Scheelite (CaWO4) leaching in mild conditions via heptatungstate sorption by MgAl– Layered Double Hydroxide

The possibility of extraction of W(VI) as heptatungstate species (W 7 O 24 6- ) from pure scheelite mineral (CaWO 4 ) under mild conditions has been evaluated using an inorganic anion exchanger MgAl–Layered double hydroxide (LDH). An optimal pH of 5 was determined for the dissolution/adsorption step while desorption was carried out using a carbonate solution at pH 11. After a leaching time of 24 h with an LDH/scheelite ratio of 1.8, up to 30 % of tungsten has been extracted while scheelite alone is almost insoluble in these conditions. Two sorption mechanisms have been assumed: exchange of heptatungstate ions with carbonate ions of the LDH and precipitation of W(VI) with aluminum cations released from LDH dissolution. Thus, this work provides a proof of concept for the use of LDH in the extraction and recovery of tungsten from scheelite through a low environmental footprint process. • Layered Double Hydroxide is able to promote the leaching of scheelite • In situ infrared spectroscopy shows the formation of polyoxometalate species • Scheelite can be dissolve in absence of concentrated acid or base