Experimental investigation of particle flow in a spiral concentrator

The spiral concentrator is a mineral processing device that separates mineral particles according to their densities and to a lesser extent particle size. In this thesis, a four-turn WALKABOUT PW1 spiral concentrator was used to investigate the particle movement inside the trough of spiral concentrator. For the experiments, a synthetic ore was prepared to mimic a real iron ore from Mont-Wright (Quebec). The sample consisted of 40% magnetite (ρ = 5.17 g/cm3) and 60% quartz (ρ = 2.65 g/cm3) with a size range smaller than 850 µm. In order to produce a comprehensive data set of particle distribution across the trough in every turn of spiral concentrator, the material was sampled at the end of every turn. The separation of mineral particles observed was as described in the literature, with small and dense particles tending towards the centre of the spiral, on the other hand, large light particles tending towards the outside of the spiral; and a small portion of the large heavy particles would report to the outside. The flow rate and physical properties of the slurry were analyzed from the sampled materials. A database produced from the experiment was used to build partition curves of the magnetite and quartz for every turn of the spiral. A partition curve model was applied to predict the recovery of magnetite in the virtual fifth turn of the spiral. The understanding of the separation mechanism gained in this study will be of interest to improve the design of spiral concentrator and to adjust the operational parameters of mineral concentration.Le spiral concentrateur est un dispositif de traitement du minerai qui peut séparer des particules minérales en fonction de leur densité et de la taille des particules. Dans cette thèse, un quatre tours WALKABOUT PW1 spirale concentrateur a été utilisée pour étudier le mouvement des particules à l'intérieur de la gouttière de concentrateur spirale. Pour réaliser les expériences, un échantillon artificielle a été préparé à imiter un véritable échantillon de minerai de fer de Mont-Wright, l'échantillon artificielle se compose de 40% de magnétite (ρ = 5,17) et 60% de quartz (ρ = 2,65) dans la gamme de taille plus petit que 850 µm. Afin de produire un ensemble de données complet de la distribution des particules à travers la gouttière de chaque tour de concentrateur spirale, le matériel a été échantillonné à la fin de chaque tour de la gouttière.La séparation des particules minérales observée était telle que décrite dans la littérature, où les particules petites et lourdes tendant vers le centre de la spirale, d'autre part, les particules grosses et légeres tendant vers l'extérieur de la spirale; et une petite partie des grosses particules lourdes ont été exceptionnellement être transportés à l'extérieur. Le débit et les propriétés physiques de la suspension ont été analysés à partir des matériaux de l'échantillon. Une base de données produite à partir des expériences a été utilisé pour construire les courbes de séparation de la magnétite et de quartz pour chaque tour de la spirale. Un modèle de courbe de séparation était appliquée à prédire la récupération de la magnétite dans le cinquième tour de la spirale virtuel. La compréhension du mécanisme de séparation acquise dans cette étude sera d'intérêt pour améliorer la conception de concentrateur spirale et d'ajuster les paramètres de fonctionnement de la concentration du minérai

Meta-Analytic Review of High Anxiety Comorbidity among Patients with Vitiligo

Background. Vitiligo is a disfiguring skin disease with profound psychosocial impacts, such as anxiety, but the reported effect sizes of associations vary. We aimed to conduct a meta-analysis to quantify the strength of association between anxiety and vitiligo and to estimate the prevalence of anxiety among individuals with vitiligo. Methods. A systematic literature search was performed in five online databases (MEDLINE, Embase, Web of Science, Cochrane Library, and PsycINFO) from inception until March 20, 2020. All of the eligible studies were comprehensively reviewed, and all of the available data were analyzed according to our predefined criteria. Results. Twenty-one studies involving 3259 patients in 11 countries were included in this meta-analysis. Compared with the healthy control group, patients with vitiligo often had concomitant anxiety (OR=6.14 [95% CI: 3.35–11.24], I2=30.1%). The pooled prevalence of anxiety in female patients was significantly higher than that in males (OR=2.24 [95% CI: 1.31–3.84], I2=0.0%). Subgroup analysis showed that the pooled prevalence of clinical anxiety disorder and anxiety symptoms was 12% (95% CI: 7%–16%, I2=76.3%) and 34% (95% CI: 21%–46%, I2=94.7%), respectively. No publication bias has been detected by Begg’s funnel plot and Egger’s test. Conclusion. Patients with vitiligo have high anxiety comorbidity, with female predominance. Dermatologists and psychiatrists should be vigilant to the presence of anxiety, apply appropriate interventions to reduce the psychological impacts in a timely manner, and thus promote recovery in vitiligo patients. However, due to some objective limitations (poor information about the OR and diversity in assessment tools among included studies), findings should be interpreted with caution