Suchergebnisse

International audience ; For more than 50 years, the treatment of bauxite residues from the Gardanne alumina plant is the subject of a conflict between the plant, the state administrations, local authorities, environmental associations and residents. A first dispute had occurred between 1965 and 1967 with the discharge of residues in Mediterranean Sea. After the Barcelona Convention (1992) and the creation of the" Parc National des Calanques", the plant had been obliged to modify the residues treatment, with a liquid effluent, always discharged in the sea, and solid wastes which are stored in Mangegarri site. Then, a new dispute had started in 2014, always about the discharge in the sea but also about the storage on land. The dispute was very intense between 2015 and 2016 and is still relevant.To focus debates, Ministry of Environment had created, in 2016, a "Commission de Suivi de Site" (CSS), with representatives of state and local authorities, management and employees of the plant, environmental associations and residents. After one year of operation, the CSS had been divided in two subcommittee, one for the sea discharge and an other for the storage on land. These committees have no decision-making role, but are spaces of information, explanation and discussion. Formally, there are no scientific representatives in these committees, but, in some case, scientific can be invited to the meetings.An OHM (Human-Environment Observatory) is a study of socio-ecosystems manmade tool, designed to respond to their complexity by implementing a comprehensive approach by combining the study of environmental science and creating dynamic for the development instead of interdisciplinarity needed. For this, each OHM is organized around a focal object - which will be studied by all environmental sciences - a founder event came deeply upset (e.g. a mining area - object - and stopping the operation - founding event). The DRIIHM LabEx, Device for Interdisciplinary Research on human-environments Interactions, aggregates the 12 human-environments observatories in a network. The OHM Bassin Minier de Provence (OHM-BMP) had been the first OHM created in 2007 by the Environment Institute of CNRS. Located in the east of the department of Bouches-du-Rhône (SE of France), between Marseille and Aix-en-Provence, it concerns seventeen towns just over 100,000 inhabitants. For nearly two centuries, the unity of this space has been built around the lignite mining and industrialization induced by the mine. This area is typical of suburban and industrial dynamics in the Mediterranean area. These dynamic, often contradictory, have been particularly affected by the permanent cessation of mining in 2003.Long before the media coverage of the red mud dispute, OHM-BMP had launched interdisciplinary studies about the potential environmental and sanitary impacts of land storage. In this way, the OHM-BMP had provided scientific informations which had been recognized as independent by the different protagonists of the conflict. This is largely because these studies are financed with CNRS and Labex money and are not an order of one or another protagonist. The other side is that the financial resources are limited and not sufficient for a complete work. It's also regrettable that the state authorities do not consider these studies which, in contrast, have the confidence of the civil society. With their interdisciplinary approach and their opening to society, the OHMs are able to participate to the increase of scientific transparency, arguments analysis and explanations of issues – all things which are necessary to the resolution of a conflict, in a participatory approach. ; Depuis plus de 50 ans, la gestion des résidus de traitement de bauxite de l'usine d'alumine de Gardanne est source de conflit entre industriel, état, collectivités locales, riverains et associations écologistes. Un premier conflit a eu lieu en 1965-1967, avec le rejet des résidus en mer. La convention de Barcelone (1992) et la création du Parc National des Calanques (2012) ont amené l'industriel à développer un nouveau mode de gestion de ses résidus, avec un effluent liquide, toujours rejeté en mer, et un résidus solide stocké à terre. Cela a relancé les débats sur les rejets en mer mais a également déclenché l'apparition d'un conflit autour du stockage à terre. Ce nouveau conflit, démarré en 2014, très intense en 2015-2016, est toujours d'actualité, avec des pics médiatiques notamment lors d'épisodes météorologiques particuliers.Pour essayer de « canaliser » ce débat, l'Etat a mis en place, en 2016, une Commission de Suivi de Site (CSS) à cinq collèges : Services de l'Etat, Collectivités locales, Industriel, Salariés, Riverains et Associations. Ultérieurement, vu l'ampleur des sujets à traiter, cette CSS a été divisée en deux sous-commissions (Terre et Mer) et, devant la violence de certains échanges, un Garant a été nommé par la Commission Nationale du Débat Public pour conserver une certaine sérénité aux débats. La CSS n'a pas de rôle décisionnaire (cela relève directement du Préfet), mais est un espace d'information, d'explication, de discussion et de suggestion d'actions à mener. Officiellement, la recherche scientifique n'est pas présente dans cette CSS mais, sous certaines conditions, des « experts » ou « sachants » peuvent être invités à la demande de l'un ou l'autre des collèges.Les Observatoires Hommes-Milieux (OHM) ont été créé par le CNRS en 2007, comme des outils de recherches interdisciplinaires, permettant la mise en œuvre, autour d'un objet partagé, de recherches disciplinaires et interdisciplinaires aptes à développer le champ de l'écologie globale, dans l'objectif de répondre à la demande sociétale et de documenter la décision politique. Les OHM sont construits autour d'un objet constitué d'un lieu caractérisé par un fait structurant qui est profondément modifié par un élément fondateur. Les 12 OHMs existant sont réunis dans le Labex DRIIHM (Dispositif de Recherches Interdisciplinaires sur les Interactions Hommes-Milieux). Dans le cas du premier OHM créé, l'OHM Bassin Minier de Provence (OHM-BMP), le territoire est celui du Bassin Minier (entre Marseille et Aix en Provence), le fait structurant l'exploitation minière et l'élément fondateur, l'arrêt assez brutal de l'exploitation minière en 2003. Avant même l'émergence médiatique du conflit, l'OHM-BMP avait lancé différentes études interdisciplinaires sur la question des impacts sanitaires et environnementaux potentiels du site de stockage. L'OHM a ainsi pu intervenir à certaines étapes du débat public, en apportant des informations nouvelles qui ont été reconnues comme indépendantes par tous les partis. Le fait que l'OHM mène ces études, financés par de l'argent publique, de sa propre initiative et non pas à la commande de tel ou tel acteur a contribué à cette confiance. L'envers de la médaille est que, de ce fait, les moyens sont limités et pas à la hauteur du travail à faire. Malgré ces réussites, on peut déplorer que l'OHM soit plus considéré par certains acteurs que d'autres, et qu'en particulier les services de l'Etat et l'industriel ne reconnaissent pas réellement cet interlocuteur qui inspire à l'inverse une certaine confiance dans la société civile. Du fait d'une forte interaction interne, grâce à laquelle se mettent en place des débats contradictoires et un affinement des dispositifs, l'OHM est à ce stade capable d'aider à l'augmentation de la transparence scientifique, l'explicitation des enjeux, l'analyse des argumentations - nécessaires à un règlement de conflit dans la perspective des approches participatives en politique, exigées de nos jours par les institutions européennes.

Abstract
Red mud (RM) cementitious materials were prepared with the thermally, thermoalkali- or thermocalcium-activated RM, steel slag (SS), and other additives. The effects of different thermal RM activation methods on the cementitious material hydration mechanisms, mechanical properties, and environmental risks were discussed and analyzed. The results showed that the hydration products of different thermally activated RM samples were similar with the main products being C-S–H, tobermorite, and Ca(OH)2. Ca(OH)2 was mainly present in thermally activated RM samples, and the tobermorite was mainly produced by samples prepared with thermoalkali- and the thermocalcium-activated RM. The mechanical properties of the samples prepared by thermally and thermocalcium-activated RM had early-strength properties, while the thermoalkali-activated RM samples were similar to the late-strength type of cement properties. The average flexural strength of thermally and the thermocalcium-activated RM samples at 14 days were 3.75 MPa and 3.87 MPa respectively, whereas, the 1000 °C thermoalkali-activated RM samples only at 28 days was 3.26 MPa; the above data could reach the single flexural strength (3.0 MPa) of the first-grade pavement blocks of the building materials industry standard of the People's Republic of China-concrete pavement blocks (JC/T446-2000). The optimal preactivated temperature for different thermally activated RM was different; the optimal preactivated temperature for both thermally and thermocalcium-activated RM was 900 °C, and the flexural strength was 4.46 MPa and 4.35 MPa, respectively. However, the optimal preactivated temperature of thermoalkali activated RM at 1000 °C. The 900 °C thermally activated RM samples had better solidified effects for heavy metal elements and alkali substances. 600~800℃ thermoalkali activated RM samples had better solidified effects for heavy metal elements. Different temperatures of thermocalcium-activated RM samples showed different solidified effects on different heavy metal elements, which may be due to the influence of thermocalcium activation temperature on the structural changes of the hydration products of the cementitious samples. In this study, three thermal RM activation methods were proposed, and the co-hydration mechanism and environmental risk study of different thermally activated RM and SS were further elucidated. This not only provides an effective method for the pretreatment and safe utilization of RM, but also facilitates the synergistic resource treatment of solid waste and further promotes the research process of replacing part of traditional cement with solid waste.