A Novel Approach to Continuous Sampling and Measurement of Uranium Containing Particulate Matter

Continuous monitoring of industrial heavy metals release into the environment is important for emission control and compliance with standards. In this research, a method for continuous monitoring of uranium-containing particles in industrial emissions was developed. A particle-into-liquid sampler (PILS) was found to be a suitable instrument for the continuous collection of uranium. dioxide (UO2) and uranium tetrafluoride (UF4) at a rate of 1-5 mg h-1 into the transporting solution. The efficiency of various solutions (as sample transport media), including water and a sodium carbonate/hydrogen peroxide (Na2CO3-H 2O2) solution for the collection of particles was evaluated. The sodium carbonate/hydrogen peroxide solution was found to be preferable to water for the collection of UO2 and UF4 because particle build-up on the impaction surface and blockages in liquid transport lines were eliminated.;The data collected in experiments show that a sample air flow rate (1 min-1) has a significant effect on particle collection efficiency. The combination of a sample air flow rate of 101 min-1 (for UO2) or 16.71 min-1(for UF4), a steam flow rate of 1.5 ml min-1 and a sample transport solution flow rate of 0.5 ml min-1 demonstrated greater than 89% recovery of the particle mass of UO2 and greater than 92% recovery for UF 4 in the sample plus impactor drain lines.;A comparison was also made between uranium concentrations in particles collected from a traditional high volume sampler (filter) with aerosols collected by the PILS. Results showed that U in particles collected with the high volume air sampler using filters was consistently higher than in aerosols collected with the PILS. The PILS and filter results show a good correlation (R 2 = 0.98); on average the PILS collected 80% of uranium found in the filter samples.;Significant quantities of rare earth elements (REE) are found in tailings of uranium ore. Therefore, a microwave digestion method was also developed for six commonly used rare earth oxides using 2% (v/v) nitric acid that can be used with PILS for continuous monitoring of rare earth elements in ambient air. Results show that using 20 ml of nitric acid (2 % v/v) and closed vessel microwave heating at 100°C for 60 minutes yields greater than 90+/-5% recoveries of all six REEs. The PILS is an effective instrument for aerosol collection into a liquid; it is very reproducible, it is easy to use, it offers a better understanding of aerosol composition and provides time-dependent information.;Keywords: Continuous emission monitoring, uranium dioxide, uranium tetrafluoride, microwave digestion, particle-into-liquid sampler, rare earth oxide, high volume air sampler.