Extraction of tungsten from scheelite concentrate using a methanesulfonic acid- phosphoric acid coleaching process followed by solvent extraction with N1923

Methanesulfonic acid (CH3SO3H) is a nonvolatile acid, and its calcium salt shows high solubility. These advantages of CH3SO3H have been utilized to leach scheelite in the presence of H3PO4. Thus, tungsten enters the solution as phosphotungsten hetempolyacid and calcium enters the solution as a soluble calcium salt. Because of the absence of solid products, over 98.5% of the scheelite was digested under the following conditions: CH3SO3H concentration of 2.5 mol/L, H3PO4 concentration of 10 g/L , a liquid/solid ratio of 10:1, a leaching temperature of 80 degrees C, and a leaching time of 4 h. Over 99.9% tungsten was extracted from the leaching solution under the following conditions: 15% N1923 concentration, an O/A ratio of 1:1, a temperature of 20 degrees C, and a contact time of 10 min. Then, CH3SO3H was regenerated by adding H2SO4 to the raffinate, producing a high-quality gypsum. Subsequently, the solution obtained from the CH3SO3H regeneration process was reused to leach scheelite after adding the consumed CH3SO3H. The efficient extraction of tungsten and the decrease in wastewater and waste residue discharge in this technology indicate its potential for industrial applications.