Complexation extraction of scheelite and transformation behaviour of tungsten-containing phase using H2SO4 solution with H2C2O4 as complexing agent
Qingsheng Liu, Tao Tu, Hao Guo, Huajin Cheng, Xuezhong Wang
Abstract
The extraction of tungsten from scheelite was carried out using a sulfuric acid solution with oxalic acid as the chelating agent. Tungsten was obtained in the form of highly soluble hydrogen aqua oxalato tungstate (H2[WO3(C2O4)·H2O]) during the leaching process, while calcium remained in the residue as calcium sulfate dihydrate (CaSO4·2H2O). About 99.2% of the tungsten was leached at 70 °C, 1.5 mol/L sulfuric acid, 1 mol/L oxalic acid, a liquid/solid ratio of 25:1 (mL/g), an oxalic acid to sulfuric acid molar ratio of 1:1, a stirring speed of 300 r/min and a leaching time of 2 h. H2[WO3(C2O4)·H2O] was thermally decomposed into tungstic acid (H2WO4), and tungsten trioxide (WO3) was directly produced by calcining H2WO4 at 700 °C for 2 h. The surface chemical reaction was determined to be the controlling step during tungsten leaching, and the apparent activation energy was calculated to be 51.43 kJ/mol.