STUDY OF AMMONIA AND ACETALDEHYDE INTERFERENCE ON A SAW BASED MERCURY VAPOUR SENSOR FOR ALUMINA REFINERY PROCESSES
In this study, the effect of ammonia (NH3) and acetaldehyde (MeCHO) on the response of a surface acoustic wave (SAW) based elemental mercury (Hg0) vapour sensor operating at 35 and 75°C was investigated. The developed sensor was based on a SAW delay line, fabricated on a ST-cut quartz substrate with a gold (Au) film sensitive layer having a thickness of 50 nm. The sensor was exposed to mercury vapour concentrations between 24 ppbv (~0.2 mg/m3) and 365 ppbv (~3.3 mg/m3) in the presence of NH3 (383.8 ppmv) and MeCHO (303.4 ppmv). The detection limit of the sensor towards HgO vapour was calculated to be ~2.5 ppbv (~0.02 mg/m3) and ~1 ppbv (~0.01 mg/m3) at operating temperatures of 35°C and 75°C, respectively. The coefficient of variance of the sensor response magnitude was calculated to be within ±5.8% and ±4.5% when exposed to repeated pulses of 365 ppbv of Hg0 vapour at 35°C and 55°C, respectively, indicating excellent repeatability of the sensor towards low concentration of HgO vapour. Results showed that in the presence of NH3 and MeCHO, the response magnitude of the sensor towards Hg0 vapour deviated by 8-10% and 1-6% at 35°C and 75°C, respectively indicating that better selectivity towards Hg0 vapor can be achieved at elevated operating temperatures. The results indicate that the developed sensor can be a potentially cheaper and more reliable alternative to the current Hg0 monitoring methods used in alumina refineries.