Testing line for processing of dissolved inorganic carbon from water for radiocarbon dating determining the efficacy of trapping carbon dioxide for an automated system
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Date
2021-11-17
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Publisher
Australian Nuclear Science and Technology Organisation
Abstract
ANSTO’s radiocarbon capability experiences a high demand for processing groundwater samples
for studies in water resource sustainability. Currently water samples are processed manually using
extraction of DIC by acidification of the water and sparging with high purity helium gas (He), then
cryogenic trapping of the CO₂ with recirculation of the He carrier gas to effect complete trapping of
the CO₂ . This method is based on that of McNichol et al. [1].
In order to increase our capacity to extract the dissolved inorganic carbon (DIC), we are developing
an automated DIC extraction system. To develop this system and test that efficacy of redesigned
traps to completely capture the CO₂ without recirculation of the carrier gas, a manual test DIC line
was set up to sparge acidified water with He. This line operates at ambient pressure (1 bar) and is
filled with He. CO₂ gas is recovered from 50ml of the water sample by adding 5ml of 85% of
phosphoric acid inside a 250ml reaction vessel. The He carrier gas is sparged at a flow rate of
30ml/min and then passed through two water traps to remove water; and two CO₂ traps to collect
CO2 gas. Complete recovery of CO₂ is determined by passing the He flow through a CO₂
analyser to verify there is no presence of residual CO₂ gas. By using a temperature controller
which was designed in-house the temperature of both the water trap and the CO₂ trap can be
adjusted from -170°C to -60°Cwhich optimises the trapping temperature. We found that the best
trapping temperatures for H₂ O and CO₂ are -110°C and -160°C, respectively. The CO₂ trapping
efficiency of our system is over 99%, this was tested by trapping a CO₂ /He gas mixture containing
1mg C of CO₂ gas. The CO₂ gas is then transferred into a storage vessel until all samples on the
system are processed. The CO₂ is then manually transferred to break seals for purification of the
CO₂ by heating to 600°C over CuO and Ag wire. The test line has also been tested with
groundwater samples.
Based on the test, we are going to construct an automated DIC line in which all manual valves in the
testing line will be replaced by automated valves to be controlled by computer. In addition, the
water samples selector and circulation loop were designed by refer the report [2]. The system will
enable the automated processing of 10 samples within 10 hours.
Description
Keywords
Testing, Dissolution, Carbon, Carbon 14, Water, Carbon dioxide, ANSTO, Extraction, Pressure range, Purification, Ground water
Citation
Yang, B., Williams, A., Nguyen, T., Varley, S., & Freeman, P. (2021). Testing line for processing of dissolved inorganic carbon from water for radiocarbon dating determining the efficacy of trapping carbon dioxide for an automated system. Poster plus presentation to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 269). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdf