Solvent extraction of tungsten and rare earth with tertiary amine N235 from H2SO4-H3PO4 mixed acid leaching liquor of scheelite

Scheelite is a calcium tungstate mineral that is an important ore of tungsten. It also contains small amounts of rare-earth metals, that enter the leaching liquor along with tungsten (W) after decomposition of the ore with H2SO4-H3PO4 mixed acid. In this study, a novel process was developed to effectively extract and separate tungsten and light rare earth (LRE) from this leaching liquor. La will represent LREs including La, Ce and Nd to be extracted in this research. First, W and La were extracted from the leaching liquor using a tertiary amine (N235). The results showed that 99.8% of W and 99.5% of La were extracted in the form of La-phosphotungstic acid complex anions under the conditions of N235 10% v/v, isooctanol 4% v/v, organic/aqueous (O/A) ratio of 1:1, pH of 2.6, temperature of 30 degrees C, and contact time of 10 min. Then, W and La were separated using a stripping process with H2SO4 solution. Nearly 99% of the La was recovered after single-stage stripping under the optimum stripping conditions of 1.5 mol/L H2SO4 solution, 10 min stripping time and O/A 1:1 at 45 degrees C, while almost no tungsten was stripped. After stripping with two cross-current extraction stages, the total La stripping reached 99.5%. Finally, the tungsten loaded on the organic phase was stripped with ammonia solution. Under the same optimum conditions, W stripping exceeded 99%. Extraction and two-stage stripping enabled effective recovery and separation of W and La from the leaching liquor. Based on above results, the process flowchart for extracting tungsten and light rare earth from scheelite was proposed. The proposed method is expected to promote further exploitation of valuable tungsten and rare-earth metals from scheelite ores.