Une étude sur l'utilisation des roches stériles comme inclusions drainantes dans les résidus miniers

RÉSUMÉ L’industrie minière génère de grandes quantités de rejets solides tels les roches stériles et les rejets de concentrateur. La gestion sécuritaire de ces rejets est un enjeu important. Les roches stériles sont typiquement entreposées dans des haldes alors que les résidus issus du traitement du minerai sont pompés sous forme de boue à l’intérieur du parc à résidus qui est ceinturé de digues. Ces résidus lâches et saturés, à granulométrie fine, se consolident lentement sous leur propre poids, ce qui augmente leur densité et leur résistance. Pour réduire les risques de nature géotechnique reliés à l’entreposage de surface des résidus miniers, on peut modifier le design des bassins en y ajoutant des inclusions drainantes composées de roches stériles à granulométrie grossière. Cette technique engendre plusieurs avantages, incluant l’accélération de la consolidation des résidus miniers fins. Les inclusions drainantes offrent un chemin de drainage préférentiel pour la dissipation des pressions d’eau en excès puisque leur conductivité hydraulique est plus de 100 fois supérieure à celle des résidus en raison de leur granulométrie grossière très étalée. Cela permet d’augmenter plus rapidement le degré de consolidation et la résistance des résidus et ainsi réduire les risques géotechniques. Cette technique de codisposition est un nouveau domaine de recherche. Des travaux récents de modélisation conceptuelle ainsi que des essais sur table sismique avec des inclusions de sable ont démontré la validité du concept. L’objectif de ce projet est de poursuivre ces travaux en abordant l’effet des inclusions de roches stériles sur la consolidation des résidus miniers en se basant sur un cas réel. Un programme d’essais a été mené pour caractériser les propriétés des résidus et des stériles provenant de la mine Osisko située à Malartic, au Québec. Ces propriétés ont ensuite été utilisées pour simuler l’influence d’inclusions drainantes ajoutées dans un parc à résidus. Cette analyse permet de dégager les éléments importants qui affectent la consolidation de résidus miniers à proximité d’inclusions drainantes.----------ABSTRACT The mining industry generates large quantity of waste materials such as waste rock and tailings. Those by-products may potentially be harmful to the environment and need to be safely contained. Waste rock is conventionally stored in piles on the surface while the tailings produced by the milling facilities are pumped as slurry inside an impoundment surrounded by dikes. Such saturated tailings tend to consolidate under their own weight after their deposition, increasing their density and resistance with time. Mine tailings can be problematic to manage as they contain a high proportion of fine particles, which give them complex geotechnical properties that can lead to dike failure in extreme cases. The design of a tailings impoundment can be modified to reduce the geotechnical risks by placing inclusions of coarse grained waste rock inside the pond. This technique offers many advantages such as increasing the consolidation rate of fine tailings. The inclusions of waste rock offer preferential drainage pathways to dissipate the excess pore water pressure inside the impoundment, as their saturated hydraulic conductivity is 100 to 1000 higher than that of tailings due to their coarser grain size. This phenomenon increases the consolidation rates and the resistance of the tailings, thus decreasing geotechnical risks. The co-disposition of waste rock and tailings is a recent research domain. Previous work on tailings tested on a seismic table and conceptual numerical modeling with simplified material properties has demonstrated the validity of this concept. The objective of this research project was to investigate the effects of waste rock inclusions on the consolidation of tailings using data coming from an actual mine site. Tailings and waste rock samples were obtained from the Osisko Malartic mine located in the province of Quebec, and characterized in the laboratory. The measured properties were used to simulate the use of waste rock inclusions in a tailings impoundment. This analysis increases our understanding of the parameters affecting the consolidation of tailings near a waste rock inclusion

Lessening Organ dysfunction with VITamin C (LOVIT): Protocol for a randomized controlled trial

International audienceBackground: Sepsis is a health problem of global importance; treatments focus on controlling infection and supporting failing organs. Recent clinical research suggests that intravenous vitamin C may decrease mortality in sepsis. We have designed a randomized controlled trial (RCT) to ascertain the effect of vitamin C on the composite endpoint of death or persistent organ dysfunction at 28 days in patients with sepsis. Methods: LOVIT (Lessening Organ dysfunction with VITamin C) is a multicenter, parallel-group, blinded (participants, clinicians, study personnel, Steering Committee members, data analysts), superiority RCT (minimum n = 800). Eligible patients have sepsis as the diagnosis for admission to the intensive care unit (ICU) and are receiving vasopressors. Those admitted to the ICU for more than 24 h are excluded. Eligible patients are randomized to high-dose intravenous vitamin C (50 mg/kg every 6 h for 96 h) or placebo. The primary outcome is a composite of death or persistent organ dysfunction (need for vasopressors, invasive mechanical ventilation, or new and persisting renal replacement therapy) at day 28. Secondary outcomes include persistent organ dysfunction-free days to day 28, mortality and health-related quality of life at 6 months, biomarkers of dysoxia, inflammation, infection, endothelial function, and adverse effects (hemolysis, acute kidney injury, and hypoglycemia). Six subgroup analyses are planned. Discussion: This RCT will provide evidence of the effect of high-dose intravenous vitamin C on patient-important outcomes in patients with sepsis. Trial registration: clinicaltrials.gov, NCT03680274, first posted 21 September 2018

Intravenous Vitamin C in Adults with Sepsis in the Intensive Care Unit

International audienceBACKGROUND Studies that have evaluated the use of intravenous vitamin C in adults with sepsis who were receiving vasopressor therapy in the intensive care unit (ICU) have shown mixed results with respect to the risk of death and organ dysfunction. METHODS In this randomized, placebo-controlled trial, we assigned adults who had been in the ICU for no longer than 24 hours, who had proven or suspected infection as the main diagnosis, and who were receiving a vasopressor to receive an infusion of either vitamin C (at a dose of 50 mg per kilogram of body weight) or matched placebo administered every 6 hours for up to 96 hours. The primary outcome was a composite of death or persistent organ dysfunction (defined by the use of vasopressors, invasive mechanical ventilation, or new renal-replacement therapy) on day 28. RESULTS A total of 872 patients underwent randomization (435 to the vitamin C group and 437 to the control group). The primary outcome occurred in 191 of 429 patients (44.5%) in the vitamin C group and in 167 of 434 patients (38.5%) in the control group (risk ratio, 1.21; 95% confidence interval [CI], 1.04 to 1.40; P = 0.01). At 28 days, death had occurred in 152 of 429 patients (35.4%) in the vitamin C group and in 137 of 434 patients (31.6%) in the placebo group (risk ratio, 1.17; 95% CI, 0.98 to 1.40) and persistent organ dysfunction in 39 of 429 patients (9.1%) and 30 of 434 patients (6.9%), respectively (risk ratio, 1.30; 95% CI, 0.83 to 2.05). Findings were similar in the two groups regarding organ-dysfunction scores, biomarkers, 6-month survival, health-related quality of life, stage 3 acute kidney injury, and hypoglycemic episodes. In the vitamin C group, one patient had a severe hypoglycemic episode and another had a serious anaphylaxis event. CONCLUSIONS In adults with sepsis receiving vasopressor therapy in the ICU, those who received intravenous vitamin C had a higher risk of death or persistent organ dysfunction at 28 days than those who received placebo. (Funded by the Lotte and John Hecht Memorial Foundation; LOVIT ClinicalTrials.gov number, NCT03680274.)