Abandoned Mine Sites Research Articles

Optimal spatial arrangement of modules for large‐scale photovoltaic farms in complex topography

AbstractThe existing methods for determining the module arrangement in photovoltaic (PV) farms are considered insufficient as they are generally limited to the environment of flat ground without considering both physical and electrical factors. The orientations of PV modules may be very diverse when installed in places with complex topography, e.g. mountains and abandoned mine sites. Thus, the received irradiance by the modules is inconsistent directly results in current differences and hence leads to significant mismatch loss in the PV arrays. This paper proposes a solution to determine the most appropriate combination of tilts and orientations of PV modules as well as the arrangement of PV arrays. The complex topographies are fully considered to minimize the mismatch loss phenomenon, and hence the power generation degradation. The solution adopts a set of models, i.e. the irradiation model for the calculation of optimal module tilts and orientations, the shadow model for shadow effect analysis, and the mismatch model for mismatch condition analysis. A two‐layer multi‐objective optimization is implemented for the optimal arrangement. The proposed solution is assessed through the case study of a 30 MW PV farm. The result confirms the effectiveness of the proposed solution for the optimal spatial module placement.

Microbial Inoculants Modify the Functions of Resident Soil Microbes to Expedite the Field Restoration of the Abandoned Mine

ABSTRACTGlobal‐scale mining activities have had significant deleterious impacts on local ecosystems and the overall environment, which will necessitate robust restoration efforts. A practical approach includes combining microbial inoculants with the technology of external soil spray seeding. This approach holds the potential for sustainable abandoned mine site restoration by enhancing plant growth through the modulation of soil nutrients and microbial communities. Nonetheless, the detailed effects of microbial inoculants on specific aspects of soil microbial community functions and their complex interactions with plant growth remain underexplored, particularly in the context of restoration efforts. To bridge this gap, we performed a four‐year field study at an abandoned carbonate mine location, using metagenomic sequencing to evaluate the influence of microbial inoculants on soil microbial functionality. Our research revealed that introducing microbial inoculants greatly enhanced essential soil parameters and notably increased plant biomass. Additionally, these inoculants altered the functional gene makeup of the microbial community, significantly boosting the relative abundance of processes such as nitrogen fixation, nitrification, denitrification, assimilatory nitrate reduction (ANRA), dissimilatory nitrate reduction (DNRA), and organic phosphorus mineralization. Conversely, there was a decrease in the relative abundance of carbon degradation, phosphorus regulation, and transport processes. We observed strong correlations between the abundance of nitrogen and phosphorus cycles and plant biomass. Crucially, microbial inoculants affect plant biomass by initially altering soil properties and subsequently coordinating nitrogen and phosphorus cycles. These findings provide valuable insights into the role of microbial inoculants in mine site restoration and offer a theoretical foundation for their broader practical application.

Microbial Inoculants Drive Changes in Soil and Plant Microbiomes and Improve Plant Functions in Abandoned Mine Restoration.

The application of microbial inoculants holds promise for the sustainable restoration of abandoned mine sites by affecting soil nutrients and microbial communities. However, the responses of plant microbial communities to microbial inoculants in mine restoration remain largely unknown. To bridge this knowledge gap, we conducted a 4-year field experiment at an abandoned carbonate mine site to assess the impacts of microbial inoculants on the soil-plant microbiome. Our findings revealed that microbial inoculants significantly changed roots, fine root bacterial and fungal communities. Further, no significant correlations were observed between the soil-plant nutrient content (Z-score) and microbial alpha diversity. However, a significantly positive correlation was found between the relative abundance of the keystone ecological cluster (Module #1) and soil-plant nutrient content. The application of microbial inoculants also increased complexity, albeit decreased stability of plant microbiome networks, alongside a reduction in stochastic assembly. Conversely, they decreased the complexity but increased the stability of soil microbiome networks, accompanied by an increase in stochastic assembly. Notably, the number of specifically enriched microbiome functional traits of roots and root nodules under the microbial inoculant treatments surpassed that of the control. In summary, our findings underscored the potential of microbial inoculants to enhance soil-plant functionality at abandoned mine restoration sites.

Resource Valuation of Kalilingseng-Cave Manganese Mining Site as a Tourist Destination Using the Travel Cost Method

General Background: Kalilingseng Cave, a former Dutch-era manganese mine in Kulon Progo, has untapped potential for educational and cultural tourism. Specific Background: Despite its historical and aesthetic value, the cave remains underdeveloped as a tourist site, lacking comprehensive economic valuation. Knowledge Gap: Prior research has not addressed the cave's economic potential as a tourism destination, leaving a gap in understanding its full value. Aims: This study aims to evaluate the tourism potential of Kalilingseng Cave using SWOT analysis and estimate its economic value through the Travel Cost Method (TCM). Results: The SWOT analysis highlights the cave’s accessibility and proximity to public facilities. TCM results show an average WTP of IDR 67,000.00, with annual economic benefits of IDR 21,775,000.00. Novelty: This research uniquely integrates SWOT and TCM to assess the tourism potential of an abandoned mining site. Implications: Proper development could make Kalilingseng Cave a sustainable tourist destination, benefiting the local economy and supporting geotourism education. Highlights: Tourism Potential: Kalilingseng Cave's historical and aesthetic value positions it as an educational and geotourism destination. Economic Valuation: The Travel Cost Method reveals an annual benefit of IDR 21,775,000.00 from visitors, indicating potential for community development. SWOT Insights: The SWOT analysis highlights strengths like accessibility and opportunities for geotourism while addressing weaknesses such as poor air circulation and lack of official management. Keywords: Ex-Manganense Mining, Kalilingseng, SWOT, Travel Cost Method

Properties, Treatment and Resource Utilization of Bauxite Tailings: A Review

A substantial amount of bauxite tailings (BTs) at abandoned mine sites have been stored in waste reservoirs for long periods, leading to significant land occupation and environmental degradation. Although many studies of the resource utilization of BTs were conducted to address this challenge, there is still a lack of efforts to systematically review the state of the art in BTs. In the present paper, a systematic literature review was carried out to summarize and analyze the properties, treatment, and resource utilization of BTs. Physical characteristics and the mineral and chemical composition of BTs are introduced. The efficacy of physical, chemical, and microbial treatment methods for BTs in terms of dehydration are outlined, and their respective benefits and limitations are discussed. Moreover, the extraction process of valuable elements (e.g., Si, Al, Fe, Li, Na, Nd, etc.) from BTs is examined, and the diverse applications of BTs in adsorption materials, ceramic materials, cementitious materials, lightweight aggregates, foamed mixture lightweight soil, among others, are studied. Finally, an efficient and smart treatment strategy for BTs was proposed. The findings of the present review provide a scientific basis and reference for future research focusing on the treatment and resource utilization of BTs.

The Identification, Spatial Distribution, and Reconstruction Mode of Abandoned Mining Areas

The rehabilitation of abandoned mining sites is an increasingly pressing issue in the context of sustainable development. Recent research has emphasized the need for a holistic approach to the abandoned mining sites and their environmental rehabilitation. Based on field analysis, environmental assessments, satellite imagery processing and geographic information operations, this paper pushes forward the existing knowledge by conducting a comprehensive assessment of abandoned mining sites in the Romanian Carpathians and by proposing innovative and sustainable rehabilitation solutions. Our findings highlight that abandoned mining sites and their surrounding territories in the Romanian mountains have significant ecological imbalances and complex socio-economic issues. The findings also suggest that by adopting innovative, integrated, and sustainability-oriented approaches, territories affected by mining can be transformed into valuable and sustainable spaces to meet human needs. We conclude by presenting the importance of innovation in ecological reconstruction and spatial–functional reintegration of mining sites in mountain areas as a useful tool in making fair decisions, both in the context of implementing appropriate development policies as well as for the resilience and environmental sustainability of mining-affected mountain areas.

After-effects of a closed copper mine: detailed analysis of environmental impacts in soil and plant samples

In several countries around the world, abandoned mining sites are blighted by pollution from metal and metalloids. Generated by mining processes, toxic pollutants have lasting effects on the ecosystem. The study examined the environmental impact of waste from a copper mine that was operated by the Caucasus Copper Limited Company between 1905 and 1928, revised and commissioned by Etibank in 1936, and ceased operations 75 years ago. Soil and plant samples (needles of Scotch pine, Pinus sylvestris L.) were collected from five specific regions around the mine and the levels of potentially toxic elements (PTEs) were determined, including As, Zn, Pb, Cd, Ni, Mn, Cr, Cu, Al, and Fe. The data obtained were used to calculate the enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), ecological risk index (ERI), human health risk index (BCF), and plant enrichment factor (EFPlant). In soil samples, the average EF values of certain elements such as As (453), Cu (59.9), Pb (30.7), Zn (5.26) were detected at high levels. However, average Igeo values indicate high pollution levels for As (8.25), Cd (6.72), Cu (4.94), Pb (4.33) and Zn (2.42), indicating the existence of serious ecological risks in the affected areas. Additionally, the average CF values indicate serious pollution levels from heavy metals such as As (1605), Cd (584), Pb (99.4), Cu (81.9), and Zn (14.6), highlighting the extensive pollution situation resulting from mining activities. Meanwhile, average ERI values indicate that Cd, As, Cu, and Pb pose serious ecological risks in the study areas.These PTEs were found in high concentrations in the waste tail and dump. Furthermore, the analysis determined that there was enrichment for Mn, Cd, Al, Cu, Pb, and Fe elements in plant samples. These PTEs have the potential to spread more widely depending on seasonal conditions and local topography. This situation demonstrates the need to measure metal and metalloids concentrations at certain times, taking into account the potential for environmental pollution of surface runoff water and underground resources in areas with high drainage potential from acid mines, such as at the Kuvarshan mine tailings site.

Predicting potential pollutant release from waste rock at the abandoned Beck mine (Karelia, Russia) by equilibrium kinetic modeling

The Beck mine, located in the Republic of Karelia, Russia, is an abandoned mining site with significant potential for environmental contamination due to the presence of potential pollutants in its waste rocks. In this study, we investigated the chemical composition of mine waters and waste rocks and developed a theoretical model to understand waterrock interactions and the release of potential pollutants. Water samples collected from various locations on the Beck mine property were analyzed for chemical composition and showed low concentrations of total dissolved solids with pH values ranging from 6.42 to 7.74. The chemical composition of natural waters was determined by ICP-MS, ICP-AES, ion chromatography, potentiometric titration, and spectrophotometry. Equilibrium kinetic modeling was used to simulate water-rock interactions. The model predicted the concentrations of major and trace elements, demonstrating that dissolutionprecipitation and complexation are the primary mechanisms shaping the chemical composition of mine waters. The dynamics of dissolution-precipitation of Fe-containing minerals highlighted the importance of the duration of water-rock interaction, with stagnant mine waters exhibiting higher concentrations of heavy metals. In addition, the presence of dissolved organic matter played a critical role in the accumulation of iron and arsenic in the studied mine waters. Overall, this study highlights the utility of equilibrium kinetic modeling in understanding the behavior of heavy metals during water-rock interactions and provides valuable insights into the potential environmental impacts of abandoned mine sites such as the Beck mine.

Conceptualizations of Abandoned Mine Land Reclamation: A Case Study of the Daniel Boone National Forest

abstract: The Daniel Boone National Forest (DBNF) contains numerous abandoned mine sites left over from eastern Kentucky's history of coal mining, many of which are leaching contaminants into the environment. The United States Forest Service is acting to reclaim these sites to mitigate negative impacts. There are several other governmental and non-governmental actors in Appalachia with different conceptualizations of reclamation's purpose. This research examines the mine land reclamation process on a protected area within a region with a history of resource extraction and builds on previous work to understand different conceptualizations of abandoned mine land reclamation in Appalachia. Content analysis was conducted on DBNF project documentation, interviews, and documentation from state and federal agencies, and NGOs. These documents indicate that government entities tend to conceptualize reclamation and its purpose in a siloed manner. This research also reveals that non-governmental actors tend to conceptualize reclamation in a holistic manner but are less able to exert control over an area. The DBNF largely conceptualizes the purpose of reclamation as achieving ecosystem restoration but may benefit from working more closely with NGOs and adopting a similarly holistic approach. Opening a dialogue between these actors could help address the knowledge gap present at the DBNF's sites.

Integrating portable X-ray fluorescence site survey and ArcGIS models for rapid risk assessment and mitigation strategies at an abandoned arsenic mine site: a case study

ABSTRACT Australia’s metalliferous abandoned mine sites (MAMSs), pose tangible threats to the environment and human health. To address these concerns, our study utilised state-of-the-art handheld XRF technology to conduct a real-time assessment of the Mole River arsenic mine site. The data revealed notably elevated levels of arsenic and manganese, with the southeast corner of the site identified as a contaminant hotspot. We used a tiered risk assessment approach to compare the detected contaminant concentrations to the Australian health investigation levels (tier 1). This led us to a broader examination of erosion vulnerabilities and the potential migration of contaminants (tier 2). Further, a hydrological assessment (tier 3) identified significant erosion in southern regions, indicating the potential for contaminants to be transported off-site through surface water runoff to Sam’s Creek and Mole River. The proximity of a reservoir to these runoff pathways brought forth additional challenges, especially during heavy rainfall events. Subsequent laboratory analysis of water samples reinforced our findings, as they confirmed heightened arsenic concentrations in Mole River downstream, accentuating the potential risks to ecosystems and human health. By integrating the XRF contour map and erosion assessment with the RUSLE model, valuable insights are gained into critical hotspots with high contamination and erosion potential. By directing rehabilitation efforts towards critical hotspots, resources can be allocated more efficiently and cost-effectively.

Application of Euler and Werner deconvolution techniques in delineating tin deposit in Okeso area, Southwestern, Nigeria

The Okeso pegmatites field was evaluated using magnetic method within abandoned mining site close to the southeastern region of Ojoku area. The study aims to delineate, identify geological boundaries and determine depth of tin deposits in the area. The acquired magnetic data was enhanced with the combination of 3D Euler and Werner deconvolution methods. Five magnetic profiles were selected and carried out on the residual anomalies around the abandoned mine site at Okeso with three of the profile lines were in the NW-SE direction and two in the NE-SW direction. The residual magnetic anomalies showed the magnetic susceptibilities of ≤ 4.5118 × 10−3 nT in the ore bearing pegmatite within the basement rocks. Results from profiles of Werner deconvolution identified some shallow tectonic structures like fractures, pegmatites and faults which are capable of hosting metallic tin deposits. The depth to the magnetic source varies from a minimum to a maximum of 300 m to 1200 m below the subsurface in all selected profiles, suggesting the shallow nature of the magnetic source in the area. Additionally, the dip angle ranges from 5.60 to 81.20, potentially attributed to Pan-African shallow structures according to the contact model. Solutions obtained from the structural index of contact and dyke reveals the presence of dyke formation and boundaries which separate rocks from one another. The trend of the lineaments/ fractures which were likely established during the Pan-African orogeny is dominant in the NE-SW direction, conforms with the trends obtained for basement structures in previous studies. Depth range produced by 3D Euler deconvolution is from 50 - 1000 m for all the lineaments. This gives an insight of approximate depth range of all the lineaments/ fractures across the whole map in the study area unlike, Werner deconvolution which is profile biased. The identical signature from all profiles implies that the tin deposit is relatively uniform, extending to a great depth in the area. This represents economically viable quantity and makes it a worthy target for investors.

Application of Euler and Werner deconvolution techniques in delineating tin deposit in Okeso area, Southwestern, Nigeria

The Okeso pegmatites field was evaluated using magnetic method within abandoned mining site close to the southeastern region of Ojoku area. The study aims to delineate, identify geological boundaries and determine depth of tin deposits in the area. The acquired magnetic data was enhanced with the combination of 3D Euler and Werner deconvolution methods. Five magnetic profiles were selected and carried out on the residual anomalies around the abandoned mine site at Okeso with three of the profile lines were in the NW-SE direction and two in the NE-SW direction. The residual magnetic anomalies showed the magnetic susceptibilities of ≤ 4.5118 × 10−3 nT in the ore bearing pegmatite within the basement rocks. Results from profiles of Werner deconvolution identified some shallow tectonic structures like fractures, pegmatites and faults which are capable of hosting metallic tin deposits. The depth to the magnetic source varies from a minimum to a maximum of 300 m to 1200 m below the subsurface in all selected profiles, suggesting the shallow nature of the magnetic source in the area. Additionally, the dip angle ranges from 5.60 to 81.20, potentially attributed to Pan-African shallow structures according to the contact model. Solutions obtained from the structural index of contact and dyke reveals the presence of dyke formation and boundaries which separate rocks from one another. The trend of the lineaments/ fractures which were likely established during the Pan-African orogeny is dominant in the NE-SW direction, conforms with the trends obtained for basement structures in previous studies. Depth range produced by 3D Euler deconvolution is from 50 - 1000 m for all the lineaments. This gives an insight of approximate depth range of all the lineaments/ fractures across the whole map in the study area unlike, Werner deconvolution which is profile biased. The identical signature from all profiles implies that the tin deposit is relatively uniform, extending to a great depth in the area. This represents economically viable quantity and makes it a worthy target for investors.

Electrochemical Behavior of Natural Manganese Oxides: Transforming Mining Waste into Energy Storage Materials

The present research explores the potential of manganese oxide waste ore in energy storage applications, focusing on supercapacitors. The investigation assesses the electrochemical capabilities of natural manganese oxides obtained from the Drama region, which has been the main mining center of Greece for manganese ore, especially that of battery-grade quality. Samples were collected from abandoned mining sites in the Kato Nevrokopi area, Drama. The structure and composition of the manganese minerals were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical tests involved the preparation of electrodes using natural nsutite and heat-treated nsutite (hausmannite). Then, the designed electrodes were subjected to cyclic voltammetry tests and charge–discharge measurements. The hausmannite electrode exhibited a higher specific capacitance of 667 F/g at a current density of 0.2 A/g, and the electrode material retained 98.3% of its initial capacitance after 1000 cycles. This study provides new perspectives on simple and efficient methods for transforming natural nsutite material from mining waste to hausmannite with greater structural homogeneity and better electrochemical behavior.

Effect of hydrochar-doping on the performance of carbon felt as anodic electrode in microbial fuel cells.

In this study, the feasibility of using hydrochars as anodic doping materials in microbial fuel cells (MFCs) was investigated. The feedstock used for hydrochar synthesis was metal-polluted plant biomass from an abandoned mining site. The hydrochar obtained was activated by pyrolysis at 500 °C in N2 atmosphere. Under steady state conditions, the current exerted by the MFCs, as well as the cyclic voltammetry and polarization curves, showed that the activated hydrochar-doped anodes exhibited the best performance in terms of power and current density generation, 0.055 mW/cm2 and 0.15mA/cm2, respectively. These values were approximately 30% higher than those achieved with non-doped or doped with non-activated hydrochar anodes which can be explained by the highly graphitic carbonaceous structures obtained during the hydrochar activation that reduced the internal resistance of the system. These results suggest that the activated hydrochar materials could significantly enhance the electrochemical performance of bioelectrochemical systems. Moreover, this integration will not only enhance the energy generated by MFCs, but also valorize metal polluted plant biomass within the frame of the circular economy.

A multi-criteria decision framework to evaluate sustainable alternatives for repurposing of abandoned or closed surface coal mines

Surface coal mines, when abandoned or closed, pose significant environmental and socioeconomic challenges. Repurposing these sites is crucial for sustainable land use and responsible resource management. This study presents a comprehensive decision framework tailored to the Indian mining context, utilizing a hybrid approach combining the analytic hierarchy process (AHP) and technique for order preference by similarity to an ideal solution (TOPSIS) methodology. The proposed framework assesses and ranks alternative repurposing options by considering a multi-criteria evaluation, including ecological, economic, social, and regulatory factors. AHP is employed to determine the relative importance of these criteria, reflecting the unique priorities and perspectives of stakeholders involved in the repurposing process. TOPSIS then identifies the optimal alternatives based on their overall performance against the established criteria. This hybrid methodology contributes to informed decision-making in the sustainable repurposing of abandoned surface coal mines in India. It aids in identifying the most viable and environmentally responsible alternatives, promoting efficient land use and resource conservation while addressing the challenges associated with abandoned mine sites. The methodology’s applicability extends globally to industries facing similar repurposing challenges, facilitating the transition toward a more sustainable and responsible land reclamation and resource management approach. The methodology is implemented using real mine data and demonstrates the analysis for evaluation among multiple alternatives such as solar parks, fish farming, eco-resorts, forestry, and museums. In our study, eco-resorts show more promise based on the significant potential for local economic development, provision of local employment, long-term revenue generation, potential for upskilling local youth in management, gardening, construction, and animal husbandry, and serving as a site for exhibitions of various arts and crafts.

A biochar selection method for remediating heavy metal contaminated mine tailings

Approximately 390,000 abandoned mines across the US pose considerable, pervasive risks to human and environmental health; world-wide the problem is even greater. Lime, organic materials, and other amendments have been used to decrease metal bioavailability (e.g., Cd, Cu, Mn, Ni, Zn) in contaminated mine wastes and to promote plant community establishment for tailings stabilization. Biochar properties (e.g., alkaline pH, metal sorbing capabilities, available nutrients, improved soil water retention) make it a potential amendment for remediating metal contaminated mine tailings. A three-step procedure was developed to identify biochars that were most effective at reducing heavy metal availability, retaining metals, and subsequently selecting biochars for use in a soil amendment laboratory trial to ultimately be utilized in heavy metal contaminated mine land settings: Step (1) a synthetic precipitation leaching procedure extract of mine tailings was produced, representing potentially available metals, and used to identify metal removal properties of 28 different biochars (e.g., made from various feedstocks and pyrolysis or gasification conditions); Step (2) evaluate how well biochars retained previously sorbed metals; and Step (3) laboratory evaluation of the most promising biochars that removed and did not releases metals, applied at 0, 1, 2.5, and 5% (by wt) to mine tailings for reducing metal bioavailability. The reported methodology and results from this study could be used to quickly identify specific biochars and application rates to reduce mine tailings metal availability and aid in future remediation of abandoned mine sites globally.

Levels of rare earth elements on three abandoned mining sites of bauxite in southern Italy: A comparison between TXRF and ICP-MS

The essential utilization of rare earth elements (REEs) for the production of several electronic devices is making the demand for them being increased all the time. This extensive use of these elements has also increased concern about human and environmental health. Previous studies have shown that REE levels are higher in environmental samples near mining sites, and they are highly possible to be transferred to biota. In this study, REE levels were determined in environmental samples collected from three abandoned mining sites of bauxite (Gargano, Otranto, and Spinazzola) in the region of Puglia, Southern Italy. The samples were digested and analyzed by two different techniques, Total X-Ray Fluorescence (TXRF) and Inductively Coupled Plasma – Mass Spectroscopy (ICP-MS) to investigate which technique is the most suitable for analysis of the REE content in samples from abandoned mining sites of bauxite. Only 6 REEs could be detected by TXRF, while all REEs were detected in all the samples by ICP-MS. Spinazzola is the richest site and Ce the most abundant REE in all three regions. REE levels are correlated between the soil and biota samples in many cases, although the calculation of the bioconcentration factor showed that REEs are not bioaccumulative. ICP-MS seems to be a more suitable technique for analysis of the whole REE content in environmental samples from abandoned mining sites of bauxite.

Continuous In-woods Production of Biochar Using a Trailer-mounted Air Curtain Burner.

Fuel treatments and other forest restoration thinning practices aim to reduce wildfire risk while building forest resilience to drought, insects, and diseases and increasing aboveground carbon (C) sequestration. However, fuel treatments generate large amounts of unmerchantable woody biomass residues that are often burned in open piles, releasing significant quantities of greenhouse gases and particulates, and potentially damaging the soil beneath the pile. Air curtain burners offer a solution to mitigate these issues, helping to reduce smoke and particulates from burning operations, more fully burn biomass residues compared to pile burning, and eliminate the direct and intense fire contact that can harm soil beneath the slash pile. In an air curtain burner, burning takes place in a controlled environment. Smoke is contained and recirculated by the air curtain, and therefore burning can be conducted under a variety of climatic conditions (e.g.,wind, rain, snow), lengthening the burning season for disposal of slash material. The mobile pyrolysis unit that continuously creates biochar was specifically designed to dispose of residual woody biomass at log landings, green wood at landfills, or salvaged logged materials and create biochar in the process. This high-carbon biochar output can be used to enhance soil resilience by improving its chemical, physical, and biological properties and has potential applications in remediating contaminated soils, including those at abandoned mine sites. Here, we describe the general use of this equipment, appropriate siting, loading methods, quenching requirements, and lessons learned about operating this new technology.

Potentially Toxic Elements (PTEs) Dispersion in Alluvial Deposits from Abandoned Mining Sites

In the watersheds of abandoned mining districts, it is common to find remains of former facilities and waste dams on stream banks and slopes—a situation that results in the transport and accumulation of metal(loid)s in alluvial deposits. To analyze this problem, an area of the former mining district of Linares–La Carolina (southern Spain) was selected to evaluate the contents and distributions of Ag, As, Ba, Cu, and Pb as potentially toxic elements (PTEs) found in the mineral paragenesis. Specifically, this study focused on the Siles Stream, which runs through a sector where underground mining for the exploitation of galena veins generated abundant mining wastes, mainly waste rock and tailings. Thirty-four sediment samples from the stream bed of the Siles Stream and two sediment samples from the Guadiel River, of which it is a tributary, were analyzed. Floodplain sediments were sampled in the stream banks at the middle and lower reaches (11 samples), as well as the riverine soils developed at the mouth of the Siles Stream (22 samples). The analyzed samples presented high levels of PTEs, in most cases with values much higher than the generic reference levels established by European and regional legislation for PTEs in soils. In the case of Pb, the main metal mined in this district, contents of up to 27,074 mg·kg−1 were observed in the stream bed sediments. Very high concentrations of Pb also appeared in the floodplain sediments, with maximum values in the middle course of the stream, where the concentration reached 43,692 mg·kg−1. With respect to the sediments of the Guadiel river bed, the Pb content was 699 mg·kg−1 before the confluence with the stream and 2537 mg·kg−1 downstream, which clearly reflects the influence of the contributions from the Siles Stream. The enrichment factors (EFs) show that the sediments present a severe to very severe anthropogenic influence for Ag, As, Ba, Cu, and Pb. The geoaccumulation index (Igeo) indicates that the entire basin is extremely polluted by Pb, to which As and Ag are added in the middle course of the stream. The potential ecological risk index (RI) and pollution load index (PLI) based on the contamination factor (CF) suggested that metal loads far exceeded the reference values. Selective chemical extraction methods were used to assess the potential bioavailability of these elements in sediment and soil samples. The results showed high concentrations of Pb in the exchangeable fraction, which poses a significant ecological risk and potential human health risks.

Source Distribution and Ecological Risk Assessments of Heavy Metals from the Soils of Riruwai Mining Area, North-Western Nigeria

Mining is an important global economic driver, contributing to human civilization’s advancement and foreign exchange revenues. However, it causes significant environmental contamination, particularly in developing nations with inadequate waste management and ineffective mining legislation. In the present study, the source distribution and ecological risk of heavy metals (HMs) from the soils of the mining area around Riruwai town, northern Nigeria, were assessed. Soil samples were obtained from active and abandoned mining sites, farmlands, and control sites and were analyzed for physicochemical characteristics and HM contents. The measured concentrations of HMs were used to evaluate the source distribution and ecological risks. The study’s findings indicated that, with the exception of Mn, Hg, and Ni, all HM concentrations were above threshold levels in all sample locations aside from the control sites. The results of the correlation analysis showed that there was a significant correlation between the HMs, indicating that they came from comparable origins. Principal component analysis and hierarchical cluster analysis results indicated that As, Cr, Hg, Ni, and Zn might originate from similar anthropogenic sources, possibly mining activities, while Cd, Mn, and Pb might come from natural sources (parent material). Results of an ecological risk assessment revealed that the soils from active and abandoned mining sites were severely polluted by HMs. The degree of pollution has begun to extend onto farmland, signifying a critical need for adequate HM pollution control in the study area.