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 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 center dot m(-3)center dot 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 center dot m(-3)center dot s(-1) at 550 rpm. The average CO2 utilization efficiency was similar to 90% with NaHCO3 precipitation of 42.3% at 70 g center dot L-1 V under 1 MPa of CO2 pressure, while the average CO2 utilization efficiency was similar to 35% under atmospheric pressure. Finally, the reaction rate equation of carbonation under high-pressure was deduced. [GRAPHICS] .