Sustainable Mining and Metallurgy

At present, sodium hydroxide alkali leaching method is usually used to extract tungsten from spent SCR denitration catalyst，and tungsten-containing alkaline leaching solution is obtained. In addition to tungsten, the alkaline leaching solution also contains impurity elements such as vanadium, silicon, and sulfur. Due to the high alkali concentration of the solution, traditional extraction and adsorption methods are difficult to implement. The traditional hydrochloric acid neutralization-calcium chloride precipitation method would take Cl^- into the system, resulting in equipment corrosion. In this paper, a new magnesium sulfate desilication-calcium oxide precipitation process was proposed to remove silicon and precipitate tungsten to prepare scheelite concentrate. In the process of magnesium sulfate desilication, by using sulfuric acid to adjust the pH value of the system to 11, under the condition of magnesium-to-silicon molar ratio of 0.9, the silicon removal rate can reach 97.6%. The desilication solution was precipitated by calcium oxide to produce scheelite concentrate. Under the optimum process conditions of calcium-to-tungsten molar ratio of 1.1 and boiling temperature of 108℃, the WO₃ content in the obtained scheelite concentrate product reached 74.69%, the sulfur content was 0.90%, and the silicon content was 1.00%, which met the requirements of YS/T 231—2015 Grade Ⅰ scheelite concentrate. The process realizes the efficient recovery of tungsten from the alkaline leaching solution of spent SCR denitration catalyst, and avoids the potential equipment corrosion issues associated with the traditional hydrochloric acid neutralization-calcium chloride precipitation method.