Selectively extracting H2WO4 of high purity from the H2SO4 decomposition product of scheelite through hydrogen peroxide coordination followed by purification using ion-exchange and solvent extraction and thermal decomposition

The discharge of ammonium-containing wastewater and saline wastewater, which are among the main sources of water pollution in China, is difficult to avoid in traditional tungsten extraction processes. Sulfuric acid decomposition of scheelite can address the issue of saline wastewater discharge, but effectively dissolving tungsten from the sulfuric acid decomposition product without causing ammonia pollution remains a challenge. To tackle these problems, this work proposes a novel process of selectively extracting tungsten from sulfuric acid decomposition products using hydrogen peroxide coordination. Under the optimum preparation conditions, 99.0% of tungsten in scheelite was transformed into tungstic acid. The extraction efficiency of tungsten from the product by hydrogen peroxide reached 99.4%, while tungsten content in residue is <1%. The conversion of tungsten from the product to peroxotungstic acid was investigated. After the purification using ion-exchange and solvent extraction, high-purity tungstic acid was obtained through thermal decomposition, with the content of each impurity element being lower than 15 mg/l. This study offers a new approach to producing high-purity tungstic acid from the sulfuric acid decomposition product of scheelite while eliminating the issues of ammonium-containing wastewater and saline wastewater.