Lead mobilization and speciation in mining waste : experiments and modeling

Mining produces significant amounts of solid mineral waste. Mine waste storage facilities are often challenging to manage and may cause environmental problems. Mining waste is often linked to contaminated mine drainage, including acidic waters with more or less elevated concentrations of trace metals such as lead. This work presents a study on the mobilization of lead from waste from two typical mining sites: Zeida and Mibladen, two now-closed former Pb–Zn mines in the Moulouya region of Morocco. Our research investigates the mobilization potential of Pb from the waste of these mines. The study involved acid–base neutralization capacity tests (ANC–BNC) combined with geochemical modeling. Experimental data allowed for the quantification of the buffering capacity of the samples and the mobilization rates of lead as a function of pH. The geochemical model was fitted to experimental results with thermodynamic considerations. The geochemical model allowed for the identification of the mineral phases involved in providing the buffering capacity of carbonated mining waste (Mibladen) and the meager buffering capacity of the silicate mining waste (Zeida). These cases are representative of contaminated neutral drainage (CND) and acid mine drainage (AMD), respectively. The results highlight the consistency between the ANC–BNC experimental data and the associated modeling in terms of geochemical behavior, validating the approach and identifying the main mechanisms involved. The modeling approach identifies the dissolution of the main solid phases, which impact the pH and the speciation of lead as a function of the pH. This innovative approach, combining ANC–BNC experiments and geochemical modeling, allowed for the accurate identification of mineral phases and surface complexation phenomena, which control the release of lead and its speciation in drainage solutions, as well as within solid phases, as a function of pH. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Thomas Baumgartl” is provided in this record*

The reuse of low sulfide mine

Les résidus miniers représentent les sous-produits minéraux finement broyés issus des procédés de traitement et d’enrichissement des minerais. Durant l’exploitation d’une mine, ces rejets sont habituellement transportés sous formes de pulpes et entreposés en surface dans des aires d’accumulation appelées parcs à résidus. Ces derniers sont des ouvrages, le plus souvent, difficiles à gérer et coûteux à restaurer. Ils sont à l’origine d’une multitude d’impacts environnementaux qui dépendent principalement de leur potentiel polluant, de leur mode de gestion, de la stabilité physique des infrastructures de confinement et des conditions climatiques spécifiques au site d’entreposage. Dans ce contexte, plusieurs études ont été entreprises afin de développer de nouvelles techniques qui permettraient une gestion effective et durable de ces sous-produits minéraux. Des voies de valorisation dans le domaine du BTP ont ainsi été explorées. Les résultats ont montré la possibilité de réutilisation de certains rejets miniers comme matériaux cimentaires et additifs pour mortiers ou béton. Toutefois, la majorité des formulations proposées n’ont pas dépassé le stade du laboratoire. De plus, l’utilisation des rejets miniers comme matériaux de construction est encore sujet à des difficultés en matière d’acceptabilité sociale et à d’innombrables préoccupations, notamment leur stabilité physico-chimique et leur éco-compatibilité. En parallèle, l’utilisation artisanale et non contrôlée des rejets miniers à faibles teneurs en sulfures comme matériaux de construction est en pleine croissance dans quelques pays tel que le Maroc. En effet, à proximité de quelques sites miniers abandonnés, ces rejets sont considérés comme des sables naturels et sont utilisés pour la confection de mortier de finition et de surfaçage des murs d’habitations. Ce recyclage artisanal peut constituer des risques mécaniques et environnementaux liés surtout à la non-conformité mécanique de ces matériaux et à la présence de concentrations non négligeables de métaux résiduels dans les rejets miniers. L’objectif de ce travail de recherche est donc d’évaluer l’impact de l’utilisation actuelle de deux rejets miniers marocains (Zeida et Mibladen), communément utilisés comme agrégats dans la région de la haute-Moulouya, sur les propriétés physico-chimiques des mortiers de finition et d’étudier, sur le long terme, le relargage des métaux lourds en scénario de lixiviation. Ce travail se donne aussi comme objectif spécifique, d’étudier la faisabilité technique d’utilisation des rejets miniers à faible teneur en sulfures comme substituant au sable conventionnel pour la confection de mortiers d’enduit et de maçonnerie.Mine tailings represent the finely ground industrial by products generated throw beneficiation of ore minerals. During mine exploitation, these tailings are generally transported in slurry form to large storage facilities, called tailings ponds or impoundments. These facilities are, in most cases, difficult to manage and expensive to rehabilitate. They are responsible for the generation of important environmental impacts and significant ecological disruptions, depending on their pollution potential, management technique, physical stability and the climate conditions. In this context, numerous studies have been conducted to develop new techniques for a sustainable management of mine tailings. The feasibility of reusing some tailings in the construction sector as cementing materials and additives for mortars or concretes were successfully achieved. However, the majority of the conducted studies are still at laboratory stages. Moreover the reuse of tailings as construction material is yet subject of numerous difficulties in term of social acceptance. Various parameters are also of concern, especially the physical and chemical stability of tailings as well as their eco-compatibility. In parallel, the uncontrolled reuse of low sulfide tailings as construction material is increasing in some developing countries (e.g. Morocco). In fact, nearby some abandoned mine sites, these tailings are considered as natural sands and are used for the manufacture of surface finishing mortars. This traditional recycling may constitute mechanical and environmental risks, principally related to tailings mechanical unconformity and to their non-negligible residual metal concentrations. Therefore, the aim of the current research is to evaluate the actual impact of two Moroccan mine tailings (named Zeida and Mibladen), commonly used as aggregates in the Upper-Moulouya region, on the mechanical properties of mortars and on their long term environmental behavior. This work has also as specific aim, to study the technical feasibility of using low sulfide tailings as sand substitute for the manufacture of rendering and masonry mortars. To attain this aim, a thorough characterization of the physical, chemical and mineralogical properties as well as the geochemical behavior of mine tailings was carried out. Mechanical properties of tailings-based mortars were then measured and compared to reference samples (sand-based mortars) using different tests such as setting time, entrained air volume and compressive strength. In parallel, mortars durability and hydration products were evaluated by mean of durability tests (wetting drying cycles, sulfate attack and acid rain simulation) and analytical methods (scanning electron microscopy, X-ray diffraction and thermo-gravimetric analysis). Finally, mortar samples were submitted to various leaching tests to evaluate the pollution potential of these matrices

A comparative study on the practical use of low sulfide base-metal tailings as aggregates for rendering and masonry mortars

International audienceThe reuse of some industrial by-products in the construction industry saves natural resources and energy, while at the same time reduces environmental problems related to their surface disposal. Mine tailings are currently among the largest industrial by-products in the world, and yet, only limited studies have been conducted to evaluate their reuse potential. Moreover, abandoned base-metal tailings are increasingly used in some developing countries for the manufacture of mortars without any control, engineering basis or environmental concern. In this study, an experimental program using mechanical tests, mineralogical investigations and leaching tests is presented to assess the use of low sulfide base-metal tailings, with varying properties, as fine aggregates for rendering and masonry mortars. An authentic case study illustrating their use in Moroccan construction is additionally presented. Overall, it was observed that the main properties affecting the performances of these tailings-based mortars are the residual Pb–Zn concentrations and the fine content of each tailing. The Pb–Zn fraction, when using the appropriate substitution level, may serve as an active set retardant improving mortars setting time. The leaching of metals was also successfully stabilized in mortars

Valorisation des rejets miniers du district Pb-Zn de Touissit-Boubker (région orientale-Maroc)

In Morocco, several mine sites were abandoned after closure without any rehabilitation plan. These sites are characterized by the presence of significant tailings volumes, which has produced significant environmental impacts. The objective of this research is to study the use of mine tailings, sourced from the abandoned Pb-Zn district of Touissit-Boubker (Morocco), as aggregates for surface finishing mortars. The study consist firstly of a fine physical, chemical and mineralogical characterization of mine tailings, followed by an evaluation of tailings-based mortars mechanical properties. The pollution potential of the tailings based mortars was also assessed in this study. The results show that mine tailings are characterized by the presence of high fine content and significant concentrations of As, Cu, Cd, Pb and Zn. The use of tailings as aggregate produces a significant increase in the amount of water needed for mixing mortars as well as a decrease in mechanical strength. The dissolution of Pb and Zn in tailings-based mortars is very limited.Au Maroc, aucun dispositif n’a été mis en place pour gérer l’abandon des anciens sites miniers. Ces derniers sont caractérisés par la persistance d’immenses tonnages de résidus miniers dont la nocivité est à l’origine, dans de nombreux cas, d’importants impacts environnementaux. L’objectif de ce travail de recherche est d’étudier la faisabilité de valorisation des rejets abandonnés du district minier Pb-Zn de Touissit-Boubker (Maroc) comme granulats fins pour mortier de finition. L’étude consiste d’abord en une caractérisation des propriétés physiques, chimiques et minéralogiques des rejets, suivie d’une évaluation des propriétés mécaniques des mortiers confectionnés. L’étude comporte aussi une évaluation du potentiel polluant des mortiers à base de ce type de rejets. Les résultats ont mis en évidence la présence d’une grande proportion de particules fines (< 63µm) et des concentrations élevées en As, Cu, Cd, Pb et Zn dans les rejets miniers. Il a été observé que l’utilisation des rejets miniers comme agrégats, pour la confection de mortiers, engendre une importante augmentation de la demande en eau nécessaire au gâchage ainsi qu’une diminution significative des résistances mécaniques en particulier à court terme. Toutefois, la stabilisation des rejets miniers dans la matrice cimentaire est effective puisque la dissolution du Pb et du Zn s’avère très limitée

Influence of superplasticizers on mechanical properties and workability of cemented paste backfill

International audienc

Lead Mobilization and Speciation in Mining Waste: Experiments and Modeling

Mining produces significant amounts of solid mineral waste. Mine waste storage facilities are often challenging to manage and may cause environmental problems. Mining waste is often linked to contaminated mine drainage, including acidic waters with more or less elevated concentrations of trace metals such as lead. This work presents a study on the mobilization of lead from waste from two typical mining sites: Zeida and Mibladen, two now-closed former Pb–Zn mines in the Moulouya region of Morocco. Our research investigates the mobilization potential of Pb from the waste of these mines. The study involved acid–base neutralization capacity tests (ANC–BNC) combined with geochemical modeling. Experimental data allowed for the quantification of the buffering capacity of the samples and the mobilization rates of lead as a function of pH. The geochemical model was fitted to experimental results with thermodynamic considerations. The geochemical model allowed for the identification of the mineral phases involved in providing the buffering capacity of carbonated mining waste (Mibladen) and the meager buffering capacity of the silicate mining waste (Zeida). These cases are representative of contaminated neutral drainage (CND) and acid mine drainage (AMD), respectively. The results highlight the consistency between the ANC–BNC experimental data and the associated modeling in terms of geochemical behavior, validating the approach and identifying the main mechanisms involved. The modeling approach identifies the dissolution of the main solid phases, which impact the pH and the speciation of lead as a function of the pH. This innovative approach, combining ANC–BNC experiments and geochemical modeling, allowed for the accurate identification of mineral phases and surface complexation phenomena, which control the release of lead and its speciation in drainage solutions, as well as within solid phases, as a function of pH