Sampling of fumarolic gases at Vulcano (Italy) and analytical results

0375 - 6505/86 $3.00 + 0.00 Pergamon Journals Ltd. © 1986 CNR.

Geothermics, Vol. 15, No. 2, pp. 201-203, 1986. Printed in Great Britain.

SAMPLING OF FUMAROLIC GASES AT VULCANO (ITALY) AND ANALYTICAL RESULTS J. H I R A B A Y A S H I Department of Inorganic Materials, Tokyo Institute o i Technology, 2-12 O-okayama, Meguro-ku, Tokyo 1~2, ,lapan (Received Oetober, 1985; accepted,/or publication January 1986)

Abslracl--A syringe containing a KOH solution was used to collect the condensing phase as well as the non-reacting gases from the fumarole. The former fraction was analysed immediately after sampling for H,S and SO: by the iodometric method and later by laboratory techniques, while the latter were stored for gas-chromatographic analysis. Similar methods were employed for sampling the gases from t~ot springs. The main differences between the two types of fumaroles are put into evidence. Volcanic gases were collected at V u l c a n o using O z a w a ' s m e t h o d (1966a,b). All the c o m p o n e n t s in volcanic gases were collected in a 100 ml-glass syringe with two m o u t h s . His m e t h o d is described here briefly.

SAMPLING METHOD AND ANALYSIS OF FUMAROLIC GASES (a) Sampling A silica glass pipe was inserted into a f u m a r o l e a n d then the two m o u t h - s y r i n g e , c o n t a i n i n g 20 ml o f 5 M K O H solution, was a t t a c h e d to the pipe (Fig. 1), Volcanic gases were c o n t i n u o u s l y collected until the total v o l u m e o f the K O H solution and c o n d e n s e d water increased to a b o u t 40 ml. DUring s a m p l i n g the syringe was cooled by water. A f t e r collection o f the volcanic gases, all the water v a p o r was c o n d e n s e d in the syringe, which is i n d i c a t e d by the increase in the v o l u m e o f liquid phase. H F , HCI, SO.,, H2S and C O : in volcanic gases were a b s o r b e d into alkaline solution. H,, He, A t , C H , , N, a n d o t h e r noble gases were not reacted with K O H a n d r e m a i n e d in the syringe as the gaseous phase (Fig. 2). SO., a n d H2S were m e a s u r e d by i n t r o d u c i n g volcanic gases into the 0.05 M K I O , - K I solution. In this solution, SO2 a n d H2S were reacted with l~ to p r o d u c e SO] a n d S, respectively. (b) Analysis The f o l l o w i n g items were m e a s u r e d : HeO

the c o n d e n s e d v o l u m e o f water plus v a p o r within the syringe

'~ ~ 2 FumaroLe

5 I00mLsyringe 0 mL

Fig. 1. The t;vo-nlouth syringe containing the KOH solution.

201

202

J. ttiraba.vasf~l

r[ •.-D. (:;as chromotoq~;]p~ r

Hp, He,Ar,CH4 N2, CO etc

i --~ VoLume

i r >< condensedin

~I

j I

t ~

I L --

+-I-H

I

i J

•

5 M KOH sol

[-- ~ d gGsesi obsorbed into 5 M KOHso[

--Pinch cock

HF ~ HCI ~

|S%]

ion- selective electrode spectrophotometry

|HzS J ~

gravlmetric anoLysm

LCO:, ~

microdiffusion anaLys~s

FumoroUc gas Fig. 2. The syringe and the different determinations in the two phases to be carried out in the laboratory. Water volume is measured in the field (Ozawa, 1966a).

HC1 HF Total sulfur

spectrophotometry using mercury thiocyanate microdiffusion analysis (Yoshida et al., 1978) gravimetry as BaSO4

SO2 1 H~S CO2 He, H2, N~, CH~ and CO Ar

gravimetry as BaSO4 (Fig. 3) microdiffusion analysis gas chromatography with TCD (Thermal Conductivity Detector) and Ar as carrier gas gas chromatography with TCD as detector and 02 as carrier gas.

SAMPLING METHOD AND ANALYSIS OF HOT SPRING GASES Hot spring gases at the Hippopotamus pond and beach were collected by a 100 ml two-mouth syringe through a glass funnel. After the sampling, 2 ml of 5 M KOH solution was added into the syringe. H2S content was measured by iodometry of the KOH solution. CO2 content was calculated by subtracting the volume of H~S and residual gas from the total. Residual gas compositions were identified by gas chromatography.

RESULTS Chemical compositions of volcanic gases from fumaroles F-1 and F-5, and hot-spring gases are shown in Tables 1 and 2, respectively. It is to be noted that the H20 content in volcanic gases from F-1 and F-5 fumaroles were very low, as compared with those of high temperature volcanic gases in Japan. The difference in the H20 content could be due to the difference in the chemical composition of magma and the mixing rate of meteoric water. The HCI content was remarkably high for the fumarolic gases with comparatively low temperature. The residual gas was mainly N2 and consisted of small amounts of H~, He and Ar. CH, and CO were not detected.

Sampling of Fumarolic Gases at Vulcano

203

FumoroLic gos [ ] --~ 2 + $O2+,12,+ H20 SO4 + 4 H + 2 [ i

i

T

i,

H2S+]121

-----~SI + 2H ++ 2I-Ig°~Yr~'Itnl

[~

- - - ~ n o react.ion

+ 1

--~SO2 ~HzS

/ KI-KIO3(OO5

--~--SO2+ HrS

,,-consumption 0 Iod ne

M) sol.

Coobng water

Fig. 3. The separation of H~S and SO., in the field by the iodometric method and later laboratory determinations (Ozawa, 1966a).

Table 1. Chemical composition of volcanic gases at Vulcano Composition of gases exclusive of water (vol.%)

Composition of R-gas {vol.°/0)

Date

Temp. H~,O °C vol. 070 HF

HCl

SO,, H2S

CO2

R*

F-1 23 Sept. 1982 F-5 23 Sept. 1982

220.4 281.7

9.9 9.5

5.7 5.4

80.8 81.6

0.7 0.8

92.0 93.1

0.1 0.2

2.8 2.5

He

H,

Ar

0.073 0.79 0,10 0.064 1.15 0,13

N:

(.'H~ CO

99.0 98.7

none none none none

*Residual gas that cannot be absorbed into alkaline solution at the time of gas sampling.

Table 2. Chemical composition of hot spring gases at Vulcano (vol.%)

Date Beach 25 Sept. 1982 Hippopotamus pond 25 Sept. 1982

Temp. ~C

H:S

CO:

R*

96.0 98.2

1.5 1.8

95.2 96.3

3,3 1,9

Composition of R-gas He H: N: CH~ 0.007 0.010

54.1 40.2 65.2 29.2

5.7 5.6

*See Table 1. The hot-spring gases emitted from the Hippopotamus

p o n d a n d t h e sea w a t e r c l o s e t o t h e

b e a c h c o n t a i n e d 95 - 9 6 % CO2. T h e r e s i d u a l gas w a s m a i n l y H2 a n d N2, a n d c o n s i s t e d o f s m a l l a m o u n t s o f C H 4 a n d H e . T h e h i g h e r c o n c e n t r a t i o n o f H2 in t h e r e s i d u a l gas w a s f o u n d f o r t h e hot-spring gases.

REFERENCES Ozawa, T. (1966a) Chemical analysis of. volcanic gases containing water vapor, hydrogen chloride, sulfur dioxide, hydrogen sulfide, carbon dioxide etc. Nippon Kagaku Zasshi 87, 848 - 853 (in Japanese). Ozawa, T. (1966b) Rapid determination of carbon dioxide, hydrogen sulfide, nitrogen and sulfur dioxide in volcanic and hot spring gases with temperatures near boiling point of water. Nippon Kagaku Zasshi 87. 959 962 (in Japanese). Yoshida, M., Makihara, Y. and Katsura, T. (1978) Separation of fluorine by a microdiffusion method aided by hexamethyldisiloxane. Nippon Kagaku Zasshi 1978-10, 1375- 1379 (in Japanese).