Acidic leaching of scheelite concentrate and production of hetero-poly-tungstate salt

The aim of this study is to investigate the utility of adding chelating agent during hydrochloric acid leaching of low-grade scheelite concentrates, obtained from Uludag, Bursa (Turkiye). Examined parameters were as follows; leaching conditions, selective precipitation of tungsten salt from the acidic leach solution in which tungsten exists as hetero-poly-tungstate, the optimum precipitation conditions, the possibility of obtaining pure and nano-sized tungsten salt. Chelating agent leaching of scheelite concentrates in acidic solutions involves fewer process steps as compared to the classical methods. Furthermore, this route enables production of pure WO3 under prevalent conditions and without generating any spent liquor. The optimum leaching conditions were found to be 80 degrees C, 2 M HCl, 1/10 solid/liquid ratio, stirring speed of 900 min(-1) and W/PO43- weight ratio of 7/1. A tungsten leaching efficiency of 98% was reached under these conditions. It was also possible to selectively precipitate a pure (over 99%) tungstate salt, within minutes, from the poly-tungstate solution at 25 degrees C by adding a 'chelate breaking agent' at a NH4+/WO3 weight ratio of greater than or equal to 1/4. (C) 1999 Published by Elsevier Science B.V. All rights reserved.