Assessment of long term mining waste behavior by a dynamic leaching test : application to contrasted physico-chemical conditions

International audienceMining activity has generated large amounts of mining wastes abandoned on the site after extraction, concentration or metallurgic processes. In this study assessment of the long term behaviour of mining wastes has been performed by the realisation of a dynamic leaching test performed with a Soxhlet device on mining wastes from two contrasted sites : Bentaillou and Saint-Salvy from south-west France. Sphalerite and galena are the source of heavy metals, (Zn, Cd and Pb) in both sites. Pyrite and pyrrothite are the main potential acid source in Saint-Salvy and Bentaillou respectively. Although both wastes display high contents of carbonate minerals associated to the metal bearing phases, their composition is different, calcite for Bentaillou and siderite for Saint-Salvy allowing different minerals transformations and drainage mining water compositions. Due to different impoundment type, dumps for Bentaillou and a dam for Saint-Salvy, oxidation reactions are favoured in the former compared to the latter. Waste drainage waters generated in situ display lower pH, Eh and higher Fe and heavy metals in drainage waters from Saint-Salvy compared to those from Bentaillou. The leaching experiments lasted 62 days and 84 days for Bentaillou sample and Saint-Salvy sample respectively corresponding to an equivalent time of 288 and 183 years respectively calculated from pluviometry in situ. During the experiment, the amounts of elements released was higher for Saint-Salvy sample ( 0.2 % of Zn, and Pb and 1,4 % of Cd) than for the Bentaillou one ( 9.7 % of Zn, and 0.15 % of Pb and 46 % of Cd). The comparison of experimental leaching results with site data on waste drainage waters demonstrated the validity of laboratory results under oxidic conditions at Bentaillou while the duration experimentally estimated for total sulphide oxidation overestimates the time calculated from the sulfate flow in field drainage waters under reducing conditions at Saint-Salv

Evaluation du comportement à long terme des déchets miniers par un essai de lessivage dynamique : application à différentes conditions physico-chimiques

National audienceLes différents processus de l'industrie minière tels que la prospection, l'extraction et le traitement génèrent d'importantes quantités de déchets miniers enrichis en métaux toxiques tels que Hg, As, Pb, Cd. Ils constituent des sources potentielles de contamination métallique pour les différents compartiments de l'environnement (sols, eaux superficielles et souterraines, atmosphère). L'évaluation du comportement à long terme des déchets miniers reste un défi pour les chercheurs. En effet, au delà des analyses de concentration totale en contaminant c'est leur mobilité qui doit être évaluée pour estimer leur impact potentiel sur l'environnement et aussi pour répondre aux questions d'aménagement des sites miniers et de gestion des déchets

Un risque d'origine anthropique : la contamination chronique par les métaux lourds à proximité d'anciens sites miniers. Le cas de la mine (plomb, zinc, cadmium) de Jebel Ressas (Tunisie nord-orientale)

L'analyse des risques en relation avec l'environnement s'intéresse surtout aux catastrophes naturelles telles que les éruptions volcaniques, les inondations, les séismes. Or, la société actuelle étant fortement marquée par le développement industriel et technologique, les risques d'origine anthropique deviennent de plus en plus prégnants.L'objectif de l'étude entreprise est de proposer une nouvelle méthode d'évaluation et de cartographie du risque de contamination métallique sur et autour d'un ancien site minier situé à proximité de la ville de Tunis. Ce type de risque que les sociologues dénomment " risques diffus " (Beck, 1992 ; Peretti-Watel, 2000), appelle une approche interdisciplinaire couvrant un large spectre depuis la géochimie jusqu'aux données sociétales afin d'intégrer les données quantitatives et qualitatives dans un même modèle. Les résultats préliminaires exposés dans cet article ont été obtenus en adoptant une démarche d'analyse du risque basée sur le couplage entre une analyse de l'intensité de l'aléa et de l'estimation du degré de vulnérabilité des enjeux, adaptés à une contamination chronique d'un écosystème

Are Cu isotopes a useful tool to trace metal sources and processes in acid mine drainage (AMD) context?

In the South-West Europe (Iberian Pyrite Belt), acid mine drainage (AMD) processes are especially problematic because they affect the environmental quality of watersheds, restricting the use of surface water. Recent studies have shown that Cu isotopes are fractionated during the oxidative dissolution of primary sulfide minerals and could be used to trace metal cycling. However the chemistry of Cu in such environment is complex because Cu is redistributed within numerous secondary minerals and strongly dependent on the hydroclimatic conditions that control key parameters (pH, redox conditions). Finally, it remains difficult to compare the various field studies and deliver some strong general tendencies because of these changing conditions. For these reasons, concerted studies on Cu isotopes fractionation in waters impacted by AMD may help to reveal the sources and transport pathways of this important pollutant. To address this issue, we used a representative scenario of strong contamination by AMD in the Iberian Pyrite Belt (SW Spain), the Cobica River. The aim of our study is to measure the Cu isotopes signature in the waters (river, mine lake, water draining waste) of the small Cobica River system (Huelva, Spain), sampled during a short period (8 h) to avoid any change in the hydro-climatic conditions. This provided an instantaneous image of the isotopic Cu signature in a small mining systems and helped us to constrain both the processes affecting Cu isotopes and their use a potential tracer of metals in contaminated environments.This work was supported by the french national programme EC2CO Biohefect/Ecodyn//Dril/MicrobiEen (INSU/CNRS, France), the Paul Sabatier University (France) and the Department of Mining, Mechanical, Energetic and Construction Engineering of the University of Huelva (Spain)

Etude de l'alteration dans le massif basaltique de Mururoa (Polynesie francaise): analyses des phases solides et fluides et modelisation thermodynamique

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79043 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Chemical and Sr isotopic compositions of 3 step leachates and residues of bulk samples, zeolites, and smectites from Lower Miocene sediments at ODP Site 166-1007

Massive clinoptilolite authigenesis was observed at about 1105 meters below sea floor (mbsf) in lower Miocene wellcompacted carbonate periplatform sediments from the Great Bahama Bank [Ocean Drilling Program, ODP Leg 166, Site 1007]. The diagenetic assemblage comprises abundant zeolite crystallized within foraminifer tests and sedimentary matrix, as well as Mg smectites. In carbonate-rich deposits, the formation of the zeolite requires a supply of silica. Thus, the objective of the study is to determine the origin of the silica supply, its diagenetic evolution, and consequently the related implications on interpretation of the sedimentary record, in terms of local or global paleoceanographic change. For lack of evidence for any volcaniclastic input or traces of Si-enriched deep fluids circulation, an in situ biogenic source of silica is validated by isotopic data and chemical modeling for the formation of such secondary minerals in shallow-water carbonate sequences. Geochemical and strontium isotopic data clearly establish the marine signature of the diagenetic zeolite, as well as its contemporaneous formation with the carbonate deposition (Sr model ages of 19.6-23.2 Ma). The test of saturation for the pore fluids specifies the equilibrium state of the present mineralogical assemblage. Seawater-rock modeling specifies that clinoptilolite precipitates from the dissolution of biogenic silica, which reacts with clay minerals. The amount of silica (opal-A) involved in the reaction has to be significant enough, at least 10 wt.%, to account for the observed content of clinoptilolite occurring at the most zeolite-rich level. Modeling also shows that the observed amount of clinoptilolite (~19%) reflects an in situ and short-term reaction due to the high reactivity of primary biogenic silica (opal-A) until its complete depletion. The episodic occurrence of these well-lithified zeolite-rich levels is consistent with the occurrence of seismic reflectors, particularly the P2 seismic sequence boundary located at 1115 mbsf depth and dated as 23.2 Ma. The age range of most zeolitic sedimentary levels (biostratigraphic ages of 21.5-22 Ma) correlates well with that of the early Miocene glaciation Mi-1 and Mi-1a global events. Thus, the clinoptilolite occurrence in the shallow carbonate platform environment far from volcanogenic supply, or in other sensitive marine areas, is potentially a significant new proxy for paleoproductivity and oceanic global events, such as the Miocene events, which are usually recognized in deep-sea pelagic sediments and high latitude deposits