Leaching of WO3 from Sulfuric Acid Converted Product of Scheelite in NH3·H2O–(NH4)2C2O4 Solution

Due to the existence of large auxiliary material consumption, huge wastewater discharge, and high production cost in present tungsten extractive metallurgy practice, a novel technology featuring sulfuric acid conversion-ammonium salts leaching was proposed. Based on the complete conversion of tungsten minerals in sulfuric acid solution, this paper studied the leaching of WO 3 from sulfuric acid converted product of scheelite in NH 3 ·H 2 O–(NH 4 ) 2 C 2 O 4 solution. The effect of leaching conditions on WO 3 leaching efficiency and solid phase transformation was systemically investigated. The WO 3 leaching efficiency was > 98% under optimized conditions of 1 mol/L (NH 4 ) 2 C 2 O 4 , 3 mol/L NH 3 ·H 2 O, 350 rpm, 5 min, and 25 °C. The formed flaky CaC 2 O 4 ·H 2 O densely covered on the surface of banding or rodlike shaped CaSO 4 , which prevented the further transformation of CaSO 4 . The morphology of leaching residue was more irregular for converted product of scheelite concentrate than that for synthetic scheelite. Minor secondary reaction between CaSO 4 and (NH 4 ) 2 WO 4 might occur with increased (NH 4 ) 2 WO 4 concentration, which could be restrained by the existence of (NH 4 ) 2 C 2 O 4 in solution due to the larger K sp value of CaC 2 O 4 ·H 2 O than CaWO 4 . The leaching process could be explained by acid–base neutralization of H 2 WO 4 and phase transformation of CaSO 4 in NH 3 ·H 2 O–(NH 4 ) 2 C 2 O 4 solution. Graphical Abstract