RECOVERY OF PURE VANADIUM PENTOXIDE FROM SPENT CATALYST BY SOLVENT-EXTRACTION

Spent catalyst generated during manufacture of sulphuric acid is an im portant secondary source of vanadium. A process was standardised for l eaching of vanadium values from spent catalyst analysing 5.6% V2O5 by alkaline and acid leaching routes under oxidizing conditions. The leac hing efficiencies were found to be more than 95% for alkaline leaching and only 80 to 85% for acid leaching. The solvent extraction study wa s, therefore, confined to only alkaline leach solution which contained dissolved alumina and silica as the major impurities. After removal o f soluble silica and metal impurities from leach liquor, it analysed a pproximately 25 g/l V2O5. Prior to solvent extraction, the pH of the s olution was adjusted to 2.5-3.0. It was purified by a solvent extracti on process using 5% v/v alamine 336, 3% v/v isodeconal in kerosene. pr ocess conditions for extraction, scrubbing and stripping wee optimised Counter current solvent extraction of leach liquor was carried out in the laboratory involving a 4 stage extraction with O/A=5/4 and a 2 st age scrubbing with acidified water (pH 3.0) with o/A=5/1 followed by a 2 stage stripping with 4 M NH3 at o/A=1/1. Under the optimised condit ions, bench scale runs were carried out in a acrylic mixer settler uni ts of capacity 0.5 l to produce kilogramme quantities of pure vanadium pentoxide. Vanadium was recovered from the strip solution analysing 1 9 g/l V2O5 either as ammonium vanadate or vanadic acid and calcines to yield pure V2O5. It was used in the preparation of europium doped ytt rium vanadate red phosphor and found to meet the requirement of high p hotoluminescence efficiency.