Cement has been widely used for low- to intermediate-level radioactive waste management; however, the long-term modelling of multiple mineral transfer between the cement leachate and the host rock of a geological disposal facility remains a challenge due to the strong physical-chemical interactions within the chemically disturbed zone. This paper presents a modelling study for a 15-year experiment simulating the reaction of crystalline basement rock with evolved near-field groundwater (pH = 10.8). A mixed kinetic equilibrium (MKE) modelling approach was employed to study the dolomite-rich fracture-filling assemblage reacting with intermediate cement leachate. The study found that the mineralogical and geochemical transformation of the system was driven by the kinetically controlled dissolution of the primary minerals (dolomite, calcite, quartz, k-feldspar and muscovite). The initial high concentration of calcium ions appeared to be the main driving force initiating the dedolomitization process, which played a significant role in the precipitation of secondary talc, brucite and Mg-aluminosilicate minerals. The modelling study also showed that most of the initially precipitated calcium silicon hydrate phases redissolved and formed more stable calcium silicon aluminium hydrate phases. The findings highlight the importance of a deep and insightful understanding of the geochemical transformations based on the type and characteristics of the host rock, where the system is under out of equilibrium conditions, and the rates of mineral reactions.

Materials held within mine tailings pose a serious risk to the environment in cases of tailings dam failure. Collapse of the tailing dam at the Stolice antimony mine in West Serbia caused a spilling of tailing slurry into the nearby river watersheds. Medium-term effects of As, Pb, Sb, Zn, and Cd from the tailings material that remained in the flooded zone 3 years after the initial exposure were evaluated. Mobility of these elements was determined by analyzing their distribution between exchangeable, reducible, oxidizable, and residual phases. Results indicate that Fe-Mn oxides represent important sinks for As, Cd, Pb, and Sb. Multivariate statistical analysis revealed that concentrations of the analyzed elements were related to sand-sized fractions, as they tended to adsorb or co-precipitate as coatings on larger particles (particularly feldspar and quartz) upon the change of redox conditions. Assessment of the most relevant physico-chemical factors, metal(loid) concentration, and mobility can be used as tool to characterize the degree of contamination of impacted sites. Percentage of sand-sized particles, content of investigated metal(loid)s, and their amount in the reducible fractions are factors determining the best remediation techniques for the area impacted by tailing spill.

High alkali-metal sulfate contents in ash from high-alkali coal are a result of the alkali metals’ strong sulfur-capturing capacity. In this work, the effects of sulfates in ash on SO₃ formation were investigated by adding alkali-metal sulfates (Na₂SO₄ and K₂SO₄) to ash and performing experiments to simulate SO₃ formation. The results show that Na₂SO₄ and K₂SO₄ addition significantly increased SO₃ formation and the formation rate increased with increasing temperature. The formed SO₃ concentration increased by 6.8 ppm (adding Na₂SO₄) and 6.3 ppm (adding K₂SO₄) at 1000 °C. These increases are the result of SO₃ release from sulfate during the formation of aluminosilicates such as NaAlSi₃O₈ (albite), NaAlSiO₄ (nepheline), KAlSiO₄ (kalsilite), and KAlSi₃O₈ (feldspar) with the SiO₂ and Al₂O₃ in the ash. This was confirmed by X-ray diffraction (XRD) and thermodynamic calculation. In addition, increasing the SO₂ concentration increased the SO₃ concentration and decreased the SO₃ conversion ratio. Graphical abstract Note: This data is mandatory.