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 (Türkiye). 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°C, 2 M HCl, 1/10 solid/liquid ratio, stirring speed of 900 min^-1 and W/PO₄^3- 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°C by adding a 'chelate breaking agent' at a NH₄⁺/WO₃ weight ratio of ≥ 1/4.