Contribution au développement de nouveaux ciments économiques à empreinte carbone réduite destinés aux remblais miniers cimentés

« RÉSUMÉ : Le remblayage minier par remblai en pâte cimenté (RPC) est une pratique courante dans les mines souterraines. Il consiste en un mélange de résidus miniers, d'eau de gâchage et d'un liant hydraulique, tel que le ciment Portland à usage général (GU), souvent combiné avec du laitier de haut fourneau granulé broyé (GGBFS) ou des cendres volantes de type F ou C (FAF ou FAC). En particulier, un liant, dit de référence, composé de 20% GU et 80% GGBFS est couramment utilisé dans la région minière de l’Abitibi-Témiscamingue. Bien que le RPC présente des avantages économiques, sécuritaires et environnementaux notables, son coût croissant est fortement influencé par le type de liant utilisé, ce qui affecte également son empreinte carbone. Par exemple, le ciment Portland est à la fois coûteux et très polluant, tandis que l'accès au laitier devient limité en raison de son utilisation croissante dans d'autres secteurs, notamment le génie civil. De plus, le transport des liants vers des mines éloignées génère des coûts supplémentaires et augmente l'empreinte carbone. Ces défis, liés à l'augmentation des coûts et des émissions de carbone, sont particulièrement critiques pour l'industrie minière au Québec. Dans ce contexte, ce projet de thèse vise à développer des liants alternatifs, plus économiques et respectueux de l'environnement, en privilégiant des matériaux disponibles localement pour leur fabrication afin réduire les coûts et l’empreinte carbone du RPC. Quatre alternatives sont explorées, incluant 1) des liants à activation alcaline composés de GGBFS et FAF activés par l’hydroxyde de sodium NaOH, la valorisation de déchets métallurgiques à savoir 2) les scories d’aciéries de four poche LFS (Ladle Furnace Slag) d’ArcelorMittal à Contrecoeur au Québec et 3) les poussières (Dusts) de désulfuration des gaz issues du procédé Circulating Dry Scrubber (CDSD) de RioTinto Fer et Titane à Sorel-Tracy au Québec, ainsi que l'utilisation 4) des argiles de la région témiscabitibienne (au Québec) comme ajout dans les ciments au calcaire et aux argiles calcinées (LC3).»

Abstract

« ABSTRACT : Mine backfilling using cemented paste backfill (CPB) is a common practice in underground mines. It consists of a mixture of mine tailings, mixing water, and a hydraulic binder, such as general-use Portland cement (GU), often combined with ground granulated blast furnace slag (GGBFS) or fly ash type F or C (FAF, FAC). Specifically, a reference binder made up of 20% GU and 80% GGBFS is commonly used in the Abitibi-Témiscamingue mining region. Although CPB offers significant economic, safety, and environmental advantages, its rising cost is strongly influenced by the type of binder used, which also impacts its carbon footprint. For instance, Portland cement GU is both expensive and highly polluting, while access to GGBFS is becoming limited due to its growing use in other sectors, especially civil engineering. Additionally, transporting binders to remote mines (e.g. Northern Québec) adds extra costs and increases the carbon footprint of CPB. These challenges, related to rising costs and carbon emissions, are particularly critical for the mining industry in Quebec. In this context, this thesis project aims to develop alternative binders that are more economical and environmentally friendly, favoring locally available materials for their production in order to reduce the costs and carbon footprint of CPB. Four alternatives are being explored, including: 1) Alkali-activated binders composed of GGBFS and FAF activated by sodium hydroxide (NaOH); The valorization of metallurgical waste, specifically 2) Ladle Furnace Slag (LFS) from ArcelorMittal in Contrecoeur, Quebec; 3) Desulfurization dusts from the Circulating Dry Scrubber (CDSD) process at RioTinto Fer et Titane in Sorel-Tracy, Quebec; 4) The use of clays from the Abitibi-Témiscamingue region (in Quebec) as an additive in Limestone Calcined Clay Cements (LC3). Regarding alkali activation, a methodological approach was developed and applied, not only to this specific case of alkali activation but also for the rest of the thesis. GU cement was replaced by a mixture of GGBFS and FAF, activated with sodium hydroxide (NaOH) at low concentrations ranging from 0.5N to 1N. unconfined compression tests showed that the formulation composed of 75% GGBFS/25% FAF, activated with NaOH at a concentration of 0.5N, could replace the reference binder (20%GU/80%GGBFS) while offering comparable compressive strengths. These strengths are attributed to the development of hydrated products, particularly calcium silicate hydrate (CSH) and hydrotalcite-like phases. It was also noted that FAF plays a crucial role in regulating the short-term heat release from hydration and improves medium-term compressive strength compared to mixes of GGBFS alone activated with NaOH. However, a preliminary economic and environmental assessment revealed that the carbon footprint and cost of NaOH present major challenges for alkali-activated binders (AAB). More detailed evaluation of this product (NaOH) in the Quebec context is necessary to advance the AAB. On the other hand, an industrial waste, constitutes the second alternative in this project. This waste CDSD has been used to replace NaOH (and/or GU), presenting economic and environmental benefits. In particular, the 20%CDSD/80%GGBFS formulation shows similar compressive strengths after 28 days of curing comparatively to the reference binder. By-products such as FAF, fine glass powder (FGP), and electric arc furnace slag (EAFS) have also been successfully integrated up to 20% in CDSD/GGBFS formulations to reduce GGBFS content. The compressive strengths developed by CDSD/GGBFS mixtures are due to hydrated products such as CSH, hydrotalcite, and monosulfoaluminates, like those found in the reference mix. Since hydration of CDSD/GGBFS mixes is slow in the short term (7 days or less), the addition of 5% clinker is recommended to address this issue.»