Vanadium Recovery From Redox Flow Cell Waste Electrolytes via Precipitation With Quaternary Ammonium Salts

Abstract

Vanadium is classified as a “critical metal”; therefore, the recycling of vanadium-containing wastes–such as electrolytes from redox flow cells–represents a valuable contribution towards the more sustainable use of this element. Among various methods for processing concentrated vanadium-containing leachates, the precipitation of NH₄VO₃ is particularly favourable, as pure V₂O₅ can be obtained through thermal treatment of the resulting precipitate. In a novel approach, N-cetyl-N,N,N, trimethylammonium bromide (CTABr), a representative of larger quaternary organic ammonium ions, was investigated for precipitation of V(V) from a diluted, neutral V(V) solution. These ions decompose upon incineration, releasing V₂O₅ from the collected precipitate. CTABr was added to a waste electrolyte containing 2,076 mg L⁻¹ (40.76 mM) of vanadium, and the V-containing precipitate was collected. Using a CTABr:V molar ratio of 1.23:1 the vanadium concentration in the filtrate was reduced to 14 mg L⁻¹ V, corresponding to over 94% removal of the initial vanadium content. Elemental analysis and thermogravimetric analysis (TGA) of the incinerated residue indicated a V₂O₅ content of 66 wt.%, without further optimisation. This new method demonstrates a general approach for the efficient recovery of vanadium from diluted waste electrolytes and vanadium-containing leachates.