Étude de l'extraction sélective du nickel d'un minerai garniéritique pauvre par sulfuration par le soufre suivie de recuit en tube scellé

The effect of sulphur, in a vacuum-sealed tube at 700 °C, on a Ni-poor garnieritic ore, leads to a selective sulphidation of nickel ; however, the extremely small grain-size of the sulphides prevents use of physical means (flotation) for their recovery. In order to improve the grain-size of the sulphides, samples were submitted, after sulphidation, to annealing in various conditions : — A single annealing, at 1 000 °C, increases the grain-size slightly, but the recovery of the sulphides remains difficult. It leads however to an important lowering of the sulphidation-ratio of iron and, so, to a sharp improvement of the chemical selectivity of the procedure. — An annealing with 3 % NaCl allows the grain-size to be increased appreciably and the selectivity to be improved simultaneously. Granulometries are obtained (D₈₀ about 10 to 20 µm) which make possible the use of physical means of recovery. The sulphides consists of Mss when the annealing is followed by a quench, and of varying sulphide phase assemblages in the case of a slow cooling, while the silicates recrystallize as orthopyroxenes.L'action du soufre, en tube scellé à 700 °C, sur un minerai garniéritique pauvre, conduit à une sulfuration sélective du nickel ; cependant, l'extrême finesse des sulfures obtenus est un obstacle à leur récupération par voie physique (flottation). Dans le but d'améliorer la taille des grains de sulfures, on a soumis un minerai ainsi sulfuré à l'action de divers recuits : — Un simple recuit à 1 000 °C donne lieu à une augmentation limitée de la taille des grains qui restent encore difficilement séparables. La baisse importante du taux de sulfuration du fer conduit cependant à une nette amélioration en ce qui concerne la sélectivité de l'opération. — Un recuit en présence de 3 % de NaCl permet d'accroître sensiblement la taille des grains tout en améliorant également la sélectivité. Les granulométries obtenues (D₈₀ compris entre 10 et 20 µm) rendent possible une séparation par voie physique. Les sulfures sont constitués de Mss lorsque le recuit est suivi d'une trempe, et d'assemblages de phases sulfurées diverses lorsque le refroidissement est lent, tandis que les silicates recristallisent en orthopyroxènes.Gruget Olivier, Delbove François, Perruchot Alain. Étude de l'extraction sélective du nickel d'un minerai garniéritique pauvre par sulfuration par le soufre suivie de recuit en tube scellé. In: Bulletin de Minéralogie, volume 103, 6, 1980. pp. 603-612

Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients

International audienceThe aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed