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.

Research regarding the geochemistry of beryllium (Be) in terrestrial environments is hindered by its high toxicity to humans and the low concentrations normally occurring in the environment. Although Be is considered an immobile element, extremely high dissolved concentrations have been detected in groundwater in the legacy Tailings Storage Facility (TSF) of Smaltjärnen, Sweden. Therefore, a detailed study was conducted to determine physiochemical parameters affecting the speciation of Be in the groundwater. Groundwater was sampled from 2016 to 2024 and filtered through 0.2 μm filters, whereas truly dissolved fraction (<1 kDa) samples were collected with dialysis membrane tubes in situ at groundwater wells. Secondary minerals on the tailings shore were studied by mineralogical methods and sequential extraction to trace the pathway whereby Be entered the downstream surface water. In part of the tailings, dissolved Be was detected in very high concentrations (average: 4.8 mg/L) in suboxic groundwater with pH from 6.0 to 6.4. Dialysis sampling in 2024 showed that more than 90% occurred as truly dissolved Be (<1 kDa). A significant correlation between Be and S was found, suggesting that sulfate complexes kept Be mobile in these pH conditions. Dissolved Be increased with decreased pH, and there is risk that the concentrations will increase further since sulfide oxidation with subsequent decrease in pH will continue for 100 of years in the TSF. In another part of the TSF, the pH was >6.4 and dissolved Be was below the detection limit, possibly due to formation of Al(OH)3 (>0.2 μm) together with F and Zn. Secondary minerals on the shore of the tailings functioned as a temporary chemical barrier, scavenging Be primarily by secondary gypsum when present and otherwise by Fe-(hydr)oxides.

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.

Tungsten (W) is an emerging contaminant of concern whose high mobility in the environment is of scientific debate. It is also a critical raw material whose mining is expected to increase. Mine waste management aims to create an anoxic environment of neutral pH to limit sulfide oxidation and acid mine drainage. This study evaluates the stability of W-minerals under such geochemical conditions to develop recommendations for W mine waste management. Intact cores of legacy mine tailings from Morkulltjärnen, Sweden, were collected and analyzed using whole rock geochemistry and XRD. Monolayers with minutes amounts of W were generated by hydroseparation and studied using SEM-EDS, automated mineralogy, and microprobe analysis. Scheelite concentrates from the decommissioned processing plant were analyzed with XRF and 7 step sequential extractions. Groundwater was collected from eight wells in the Morkulltjärnen tailings in 2023 and 2024 and analyzed for 71 elements, anions and chemophysical parameters. This is one of the first field studies presenting mineralogical signs of scheelite weathering with tabular morphology, rod-shaped and porous structure, and loss of W from the crystal lattice, leading to very high concentrations (up to 23 mg/L) of dissolved W in anoxic and alkaline groundwater. This shows that standard mine waste management practices are unsuitable for scheelite, and action is needed to limit W mobilization into the surrounding environment from scheelite-rich tailings. Adsorption onto Fe-(hydr)oxides may be effective for controlling W mobilization from legacy mine waste, but in new mines, sulfides and tungstates should be separated in the processing plant and stored under anoxic and oxic conditions, respectively.

Acid sulfate soils (AS-soils) are sulfide-bearing sediments that remain benign in waterlogged conditions but become environmentally harmful after exposure to oxygen. Sulfide oxidation generates acidity, element mobilization, compositional changes in soils and water bodies, and adverse effects on biota. This study enhances the geochemical and mineralogical understanding of the element source in oxidized and unoxidized AS-soils samples from Luleå, northern Sweden. An adapted sequential extraction scheme was conducted to determine the element distribution in primary and secondary phases. The extraction differentiates the H2O-soluble from the exchangeable fraction, labile and stable organic fractions, differentiated reducible from oxidisable phases, and residual fractions. Mineralogical changes were monitored at each step of the extraction sequence. Compositional maps obtained through microprobe quantified trace elements within the pyrite structure, which are susceptible to mobilization after weathering. The mineralogical and compositional findings of this study support strategies to mitigate environmental impacts from AS-soils oxidation. It is shown that framboidal pyrites are highly reactive to oxidation, contributing to acidification and releasing elements such as Cu, Mn, Mo, and Ni, highlighting sulfide exposure risk. In unoxidized samples, S is present in primary Fe sulfides and as organic S, while in oxidized samples, S occurs as secondary sulfate minerals. Organic matter strongly associates with Cu, Mo, and S, and is an important source of these elements in the sediments. From the most labile phases and pore water, Cd, Mn, Mo, and S were predominantly leached, indicating their high bioavailability. These findings demonstrate the importance of maintaining AS-soils in waterlogged conditions to prevent acidification and metal mobilization.

Acid sulfate soils (AS-soils) are a common feature along coastlines in many countries that can have significant environmental and economic impacts. AS-soils oxidation may cause soil and water acidification, the release and mobilization of metals and the formation of new precipitated phases. In northern Sweden, some soils are already oxidized and constitute an environmental concern. This study aimed to analyze the geochemistry and mineralogy of AS-soils profiles by identifying element depletion and accumulation zones, the parent material, minerals that contribute to acidity and their oxidation products as well as anomalous element content values that could be related to anthropogenic sources. Two soil profiles were drilled close to the Lule River in Södra Sunderbyn, Luleå. The profiles were characterized by an oxidized zone (OZ) with a declining trend in element content, a transition zone (TZ) where elements tended to accumulate and a reduced zone (RZ) where elements had their maximum content. The pH was a key determinant of the element distribution. Cadmium, Co, Ni and Zn were found to be typical elements released into the environment during AS-soils oxidation. After sample incubation, pH measurements showed a pronounced decrease in layers with higher S and total organic carbon (TOC) content. Both profiles developed a larger thickness of potential acid-risk sediments according to S, TOC and pH measurements during incubation. Iron sulfides were identified as the main acidity generators, represented by an abundance of framboidal pyrites with a Mn-rich rim formed under anoxic-euxinic conditions. Iron sulfates and iron oxyhydroxides (FeOOH, FeOH3) were identified as the most common products of oxidation processes.

Waste rocks (WRs) from a lignite-producing coalfield and fly ash (FA) produced from the same lignite have been investigated in this study with a primary objective to determine the potential for co-disposal of WRs and FA to reduce the environmental contamination. Mixing WRs with FA and covering WRs with FA have been investigated. Particle size effect caused ≤2 mm particles to produce low pH (~2) and metal-laden leachates, indicating higher sulphide minerals’ reactivity compared to larger particles (≤10 mm, pH ~ 4). Co-disposal of FA as mixture showed an instantaneous effect, resulting in higher pH (~3–6) and better leachate quality. However, acidity produced by secondary mineralisation caused stabilisation of pH at around 4.5–5. In contrast, the pH of the leachates from the cover method gradually increased from strongly acidic (pH ~ 2) to mildly acidic (pH ~ 4–5) and circumneutral (pH ~ 7) along with a decrease in EC and elemental leaching. Gradually increasing pH can be attributed to the cover effect, which reduces the oxygen diffusion, thus sulphide oxidation. FA cover achieved the pH necessary for secondary mineralisation during the leaching experiment. The co-disposal of FA as cover and/or mixture possesses the potential for neutralisation and/or slowing down AMD and improving leachate quality.

Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate ( >  0.22 μm), colloidal (0.22 μm–1 kDa), and truly dissolved (<  1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57μM with Fe dominantly as particulate Fe. The loss of >  99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ⁵⁶Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ⁵⁶Fe values close to the river mouth (about -0.20 ‰) and positive δ⁵⁶Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ⁵⁶Fe values, representing chemically reactive ferrihydrites. The positive δ⁵⁶Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ⁵⁶Fe composition in the Arctic Ocean.

Lignite fly ash (FA) and waste rocks (WRs) were mixed in three different ratios (1:1, 1:3 and 1:5) and studied to compare the effects of adding FA on acid mine drainage generation from coal mining WRs, leachability of elements and the potential occurrence of the secondary minerals. FA mixed with WRs showed significant differences in pH levels compared to previous research. The 1:1 mixture performed best of all the three mixtures in terms of pH and leachability of elements, mainly due to the higher proportion of FA in the mixture. The pH in the 1:1 mixtures varied between 3.3 and 5.1 compared to other mixtures (2.3–3.5). Iron and SO₄²⁻ leached considerably less from the 1:1 mixture compared to the others, indicating that the oxidation of sulphides was weaker in this mixture. Aluminium leached to a high degree from all mixtures, with concentrations varying from mg L⁻¹ to g L⁻¹. The reason behind this increase is probably the addition of FA which, due to acidic conditions and the composition of the FA, increases the availability of Al. For the same reason, high concentrations of Mn and Zn were also measured. Geochemical modelling indicates that the 1:1 mixture performs better in terms of precipitation of Al³⁺ minerals, whereas Fe³⁺ minerals precipitated more in mixtures containing less FA. These results suggest that, with time, the pores could possibly be filled with these secondary minerals and sulphate salts (followed by a decrease in sulphide oxidation), improving the pore water pH and decreasing the leachability of elements. Since grain size plays a crucial role in the reactivity of sulphides, there is a risk that the results from the leaching tests may have been influenced by crushing and milling of the WR samples.

The present study addresses the geotechnical and chemical properties of sealing materials using a paper mill by-product, fly ash, on top of sulfide-bearing mine waste tailings after 5 years of field application. From a geotechnical perspective, the low in situ bulk density (≤ 1500 kg/m³) ensured a high degree of water saturation (90.2%) for the field-applied ash. The chemical characteristics and behaviors of the fly ash samples reflected a high long-term leaching capacity (liquid-to-solid ratio of 10 cm³/g) and high alkalinity (liquid-to-solid ratio of up to 500 cm³/g). The laboratory leaching results suggested that none of the elements released from the field-applied ash exceeded the EU limits for inert materials, and the concentrations of elements were far below the limits for hazardous materials at landfill sites. Based on the in situ and laboratory characterizations of the field-applied ash, the fly ash sealing material was considered geotechnically stable. However, a number of geotechnical parameters could not be measured due to the cementation of the ash. Moreover, the chemical composition of the field-applied ash exhibited considerable variations when compared with that of the raw ash generated from the same paper mill. Overall, the field-applied ash displayed high alkalinity and effectively buffered the acid generated from sulfidic tailings for long-term sealing purposes.