Previous Article in Journal
Comparing the Long-Term Stability and Measurement Performance of a Self-Made Integrated Three-in-One Microsensor and Commercial Sensors for Heating, Ventilation, and Air Conditioning (HVAC) Applications
Previous Article in Special Issue
Removal of Cu and Pb in Contaminated Loess by Electrokinetic Remediation Using Novel Hydrogel Electrodes Coupled with Focusing Position Adjustment and Exchange Electrode
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Processes
Volume 13
Issue 10
10.3390/pr13103307
processes-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Assessing Soil and Water Pollution: A Case Study of an Abandoned Coal Mine for Remediation and Repurposing in Mpumalanga Province, South Africa

by
Nkanyiso Mlalazi
1,*,
Charles Mbohwa
2,
Shumani Ramuhaheli
1 and
Ngonidzashe Chimwani
3
1
Department of Mechanical, Bioresources & Biomedical Engineering, School of Engineering, University of South Africa, Roodepoort, Johannesburg 1709, South Africa
2
Department of Industrial Engineering, School of Engineering, University of South Africa, Roodepoort, Johannesburg 1709, South Africa
3
Department of Mining, Minerals and Geomatics Engineering, School of Engineering, University of South Africa, Roodepoort, Johannesburg 1709, South Africa
*
Author to whom correspondence should be addressed.
Processes 2025, 13(10), 3307; https://doi.org/10.3390/pr13103307 (registering DOI)
Submission received: 4 August 2025 / Revised: 27 August 2025 / Accepted: 28 August 2025 / Published: 15 October 2025
(This article belongs to the Special Issue Advances in Heavy Metal Contaminated Soil and Water Remediation)
Browse Figures
Versions Notes

Abstract

Despite South Africa’s robust environmental legislation governing the mining industry, abandoned coal mines persist as a significant environmental concern, largely due to some companies evading accountability. This study assesses the level of contamination at an abandoned coal mine site in Mpumalanga, South Africa, and proposes preliminary remediation strategies and potential site repurposing options. The analysis included measuring parameters such as pH, electrical conductivity (EC), sulphates (SO4), calcium (Ca), iron (Fe), manganese (Mn), magnesium (Mg), and lead (Pb) in both soil and water samples. Additionally, soil samples were analyzed for ammonia (NH3), while water samples were analyzed to determine total suspended solids (TSSs) and total dissolved solids (TDSs). The results revealed that soil samples exceeded prescribed thresholds for SO4 and Pb, according to Soil Screening Values 1 (SSV1) for protection of land and resources. Water samples also showed exceedances for several parameters, except for Mg and Pb, as per South African National Standards and guidelines. Water quality assessment using the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) yielded scores of 43.33 and 15.56, indicating poor quality for livestock watering and unsuitability for domestic use, respectively. These results suggest threatened water conditions, highlighting significant implications for human health and ecosystem. The study recommends a circular economy-driven approach to environmental remediation, where acid mine drainage is treated using passive systems like constructed wetlands, and phytomining is used to extract valuable metals or minerals. Invasive alien species are harvested and converted into compost, reducing waste and promoting sustainable land use. This approach not only restores the site but also generates economic opportunities through resource recovery, paving the way for sustainable post-mining land uses.

1. Introduction

Coal is a dominant energy source, contributing 27.1% of the global energy mix and ranking as the second-most-important energy source [1]. In South Africa, coal is a key strategic mineral, accounting for around 80% of the electricity produced in 2022 [2], while also directly employing 90,977 people [3] and supporting an estimated 170,000 indirect jobs [4]. Despite the benefits, coal mining comes with significant environmental and health costs. Although South Africa has robust environmental legislation, including the Mineral and Petroleum Resources Development Act (MPRDA), the National Environmental Management Act (NEMA), the National Water Act (NWA), and the National Environmental Management: Waste Act (NEM:WA), which aim to regulate and alleviate environmental effects of mining, the industry continues to pose significant environmental pollution [5].
The primary factor leading to uncontrollable pollution from mines is the issue of deserted mines and inadequate rehabilitation which result from the business rescue and winding-up processes, and non-compliance with regulatory requirements by some mining companies [6,7,8,9,10]. Furthermore, the government’s efforts to address the legacy of abandoned mines have been slow or lacking [11,12]. Consequently, substantial waste with potentially toxic elements and compounds, including heavy metals, are released into the environment, presenting serious threats to aquatic and terrestrial ecosystems, water resources, and public health due to its persistence and ability to bioaccumulate [13,14,15,16,17,18].
Coal mining activities alter soil physicochemical properties, structure, horizons, microorganisms, and nutrient cycles [19]. Elevated metal content in soil, exceeding local background levels and receptor tolerance, poses severe risks to public health, food safety, agricultural productivity, and ecosystem health [16,17,20]. In Mpumalanga Province, coal mining has caused substantial environmental degradation, with acid mine drainage (AMD) and contaminated runoff posing threats to water quality and ecosystem health [21,22]. Witbank (eMalahleni) is a notable example, with approximately 22 coal mines operating in the area [23]. A century of coal mining in Witbank coalfields has resulted in significant environmental, social, and health impacts [24]. Studies have shown that coal mining can contaminate rivers, posing risks to aquatic life and human well-being [25,26]. Thus, regular assessments of chemical, physical, and biological properties of rivers and their tributaries are crucial to understanding and mitigating these impacts [27].
Various water quality assessment tools and indices have been developed to evaluate the state of water in abandoned mines, rivers, and reservoirs. Notable indices include the Canadian Council of Ministers of the Environment Water Quality Index, as well as organic pollution, trace metal pollution, comprehensive pollution, and general water quality indices. These tools collectively provide a robust framework for assessing and managing water quality, as supported by recent studies [28,29,30]. Researchers have used these indices to investigate coal mining impacts on water resources [25], water contamination in rivers [29,31], dams [32], and lakes [33]. The concentration of heavy metals in soils impacted by mining and the bioaccumulation of these metals in plant samples were investigated by several researchers [13,34,35,36].
Existing research on abandoned mines in South Africa has largely overlooked the application of water quality assessment indices and the development of practical remediation plans. This study fills this gap by presenting a remediation plan that encompasses AMD treatment, soil remediation, and sustainable post-mining land use options, promoting a circular economy approach. This work seeks to answer the following research questions: (1) What is the extent of soil and water pollution at the abandoned coal mine site? (2) How does the water quality at the site compare to national and international standards? (3) What remediation strategies can be employed, to mitigate the impact of coal mining? It is hypothesized that the abandoned coal mine site exhibits significant levels of soil and water pollution, exceeding national and international standards, and that the water quality poses to human health and the environment.

2. Methodology

2.1. Study Area

The study site, spanning approximately 6.76 hectares, is located on portion 60 of the farm KwaGuqa 313 JS within the EMalahleni Local Municipality, Nkangala district municipality, Mpumalanga Province, South Africa. Specifically, it lies in the B11K quaternary catchment area, about 900 m west of the R544 tar road to Verena and 600 m north of the N4 highway. The site falls within the Eastern Highveld Grassland vegetation unit (Gm 12) of the Mesic Highveld Grassland Bioregion in the Grassland Biome. The site was previously utilized by the adjacent community for farming before mining activities commenced.
The study area falls within the summer rainfall region of Mpumalanga province which experiences a Highveld climate with pronounced seasonal variations. Temperatures range from −3 °C to 20 °C in winter and 12 °C to 29 °C in summer. The area receives most of its rainfall (about 91% of the annual total) during the wet season from October to April, with an average annual precipitation of 674 mm [37]. Frost is a regular occurrence, with 13 to 42 days of frost per year, particularly at higher elevations [38]. The study area’s geology and soils comprise predominantly red and yellow sandy soils formed on shales and sandstones of the Madzaringwe formation, which is part of the Karro Super Group Geology and soils [38]. The study area’s topography is generally flat with gentle slopes and shallow sandy terrain, featuring subdued relief [39]. Coal mining in the area primarily employs opencast mining methods due to the shallow depth of coal deposits [40]. Figure 1 shows the extent of the site under study.

2.2. Sampling and Analysis Techniques

Water and soil sampling points were strategically chosen to target potential pollution sources and areas of concern. Sampling of soil and water samples was performed on the same day.

2.2.1. Soil Sampling

The soil samples were strategically collected from the southern end of the site and near the stream to evaluate the chemical status and potential contamination caused by the abandoned mine. Five samples were extracted from 0 to 30 cm depth with a stainless-steel spade, which was cleaned between each use to prevent cross-contamination. Each sample consisted of triplicate subsamples collected within a 2 m radius, and each location’s GPS coordinates were recorded. The samples were packed in labelled polyethylene bags and transported to Environmental Pollution Laboratory (EPL), a South African National Accreditation System (SANAS) accredited laboratory within 24 h.

2.2.2. Surface Water Sampling

Samples of water were collected from four points: two within the abandoned coal mine and two from the adjacent stream. Grab sampling was employed, using a plastic bailer to collect water, which was then transferred to 1 L plastic bottles. To prevent contamination, water from each site was used to rinse the bailer prior to sampling. Each bottle was labelled with sample name, date, and time. Samples were collected during the day and transported to the EPL in Pretoria in a cooler box. The sampling points effectively represented the objectives of the study. Figure 2 shows the soil sampling locations and surface water sampling points within the surface water drainage system.

2.3. Analysis

Extraction and analysis of samples was performed at the EPL according to the National Environmental Management Waste Act (Act No 59 of 2008). EPL adheres to a rigorous quality assurance system, compliant with ISO/IEC 17025 standards [41]. It utilizes internationally validated calibration standards with external traceability to ensure accurate and high-quality data in every analysis. Table 1 below shows the methods and the instruments used by EPL in soil and water analysis.

2.4. Water Quality Assessment Index

Analyses were conducted according to the South African Bureau of Standards (SABS) methods. Water quality assessments were benchmarked against SANS 241: 2015 for drinking water and SA DWAF guidelines for livestock watering. The CCME Water Quality Index (CCME-WQI) was used to evaluate water pollution levels based on measured parameters, providing a simplified and trend-analyzable representation of water quality data, as outlined in Equation (1) [25].
C C M E − W Q I = 100 − F 1 2 + F 2 2 + F 3 2 1.732
where F1 denotes the number of variables which fail to meet their objectives, as defined in Equation (2).
F 1 = N u m b e r   o f   f a i l e d   v a r i a b l e s T o t a l   n u m b e r   o f   v a r i a b l e s × 100
F2 represents the number of individuals not meeting the objectives also known as the frequency.
F 2 = N u m b e r   o f   f a i l e d   t e s t s T o t a l   n u m b e r   o f   t e s t s × 100
F3, also referred to as amplitude, quantifies the extent to which objectives were not met and is calculated as follows:
If the test value should be less than the objective,
E x c u r s i o n i = F i a l e d   t e s t   v a l u e i O b j e c t i v e i − 1
If the test value should be greater than the objective,
E x c u r s i o n i = O b j e c t i v e i F i a l e d   t e s t   v a l u e i − 1
The degree of noncompliance is determined by calculating the normalized sum of excursions (nse) as shown in Equation (6)
n s e = ∑ i = 1 n e x c u r s i o n N u m b e r   o f   t e s t s
Thus,
F 3 = n s e 0.01 n s e + 0.01
If the CCME–WQI is from 0 to 25, the WQI is classified as unsuitable, while the ranges 26 to 50, 51 to 70, 71 to 90 and 91 to 100 are classified as very poor, poor, good and excellent, respectively [42].
All soil analysis and water quality analyses for surface water samples are represented as the mean.

3. Results and Discussion

3.1. Physico-Chemical Data: Soils

The physico-chemical data of the measured parameters for the soil are presented below in Table 2. All soil monitoring sites exhibited pH levels within the 3.5–5.0 range, characteristic of acidic conditions.
Acidic pH results from acid mine water formed by pyrite (FeS2) oxidation in coal [42]. Sulphates (SO4) are also generated abundantly through mining activities. Notably, SO4 concentrations at S4 and S5 exceeded the 2000 mg/L limit for soil screening value 1 (SSV1), (the soil quality standards that safeguard human health and ecosystems from toxic risks, considering multiple exposure routes and potential water contamination), coinciding with the highest electrical conductivity (EC) values at these sites. Ammonia (NH3) concentrations followed the order: S5 > S1 > S4 > S3 > S2.
S2 showed better soil quality parameters (lowest levels of (NH3), SO4, and EC, as well as a less acidic pH compared to the other samples, possibly due to its location or the absence of coal remnants and water drainage (which is acidic) in the sampling area. S5, located in a low-lying area near the stream, exhibited the most deteriorated soil quality parameters (highest NH3, SO4 and EC), likely due to the accumulation of contaminants transported by surface runoff, seepage, leaching, and gravity-driven transport from the abandoned mine. S5’s poses a high risk of contamination. S4 and S3 were obtained from stockpiled material, while S1 was sampled near the coal remnants. The high levels of SO4 and acidity in the soils may be attributed to AMD or oxidation of sulphide minerals in the soil [43]. The elevated NH3 levels could be linked to decomposition of organic matter (in S5) or contamination from nearby sources including the community [44]. These findings are consistent with previous studies, highlighting the environmental risks associated with abandoned coal mines and their impact on soil quality [45].
The element concentrations (mg/kg) ranged from 9373–58,497 for Fe, 43.70–67.82 for Mn, and 8.61–45.48 for Pb. Concentrations of Ca and Mg ranged from 225.70 to 4562.00 mg/kg and 73.43 to 164.40, respectively. Based on the South African guidelines, the concentrations of Pb in S4 and S5 were above the SSV1 standard. The average levels in this study area are higher than those reported in the Mpumalanga province rangeland in 2006 [46]. The high concentrations of Ca, Fe, Pb and Mg especially in S4 and S5 may be related to the acidic pH and high EC values observed at this site and their location within the study site in relation to the potential contaminant sources. Acidic conditions can lead to increased mobility and solubility of the metals, allowing them to be more easily transported and accumulated in the soil [47]. The high SO4 levels in S4 and S5 may also contribute to the elevated Ca, Fe, Pb and Mg concentrations, as SO4 can form complexes with these metals, increasing their mobility and bioavailability [48]. The fact that Sample 2 had the lowest concentrations of Ca, Mg, Pb and Fe may be related to its relatively less acidic pH, lower conductivity and its location relative to contaminants sources. This suggests that Sample 2 may be less impacted by the mining activities, resulting in lower levels of metal contamination [45].
The Pb content in the coal samples varies significantly, with levels in S1, S2, and S3 (13.83, 8.16, and 13.83 mg/kg, respectively) comparable to those in U.S. and Chinese coals (11 mg/kg and 15.1 mg/kg) [49,50], but higher than global averages for hard and low-rank coals (9.0 mg/kg and 6.6 mg/kg, respectively [51]. However, S4 and S5 exhibit significantly higher Pb contents (45.48 and 29.76 mg/kg, respectively), exceeding the worldwide mean. This suggests potential Pb enrichment or contamination in these samples, possibly related to the mining activities.
Our findings are consistent with existing research on the environmental impact of coal mining, which has reported elevated levels of metals in surrounding environments. For example, Akbar et al [13] found excessive levels of cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), and Pb, exceeding WHO limits. Similarly, Xiao et al [17] reported high concentrations of (Pb), Cd, (Ni), and Cu in soils near coal mining and processing sites over a 10-year period. While our study’s metal content averages were generally lower than those reported at the Greenside coal mine in Witbank, Mpumalanga [20], the pH levels at our site were more acidic. These findings collectively highlight the environmental concerns associated with coal mining activities.
Heavy metals (such as Pb) contamination in soil and materials left on the surface poses serious environmental and health risks owing to their bioaccumulation, toxicity, and potential release into the environment [52,53]. Soil pollution can harm organisms which dwell in the soil and their consumers, disrupting the ecosystem [54]. Soil microorganisms and vegetation are particularly vulnerable to pollution, and the initial risk (Ri) they face can have cascading impacts through the food web [55]. The conditions at the study site (low pH, high SO4 levels, and elevated Pb and Fe concentrations), particularly at S5, may favour the growth of certain alien invasive species that adapt to stressful conditions. Figure 3 below shows some of the alien and invasive species at the study site.
The presence of the invasive and alien plant species is a symptom of a highly modified ecosystem. The invasive species on the study site include Acacia mearnsii (black wattle), Eupatorium macrocephalum (Pom pom), Ipomoea purpurea (common morning glory, Solanum mauritianum (bug weed), Mirabilis jalapa (Four o’clock), Eucalyptus diversicolor (Karri), Pennisetum clandestinum (Kikuyu grass). Alien and invasive species pose a serious threat to native ecosystems, competing with and replacing indigenous plant species, leading to veld degradation, reduction in biodiversity, and alteration of ecosystem processes [56,57]. These invasive species can invade various habitats, including woodlands, waste areas, arable land, roadsides, riverbanks, and coastal dunes, outcompeting native vegetation and altering community composition and ecosystem function [58]. Species along watercourses can reduce stream flow, while species like kikuyu can crowd out desirable species, further exacerbating ecosystem degradation [59]. The alteration of ecosystems can have far-reaching impacts on livelihoods, food security, and cultural practices, emphasizing the need for effective management and control of invasive species.
The catchment’s water supply is substantially polluted by the river inflow, which in turn leads to severe sanitary and ecological problems [60,61]. The surface runoff can mobilize the heavy metals from spoil or refuse dumps, potentially contaminating subsurface soil and nearby water resources through leaching [62].

3.2. Physico-Chemical Data: Water

Generally, surface water monitoring sites show high levels of contamination. The assessed water quality data revealed that the surface water from all monitoring points exhibited some degree of contamination, likely linked to coal mining and associated activities. Largely, the site has acidic water, high EC, TDS, TSS and SO4 exceeding several monitoring standards as shown in Table 3 below. The pH, TSS, SO4, Fe and Mn at all the sampling points exceeded at least one of the standards. EC for W1 and W2 (the sampling points within the mine) were above the discharge and irrigation general standards. Additionally, the TDS for W1 and W2 exceeded the livestock watering and the domestic use SANAS guidelines. W3 and W4 surface water monitoring sites located within the tributary showed an improved water quality compared to W1 and W2.
The elevated concentrations of SO4, together with the low pH, are characteristic of AMD, a serious environmental issue related to coal mining [63]. The presence of oxygen, water, and acidophilic bacteria accelerates the AMD process, generating acidic runoff and facilitating heavy metal leaching. The resulting sulfuric acid can mobilize heavy metals like Mn, arsenic (As), nickel (Ni), chromium (Cr), and Pb from surrounding rocks, soil, and water, further contaminating the environment and posing significant ecological and health risks [64]. Although other heavy metals concentrations were beyond the scope of the present study, the analysis of samples at mine sites like the Greenside coal mine in Mpumalanga, as well as background concentrations has shown high concentrations of these heavy metals [20].
Mn concentrations in water samples exceeded the water standards although its concentractions decreased in the order W1 > W2 > W3 >W4. As distance increases from coal mines, the levels of potentially toxic elements and polycyclic aromatic hydrocarbons in plants and soil tend to decline. This trend aligns with various studies including Song et al. [65] and Yakovleva et al. [66], who demonstrated the impact of coal mining activities on environmental pollution and potential health risks in surrounding areas. This could be the reason for improved water quality on sample W3 and W4 further from the site. Moreover, the effect of dilution of the mine water with the stream water may have led to the observed results.
Fe concentrations also exceeded the standards; however, the concentrations were in the order W3 > W4 > W1 >W2. The stream water has high Fe concentrations compared to the water on the abandoned mine. This may be attributed to rapid pH neutralization as the AMD from the mine enters the stream, resulting in metal precipitation and deposition in the bottom sediments within the localized discharge area [67,68], especially for W3 where the effluent from the mine enters the tributary (Fe concentration is 7.73 mg/L) which decreased to 4.93 downstream at W4 due to dilution [68].
The findings from the CCME-WQI analysis further proved that the water quality for both livestock and domestic use is poor, with scores of 43.33 and 15.56, respectively. These figures translate to poor water quality for livestock watering and water that is unsuitable for domestic use. This shows that water quality at the sight is threatened. These findings are consistent with other research in Mpumalanga Province. Laisani and Jegede [69] also reported increased chemical pollution and siltation of water, streams and other water bodies due to increased sediment loads at various mining impacted locations. According to the Department of Water and Sanitation (Mpumalanga), rivers such as the Olifants River and Wilge River are heavily polluted due to mining and other human activities. Reports also indicate that abandoned mines are negatively affecting agricultural activities in areas like Kendal and Ogies due to land degradation, resulting in large sinkholes and burning coal. Mining activities can leave lasting environmental legacies, including soil pollution that impacts nutrient availability and microbial activity [70]. Even after mining operations cease, these sites can remain significant environmental liabilities, requiring ongoing monitoring and remediation efforts to mitigate their effects on ecosystems and human health.
Our findings on surface water quality indices align with Magagula et al.’s [25] study, which assessed water quality in the Middelburg area, also impacted by coal mining activities in Mpumalanga. Similar to their results, our study found that the surface water quality at the study site was compromised, with our assessment indicating poor quality for livestock watering and unsuitability for domestic use. Magagula et al.’s study reported surface water quality ranging from poor to fair, with some sites showing very poor water quality, particularly in summer seasons. Both studies highlight the need for proper water management systems to mitigate impacts on water resources.
Hasii and Gasii’s [21] investigation into the complex relationship between coal mining and water resources revealed that despite coal’s significant role in energy production, mining activities lead to water contamination, soil degradation, and chemical exposure. Their findings, consistent with observations in mining regions globally, underscore the importance of implementing effective strategies, best practices, and advanced water management techniques to mitigate these environmental impacts. This supports our assessment of water and soil quality, highlighting the need for preventive measures, particularly regarding acid mine drainage. Further, Simpson et al.’s [22] review highlights the pressing concerns in Mpumalanga Province, where coal mining threatens food security and strains water availability and quality. The province’s high-potential arable land and significant coal reserves create conflicting interests, leading to water quality deterioration from acid mine drainage and contaminated runoff. This assessment underscores the need for a holistic approach, considering the interconnectedness of energy, food, and water security. Our findings on soil and water quality in Mpumalanga support the need for a comprehensive remediation plan, integrated policy-making, and sustainable development strategies that balance competing interests and protect the province’s natural resources.

4. Opportunities for Remediation and Value-Added Benefits

Our findings reveal that abandoned mine waste is undergoing oxidation, generating AMD and resulting in elevated metal concentrations in both soil and water, which in turn promotes the proliferation of alien species. Given these concerns, a rehabilitation plan prioritizing sustainable development goals, and circular economy principles, aligning with potential end-use scenarios, is crucial. Adopting remediation or treatment approaches to neutralize acidity, curb metal leaching, and eliminate invasive alien species is an important step toward effective waste management and repurposing the land for potential end use. Figure 4 below shows the abandoned mined site and the features associated with it. The potential remediation plan is also presented as well as value-adding products.

4.1. AMD Treatment

AMD emanates from the mined area, as shown by the low pH values at W1-W4. While various AMD treatment technologies, single or combined, can be used to achieve effective treatment [71], passive treatment approaches for AMD are advantageous due to their reduced resource requirements and infrequent reagent additions [72]. Furthermore, these systems operate without power and require minimal maintenance, rendering them a cost-effective solution, particularly suitable for abandoned mine sites. Passive treatment systems utilize natural geochemical and biological processes to improve mine water quality by passing it through a controlled environment [73]. Abiotic passive treatments, such as open limestone channels and limestone leach beds, generate alkalinity to neutralize AMD and raise pH, promoting metal oxidation and precipitation [74]. However, the use of lime and limestone as prevalent reagents for AMD remediation is often hindered by the formation of sludge, which can lead to armouring on the reagent surface, thereby limiting dissolution and causing system clogging [75]. In contrast, biotic passive treatments, including bioreactors and wetlands, harness natural biological processes under anaerobic or aerobic conditions to neutralize AMD and precipitate contaminants like metals over time [74]. Ramla and Sheridan [76] demonstrated the use of indigenous South African grass, Hyparrhenia hirta, as an organic substrate for SO4-reducing bacteria, which led to the reduction of SO4 to sulphides. Constructed wetlands, which leverage neutralizing agents, plants, and organic substrates, can be a viable alternative for the study site as noted by [77]. Constructed wetlands effectively neutralize acidity, remove metals, and enhance microbial SO4 reduction, resulting in a treated effluent that can be reused for various purposes [77]. The constructed wetland approach, as an attractive approach, warrants further investigation to tailor it to the site’s specific conditions.

4.2. Remediation, Reclamation, and Restoration of the Soils

A typical mining-impacted site can be remediated in situ using various conventional physico-chemical techniques, including the isolation of soil and containment, vitrification, solidification and stabilization, soil flushing, and electrokinetic remediation [78]. These methods are often prohibitively expensive, damaging to soil structure, and harmful to microbial communities, rendering them unsustainable for large-scale use. In contrast, phytoremediation, which harnesses the power of plants and their associated microorganisms to remediate environmental pollutants, presents a more cost-effective and attractive alternative [79]. By leveraging soil amendments and agronomic practices, phytoremediation can remove, contain, or neutralize toxins [80]. According to Xie et al. [81], three key strategies for reclaiming abandoned mine lands include stabilizing surfaces to prevent erosion, containing toxic pollutants, and restoring the natural landscape. However, Mahar et al [53] advocates for the use of hyperaccumulator plant species for the phytoextraction of the metals. This does not only reduce the metal content in the environment, but the hyperaccumulator plant species can be harvested and combusted to obtain bio-ore [53]. Due to this value-added benefit with the phytoextraction, this strategy becomes a preferred strategy for the remediation of the abandoned mine.
Prior to implementing phytoremediation strategies at the study site, the study site can be divided into two distinct areas: (i) the riparian area and (ii) the remainder of the mine site. The riparian area must be protected from rehabilitation activities. Restoration of the riparian area, including eradicating invasive plant species should be performed through strategies that minimize soil disruption and erosion risk. This can be achieved through careful planning and execution, avoiding heavy machinery and extensive excavation in favour of more nuanced and soil-friendly techniques. The alien and invasive species can then be composted and repurposed as natural fertilizers to enrich the soil and improve its structure [82]. The ecosystem function and biodiversity must be restored in the riparian area by planting hyperaccumulator native plant species. Containerised plants may be used to reduce soil disturbance and promote health plant establishment. Existing pathways or trails to access the planting area must be used. Alternatively, access routes to the riparian area must be planned to minimize disturbances. Foot traffic in the riparian area must be limited to prevent soil compaction and damage to vegetation.
In the remainder of the mine site, coal remnants (marked as 2 on Figure 4) should be removed and can be used in domestic energy production. The residual coal poses a significant health and economic risk to nearby communities due to its susceptibility to spontaneous combustion [83,84].
Just like the riparian area, the remainder of the mine site the must be planted with fast-growing, indigenous hyperaccumulator plant species such as Berkheya coddii that can extract valuable metals. The benefits of recovering minerals and metals from mine wastes are multifaceted, including environmental mitigation, revenue generation, and supply of feedstock materials for industrial processes. By valorizing mine wastes, a circular economy can be promoted thereby achieving Sustainable Development Goals (SDGs) [85]. For instance, the Mn concentration in the water at the study site is high, presenting an opportunity to extract Mn, a metal crucial for steel alloying and electric vehicle battery production [86]. Notably, pyrite from the study site can be repurposed as a valuable feedstock for sulfuric acid production and iron (Fe) recovery [87]. However, metal recovery from mine wastes faces constraints such as low metal concentrations, limited accessibility, presence of hazardous elements like As, insufficient recovery technologies, and high reprocessing costs [88].
Grass species, such as vetiver grass, with deep roots and tolerance to elevated heavy metal concentrations, adaptability to different climatic conditions and a wide pH range, Mlalazi et al [89] can be planted on the slope (shown by number 2 on Figure 4). Vetiver grass is high in carbon sequestration and can also be harvested for bioenergy production [89]. Numerous benefits, such as improved water quality, reduced soil erosion, and enhanced ecosystem health and functionality, may be achieved. These outcomes will preserve natural resources, ultimately leading to a more sustainable environment for future generations [90,91]. Successfully rehabilitating the abandoned mine could increase arable land for farming, significantly contributing to global food security and helping to meet the needs of a growing population [92,93]. Moreover, the community can produce surplus food for selling, thereby increasing economic activity in the area and generating new income streams [94]. This is important, as the closure of the mine likely resulted in job losses and reduced economic activity, affecting the livelihoods of local residents who may have been previously employed in the mining industry, either on a permanent or temporary basis.

5. Conclusions

This study assessed the ecological risks created by abandoned coal mine in eMalahleni, Mpumalanga province, South Africa, by analyzing various parameters in water and soil samples. The analysis included pH, EC, SO4, Ca, Fe, Mg, Mn, and Pb concentrations, as well as NH3 in soil samples and TSS and TDS in water samples. It was shown that the mean concentrations of heavy metals in both water and soil samples exceeded local background levels. Notably, the Pb levels in the soil samples surpassed the South African guidelines for water source protection, which is dangerous to human and animal health. Furthermore, several water quality parameters, excluding Ca, Mg, and Pb, exceeded acceptable limits, highlighting potential environmental concerns. In conclusion, the abandoned coal mine site can be remediated and reclaimed through a combination of passive treatment approaches, such as constructed wetlands, and phytoremediation techniques. By leveraging natural geochemical and biological processes, acidity can be neutralized, metals can be removed, and microbial SO4 reduction can be promoted, ultimately producing a treated effluent suitable for various end-uses. Phytomining can also extract valuable metals, generate revenue and promote a circular economy. The remediation process can yield numerous environmental benefits such as improved water quality, reduced soil erosion, improved water quality, and ecosystem health. Further, rehabilitating the mined area can increase arable land for farming, contributing to global food security and generating new income streams for the local community. By adopting a sustainable and cost-effective approach, more sustainable environment for future generations can be created and the local economy can be supported.

Author Contributions

Conceptualization, N.M.; methodology, N.M.; software, N.M.; validation, N.M. and N.C.; formal analysis, N.M. and N.C.; investigation, N.M.; resources, N.M.; data curation, N.M.; writing—N.M., N.M. and N.C.; visualization, N.M. and N.C.; supervision, C.M. and S.R. project administration, N.M.; funding acquisition, N.M. All authors have read and agreed to the published version of the manuscript.

Funding

The APC was funded by the University of South Africa. Analysis of the samples was funded by Procon Environmental Technologies.

Data Availability Statement

The laboratory results are available on request.

Conflicts of Interest

The laboratory analysis was funded by Procon Laboratory Technologies. The authors declare no conflicts of interest.

References

  1. Zocche, J.J.; Sehn, L.M.; Pillon, J.G.; Schneider, C.H.; Olivo, E.F.; Raupp-Pereira, F. Technosols in coal mining areas: Viability of combined use of agro-industry waste and synthetic gypsum in the restoration of areas degraded. Clean. Eng. Technol. 2023, 13, 100618. [Google Scholar] [CrossRef]
  2. Pierce, W.; le Roux, M. Statistics of Utility-Scale Power Generation in South Africa; CSIR Energy Centre: Pretoria, South Africa. 2023. Available online: https://researchspace.csir.co.za/dspace/bitstream/handle/10204/12067/Statistics_of_utility-scale_powergeneration_in_South_Africa_ (accessed on 23 April 2025).
  3. Minerals Council South Africa. Facts & Figures Pocketbook 2022; Minerals Council South Africa: Johannesburg, South Africa, 2023. [Google Scholar]
  4. Chamber of Mines of South Africa. National Coal Strategy for South Africa 2018; Minerals Council South Africa: Johannesburg, South Africa, 2018; Available online: https://www.mineralscouncil.org.za/downloads?task=download.send&id=535&catid=22&m=0 (accessed on 23 June 2025).
  5. Hassan, A.S. Coal mining and environmental sustainability in South Africa: Do institutions matter? Environ. Sci. Pollut. Res. 2023, 30, 20431–20449. [Google Scholar] [CrossRef]
  6. Almano, Z. The Rehabilitation and Closure of Mines: A Failure in the Protection of Human Rights; Mineral Law in Africa; University of Cape Town: Cape Town, South Africa, 2022. [Google Scholar]
  7. Mpanza, M.; Adam, E.; Moolla, R. A critical review of the impact of South Africa’s mine closure policy and the winding-up process of mining companies. J. Transdiscipl. Res. South. Afr. 2021, 17, 21. [Google Scholar]
  8. Mpanza, M.; Adam, E.; Moolla, R. Dust deposition impacts at a liquidated gold mine village: Gauteng province in South Africa. Int. J. Environ. Res. Public Health 2020, 17, 4929. [Google Scholar] [CrossRef]
  9. Humby, T.L. ‘One environmental system’: Aligning the laws on the environmental management of mining in South Africa. J. Energy Nat. Resour. Law 2015, 33, 110–130. [Google Scholar] [CrossRef]
  10. Centre for Environmental Rights. The Truth About Mining Rehabilitation in South Africa; Centre for Environmental Rights: Cape Town, South Africa, 2018. [Google Scholar]
  11. Mabaso, S.M. Legacy gold mine sites & dumps in the Witwatersrand: Challenges and required action. Nat. Resour. 2023, 14, 65–77. [Google Scholar] [CrossRef]
  12. Department of Mineral Resources and Energy. Progress in Dealing with Derelict and Ownerless Mines; Department of Mineral Resources: Pretoria, South Africa. 2019. Available online: http://pmg-assets.s3-website-eu-west-1.amazonaws.com/141112derelict.ppt (accessed on 11 May 2025).
  13. Akbar, W.A.; Rahim, H.U.; Irfan, M.; Sehrish, A.K.; Mudassir, M. Assessment of heavy metal distribution and bioaccumulation in soil and plants near coal mining areas: Implications for environmental pollution and health risks. Environ. Monit. Assess. 2024, 196, 97. [Google Scholar] [CrossRef]
  14. Kumar, S.; Banerjee, S.; Ghosh, S.; Majumder, S.; Mandal, J.; Roy, P.K.; Bhattacharyya, P. Appraisal of pollution and health risks associated with coal mine contaminated soil using multimodal statistical and Fuzzy-TOPSIS approaches. Front. Environ. Sci. Eng. 2024, 18, 60. [Google Scholar] [CrossRef]
  15. Ai, Y.; Chen, H.; Chen, M.; Huang, Y.; Han, Z.; Liu, G.; Li, J. Characteristics and treatment technologies for acid mine drainage from abandoned coal mines in major coal-producing countries. J. China Coal Soc. 2023, 48, 4521–4535. [Google Scholar]
  16. Jiang, C.; Zhao, Q.; Zheng, L.; Chen, X.; Li, C.; Ren, M. Distribution, source and health risk assessment based on the Monte Carlo method of heavy metals in shallow groundwater in an area affected by mining activities, China. Ecotoxicol. Environ. Saf. 2021, 224, 112679. [Google Scholar] [CrossRef] [PubMed]
  17. Xiao, X.; Zhang, J.; Wang, H.; Han, X.; Ma, J.; Ma, Y.; Luan, H. Distribution and health risk assessment of potentially toxic elements in soils around coal industrial areas: A global meta-analysis. Sci. Total Environ. 2020, 713, 135292. [Google Scholar] [CrossRef]
  18. Chen, L.; Miller, S.A.; Ellis, B.R. Comparative human toxicity impact of electricity produced from shale gas and coal. Environ. Sci. Technol. 2017, 51, 13018–13027. [Google Scholar] [CrossRef] [PubMed]
  19. Huang, Y.; Kuang, X.; Cao, Y.; Bai, Z. The soil chemical properties of reclaimed land in an arid grassland dump in an opencast mining area in China. Rsc. Adv. 2018, 8, 41499–41508. [Google Scholar] [CrossRef]
  20. Zerizghi, T.; Guo, Q.; Tian, L.; Wei, R.; Zhao, C. An integrated approach to quantify ecological and human health risks of soil heavy metal contamination around coal mining area. Sci. Total Environ. 2022, 814, 152653. [Google Scholar] [CrossRef]
  21. Hasii, O.; Gasii, G. Coal mining and water resources: Impacts, challenges, and strategies for sustainable environmental management. In Proceedings of the IOP Conference Series: Earth and Environmental Science, Online, 8–10 November 2023; IOP Publishing: Bristol, UK, 2024; Volume 1348, p. 012017. [Google Scholar] [CrossRef]
  22. Simpson, G.B.; Badenhorst, J.; Jewitt, G.P.; Berchner, M.; Davies, E. Competition for land: The water-energy-food nexus and coal mining in Mpumalanga Province, South Africa. Front. Environ. Sci. 2019, 7, 86. [Google Scholar] [CrossRef]
  23. Bench Marks Foundation. South African Coal Mining, Corporate Grievance Mechanisms, Community Engagement Concerns, and Mining Impacts; Policy Gap 9; Bench Marks Foundation: Johannesburg, South Africa, 2014. [Google Scholar]
  24. Centre for Environmental Rights. Zero Hour: Poor Governance of Mining and the Violation of Environmental Rights in Mpumalanga; Centre for Environmental Rights: Cape Town, South Africa, 2016. [Google Scholar]
  25. Magagula, M.; Atangana, E.; Oberholster, P. Assessment of the Impact of Coal Mining on Water Resources in Middelburg, Mpumalanga Province, South Africa: Using Different Water Quality Indices. Hydrology 2014, 11, 113. [Google Scholar] [CrossRef]
  26. Atangana, E.; Oberholster, P.J. Using heavy metal pollution indices to assess water quality of surface and groundwater on catchment levels in South Africa. J. Afr. Earth Sci. 2021, 182, 104254. [Google Scholar] [CrossRef]
  27. Yadav, H.L.; Jamal, A. Assessment of water quality in coal mines: A quantitative approach. J. Chem. 2018, 11, 46–52. [Google Scholar]
  28. Uddin, M.G.; Nash, S.; Olbert, A.I. A review of water quality index models and their use for assessing surface water quality. Ecol. Indic. 2021, 122, 107218. [Google Scholar] [CrossRef]
  29. Son, C.T.; Giang, N.T.H.; Thao, T.P.; Nui, N.H.; Lam, N.T.; Cong, V.H. Assessment of Cau River water quality assessment using a combination of water quality and pollution indices. J. Water Supply Res. Technol. AQUA 2020, 69, 160–172. [Google Scholar] [CrossRef]
  30. Kachroud, M.; Trolard, F.; Kefi, M.; Jebari, S.; Bourrié, G. Water quality indices: Challenges and application limits in the literature. Water 2019, 11, 361. [Google Scholar] [CrossRef]
  31. Karim, M.; Das, S.K.; Paul, S.C.; Islam, M.F.; Hossain, M.S. Water quality assessment of Karrnaphuli River, Bangladesh using multivariate analysis and pollution indices. Asian J. Environ. Ecol. 2018, 7, 1–11. [Google Scholar] [CrossRef]
  32. Oberholster, P.F.; Goldin, J.; Xu, Y.; Kanyerere, T.; Oberholster, P.J.; Botha, A.M. Assessing the adverse effects of a mixture of AMD and sewage effluent on a sub-tropical dam situated in a nature conservation area using a modified pollution index. Int. J. Environ. Res. 2021, 15, 321–333. [Google Scholar] [CrossRef]
  33. Mishra, S.; Sharma, M.P.; Kumar, A. Assessment of surface water quality in Surha Lake using pollution index, India. J. Mater. Environ. Sci. 2016, 7, 713–719. [Google Scholar]
  34. Du, Y.; Tian, Z.; Zhao, Y.; Wang, X.; Ma, Z.; Yu, C. Exploring the accumulation capacity of dominant plants based on soil heavy metals forms and assessing heavy metals contamination characteristics near gold tailings ponds. J. Environ. Manag. 2024, 351, 119838. [Google Scholar] [CrossRef]
  35. Shi, J.; Qian, W.; Jin, Z.; Zhou, Z.; Wang, X.; Yang, X. Evaluation of soil heavy metals pollution and the phytoremediation potential of copper-nickel mine tailings ponds. PLoS ONE 2023, 18, e0277159. [Google Scholar] [CrossRef]
  36. Espinoza, S.E.; Quiroz, I.A.; Magni, C.R.; Yáñez, M.A.; Martínez, E.E. Long-term effects of copper mine tailings on surrounding soils and sclerophyllous vegetation in Central Chile. Water Air Soil Pollut. 2022, 233, 288. [Google Scholar] [CrossRef]
  37. South African Weather Service. Climate Data for Mpumalanga; South African Weather Service: Pretoria, South Africa, 2023. [Google Scholar]
  38. Rutherford, M.C.; Mucina, L.; Powrie, L.W. Biomes and bioregions of southern Africa. Veg. S. Afr. Lesotho Swazil. 2006, 19, 30–51. [Google Scholar]
  39. Cairncross, B.; McCarthy, T.S. A geological investigation of Klippan in Mpumalanga province, South Africa. S. Afr. J. Geol. 2008, 111, 421–428. [Google Scholar] [CrossRef]
  40. Wilson, M.G.C.; Anhaeusser, C.R. The Mineral Resources of South Africa, 6th ed.; Handbook 16; Council for Geoscience: Pretoria, South Africa, 1998. [Google Scholar]
  41. ISO/IEC 17025; General Requirements for the Competence of Testing and Calibration Laboratories. International Organization for Standardization (ISO): Geneva, Switzerland, 2005.
  42. Ramakrishnaiah, C.R.; Sadashivaiah, C.; Ranganna, G. Assessment of water quality index for the groundwater in Tumkur Taluk, Karnataka State, India. J. Chem. 2009, 6, 523–530. [Google Scholar]
  43. Asif, M.R.; Ye, B.; Ye, C. Acid sulfate soils: Formation, identification, environmental impacts, and sustainable remediation practices. Environ. Monit. Assess. 2025, 197, 484. [Google Scholar] [CrossRef]
  44. World Health Organization (WHO). Guidelines for Drinking-Water Quality, 4th ed.; World Health Organization: Geneva, Switzerland, 2017. [Google Scholar]
  45. Favas, P.J.C.; Pratas, J.; Prasad, M.N.V. Review of the environmental impacts of abandoned mines in South Africa. Environ. Sci. Pollut. Res. 2016, 23, 33–45. [Google Scholar]
  46. Steyn, C.E.; Herselman, J.E. Trace element concentrations in soils under different land uses in Mpumalanga Province, South Africa. S. Afr. J. Plant Soil 2006, 23, 230–236. [Google Scholar] [CrossRef]
  47. Grantcharova, M.M.; Fernández-Caliani, J.C. Soil acidification, mineral neoformation and heavy metal contamination driven by weathering of sulphide wastes in a Ramsar wetland. Appl. Sci. 2021, 12, 249. [Google Scholar] [CrossRef]
  48. Ying, H.; Zhao, W.; Feng, X.; Gu, C.; Wang, X. The impacts of aging pH and time of acid mine drainage solutions on Fe mineralogy and chemical fractions of heavy metals in the sediments. Chemosphere 2022, 303, 135077. [Google Scholar] [CrossRef] [PubMed]
  49. Dai, S.; Ren, D.; Chou, C.L.; Finkelman, R.B.; Seredin, V.V.; Zhou, Y. Geochemistry of trace elements in Chinese coals: A review of abundances, genetic types, impacts on human health, and industrial utilization. Int. J. Coal Geol. 2012, 94, 3–21. [Google Scholar] [CrossRef]
  50. Orem, W.H.; Finkelman, R.B. Coal formation and geochemistry. In Treatise on Geochemistry; Elsevier: Amsterdam, The Netherlands, 2003; Volume 7, pp. 191–222. [Google Scholar]
  51. Ketris, M.Á.; Yudovich, Y.E. Estimations of Clarkes for Carbonaceous biolithes: World averages for trace element contents in black shales and coals. Int. J. Coal Geol. 2009, 78, 135–148. [Google Scholar] [CrossRef]
  52. Rouhani, S.; Zhang, Y.; Liu, X. Heavy metal pollution in soil and its impact on human health: A review. Sci. Total Environ. 2023, 858, 159746. [Google Scholar]
  53. Mahar, A.; Wang, P.; Ali, A.; Awasthi, M.K.; Lahori, A.H.; Wang, Q.; Zhang, Z. Challenges and opportunities in the phytoremediation of heavy metals contaminated soils: A review. Ecotoxicol. Environ. Saf. 2016, 126, 111–121. [Google Scholar] [CrossRef]
  54. Lu, J.; Lu, H.; Wang, W.; Feng, S.; Lei, K. Ecological risk assessment of heavy metal contamination of mining area soil based on land type changes: An information network environ analysis. Ecol. Model. 2021, 455, 109633. [Google Scholar] [CrossRef]
  55. Chen, H.; Teng, Y.; Lu, S.; Wang, Y.; Wang, J. Contamination features and health risk of soil heavy metals in China. Sci. Total Environ. 2011, 409, 4565–4574. [Google Scholar] [CrossRef] [PubMed]
  56. Richardson, D.M.; Van Wilgen, B.W. Invasive alien plants in South Africa: How well do we understand the ecological impacts?: Working for water. S. Afr. J. Sci. 2004, 100, 45–52. [Google Scholar]
  57. van Wilgen, B.W.; Richardson, D.M.; Le Maitre, D.C.; Marais, C.; Magadlela, D. The economic consequences of alien plant invasions: Examples of impacts and approaches to sustainable management in South Africa. Environ. Dev. Sustain. 2001, 3, 145–168. [Google Scholar] [CrossRef]
  58. Henderson, L. Alien Weeds and Invasive Plants. A Complete Guide to Declared Weeds and Invaders in South Africa; Food and Agriculture Organization of the Unites States: Rome, Italy, 2001. [Google Scholar]
  59. Le Maitre, D.C.; Versfeld, D.B.; Chapman, R.A. Impact of Invading Alien Plants on Surface Water Resources in South Africa: A Preliminary Assessment; CSIR Division of Water, Environment and Forestry Technology, Stellenbosch: Capetown, South Africa, 2000. [Google Scholar]
  60. Singh, V.K.; Singh, K.P.; Mohan, D. Status of heavy metals in water and bed sediments of river Gomti–A tributary of the Ganga river, India. Environ. Monit. Assess. 2005, 105, 43–67. [Google Scholar] [CrossRef] [PubMed]
  61. Sigua, G.C.; Tweedale, W.A. Watershed scale assessment of nitrogen and phosphorus loadings in the Indian River Lagoon basin, Florida. J. Environ. Manag. 2003, 67, 363–372. [Google Scholar] [CrossRef]
  62. De, S.; Mitra, A.K. Mobilization of heavy metals from mine spoils in a part of Raniganj coalfield, India: Causes and effects. Environ. Geosci. 2004, 11, 65–76. [Google Scholar] [CrossRef]
  63. Reddick, J. Environmental impacts of coal mining. Int. J. Coal Geol. 2016, 157, 104–123. [Google Scholar]
  64. Lechner, A.M.; Baumgartl, T.; Matthew, P.; Glenn, V. The impact of underground longwall mining on prime agricultural land: A review and research agenda. Land Degrad. Dev. 2016, 27, 1650–1663. [Google Scholar] [CrossRef]
  65. Song, W.; Xu, R.; Li, X.; Min, X.; Zhang, J.; Zhang, H.; Li, J. Soil reconstruction and heavy metal pollution risk in reclaimed cultivated land with coal gangue filling in mining areas. Catena 2023, 228, 107147. [Google Scholar] [CrossRef]
  66. Yakovleva, E.V.; Gabov, D.N.; Beznosikov, V.A.; Kondratenok, B.M. Accumulation of polycyclic aromatic hydrocarbons in soils and plants of the tundra zone under the impact of coal-mining industry. Eurasian Soil Sci. 2016, 49, 1319–1328. [Google Scholar] [CrossRef]
  67. Galván, L.; Olías, M.; Cerón, J.C.; de Villaran, R.F. Inputs and fate of contaminants in a reservoir with circumneutral water affected by acid mine drainage. Sci. Total Environ. 2021, 762, 143614. [Google Scholar] [CrossRef] [PubMed]
  68. Mosley, L.M.; Biswas, T.K.; Dang, T.; Palmer, D.; Cummings, C.; Daly, R.; Kirby, J. Fate and dynamics of metal precipitates arising from acid drainage discharges to a river system. Chemosphere 2018, 212, 811–820. [Google Scholar] [CrossRef]
  69. Laisani, J.; Jegede, A.O. Impacts of coal mining in Witbank, Mpumalanga province of South Africa: An eco-legal perspective. J. Rev. Glob. Econ. 2019, 8, 1586–1597. [Google Scholar] [CrossRef]
  70. Wen, H.; Zhang, Y.; Cloquet, C.; Zhu, C.; Fan, H.; Luo, C. Tracing sources of pollution in soils from the Jinding Pb–Zn mining district in China using cadmium and lead isotopes. Appl. Geochem. 2015, 52, 147–154. [Google Scholar] [CrossRef]
  71. Mosai, A.K.; Ndlovu, G.; Tutu, H. Improving acid mine drainage treatment by combining treatment technologies: A review. Sci. Total Environ. 2024, 919, 170806. [Google Scholar] [CrossRef]
  72. Skousen, J.; Zipper, C.E.; Rose, A.; Ziemkiewicz, P.F.; Nairn, R.; McDonald, L.M.; Kleinmann, R.L. Review of passive systems for acid mine drainage treatment. Mine Water Environ. 2017, 36, 133–153. [Google Scholar] [CrossRef]
  73. Bai, S.J.; Li, J.; Yuan, J.Q.; Bi, Y.X.; Ding, Z.; Dai, H.X.; Wen, S.M. An innovative option for the activation of chalcopyrite flotation depressed in a high alkali solution with the addition of acid mine drainage. J. Cent. South Univ. 2023, 30, 811–822. [Google Scholar] [CrossRef]
  74. Rezaie, B.; Anderson, A. Sustainable resolutions for environmental threat of the acid mine drainage. Sci. Total Environ. 2020, 717, 137211. [Google Scholar] [CrossRef]
  75. Kefeni, K.K.; Msagati, T.A.; Mamba, B.B. Acid mine drainage: Prevention, treatment options, and resource recovery: A review. J. Clean. Prod. 2017, 151, 475–493. [Google Scholar] [CrossRef]
  76. Ramla, B.; Sheridan, C. The potential utilisation of indigenous South African grasses for acid mine drainage remediation. Water SA 2015, 41, 247–252. [Google Scholar] [CrossRef]
  77. Naghoum, I.; Edahbi, M.; Melián, J.A.H.; Doña Rodriguez, J.M.; Durães, N.; Pascual, B.A.; Salmoun, F. Passive Treatment of Acid Mine Drainage Effluents Using Constructed Wetlands: Case of an Abandoned Iron Mine, Morocco. Water 2025, 17, 687. [Google Scholar] [CrossRef]
  78. Dada, E.O.; Njoku, K.I.; Osuntoki, A.A.; Akinola, M.O. A review of current techniques of physico-chemical and biological remediation of heavy metals polluted soil. Ethiop. J. Environ. Stud. Manag. 2015, 8, 606–615. [Google Scholar] [CrossRef]
  79. Wan, X.; Lei, M.; Chen, T. Cost–benefit calculation of phytoremediation technology for heavy-metal-contaminated soil. Sci. Total Environ. 2016, 563, 796–802. [Google Scholar] [CrossRef] [PubMed]
  80. Kafle, A.; Timilsina, A.; Gautam, A.; Adhikari, K.; Bhattarai, A.; Aryal, N. Phytoremediation: Mechanisms, plant selection and enhancement by natural and synthetic agents. Environ. Adv. 2022, 8, 100203. [Google Scholar] [CrossRef]
  81. Xie, L.; van Zyl, D. Distinguishing reclamation, revegetation and phytoremediation, and the importance of geochemical processes in the reclamation of sulfidic mine tailings: A review. Chemosphere 2020, 252, 126446. [Google Scholar] [CrossRef]
  82. Niedrite, E.; Klavins, L.; Dobkevica, L.; Purmalis, O.; Ievinsh, G.; Klavins, M. Sustainable control of invasive plants: Compost production, quality and effects on wheat germination. J. Environ. Manag. 2024, 371, 123149. [Google Scholar] [CrossRef]
  83. Bai, G.; Zeng, X.; Li, X.; Zhou, X.; Cheng, Y.; Linghu, J. Influence of carbon dioxide on the adsorption of methane by coal using low-field nuclear magnetic resonance. Energy Fuels 2020, 34, 6113–6123. [Google Scholar] [CrossRef]
  84. Zhou, C.; Zhang, Y.; Wang, J.; Xue, S.; Wu, J.; Chang, L. Study on the relationship between microscopic functional group and coal mass changes during low-temperature oxidation of coal. Int. J. Coal Geol. 2017, 171, 212–222. [Google Scholar] [CrossRef]
  85. Kinnunen, P.H.M.; Kaksonen, A.H. Towards circular economy in mining: Opportunities and bottlenecks for tailings valorization. J. Clean. Prod. 2019, 228, 153–160. [Google Scholar] [CrossRef]
  86. Summerfield, D. Australian Resource Reviews: Iron Ore 2019; Australian Government: Canberra, Australia, 2020. [Google Scholar]
  87. Santander, M.; Valderrama, L. Recovery of pyrite from copper tailings by flotation. J. Mater. Res. Technol. 2019, 8, 4312–4317. [Google Scholar] [CrossRef]
  88. Naidu, G.; Ryu, S.; Thiruvenkatachari, R.; Choi, Y.; Jeong, S.; Vigneswaran, S. A critical review on remediation, reuse, and resource recovery from acid mine drainage. Environ. Pollut. 2019, 247, 1110–1124. [Google Scholar] [CrossRef]
  89. Mlalazi, N.; Chimuka, L.; Simatele, M.D. Synergistic effect of compost and moringa leaf extract biostimulants on the remediation of gold mine tailings using chrysopogon zizanioides. Sci. Afr. 2024, 26, e02358. [Google Scholar] [CrossRef]
  90. Ukhurebor, K.E.; Aigbe, U.O.; Onyancha, R.B.; Ndunagu, J.N.; Osibote, O.A.; Emegha, J.O.; Darmokoesoemo, H. An overview of the emergence and challenges of land reclamation: Issues and prospect. Appl. Environ. Soil Sci. 2022, 2022, 5889823. [Google Scholar] [CrossRef]
  91. Holcombe, S.; Keenan, J. Mining as a Temporary Land Use Scoping Project: Transitions and Repurposing; The University of Queensland: Brisbane, Australia, 2020. [Google Scholar]
  92. de Paulo Farias, D.; dos Santos Gomes, M.G. COVID-19 outbreak: What should be done to avoid food shortages? Trends Food Sci. Technol. 2020, 102, 291. [Google Scholar] [CrossRef] [PubMed]
  93. Kopittke, P.M.; Menzies, N.W.; Wang, P.; McKenna, B.A.; Lombi, E. Soil and the intensification of agriculture for global food security. Environ. Int. 2019, 132, 105078. [Google Scholar] [CrossRef] [PubMed]
  94. Sengupta, D.; Chen, R.; Meadows, M.E. Building beyond land: An overview of coastal land reclamation in 16 global megacities. Appl. Geogr. 2018, 90, 229–238. [Google Scholar] [CrossRef]
Processes 13 03307 g001
Figure 1. Locality map of the geographic location of portion 60 of Farm 313 JS KwaGuqa (the study site), generated using ArcGIS.
Figure 1. Locality map of the geographic location of portion 60 of Farm 313 JS KwaGuqa (the study site), generated using ArcGIS.
Processes 13 03307 g001
Processes 13 03307 g002
Figure 2. Surface water and soil sampling points within the study site and the water drainage system.
Figure 2. Surface water and soil sampling points within the study site and the water drainage system.
Processes 13 03307 g002
Processes 13 03307 g003
Figure 3. Pictures of some alien and invasive plant species concentrated on the western side of the study site where the S5 was taken from, adjacent to a water course.
Figure 3. Pictures of some alien and invasive plant species concentrated on the western side of the study site where the S5 was taken from, adjacent to a water course.
Processes 13 03307 g003
Processes 13 03307 g004
Figure 4. Photograph of the abandoned open-cast mine site, showing unlevelled ground, coal remnant and eroded stockpile or overburden. A stream runs along the western side, with the invasive alien tree species dominating the riparian zone. A nearby community is situated approximately 10 metres from the stream, although not visible in this image. Steps to remediation of the site and value adding benefits are shown on the left.
Figure 4. Photograph of the abandoned open-cast mine site, showing unlevelled ground, coal remnant and eroded stockpile or overburden. A stream runs along the western side, with the invasive alien tree species dominating the riparian zone. A nearby community is situated approximately 10 metres from the stream, although not visible in this image. Steps to remediation of the site and value adding benefits are shown on the left.
Processes 13 03307 g004
Table 1. Summary of the parameters measured, method used and instrument used in the analysis of water and soil samples.
Table 1. Summary of the parameters measured, method used and instrument used in the analysis of water and soil samples.
Method No.Based onInstrument
pHEPL-WL-003Standard method for the examination of water and wastewaterElectrode
ECEPL-WL-001Probe
TDSEPL-WL-004Gravimetric
TSSEPL-WL-014Gravimetric
Metals (Total)EPL-WL-007EPA6010ICP-OES
Table 2. Physicochemical properties of the soils (mean ± SD) and the soil screening values.
Table 2. Physicochemical properties of the soils (mean ± SD) and the soil screening values.
SSV1 All Land Uses Protective of the Water ResourcesProtection of the Ecosystem Health (SSV3)S1S2S3S4S5
pH 4.16 ± 0.284.99 ± 0.674.22 ± 0.143.82 ± 0.094.66 ± 0.45
EC (mS/m) 14.5 ± 1.371.6 ± 0.2114.2 ± 1.2827.4 ± 1.6734.7 ± 2.97
NH3 as N 41.04 ± 2.2511.67 ± 1.4414.61 ± 1.6615.89± 1.1353.94 ± 4.29
SO44000 2648.00 ± 133.54<200 1815.00 ± 78.056130.00 ± 115.2812,868.00 ± 401.38
Ca 3307.00 ± 107.11225.70 ± 7.29600.80 ± 29.341930.00 ± 203.274562.00 ± 53.21
Fe 9373.00 ± 205.2915,176.00 ± 629.5625,573.00 ± 923.2124,781.00 ± 523.4158,497.00 ± 800.25
Mg 81.08 ± 9.9873.43 ± 7.1173.95 ± 5.97125.50 ± 9.32164.40 ± 7.21
Mn74036,00067.82 ± 5.2354.53 ± 7.5745.44 ± 1.3364.17 ± 4.2243.70 ±1.98
Pb2010013.83 ± 1.118.61 ± 0.8913.83 ± 0.9845.48 ± 3.3329.76 ± 1.09
The values written in red font colour exceed the SSV1.
Table 3. Concentrations of the water parameters measured at the study site against the standards/guidelines.
Table 3. Concentrations of the water parameters measured at the study site against the standards/guidelines.
Discharge General Standard (mg/L)Irrigation General Standard (mg/L)Livestock Watering (DWA) (mg/L)Aquatic Ecosystem (DWA) (mg/L)Domestic Use SANAS 241(15) (mg/L)W1W2W3W4
(mg/L)(mg/L)(mg/L)(mg/L)
pH5.5–9.55.5–9.5--5–9.73.41 ± 0.223.39 ± 0.313.64 ± 0.233.76 ± 0.28
EC * (mS/m)150150--≤170314.10 ± 9.87257.93 ± 10.45130.05 ± 6.76124.21 ± 6.45
TDS--≤2000-≤20003337.78 ± 78.212803.02 ± 81.891226.12 ± 69.561093.15 ± 57.65
TSS2525---670.11 ± 11.23437.33 ± 7.76385.11 ± 13.98360.24 ± 22.69
SO4--≤1500-≤5001955.00 ± 87.251766.00 ± 75.44731.40 ± 47.94681.00 ± 53.98
Ca--≤1000--647.70 ± 43.23367.40 ± 29.67156.10 ± 10.95 140.20 ± 14.77
Fe0.3---≤22.95 ± 0.761.95 ± 0.207.73 ± 0.944.93 ± 0.11
Mg--≤500--60.42 ± 3.3464.96 ± 9.0920.08 ± 3.2620.88 ± 4.45
Mn0.1-≤10≤0.18≤0.512.86 ± 2.6512.64 ± 3.8610.23 ± 1.1110.57 ± 0.45
Pb0.010.01≤0.1≤0.0012≤0.01<0.05 <0.05<0.05<0.05
The values written in bold red font exceed more than one standard/guideline while the ones in red and not bold indicate exceedance of only one standard/guideline (where guideline or standard values are not provided, - is used). * EC units are mS/m
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Mlalazi, N.; Mbohwa, C.; Ramuhaheli, S.; Chimwani, N. Assessing Soil and Water Pollution: A Case Study of an Abandoned Coal Mine for Remediation and Repurposing in Mpumalanga Province, South Africa. Processes 2025, 13, 3307. https://doi.org/10.3390/pr13103307

AMA Style

Mlalazi N, Mbohwa C, Ramuhaheli S, Chimwani N. Assessing Soil and Water Pollution: A Case Study of an Abandoned Coal Mine for Remediation and Repurposing in Mpumalanga Province, South Africa. Processes. 2025; 13(10):3307. https://doi.org/10.3390/pr13103307

Chicago/Turabian Style

Mlalazi, Nkanyiso, Charles Mbohwa, Shumani Ramuhaheli, and Ngonidzashe Chimwani. 2025. "Assessing Soil and Water Pollution: A Case Study of an Abandoned Coal Mine for Remediation and Repurposing in Mpumalanga Province, South Africa" Processes 13, no. 10: 3307. https://doi.org/10.3390/pr13103307

APA Style

Mlalazi, N., Mbohwa, C., Ramuhaheli, S., & Chimwani, N. (2025). Assessing Soil and Water Pollution: A Case Study of an Abandoned Coal Mine for Remediation and Repurposing in Mpumalanga Province, South Africa. Processes, 13(10), 3307. https://doi.org/10.3390/pr13103307

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop