Carbonation of Na₃VO₄ Solution with CO₂ for Recovery of NaHCO₃ and NH₄VO₃: Kinetic Analysis of Carbonation Process

Abstract

Owing to the high Na/V molar ratio of Na₃VO₄ solution, traditional precipitation of vanadium will consume more H₂SO₄ and discharge ammonia–nitrogen wastewater with more Na₂SO₄. In present work, a new process was proposed, in which CO₂ was employed to carbonate Na₃VO₄ solution with simultaneous recovery of NaHCO₃, followed by NH₄VO₃ precipitation and solution recycling. Carbonation kinetics of Na₃VO₄ solution under both atmospheric and high pressures were studied. Under atmospheric pressure, the solution pH first decreased rapidly, slowly, rapidly again with carbonation time, and finally stabilized at pH  7.3; the formation of CO₃²⁻ and its conversion to HCO₃⁻ mainly occurred and the CO₂ absorption rates of different vanadium concentrations were almost the same (about 0.026 mol·m⁻³·s⁻¹) at pH of 9.0‒9.6. Under high pressure, the reaction rates at early stage increased with CO₂ pressure and vanadium concentration, and stirring speed had the most significant effect on reaction rate with the highest CO₂ absorption rate of 1.73 mol·m⁻³·s⁻¹ at 550 rpm. The average CO₂ utilization efficiency was ~ 90% with NaHCO₃ precipitation of 42.3% at 70 g·L⁻¹ V under 1 MPa of CO₂ pressure, while the average CO₂ utilization efficiency was ~ 35% under atmospheric pressure. Finally, the reaction rate equation of carbonation under high-pressure was deduced.

Graphical Abstract