Extraction and separation of molybdenum and vanadium from alkaline leaching

Abstract

Extraction of vanadium and molybdenum from alkaline leaching solution of boiler ash was investigated. The ash coming from heavy oil-fired electrical power station was leached with 8 mol dm^-3 sodium hydroxide at 373 K. The leaching solution was cooled to 278 K; an alkali-precipitate was precipitated. The precipitate was dissolved in sulfuric acid and a selective solvent extraction process was applied. First, almost all the molybdenum was extracted with 1.5% (v/v) tri-n-dodecylamine/kerosene, stripped with 0.5 mol dm^-3 NaOH and precipitated with CaCl₂ as CaMoO₄, then acidified with 30% HNO₃, the resulting H₂MoO₄.H₂O was calcinated at 723 K for 4 hours to give molybdenum oxide, next the vanadium was extracted from the raffinate coming from the first solvent extraction with 25% (v/v) tri-n-dodecylamine/kerosene at pH 1.8, stripped with 0.5 mol dm^-3 NaOH, precipitated with (NH₄)_2SO₄ at pH between 7.5-8.5 as ammonium metavanadate and calcinated at 773 K for twenty four hours to yield 99.9% vanadium pen toxide.