The investigation of dissolution behavior of gangue materials during the dissolution of scheelite concentrate in oxalic acid solution

Scheelite mineral which includes CaWO4 as a main compound is one of the most important raw materials used for the industrial production of W. Scheelite concentrate used in this study included CaMoO4 and the oxides of Fe, Ca, Si, P, Al, Mn, S, Zn, Mg, Ba, K, Ti and Sr as gangue materials. CaWO4 reacts with oxalic acid (H2C2O4) to form water-soluble hydrogen aqua oxalato tungstate (H2[WO3(C2O4)H2O]) and insoluble calcium oxalate monohydrate (CaC2O4H2O). Additionally, the dissolution behavior of gangue materials during the leaching of the scheelite concentrate in H2C2O4 solution must be known for the designing of the purification process applied in the industrial production of pure W. The aim of this study was to investigate the effects of temperature and H2C2O4 concentration on the dissolution of gangue materials in the scheelite concentrate. It was found that while the oxides of Si, P, Al, S, Zn, Ba, K, Ti and Sr were not dissolved in H2C2O4 solution, the oxides of Ca, Mo, Fe and Mn were dissolved forming complex oxalate ions. MgC2O4 which was formed from MgO in the scheelite concentrate was also dissolved due to its high solubility.