Testing line for processing of dissolved inorganic carbon from water for radiocarbon dating determining the efficacy of trapping carbon dioxide for an automated system

Dr Bin Yang1, Mr Alan Williams2, Mr Tan Nguyen1, Mr Simon Varley1, Mr Peter Freeman1

1Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, Australia, 2Deceased, ,

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 H₂O 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.
References:
[1] McNichol, A. P. et al., Radiocarbon 36: (1994) pp. 237–246
[2] Gospodinova, K, et al., Limnology and Oceanography: Methods 14(1): (2016)24–30. doi: 10.1002/lom3.10066


Biography:

Dr. Bin Yang; PhD in Physics; University of Bologna, Italy
Dr Yang has been working in the Centre of Accelerator Sciences of the Australian Nuclear Science and Technology Organisation (ANSTO) since 2008. He has developed Mark II Laser Heated Furnace and Micro Conventional Furnace for processing thousands of samples, including important and valuable samples from Antarctica. The above-mentioned apparatus have enhanced ANSTO’s capacity in the graphitisation of micro-gram samples and led to the publication of many high quality articles. He is interested in radiocarbon analysis for different types of samples such as water, land gas and aerosol for environmental research.

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Date

Nov 17 2021

Time

WEDNESDAY
1:30 pm - 1:55 pm