[Determination of sulfite in flue gas desulfurization with seawater by ion chromatography]

The technology for flue gas desulfurization (FGD) with seawater is widely adopted by coal-fired power plants in coastal areas. SO2 in the flue gas is absorbed by alkaline seawater and transfered in aqueous phase as sulfite (SO3(2-)), and most SO3(2-) is transformed to sulfate (SO4(2-)) after an aeration process. The remaining SO3(2-) in the seawater discharged to sea area may be harmful to marine organism because of its biological toxicity, thus it is necessary to determine the concentration of SO3(2-) in the seawater for desulfurization. In this study, the method of determination of SO3(2-) in the seawater by ion chromatography was investigated. The separation was achieved on an IonPac AS14A column with 14 mmol/L NaOH-12 mmol/L Na2 CO3 solution as the mobile phase at a flow rate of 1.2 mL/min, and the detection was performed by a pulsed amperometric detector. Formaldehyde was added as a protective agent when sampling because the SO3(2-) is easy to be oxidized. To avoid the formation of Mg (OH)2 in the mobile phase with high pH value which might block the column, the Mg(2+) in seawater was precipitated by NaOH solution (pH 12.0) before sample determination. The method showed good linearity within the range of 0-100 mg/L with an average recovery of 116.8%. The method detection limit (MDL) reached as low as 0.05 mg/L. The relative standard deviations (RSD) for seawater matrix samples spiked at levels of 7.5, 25.0 and 75.0 mg/L were 2.1% 3.1% and 4.0% (n = 9) , respectively. The method has been applied for the determination of SO3(2-) in flue gas desulfurization seawater with the advantages of being fast, sensitive and selective.