EXPERIMENTAL INVESTIGATION OF SULFUR ISOTOPIC FRACTIONATION BETWEEN DISSOLVED AND GASEOUS H2S

In this study sulphur isotope fractionation between undissociated diss olved H2S and H2S gas has been investigated experimentally. Such measu rements were carried out at temperatures of 11 degrees, 20 degrees and 30 degrees C. The experiment was performed at pH = 5, at which H2S re mains nearly totally undissociated. The experimental conditions were a s follows: (1) an aliquot of distilled water was saturated with H2S at a pressure of 1 atm; (2) the system containing gaseous and dissolved H2S was kept at constant temperature for a certain time; and (3) the g as phase was separated from the solution prior to sulphur extraction f rom both phases, which was prepared in the form of SO2 gas for isotopi c analysis. The results obtained show that dissolved undissociated H2S is enriched in the heavy isotope with respect to gaseous hydrogen sul phide in the temperature range 11-30 degrees C. In this temperature ra nge the permil fractionation obeys the following formula: Delta(34)S = + (2.75 + 0.15) +/- (56 +/- 7) . 10(-3)t (degrees C) The fractionatio n factor, alpha, can be calculated from the following expression: alph a = 1 + 0.001 Delta S-34.