Leaching of WO3 from sulfuric acid converted product of scheelite in NH3·H2O−NH4HCO3 solution

The leaching of sulfuric acid converted product of scheelite in NH 3 ·H 2 O−NH 4 HCO 3 solution was systemically studied to improve sulfuric acid conversion−ammonium salts leaching technology route for ammonium paratungstate production. The results showed that the WO 3 leaching efficiency was about 99% under optimal conditions of 350 r/min, liquid-to-solid ratio of 3 mL/g, 1 mol/L NH 4 HCO 3 , 4 mol/L NH 3 ·H 2 O, 25 °C, and 15 min. During the leaching, CaSO 4 almost had no change and was still in a banding or rod-like shape in short leaching time, while conglobate CaCO 3 was gradually formed on the CaSO 4 surface. A secondary reaction might occur between CaSO 4 and WO 4 2− , which could be restrained by a certain amount of CO 3 2− in the solution. There was no CaCO 3 phase determined by XRD in leaching residue of converted product for scheelite concentrate under optimal conditions, which was different from that for synthetic scheelite. The leaching process could be explained by neutralization reaction of H 2 WO 4 and solid transformation of CaSO 4 in NH 3 ·H 2 O−NH 4 HCO 3 solution.