Artisanal and small-scale mining (ASM) has emerged as a vital economic lifeline for millions across Africa, Asia, and Latin America, driven by increasing gold prices, global demand, unemployment, and poverty. This sector accounts for approximately 28.9% of Ghana’s GDP and provides a livelihood for nearly 70% of Ghanaians, predominantly those residing in rural areas. However, this sector faces numerous environmental and health challenges, including uncontrolled mine waste disposal, contaminating water and soil with heavy metals. This review critically examines the environmental consequences of ASM waste management, focusing on informal underground tailings disposal. Using a dual-method strategy that combines systematic review and literature analysis, the study synthesizes 110 Scopus-indexed publications (2004–2024) to examine how ASM activities affect the safety, health, and ecosystems of Ghanaian ASM communities. Key findings reveal critical gaps in long-term waste management strategies, inadequate attention to health risks, and a lack of holistic socio-environmental assessments of ASM operations. The study underscores the urgent need for evidence-based interventions, including stricter regulatory enforcement, community-centered remediation, and sustainable livelihood alternatives. By addressing these gaps in Ghana, similar ASM-dependent economies can transform this sector into a force for equitable development without sacrificing environmental integrity or public health. Future research should prioritize cost-effective remediation technologies and policy frameworks that are tailored to the realities of informal mining communities.

Uranium (U) is a chemically toxic contaminant, and elevated concentrations in groundwater pose environmental and public health concerns in mining-impacted regions. U mobilization from mine-affected bedrock can contribute to groundwater contamination, yet the geochemical controls governing U release and transport under environmentally relevant conditions remain incompletely understood. This study investigates the roles of pH, complexing ligands, and mineralogy on U mobilization from pegmatite and trachyandesite rocks collected from Leveäniemi open pit, an active iron ore mine in Northern Sweden. Elevated U concentrations have been detected in groundwater entering the open pit through rock fractures. A systematic experimental approach combining batch leaching and dynamic flow through experiments was applied across a range of geochemical conditions, including varying acid concentrations, pH (acidic to alkaline), and ligand concentrations representative of groundwater (SO₄²⁻, NO₃⁻, Cl⁻, and HCO₃⁻) at environmentally relevant concentrations. The results demonstrate that U mineral dissolution and U mobilization are governed by distinct geochemical controls. Significant dissolution occurs under acidic and strongly alkaline conditions, with uraninite identified as the primary reactive U-bearing mineral, whereas other U-bearing minerals are comparatively resistant. Under neutral pH conditions representative of groundwater, U release is limited and controlled by surface-mediated processes rather than bulk mineral dissolution. However, the carbonate ligand promotes the formation of stable uranyl-carbonate and Ca-uranyl-carbonate complexes, enhancing U solubility and transport. These findings show that even limited mineral reactivity can sustain dissolved U concentrations over time and that groundwater composition plays a critical role in controlling U mobility. This is environmentally significant because such conditions are typical of groundwater systems, indicating that U can remain mobile and contribute to long-term contamination of water resources and downstream aquatic ecosystems. This study distinguishes the geochemical conditions that dissolve U-bearing minerals from those that sustain dissolved U transport under environmentally relevant groundwater conditions, providing new insight into mechanisms governing U transport in mine-impacted groundwater and supporting improved prediction, monitoring, and mitigation of U contamination of downstream recipients.

This study investigates the mechanisms controlling arsenic (As) removal and retention during Fenton treatment of mine wastewater from 2015 to 2025. Results show a substantial decrease (sevenfold) in dissolved As concentrations during treatment accompanied by an increase in particulate As (sixfold), indicating transfer of As from aqueous to the solid phase. Sequential extraction results suggest that As is proportionally associated with Fe oxide phases (≈13.2%). These observations indicate that As removal is primarily controlled by adsorption and co-precipitation with Fe(III) (oxyhydr)oxide precipitates formed during the Fenton reaction and subsequent liming. The findings provide insights into the geochemical processes governing As stabilization in mine wastewater treatment systems and highlight implications for the long-term management of treatment residues. 

Förekomst av järnsulfider i berg som bryts för infrastrukturprojekt har på senare åruppmärksammats som en potentiell miljörisk, eftersom oxidation av sulfidmineral kan ge upphovtill sura och metallhaltiga lakvatten. Trots att den totala mängden berg som hanteras inominfrastruktursektorn är mindre än avfallsvolymerna från gruvindustrin är kunskapen begränsadom hur sulfidförande bergmaterial kan användas utan att orsaka negativa miljöeffekter. Dettaprojekt (2021–2024) har finansierats av Trafikverket och syftar till att öka förståelsen förgeokemiska processer i sulfidförande berg. Studierna omfattar främst metamorfa sedimentärabergarter med förhöjda svavelhalter jämfört med den genomsnittliga kontinentala jordskorpan.De dominerande sulfiderna är pyrit och magnetkis, medan mindre mängder kopparkis, blyglansoch zinkblände också har identifierats. Mineralogiska och geokemiska analyser har genomförtsmed bland annat polarisationsmikroskopi, mikro-XRF, SEM, EMPA och ICP-teknik för attkarakterisera både bergmaterial och lakvatten.Kinetiska lakningsförsök har utförts på bergmaterial från Förbifart Stockholm och tunnelbyggemed material från Tunnelbygge Högdalen. Resultaten visar att magnetkis vittrar betydligtsnabbare än pyrit, som förblev i stort sett opåverkad efter fyra års lakning av Förbifart Stockholm.Bergmaterialet från Tunnelbygge Högdalen uppvisar fortfarande neutrala förhållanden och lågutlakning av metaller. Sulfider som är inkapslade i mer motståndskraftiga mineral, såsom kvarts,visar lägre benägenhet att oxidera än frilagda sulfider eller sulfider inneslutna i lättvittrade mineral,såsom biotit. Utlakningen domineras av metallerna Cu, Co och Ni, vilka främst är associerademed magnetkis. Inledningsvis har karbonater och cement buffrat pH och därmed fördröjtförsurningen. Kinetisk lakning begränsas av att försöken är både tidskrävande och kostsamma,vilket kan försvåra tillämpningen som beslutsunderlag i projekt med korta planerings- ochgenomförandetiderFältstudier av tidigare bergupplag i Kil, Hemavan och Uddevalla visar att sura och metallhaltigavatten kan förekomma långt efter att upplagen har avlägsnats. Förhöjda halter av bland annat Cu,Co, Ni och Al har uppmätts nedströms upplagsområdena. Det är dock osäkert om själva upplagenutgör den enda källan eller om bidraget från sekundära utfällningar och omkringliggande upplagär betydande. Resultaten visar att långvarig lagring av krossat sulfidförande berg i öppna upplagskapar gynnsamma förhållanden för sulfidoxidation genom hög exponering för syre ochbetydande vattentransport.Projektet visar också att de statiska testmetoderna ABA och NAG ofta ger osäkra resultat för bergmed låga halter av sulfider och karbonater. Bedömningen av miljörisker bör därför baseras på enkombination av geologiska, mineralogiska och geokemiska analyser. Något generellt gränsvärdeför svavelhalt som avgör om ett bergmaterial är lämpligt att använda är svårt att fastställa, eftersombland annat när och hur länge ett surt lakvatten kan förekomma beror på mängden bergmassorsom är begränsad i exempelvis en vägkonstruktion. En möjlig strategi är att använda sulfidförandeberg i vägkonstruktioner, där kompaktering och asfalttäckning kan begränsa syretillförseln ochdärmed minska sulfidoxidationen och utlakningen. Kunskapen om geokemiska processer i sådanakonstruktioner är dock fortfarande begränsad och ytterligare forskning behövs. Reaktivtransportmodellering är ett lovande verktyg för att förutsäga långsiktig sulfidoxidation ochutlakning under olika förhållanden för syre- och vattentillgång. Vetenskapliga publikationer omdetta arbete är under framtagande och kommer att komplettera rapportens resultat.

This study investigates whether a naturally formed dry crust in sulfide-rich soil can serve as abarrier that limits oxygen and water penetration, thereby reducing sulfide oxidation, and isfunded by the Swedish Transport Agency (Trafikverket)t. Sulfide soils contain iron sulfides that,when exposed to oxygen and moisture, generate acidity and mobilize metals. In many miningenvironments, prolonged oxidation leads to the formation of hardpan, a dense, cemented layerdominated by secondary minerals such as Fe-oxyhydroxides and gypsum, which can restrict thetransport of water and oxygen. The present work examines whether the dry crust identified inÖverkalix, Sweden, exhibits similar properties.Soil samples were collected from the crust and analyzed chemically and mineralogically usingICP-SFMS, XRD, and SEM-EDS; the results were compared with those from previouslystudied acid sulfate soils (ASS). The dry crust contained very low sulfur but high iron andphosphorus, indicating nearly complete sulfide oxidation and extensive secondary mineralformation. XRD confirmed a silicate-dominated matrix with 4.5% ferrihydrite. SEM-EDSrevealed Fe-O-rich precipitates and accessory minerals, including REE-bearing phosphates.Compared with ASS profiles, the crust showed elevated As and Cu, consistent with strong metalretention by Fe oxyhydroxides.Despite high Fe content and fine-grained structure, the dry crust did not qualify as a hardpan. Ithad unusually high water content (~49%), lacked cementation, and could not be recovered as anintact monolith, rendering oxygen diffusion testing impossible. Its behavior suggests that whilethe crust can temporarily retain metals through adsorption and co-precipitation, rewetting mayremobilize them. Thus, although the crust shows characteristics favorable for potential barrierformation, it does not currently exhibit the mechanical strength or low permeability associatedwith hardpans. Understanding these processes, however, may help guide strategies tointentionally induce hardpan-like stabilization in sulfide-bearing soils.

Uranium (U) release from mining is an environmental concern due to U's chemical toxicity and radioactivity. In Sweden, U is classified as a river basin-specific pollutant (RBSP), emphasizing the need to minimize its release from mining activities. This study aims to trace the sources of U contributing to elevated concentrations in mine water from Leveäniemi open pit, Northern Sweden, to inform point-source prevention measures to mitigate U release. The study investigates U leaching rates from key rock types forming the open pit walls and evaluates groundwater entering the open pit through drainage pipes and fractures as a potential source of U. Minewall weathering stations showed higher U leaching rates from pegmatites compared to other rock types. The pegmatite station where uraninite was the predominant mineral had a leaching rate averaging 1800 μg/m2/wk, compared to 430 μg/m2/wk at the station where pyrochlore was the predominant U mineral and uraninite occurred as inclusions in pyrochlore. However, pegmatites cover a small area of the exposed surface in the open pit compared to trachyandesite, which leached at a lower average rate of 30 μg/m2/wk. Groundwater entering the open pit through fractures and drainage pipes was also identified as a significant source of U in the mine water, further influencing mine water U concentrations. Careful handling of pegmatite-containing waste rock is essential to prevent increased U leaching in both the open pit and waste rock dumps. This study highlights the importance of identifying rocks with high U release potential before exposure during mining. Additionally, understanding the distribution of these high U-release rock types along groundwater flow paths can also help to predict groundwater U concentrations and inform site-specific management strategies to mitigate U contamination in downstream recipients.

Acid sulfate soils (AS-soils), common in coastal, estuarine, and mining-impacted areas, form under reducing conditions and can cause severe environmental degradation by releasing acidity and mobilizing heavy, trace, and toxic metals when sulfide minerals oxidize under changing hydrological conditions. AS-soils exhibit redox gradients that govern iron (Fe) and sulfur (S) cycling, affecting their mobility, mineral forms, and isotopic compositions. This study combines Fe/S ratios, δ56Fe and δ34S isotope systematics, sequential extractions, and groundwater monitoring to assess redox-driven processes in two AS-soil profiles from northern Sweden. In reduced zones, negative δ56Fe and δ34S values signal microbial Fe(III) and sulfate reduction, producing Fe(II) and sulfides. In oxidized zones, secondary Fe (oxy)hydroxides and sulfates form, inheriting isotopic signals from precursor sulfides. Groundwater δ56Fe enrichment reflects Fe oxidation, while high δ34S values (up to +45.2 ‰) indicate ongoing sulfate reduction. Groundwater Fe/S ratios (0.07–8.24) reveal redox interactions but are unreliable as sole redox indicators. Sequential extractions show that redox-sensitive pools—water-soluble, exchangeable, and organic-bound phases—exhibit strong isotope fractionation and drive short-term cycling, despite their small mass. Isotopic signals from different Fe phases within each profile likely offset each other when measured in bulk (∼0.06–0.11 ‰), diluting any clear redox-related patterns. Similarly, δ34S values trace a shift from oxidized to stable sulfide-bound forms across depths and redox zones. The results emphasize the value of combining isotopic and phase-specific analyses to unravel redox heterogeneity, trace element fluxes, and identify acidification-prone zones. Environmentally, maintaining saturated conditions, encouraging reducing environments, and monitoring reactive Fe and S fractions can help limit the mobilization of heavy, trace, and toxic metals in AS-soils under shifting hydrology.

Most mine closure strategies focus on preventing and treating metal(loid)s leachate (ML) from mine waste but designing effective and cost-efficient mitigation measures at an early stage can significantly improve mine closure outcomes. ML release can originate from multiple sources, including underground or open pit mines, mineral processing plants, waste rock piles and water management systems, which require different mitigation measures due to site-specific water and waste characteristics and prevailing chemical and climatic conditions. Therefore, mine closure approaches should prioritise source control, encompassing not only ore and mine waste but also water quality. Diagnostic assessments are crucial in identifying ML risks and sources as well as predicting potential environmental contamination. These assessments should account for microscale factors, e.g. mineral composition, distribution of trace metals, and mechanical and physical properties of mine waste and environmental factors, including geology, climate and hydrology. 

Our study integrates geochemical, mineralogical, and isotopic approaches to identify sources of ML and its mobility from the exploration phase and along the mine value chain. A holistic understanding enables the implementation of early-stage, cost-effective mitigation strategies, such as inhibition and cementation, which can reduce environmental risks and closure costs. Inhibition, or chemical passivation, focuses on secondary precipitation on the reactive mineral surface, preventing it from weathering. Cementation complements inhibition by forming a physical barrier to stabilise mine waste. In our ongoing small-scale column leaching experiments, inhibition and cementation effectively prevent acid mine drainage formation in sulphidic waste rock. Stable isotopes have proven efficient in tracing the mechanisms, transport and mobility of targeted elements, and the effectiveness of preventive techniques. Additionally, radiogenic isotope studies at an iron ore mine in Northern Sweden have provided insights into key weathering processes affecting uranium mobility from the primary contamination source. This article will showcase several case studies and a framework for AMD prevention technologies.