Medium and highly sulfidic tailings are high-volume wastes that can lead to severe environmental damage if not properly managed. Due to the high content of sulfide minerals, these tailings can undergo weathering if put in contact with oxygen and water, generating acid mine drainage (AMD). The moderate-to-high sulfide content is also an important technical limitation for their implementation in the production of construction materials. This paper reviews the use of sulfidic tailings as raw material in construction products, with a focus on cement, concrete, and ceramics. When used as aggregates in concrete, this can lead to concrete degradation by internal sulfate attack. In building ceramics, their implementation without prior treatment is undesirable due to the formation of black reduction core, efflorescence, SO_x emissions, and their associated costs. Moreover, their intrinsic low reactivity represents a barrier for their use as supplementary cementitious materials (SCMs) and as precursors for alkali-activated materials (AAMs). Nevertheless, the production of calcium sulfoaluminate (CSA) cement can be a suitable path for the valorization of medium and highly sulfidic tailings. Otherwise difficult to upcycle, sulfidic tailings could be used in the clinker raw meal as an alternative raw material. Not only the SO₃ and SiO₂-rich bulk material is incorporated into reactive clinker phases, but also some minor constituents in the tailings may contribute to the production of such low-CO₂ cements at lower temperatures. Nevertheless, this valorization route remains poorly explored and demands further research.

In this work, we investigate the use of pyrite-rich tailings from an operational mine as mineral admixture in different cement matrices [Portland cement, calcium aluminate cement (CAC), and calcium sulfoaluminate cement (CSA)]. Hydration and microstructure changes were studied on cement pastes produced with a 30 wt% replacement of cement with tailings, up to 200 days. Based on our results, the effect of the tailings on the hydration of Portland cement is limited to a physical effect, and no sulfide-induced degradation is observed. In the CAC and CSA pastes, minor mineral phases present in the tailings chemically react, leading to changes in the mineral phase composition of CAC and CSA hydrated pastes. In addition, in all cement pastes studied, and more effectively in the CSA pastes, most of the metal(loid)s contained in the tailings were safely immobilized. Cement chemistry notation: C: CaO; A: Al₂O₃; F: Fe₂O₃; S: SiO₂; S̅: SO₃; c: CO₂; H: H₂O.

Priorização na Resolução de Manifestações Patológicas em Estruturas de Concreto Armado: Método GUT

Many recent studies show that the enforced carbonation of basic oxygen furnace (BOF) slags is a promising method to sequester CO ₂ in the material while improving their volume stability, which may enhance their suitability for construction applications. Some potential applications include the use of carbonated BOF slags as a replacement for natural aggregates in concrete, in the production of shaped monoliths, or, after particle size reduction, as an alternative binder and a supplementary cementitious material (SCM). In this study, experiments and thermodynamic modelling are used to investigate phase changes and the CO ₂ uptake of two different size fractions of a BOF slag (0–3 mm and 0.5–3 mm) upon enforced carbonation, in addition to the effect of pre-conditioning duration (2 or 24 h) at 10 wt.% moisture. The enforced carbonation process was carried out on the moist BOF slag in an autoclave at 0.1 barG overpressure and 40 ℃, using a gas mixture containing 30% CO ₂ and 70% N ₂ for 24 h. The experiments show that the uncarbonated size fractions have considerable differences in phase composition, which ultimately define their final CO ₂ binding capacity. Pre-conditioning at 10 wt.% moisture had little impact on CO ₂ -uptake and phase assemblage. This was attributed to the pre-hydrated initial state of the materials, as revealed by XRD and TGA. The reaction sequence and the water release during carbonation in the autoclave were not accurately predicted by thermodynamic modelling. However, this could potentially be addressed by the implementation of kinetic models and adequate consideration of the reactivity of the amorphous fraction of the BOF slag.