Sr, Sm-Nd and Pb-Pb isotopic contribution to their tectonic-thermal history (Kaapvaal Craton, South Africa)

Sequential leaching was completed by successive interactions of ultra-pure H2O, HAc, HCl and HNO3 with silicified/carbonated Archaean whole rocks from Barberton Greenstone belt of South Africa. The purpose of this experiment was an identification of the minerals interacting with each reagent and, therefore, a detailed succession of isotopically dated tectonic-thermal episodes recorded in these minerals. The contents of the major, trace and rare-earth elemental, together with the Sr, Nd and Pb isotopic compositions of untreated, leachate and residue triplets allowed identification and analysis of various types of carbonates and sulfates mixed with insoluble silicates. The samples yield two overall geological age milestones at 2.9 ± 0.1 and 2.1 ± 0.1 Ga, as well as varied age values, some with large uncertainties. A further event at about 1.6 ± 0.1 Ga is suggested probably in relation with the emplacement of the Bushveld complex or of further intrusive complexes of the Kaapvaal Craton.While the basics of the different used isotopic systems can be considered to be similar, the Rb-Sr method appears to be the best suited to detail the studied rocks, especially their sensitive soluble minerals. The Sm-Nd method is less flexible because of its inherent need of widely ranging Sm/Nd ratios that depend on the mineral assemblage. In the case of the Rb-Sr ages well constrained by isochron arrays, more similar ages were obtained by tentatively called isotrends that consist in data points slightly scattered along the arrays giving higher uncertainties, especially with the Sm-Nd method. The fact that these isotrends gave similar ages in addition to those of the isochrons comforts the historic evolution of the studied material.These scatters most probably correspond to slight changes in the chemical characteristics of minerals leached by the successive reagents, but analytical uncertainties cannot be completely excluded, especially in the case of the HNO3 leaching step. Finally, the Pb-Pb method appears to be of a more limited application, possibly because of possible metal contamination of the host rocks, either during their evolution in a region characterized by metal-rich concentrations or more recently during discrete surficial to sub-surficial alteration/weathering processes. In terms of leaching efficiency, that with H2O removed expectedly the lowest amounts of soluble components followed by HNO3, the two efficient removers being dilute HAc and HCl. In turn, the obtained geochronological ages consolidate previously published ages that concentrate on post-depositional tectonic-thermal events within the Kaapvaal Craton during about 1.0 Ga. However, they also suggest some reconsideration for other ages of the literature.

Current Status and Trend of Landfill Technology -- Quantitative Analysis of Landfill Profiles Based on Histcite

Analyzing the development in China’s landfill technology research ranges from 1997 to 2020 at the aspects of chronological distribution, high-yield journals, high-yield research institutions and keyword hotspot through Histcite, which sets landfill relevant studies in Web of Science as statistical samples. The result indicates: 1) The engineering application of landfill has declined, but the interest in landfill academic research has increased per year. 2) Although China’s landfill technology is globally highly researched, the depth and recognition of research need to be further improved from the facets of cited times. 3) Landfill articles published in JOURNAL OF HAZARDOUS MATERIALS have the highest impact factor and better recognition. 4) Tongji University is the critical institute of landfill technology research. 5) The research hotspots in recent 24 years are leachate treatment methods, leachate composition analysis, landfill gas treatment and oxidation repair technology, etc.

Comparison of Landfill Leachate Properties by LPI and Phytotoxicity-A Case Study

The formation of leachate is one of the inevitable consequences associated with the operation of landfills. In addition to the study of physicochemical composition, toxicity is an important parameter taken into account, among others because of the need to subject leachate to treatment before discharge into the environment. The aim of this study was to determine the degree of leachate contamination using LPI and toxicity index. An analysis of the relationship between the toxic effect on plants and the calculated LPI values was also carried out to assess whether they could provide a measure of leachate toxicity when selecting a treatment method. The research conducted was to determine the degree of leachate contamination using LPI and toxicity index. An analysis of the relationship between the toxic effect on plants and the calculated LPI values was also carried out to assess whether they could provide a measure of leachate toxicity when selecting a treatment method. Calculated values of the leachate pollution index showed that leachates from selected Polish landfills are characterized by low and medium levels of LPI values. The variation in index values obtained was particularly evident between active and closed landfills and was related to the physicochemical composition of leachates. In closed landfills this value ranged from 7.4 to 11.1, while in active landfills from 12.9 to 15.9. The variation in index values obtained was particularly evident between active and inactive landfills and was related to the physicochemical composition of leachates. Phytotoxicity tests showed that leachate at low concentrations can promote plant growth. At higher concentrations (50 and 100%), leachates caused inhibition of root and shoot growth, which correlated with high LPI values. The results confirmed the relationship between the toxic effect on plants and the LPI values, so it can be considered as a reliable indicator of leachate toxicity.

Economic aspects of landfill leachate treatment using reverse osmosis membranes

Introduction. Landfill leachates contain highly concentrated organic products of waste degradation and mineral salts. Concentrations of organic matter demonstrate high COD values up to 5,000 mg/l, concentrations of ammonium ions reach 2,500 mg/l, while the total salt content may reach 15,000 mg/l. Two to three reverse osmosis treatment stages may be nee­ded to produce the water that meets effective regulations governing the composition of water discharged into the environment. Also, high salt content and COD values dramatically reduce the membrane capacity. The co-authors explored the use of nanofiltration membranes at the first stage of the leachate treatment in an effort to reduce membrane operation costs.&#x0D; Materials and methods. The experiments, conducted within the framework of this research undertaking, allowed to identify a change in the concentrations of contaminants, dissolved in the leachates of reverse osmosis and nanofiltration membranes, as well as the reduced capacity of membranes at each stage of treatment. The co-authors have studied the alternative methods that may ensure maximal reduction of the concentrate consumption in the process of leachate treatment. Principal dependencies, derived as a result of the research, enabled the co-authors to identify the concentrate consumption rates depending on the extent of treatment focused on ammonium ions. The co-authors describe the methodology employed to identify the area of membranes at each treatment stage depending on the leachate composition.&#x0D; Results. Calculations of operating costs are provided for three compositions of leachates, typical for the Moscow region, depending on the treatment methodology and further recovery of membrane concentrates.&#x0D; Conclusions. Nanofiltration membranes can be used at the first stage of the landfill leachate treatment in the case of high COD and salt content. The application of nanofiltration membranes allows to reduce the concentrate consumption rate and cut operating costs. A new technology is developed to split the concentrate into two flows: the flow that has a high organic matter content, and the flow that has a high content of mineral salts, sodium and ammonium chlorides in order to facilitate the recovery of the concentrate.

Geotechnical engineering and alternative aggregates, tailings

Originally geotechnical engineering is connected with ground with rock and soil environment, focused on geotechnical structures which are in interaction with ground, and therefore we often speak about construction on, with or in ground. However, during last decades, especially with increasing focus on environment protection, geotechnical engineering is dealing also with other materials, denoted as alternative aggregates. They are mostly a byproduct of mining or industrial activities for which a method of future use is being sought. Typical examples are fly ash, construction and demolition waste, slag and different tails from chemical treatment of target ores which have similar character as natural soil and are produced in large volumes. Therefore, there is legitimate question about their possible use in earth structures, preferably of transport engineering. If external circumstances (e.g. distance of origin from the place of use) are favourable, geotechnical engineering is focused on two basic aspects - on possible negative impact on environment due the chemical composition of leachate or on structural stability. If there is no opportunity for their further use we have to guarantee safe deposition. In this case we are speaking about earth structures of environmental engineering as tailing dams, spoil heaps, landfills and are responsible for their safety. The paper is therefore focused on three main problems: Utilization of alternative aggregates (e.g. large volume waste) in transport engineering; Problems of earth structures of environmental engineering, where large volume waste is stored, as e.g. tailing dams and Structural collapse of tails studied in micro scale in laboratory.

Leachate composition of lead and cadmium ions from solidified mortar mixed with Nanosilica

Soils contaminated with Cd and Pb ions are a great problem that affects human health and the environment. Intending to decrease the environmental risk. Solidification/ stabilization (S/S) is one of the commonly used and economic remediation technologies to treat contamination by heavy metals in soils compared with other remediation technology. To understand the leaching mechanism from the (S/S) process, the EPA Semi-dynamic Tank Leaching method 1315 and unconfined compressive strength test was carried out to test the effectiveness and performance of the solidification process of contaminated sands with Pb and Cd ions by using ordinary Portland Cement locally produced and nanomaterial. Tow mix designs were performed on the contaminated sands at three different pollution concentrations and three ratios of synthesized Nanosilica from rice husk as additive replacement of cement. The Nanosilica as-prepared has amorphas form, average diameter equal to 52.83 nm and surface area around 618 m2/g. This paper discusses the effects of Nanosilica on leaching contamination from solidifying samples and compressive strength. The leaching rate of lead and cadmium ions from the test specimens demonstrated the effectiveness of nanoparticles in reducing the release of contaminant. Diffusion studies from the S/S matrixes indicated low and very low mobility of lead and cadmium ions respectively. For all test specimens, the mean leachability index was found to be higher than 9.

Application of Electrocoagulation with a New Steel-Swarf-Based Electrode for the Removal of Heavy Metals and Total Coliforms from Sanitary Landfill Leachate

Sanitary landfill leachate (LL) composition varies according to climate variables variation, solid waste characteristics and composition, and landfill age. Leachate treatment is essentially carried out trough biological and physicochemical processes, which have showed variability in efficiency and appear a costly solution for the management authorities. Electrocoagulation (EC) seems a suitable solution for leachate treatment taking into account the characteristics of the liquor. One of the problems of EC is the electrode passivation, which affects the longevity of the process. One solution to this problem could be the replacement of the electrode by one made of recyclable material, which would make it possible to change it frequently and at a lower cost. The objective of the present work was to evaluate the removal of heavy metals (As, Ba, Cd, Cr, Cu, Fe, Pb, Mn, Ni, Se and Zn) and coliforms from a LL by EC using electrodes made from steel swarf (SfE) up to 8 h. Removal efficiencies of detected heavy metals were 51%(Cr), 59%(As), 71%(Cd), 72%(Zn), 92%(Ba), 95%(Ni) and &gt;99%(Pb). The microbial load of coliforms in leachate was reduced from 10.76 × 104 CFU/mL (raw leachate) to less than 1 CFU/mL (after treatment with SfE) (i.e., approximately 100% reduction). The use of SfE in EC of LL is very effective in removing heavy metals and coliforms and can be used as alternative treatment solution for such effluents.

Impacts of litter decay on organic leachate composition and reactivity

Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.

Effect of Na from the leachate of spent Li-ion batteries on the properties of resynthesized Li-ion battery cathodes

The explosion of spent Li-ion batteries (LIBs) during the LIB recycling process is often avoided by the discharging process where spent LIBs are soaked into NaCl solutions. Because Na can be incorporated into resynthesized cathode active materials, we synthesize LiNi0.8Co0.1Mn0.1O2 active materials with extra Na in the simulated coprecipitation solution whose composition was matched to the actual industrial leachate composition. The morphological, structural, and electrochemical properties of the active materials are investigated. The addition of Na does not affect the precursor particle growth during the coprecipitation and the resulting morphology of active materials. Structural analyses show that Na-containing active materials have a favorable environment for the diffusion of Li ions. Overall, Na from the leachate of spent LIBs could be incorporated into the resynthesized cathode active materials unless they are washed thoroughly. Although excessive Na affects the electrochemical properties of cathode active materials adversely, the residual Na after the thorough washing has a beneficial effect on cyclability and rate performance as confirmed by low charge transfer and surface film resistances and high Li ion coefficients.

The capacity of ion adsorption and purification for coniferous forests is stronger than that of broad-leaved forests

In the past few decades, industrialization has caused a large number of pollutants to be released into the atmosphere. Forest ecosystems play an important function in regulating the biogeochemistry and the circulation of metal ions pollutants. Forest ecosystems affect the absorption of pollutants and dissolution of nutrients from the atmosphere and vegetation canopy, thereby influencing the content and composition of forest floor leachate and soil solution. This study examined changes in acid anions (NO3−, SO42−, Cl−) and metal cations (K+, Ca2+, Na2+, Mg2+, Fe3+, Pb2+, Cu2+, Cd2+) in rainfall, throughfall, stemflow, and forest floor leachate for five different forests (Larix principis-rupprechtii, Picea wilsonii, Picea crassifolia, Betula platyphylla and Rhododendron communities). The results showed that the enrichment capacity of acid anions and metal cations in the vegetation canopy of the coniferous forests (L. principis-rupprechtii, P. wilsonii, P. crassifolia) was stronger than that of the broad-leaved forests (B. platyphylla and Rhododendron communities). The content of acid anions and metal cations in stemflow of coniferous forests were 3.7–5.6 times and 0–9.3 times higher than those of broad-leaved forests, respectively. Corresponding values in throughfall were 1–1.4 times and 0.3–2.4 times, respectively. The contents of NO3−, Cl−, K+, Mg2+, Fe3+, Pb2+, Cu2+, and Cd2+ in leachate filtered from the soil layers that are deepening gradually showed consistent decreasing trend for all the forest stands. In addition, NO3−, Cl−, K+, Mg2+, Fe3+, and Pb2+ were also concentrated in the topsoil, except for Cu2+ and Cd2+. Nevertheless, SO42− and Na+ were concentrated in the subsoil, whereas Ca2+ was concentrated in the upper soil layers. Soil organic carbon (SOC) and total nitrogen (TN) contents in coniferous forest stands were 20–37% and 34–63% higher than those in broad-leaved forest stands, respectively. This results also shown that the contents of OC and TN has a strong correlation with the content of partial metal cations in soil and litter, indicating that coniferous forest stands had stronger ion scavenging and adsorption capacity in soil layer and litter layer than broad-leaved forest stands. Therefore, L. principis-rupprechtii, P. wilsonii, P. crassifolia had higher air pollutant adsorption and soil pollution remediation capacities than the other two forests. Thus, we recommend planting coniferous tree species (L. principis-rupprechtii, P. wilsonii and P. crassifolia) for eco-rehabilitation and water purification to improve the ecological service function of forest ecosystems.

Lithium and chlorine isotopic constraints on fluid sources and evolution at the Luziyuan distal skarn Zn–Pb–Fe–(Cu) deposit, western Yunnan Province, China

The sources and temporal evolution of fluids related to distal skarn mineralization strongly influence the minerals that form, but remain poorly understood. In this study, we use the lithium and chlorine isotopic compositions of fluid-inclusion leachates (FIL) to elucidate the nature and evolution of fluids that formed the Luziyuan distal skarn Zn–Pb–Fe–(Cu) deposit, China. The δ7Li values of prograde skarn stage rhodonite FIL (+5.37‰–+7.31‰) are similar to those of typical magmatic fluid. The δ7Li values (+11.69‰–+12.54‰) of actinolite FIL are higher than those of rhodonite FIL; this is attributed to Rayleigh fractionation within a closed magmatic–hydrothermal system. It is inferred that up to 70% of fluid-borne Li is sequestered by hydrous minerals during retrograde skarn alteration, consistent with conclusions drawn from previous studies of fluid-inclusions. The δ7Li values of galena FIL (+9.78‰–+13.19‰), black sphalerite FIL (+11.62‰), and reddish-brown sphalerite (+10.44‰–+11.66‰) overlap with those of actinolite FIL, indicating that phase separation occurred during Zn–Pb mineralization at the Luziyuan deposit. The low δ7Li values of light-yellow sphalerite FIL (+6.75‰) and calcite FIL (+3.95‰–+6.49‰) record external fluid input, probably meteoric water. The positive δ37Cl values of rhodonite FIL (+1.82‰–+1.83‰) are consistent with those of magmatic fluids. However, the δ37Cl values of actinolite FIL (+0.49‰) are lower than those of rhodonite FIL, indicating that FIL within hydrous minerals might not record fluid sources reliably.

Environmental and geochemical characterization of alkaline mine wastes from Phalaborwa (Palabora) Complex, South Africa

A detailed characterization of alkaline tailing ponds and waste rock dumps from Phalaborwa Igneous Complex (PIC) South Africa, has been accomplished. The study goes beyond the environmental characterization of mining wastes, offering the first insight towards the recycling of the wastes as alkaline reagent to neutralize acid industrial wastewater. To achieve these aims, tailings and waste rocks were characterized using a combination of conventional, novel and modified Acid Rock Drainage (ARD) prediction methodologies, as well as South African leachate tests, sequential extractions and pseudo-total digestions. The scarcity of Fe-sulphide minerals and the abundance of alkaline minerals indicated that PIC wastes are not ARD producers. The highest neutralization potential was found in the carbonatite rocks and East tailing samples (range between 289 and 801 kg CaCO3 eq/t). According to the National Environmental Management Waste Act (59/2008) of South Africa, tailing ponds and waste rock dumps from PIC classify as non-hazardous (Type 3 waste). The sequential extractions showed that the different fractions from most of the samples would mostly release sulphate and non-toxic elements, such as Ca, Mg, Na and K, which might be a concern if leached in high concentration. In addition, relatively high concentrations of radionuclides, such as U and Th (average of 6.7 and 36.3 mg/kg, respectively) are present in the non-labile fraction of PIC wastes, while the leachable concentrations were always below 0.006 mg/L. Among PIC wastes, East tailing would be the best option as alkaline reagent to neutralize acid wastewater because of its high neutralization potential and non-harmful leachate composition. In general, this study exposes the shortcomings in mine waste characterization, particularly for alkaline mine wastes, and introduces the assessment of potential revalorization as a novel practice in mine waste characterization that, if extended as a regular practice, would facilitate a circular economy approach to the mining industry with its consequent economic and environmental benefits.