Leaching kinetics of tungsten in scheelite tailings in sodium carbonate solutions at low temperatures (25-75C)

The leaching kinetics of tungsten in scheelite tailings in sodium carbonate solutions at low temperatures (25-75 & DEG;C) were found to closely follow the predicted values based on the shrinking core model (SCM), originally developed at elevated temperatures (150-190 & DEG;C). Temperature demonstrated a profound positive effect on the leaching kinetics of scheelite. The apparent rate constants, k values, determined from leaching the scheelite tailings at low temperatures, were found to be a few orders of magnitude lower than those obtained at elevated temperatures (i.e. & SIM; 10-7 vs. 10-4 s-1). The time required to extract over 90% of tungsten was estimated to be 15 days at 75 & DEG;C, in contrast to 2 h at 200 & DEG;C. The experimental kinetic data from leaching the scheelite tailings were found to consistently outperform the kinetic model prediction, by as much as 70% and 400% at 50 and 25 & DEG;C, respectively. As observed at elevated temperatures, an increase in sodium carbonate concentration or agitation speed had little effect on the leaching kinetics at low temperatures. This study demonstrated the potential use of sodium carbonate solutions as a non-aggressive lixiviant in a percolation or dump leach operation, which could be considered as an environmentally viable reprocessing option for scheelite tailings. Il a ete constate que la cinetique de lixiviation du tungstene des residus de scheelite dans des solutions de carbonate de sodium a basse temperature (25-75 & DEG;C) suivait de pres les valeurs predites basees sur le modele a c & OELIG;ur retrecissant (SCM), originellement developpe a des temperatures elevees (150-190 & DEG;C). La temperature a demontre un effet positif profond sur la cinetique de lixiviation de la scheelite. Les constantes cinetiques apparentes, valeurs k, determinees a partir de la lixiviation des residus de scheelite a basse temperature, se sont revelees etre de quelques ordres de grandeur inferieures a celles obtenues a des temperatures elevees (c.-a-d. & SIM;10-7 contre 10-4 s-1). Le temps requis pour extraire au-dela de 90% du tungstene a ete estime a 15 jours a 75 & DEG;C, contre 2 heures a 200 & DEG;C. On a trouve que les donnees cinetiques experimentales de la lixiviation des residus de scheelite surpassaient regulierement les predictions du modele cinetique, jusqu'a 70% et 400% a 50 et 25 & DEG;C, respectivement. Comme observe a des temperatures elevees, une augmentation de la concentration du carbonate de sodium ou de la vitesse d'agitation avait peu d'effet sur la cinetique de lixiviation a basse temperature. Cette etude a demontre l'utilisation potentielle de solutions de carbonate de sodium comme lixiviant non agressif dans une operation de percolation ou de lixiviation de decharge, ce qui pourrait etre considere comme option de retraitement ecologiquement viable pour les residus de scheelite.