En l’espace de cinquante ans l’exploitation minière d’uranium en France a généré 163 millions de tonnes de stériles miniers à l’échelle du territoire. Ces stériles, stockés sous forme de verses sont sujets à une altération météorique accrue par rapport à un massif granitique naturel. Dans le cadre du plan de gestion des matériaux et déchets radioactifs (PNGMDR) les stériles miniers sont l’objet d’une attention particulière visant à caractériser leur impact environnemental. Cette étude précise la géostructure des verses à stériles avec le développement d’un modèle structural typique pour aboutir à une caractérisation géochimique et minéralogique de ces stériles et permettre d’évaluer la stabilité de l’uranium. De cette étude, il apparaît très clairement que l’uranium est principalement associé aux phosphates, dans des phases héritées telles que les monazites ou sous formes d’uranyle-phosphates secondaires. Lorsque l’U est associé à des oxyhydroxydes de fer amorphes, le phosphore est également présent. Cette étude illustre le rôle majeur que peuvent jouer les oxyhydroxydes de fer et le phosphore dans le piégeage de l’uranium. Ces phases constituent un piège efficace et relativement stable, permettant de limiter les concentrations en uranium en solution à condition que les conditions environnementales restent stables. Quand bien même des changements d’équilibre auraient lieu, la présence de smectite dans les échantillons de la verse à stériles présente une barrière supplémentaire à la diffusion de l’uranium dans l’environnement. / In a time span of 50 years uranium mining in France generated 163 Mt of waste rocks. These form waste rocks piles which are subjected to enhanced weathering compared to natural granitic outcrops. Therefore, as part of the French radioactive waste and material management plan (PNGMDR), waste rocks are studied in order to assess their potential environmental impact. This study specifically focuses on the internal structure of waste rock piles complemented by geochemistry and mineralogical data, in order to develop a model that assesses the waste rock pile’s weathering state and uranium’s stability. Results show uranium (U) is mainly associated to phosphates, either in primary accessory minerals, such as monazites, or crystallized in secondary uranyl-phosphates. When U is associated to amorphous iron oxyhydroxides, phosphorous is also associated. The importance of iron oxyhydroxides and phosphorous in uranium trapping is clearly demonstrated. Both iron oxyhydroxides as well as uranyl-phosphates form efficient and stable U traps, limiting U dissolution as long as pH, redox and temperature parameters remain stable. In case of variable conditions, smectite identified in the waste rock pile might also play a role in preventing further uranium diffusion.

Waste rocks (WRs) from coal mining and fly ash (FA) from coal combustion were studied to determine the potential of the WRs to generate AMD, FAs to neutralise it and estimate their impacts on environment. The ultimate goal was to develop a methodology based on co-disposal to mitigate the environmental problems associated to both wastes. Two methods for co-disposal were tested: i) Mixing WRs and FAs and ii) covering WRs with FAs. WRs were sampled from the Lakhra coal mines in Pakistan (PK), which has an estimated coal reserves of 1.3 Btonne, varying from lignite to sub-bituminous quality. The FA was sampled from a power plant utilising coal from Lakhra coal mines and is situated in close vicinity (15km) of the mine site. For comparative purposes a bituminous FA from Finland (FI) and biomass FA from Sweden (SE) were also characterised. The WRs and FA samples were characterised by mineralogical and geochemical methods. Besides organic material (coal traces), quartz, pyrite, kaolinite, hematite, gypsum and traces of calcite, lime, malladerite, spangolite, franklinite and birnessite were identified in WRs by XRD. The major elements Si, Al, Ca and Fe were in the range (wt. %) of 8 – 12, 6 – 9, 0.3 – 3 and 1 – 10, respectively, with high S concentrations (1.94 – 11.33 wt. %) in WRs. The AMD potential of WRs ranged from -70 to -492 kg CaCO3 tonne-1. All FAs contained quartz, with iron oxide, anhydrite and magnesioferrite in PK, mullite and lime in FI and calcite and anorthite in SE. The Ca content in SE was 6 and 8 times higher compared to PK and FI, respectively. FAs were enriched in As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn compared to continental crust. The acid neutralising potential of PK was equivalent to 20 kg CaCO3 tonne-1 compared to 275 kg CaCO3 tonne-1 (SE) and 25 kg CaCO3 tonne-1 (FI). During the period of 192 days in weathering cell experiments (WCE), the pH of leachates from most acidic WRs was maintained from 1 to 2.5, whereas, the less acidic WRs produced leachates of mildly acidic (2.7) to neutral (7.3) pH. The leachates from very acidic WRs ranged in the concentrations of Fe, SO24− and Al from mg L-1 to g L-1. The samples were subjected to column leaching experiments (CLE) in which mixture (FA:WR; 1:3) and cover (FA:WR; 1:5) cases were mimicked (with 10mm particle size) and effects of particle size (2, 5 and 10mm) on element leaching were studied. Despite having the lowest acid-neutralisation potential compared to FI and SE, co-disposal of PKFA as mixture readily provides acid buffering minerals, resulting in better start-up pH conditions and leachate quality. However, acidity produced by secondary mineralisation contributes towards the acidification of the system, causing stabilisation of pH at around 4.5−5. Secondary mineralisation (especially Fe- and Al-mineral precipitation) also removes toxic elements such as As, Pb, Cu, Zn, Cd, Co, Ni and Mn, and these secondary minerals can also buffer acidity when the pH tends to be acidic. In contrast, the pH of the leachates from the PKFA cover scenario gradually increased from strongly acidic to mildly acidic and circumneutral along with decrease in EC and elemental leaching in different WRs. Gradually increasing pH can be attributed to the cover effect, which reduces oxygen ingress, thus sulphide oxidation, causing pH to elevate. Due to the fact that pH~4–5 is sufficient for secondary Fe- and Al-mineral precipitation which also removes toxic elements (such as Cd, Co, Cu, Zn and Ni) by adsorption and/or co-precipitation, the FA cover performs well enough to achieve that pH until the conclusion of the CLE. However, due to the slower reactivity of the buffering system (additional to the initial flush-out), leaching in the beginning could not be restricted. The co-disposal of FA as cover and/or mixture possesses potential for neutralisation of AMD and improving leachate quality significantly. Particle size of the WRs affected the leaching of the sulphide related elements (such as Fe, S, Zn, Co, Cr, Cu, Mn and Ni) in CLE and WCE. Experiments with ≤1mm particle size constantly produced acidic and metal laden leachates. Co-disposal of FA and WRs as cover and mixture need to be investigated on pilot-scales before full-scale application.

Gruvavfall, i form av gråberg, från Kiirunavaara-gruvan i Kiruna, norra Sverige undersöktes för att se om surt lakvatten kan bildas från gråberget och om detta kan ha en påverkan på hur mycket kväve som kan lakas ut från gråberget. För detta ändamål gjordes dels en mineralogisk undersökning av gråberget, med siktning, röntgendiffraktion (XRD) och grundämnesanalys och dels laborativa skakförsök. Från skakförsöken, där olika kornstorlekar (8-16 mm, 2-4 mm och mindre än 1 mm) blandades med avjoniserat vatten med L/S-kvoten 10, kunde förändringar i pH, alkalinitet och lösta joner undersökas över en 10-veckors period.                       De främsta mineralen i gråberget i Kiirunavaara visades vara plagioklas, kvarts och biotit. I gråberget finns även 18 g pyrit/kg gråberg. Skakförsöken indikerar att lakvattnet från gråberget i Kiirunavaara är alkaliskt med ett pH över 9. Vittring av sulfidmineral sker, men neutraliseras av buffrande mineral som kalcit och ingen potential till produktion av surt lakvatten finns. Kväveutlakningen sker främst under de första dygnen, men mer än hälften av de kväveföreningar som antas finnas i gråberget lakas inte ut. Både nitrat och ammonium visade signifikanta korrelationer med pH, där högre pH-värden tydde på högre nitratkoncentrationer och lägre pH-värden på högre ammoniumkoncentrationer. Detta indikerar att även om inget samband kunde ses mellan produktion av surt lakvatten och kväveutlakning, så är mängden av olika kväveföreningar som lakas ut beroende av lakvattnets pH-värde. / Mining waste rock from the Kiirunavaara-mine in northern Sweden was studied to determine if there is a potential for production of acid mine drainage (AMD), if there is a leaching of nitrogen compounds from the waste rock and if a correlation between the two processes can be seen. A mineralogical characterization of the waste rock was done through dry sieving, X-Ray Diffraction (XRD) and elemental analysis. Through shake flask experiments, where waste rock of three different grain sizes (8-16 mm, 2-4 mm and less than 1 mm) were mixed with deionized water (L:S-ratio of 10), the change in pH, alkalinity and dissolved ions during a 10-week period was determined.                       The waste rock in Kiirunavaara was found to consist mainly of plagioclase, quartz and biotite, but the waste rock also contains 18 g pyrite per kg waste rock. The shake flask experiments indicate that the mine drainage from the waste rock in Kiirunavaara is alkaline, with a pH above 9. Weathering of sulphide minerals occur, but are neutralised by buffering minerals such as calcite and thus no potential for AMD-production exists. The leaking of nitrogen compounds occurs mainly during the first few days. Both ammonium and nitrate showed significant correlations with pH, where lower pH-values typically exhibited higher ammonium concentrations, while higher pH-values correlated with higher nitrate concentrations.