Fumarolic gas

A radiochemical method for the determination of Rn-220 in fumarolic gas is studied. Both condensed water and non-condensing gas are collected together and Pb-212 is precipitated as PbS. After dissolving the precipitate in conc.HCI, it is mixed with an emulsion scintillator solution for activity measurements. As Pb-214 is simultaneously measured, the observed ratio of Pb-212 /Pb-214 gives Rn-220/Rn-222. This method is superior to the method of directly measuring Rn-220 for the samples in which Rn-220/Rn-222 ratios are less than unity. This method and the previously proposed direct method were applied in the field, and new data obtained. An attempt was also made to understand the formation and transport of radon underground. 

The Rn-222 concentrations in the soil gas, fumarolic gas, atmosphere, and in the underground water have been measured extensively for the studies of seismology, uranium mining, environmental science and geochemistry. It has been known that its concentrations are often very high in fumarolic gases and in the underground water, the reason for which is, however, not clarified yet. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

Giggenbach W. F. (1987). Redox processes governing the chemistry of fumarolic gas discharges from White Islands, New Zealand. Appl Geochem., 2 143-161. 

Sano Y. and Marty B. (1995) Origin of carbon in fumarolic gas from island arcs. Chem. Geol. 119, 265 -274. 

In general, and as illustrated for the 1977 study of 100°C fumarole at Kilauea, essentially all of the mercury and the other metals are trapped in the 0° condensate (Table 5). Thus, fumarolic gas collectors for metal studies can be simplified. The observed Hg/S weight ratio in the Kilauea condensate was 0.9 X 10 . The Hg/S ratios from the other investigations are summarized in Table 4. Values range from 0.7 to 14 X 10 with a suggestion that Hg/S may increase as the S/Cl decreases. Dedeurwaerder et al. (1982) were part... 

Figure 3 Hg sampling apparatus used to collect fumarole gas samples (after Patterson and Settle, 1987).

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