Application of Ion Chromatography for the Determination of Nitrate in Process Streams of Thermal Denitration Plant

Abstract

A simple, accurate, and rapid analytical methodology for the determination of nitrate content in process streams of thermal denitration plant has been developed. The nitrate content in these process streams varies over a wide range of concentration (0.1–150 g L−1). Quantitative determination of nitrate was accomplished by anion exchange chromatography with conductometric detection in suppressed mode. The method requires a simple sample dilution step. A Metrosep A supp 3 analytical column connected in series with a Metrosep RP guard column was used for nitrate separation. A solution containing a mixture of 1.8 mM Na2CO3 and 1.7 mM NaHCO3 was used as eluent. The limit of detection for the determination of nitrate is 0.02 µg mL−1 and the relative standard deviation was 5% for the overall method. No interference was observed from either the chloride or closely eluting “system peak” in the determination of nitrate. The method was validated using an ion selective electrode based determination. The method has a high throughput and 6 samples were analyzed per hour to provide the data on the process parameters. No interference was observed from the other anionic impurities, namely chloride and sulphate. In the case of process streams from thermal denitration of Zr raffinate the method requires a sample pretreatment for the removal of large excess of zirconium from the sample matrix. Onguard-H cartridges were found most suitable for this purpose. The concentration of different anions could be measured simultaneously.