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 CaCl 2 as CaMoO 4 , then acidified with 30% HNO 3 , the resulting H 2 MoO 4 .H 2 O 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 (NH 4 )_2SO 4 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.
Highlights
There are increasing environmental concern in the world regarding the possible leaching of heavy metals from fly ash and boiler ash, generated by the electrical power stations that use heavy oil as a source of fuel, into land and ground water
Preparatory tests were performed to determine the principal parameters controlling the extraction of V and Mo from sulfate solution (mixing time, octanol-2 (%) in the organic phase, pH of the aqueous phase, TDA concentration, concentration of V in aqueous solutions, temperature)
Tests have proved that the addition of the octanol-2 in the range of 5-15% (v/v) to the organic phase (TDA/kerosene) did not affect the extraction of V and Mo (Fig. 3) and it was found that 5% (v/v) of octanol-2 is the minimum required concentration to prevent third-phase formation
Summary
There are increasing environmental concern in the world regarding the possible leaching of heavy metals from fly ash and boiler ash, generated by the electrical power stations that use heavy oil as a source of fuel, into land and ground water. Ash contains some valuable metals especially V, Ni and Mo which can be leached with acidic and alkaline solutions, selective precipitation is applied to separate the desired elements. Bal et al [12] studied the influence of temperature, NaOH concentration, and the pH on the stripping of V from Aliquat 336. He indicated that the limiting step of the stripping process consists in the slow transformation of the extracted polyoxometallate species (H2V10O42−8 ) into HVO24−.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
