Solvent extraction of vanadium from a stone coal acidic leach solution using D2EHPA/TBP: Continuous testing

This paper reports on continuous testing of a process for the recovery of vanadium from a H2SO4-HF solution, generated from the leaching of stone coal, by solvent extraction using a D2EHPA/TBP mixture as the extractant. Three unit processes are included: fully continuous countercurrent solvent extraction and stripping; oxidation and precipitation; and calcination. The solvent-extraction circuit was operated for 96 h. With six stages of countercurrent extraction, 97.7% vanadium, 98.3% molybdenum, and 97.9% titanium were extracted, while the sodium, potassium, fluorine, and nickel impurities were barely extracted. Scrubbing removed co-extracted and aqueous-entrained zinc, magnesium, silicon, and arsenic impurities. Most co-extracted impurities were scrubbed in two stages. Using five stages of stripping, more than 99.8% of the vanadium was stripped, yielding a vanadium concentration in the loaded strip solution of 34.1 g/L. Co-extracted molybdenum(VI), titanium(IV), and iron(III) remaining in the stripped organic phase were removed by a saturated sodium carbonate solution and the regenerated organic was reused for vanadium extraction. Vanadium was selectively precipitated with 98.5% efficiency from the loaded strip solution by oxidation and precipitation with ammonium sulfate. A high-purity V2O5 (99.61%) product was successfully produced by this flowsheet.