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

Owing to the high Na/V molar ratio of Na 3 VO 4 solution, traditional precipitation of vanadium will consume more H 2 SO 4 and discharge ammonia–nitrogen wastewater with more Na 2 SO 4 . In present work, a new process was proposed, in which CO 2 was employed to carbonate Na 3 VO 4 solution with simultaneous recovery of NaHCO 3 , followed by NH 4 VO 3 precipitation and solution recycling. Carbonation kinetics of Na 3 VO 4 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 CO 3 2− and its conversion to HCO 3 − mainly occurred and the CO 2 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 CO 2 pressure and vanadium concentration, and stirring speed had the most significant effect on reaction rate with the highest CO 2 absorption rate of 1.73 mol·m −3 ·s −1 at 550 rpm. The average CO 2 utilization efficiency was ~ 90% with NaHCO 3 precipitation of 42.3% at 70 g·L −1  V under 1 MPa of CO 2 pressure, while the average CO 2 utilization efficiency was ~ 35% under atmospheric pressure. Finally, the reaction rate equation of carbonation under high-pressure was deduced. Graphical Abstract