Extraction of vanadium from ammonia slag under near-atmospheric conditions

Abstract

A process for extracting vanadium from ammonia slag is proposed in this work, taking advantage of the nature of V5+ vanadate ions condensing into a solid phase around a pH of 2. The slag is a mixture of oxides of Ca (36.0 mass %), Si (28.4 mass %), Al (9.3 mass %), Fe (7.1 mass %), V (6.9 mass %), S (3.9 mass %), Na (2.7 mass %), Ni (2.5 mass %), Mg (1.3 mass %), and other (K, P, and Ti) (1.9 mass %). The difficulty with extraction originates from the oxyanionic character of the vanadate ions, leading to the formation of vanadate salts with the concomitant cations. In contrast, a stepwise-pH-control process that is proposed in this work is effective for separating vanadium from the slag, as (1) the Si component in the slag is filtered off as the residue at the initial leaching step; (2) Fe, Al, and other cations are precipitated as the vanadate salts at pH 6, leaving Ca2+(aq) in the solution; (3) the vanadate component is transferred to the liquid phase by dissolving the precipitate in a NaOH(aq) solution of pH 13, leaving Fe, Ti, and Ni ions in the solid phase; and finally, (4) the pH of the solution is adjusted to 2. The vanadium component is solidified as sodium vanadate and V2O5. The maximum yield of vanadium from the slag is evaluated as 80.7%, obtaining for NaV6O15 and V2O5 with a purity of 97 mass %.