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

Abstract

ABSTRACT The leaching kinetics of tungsten in scheelite tailings in sodium carbonate solutions at low temperatures (25–75°C) were found to closely follow the predicted values based on the shrinking core model (SCM), originally developed at elevated temperatures (150–190°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. ∼ 10−7 vs. 10−4 s−1). The time required to extract over 90% of tungsten was estimated to be 15 days at 75°C, in contrast to 2 h at 200°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°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.