Radium isotopes and their decay products are used to estimate the time since the accumulation of radium in impacted soils and sediments from crude oil and gas wastewater spills (Lauer & Vengosh, 2016). The retention of unsupported 226Ra and 228Ra from spill water to soil and the ingrowth of Ra progeny result in three independent age dating methods using the 228Th/228Ra, 210Pb/226Ra, and 228Ra/226Ra activity ratios. Here, we present an original method based on the accumulation of the alpha-recoil ed 228Ra and 224Ra atoms from soil and sediments to a spilled Non-Aqueous Phase Liquid (NAPL), initially not containing radium. In order to test this method, two different experiments were carried out. About 35 grams of monazite sand was left to react with 11 mL of white petroleum distributed by PIC S.r.l., (test 1) or distilled water (test 2) for a period of 6 months. Periodically, about 2-mL aliquots of reagent solutions were sampled, counted by gamma spectrometry and then reinjected into the glass vials. 228Ra and 224Ra activity concentrations were indirectly determined using their gamma-emitting daughter products, 228Ac peaks at 338/911 keV and 212Pb peak at 238 keV, respectively. As expected, 228Ra accumulation in the liquid phase is not detectable at the beginning, while that of 224Ra is. Since its abundance is inferred from 212Pb, we expect that other processes besides 224Ra recoil affects 212Pb activity, because 212Pb derives from the decay of 220Rn (thoron) which is a gas and thus have a higher mobility. Actually, liquid phase also depends on thoron recoil and diffusion from the sand to the liquid phase, counterbalanced by 220Rn decay and escape to the air phase in the glass vial. In order to quantify these thoron fluxes, proper experiments are in progress. From these data, proper equations to describe radium accumulation curves were obtained and compared with the theoretical ones. By resolving these equations with respect to time, the age of a spill can be obtained and applied to natural systems. A further observation is that 212Pb activity in white petroleum is 2.6 times that measured in distilled water. This may be due to a different solubility either of radium or radon in the NAPL. Since radon distribution coefficient between white petroleum and water at ambient temperature is known (De Simone et al., 2017) and that of radium is not, ad-hoc testing in a large range of pH is in progress to assess this. The final step will be to apply this new information to a real case-study. References De Simone G., Lucchetti C., Pompilj F., Galli G. & Tuccimei P. 2017. Laboratory simulation of recent NAPL spills to investigate radon partition among NAPL vapours and soil air. Appl. Radiat. and Isotop., 120, 106-110. Lauer N., & Vengosh A. 2016. Age Dating Oil and Gas Wastewater Spills Using Radium Isotopes and Their Decay Products in Impacted Soil and Sediment. Environ. Sci. Technol. Lett. , 3, 205-209.
Radium isotopes and their decay products to assess the age of a NAPL-spill
Voltaggio M;
2017
Abstract
Radium isotopes and their decay products are used to estimate the time since the accumulation of radium in impacted soils and sediments from crude oil and gas wastewater spills (Lauer & Vengosh, 2016). The retention of unsupported 226Ra and 228Ra from spill water to soil and the ingrowth of Ra progeny result in three independent age dating methods using the 228Th/228Ra, 210Pb/226Ra, and 228Ra/226Ra activity ratios. Here, we present an original method based on the accumulation of the alpha-recoil ed 228Ra and 224Ra atoms from soil and sediments to a spilled Non-Aqueous Phase Liquid (NAPL), initially not containing radium. In order to test this method, two different experiments were carried out. About 35 grams of monazite sand was left to react with 11 mL of white petroleum distributed by PIC S.r.l., (test 1) or distilled water (test 2) for a period of 6 months. Periodically, about 2-mL aliquots of reagent solutions were sampled, counted by gamma spectrometry and then reinjected into the glass vials. 228Ra and 224Ra activity concentrations were indirectly determined using their gamma-emitting daughter products, 228Ac peaks at 338/911 keV and 212Pb peak at 238 keV, respectively. As expected, 228Ra accumulation in the liquid phase is not detectable at the beginning, while that of 224Ra is. Since its abundance is inferred from 212Pb, we expect that other processes besides 224Ra recoil affects 212Pb activity, because 212Pb derives from the decay of 220Rn (thoron) which is a gas and thus have a higher mobility. Actually, liquid phase also depends on thoron recoil and diffusion from the sand to the liquid phase, counterbalanced by 220Rn decay and escape to the air phase in the glass vial. In order to quantify these thoron fluxes, proper experiments are in progress. From these data, proper equations to describe radium accumulation curves were obtained and compared with the theoretical ones. By resolving these equations with respect to time, the age of a spill can be obtained and applied to natural systems. A further observation is that 212Pb activity in white petroleum is 2.6 times that measured in distilled water. This may be due to a different solubility either of radium or radon in the NAPL. Since radon distribution coefficient between white petroleum and water at ambient temperature is known (De Simone et al., 2017) and that of radium is not, ad-hoc testing in a large range of pH is in progress to assess this. The final step will be to apply this new information to a real case-study. References De Simone G., Lucchetti C., Pompilj F., Galli G. & Tuccimei P. 2017. Laboratory simulation of recent NAPL spills to investigate radon partition among NAPL vapours and soil air. Appl. Radiat. and Isotop., 120, 106-110. Lauer N., & Vengosh A. 2016. Age Dating Oil and Gas Wastewater Spills Using Radium Isotopes and Their Decay Products in Impacted Soil and Sediment. Environ. Sci. Technol. Lett. , 3, 205-209.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
