Deep arsenic removal of high-arsenic V2O5 for the preparation of vanadium electrolyte

High-arsenic vanadium pentoxide is a vanadium product from stone coal and Bayer crystallized vanadium slag. Excessive arsenic impurity is a serious limiting issue to prepare vanadium electrolyte of all-vanadium redox flow batteries. Density functional theory simulations verified that the adsorption energy, binding energy, and desorption energy of arsenic ions with typical C-OH sites on graphite electrode were higher than those of vanadium ions. Arsenic ions would occupy the reaction sites and hinder the redox reaction of vanadium ions, which deteriorated vanadium electrolyte performances. A combined strategy based on reduction roasting and sulfidation precipitation was proposed to realize deep arsenic removal from high-arsenic V 2 O 5 . Phase characterization of high-arsenic V 2 O 5 revealed that arsenic existed as As 2 O 5 (69 wt%) and As 2 O 3 (31 wt%). Thermodynamic calculations demonstrated that effective arsenic removal was feasible based on reduction roasting using V 2 O 3 and sulfidation precipitation using Na 2 S. The removal efficiency of arsenic reached 68.3 % under the reduction roasting conditions of n (V2O3) /n (As2O5)  = 8:1, 650 °C and 4  h. Under the sulfidation precipitation conditions of n (S2-) /n (As3+)  = 9:1, 80 °C and pH = 3, the precipitation efficiency of arsenic was 82 %. The total arsenic removal efficiency in the whole process for vanadium electrolyte preparation from high-arsenic V 2 O 5 reached 99.5 %. The arsenic content in as-prepared vanadium electrolyte was only 1  ppm, which met the requirements of China national standard (GB/T 37204–2018). As-prepared vanadium electrolyte exhibited comparable electrochemical performances with commercial vanadium electrolyte. The proposed strategy achieves deep arsenic removal of high-arsenic V 2 O 5 and is of great significance for the preparation of vanadium electrolyte.