The Solubility of Sulfur in Na2O–SiO2 Melts under Various Oxygen Partial Pressures at 1100 °C, 1250 °C, and 1300 °C

Abstract

The solubility of sulfur in Na2O–SiO2 melts with the Na2O/SiO2 molar ratios of 1/3, 1/2, and 1/1 was investigated by varying the oxygen partial pressure at 1100, 1250, and 1300 °C. The results at 1100 °C are complicated, for the equilibrium state within the gas phase is not established. From the experiments at 1250 and 1300 °C, the following conclusions are reached: (1) When the temperature and the Na2O/SiO2 ratio in the melt are constant, the solubility of sulfur increases with an increase of the total amount of sulfur in the gas phase. (2) When the temperature, the Na2O/SiO2 ratio, and the total amount of sulfur in the gas phase are constant, the solubility of sulfur shows its minimum at a specific oxygen partial pressure; at higher oxygen partial pressures, the sulfur dissolves in the melts mostly as sulfate, while at lower oxygen partial pressures, the sulfur dissolves mostly as sulfide. (3) When the temperature and the total amount of sulfur in the gas phase are constant, the solubility rises greatly with an increase in the Na2O/SiO2 ratio in the melt. (4) When the Na2O/SiO2 ratio in the melt and the total amount of sulfur in the gas phase are constant, the minimum point of the solubility shifts in the direction of higher oxygen partial pressures as the temperature increases. This corresponds to the shifts of the equilibrated gas composition as the temperature increases.

Modelling the sulfate capacity of simulated radioactive waste borosilicate glasses

“…Principally this is a result of changes in SiO 2 content and, as expected based on previous studies [18][19][20][21], sulfate content increases with decreasing SiO 2 content. However, changes in the proportions of the other constituents also arise making it necessary to a consider both glass composition and structure if accurate modelling of sulfate capacity is to be carried out.…”

“…temperatures play a role, since lower melting temperatures can enhance the sulfate capacity and solubility in some oxide melts [18][19][20]. However, other possible explanations also exist and further work is required to explain this behaviour.…”

“…Glass composition plays a key role in determining sulfate capacity and solubility [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and the relative concentrations of O 0 , O -and O 2-(bridging oxygen, non-bridging oxygen and free oxygen, respectively) are major factors in this [4,6,10,[18][19][20][21]. A number of research papers and reviews have been published concerning prediction or modelling of the capacity and solubility of sulfate and other anionic species in oxide glasses (see, for example, [4,6,10,19,20] and references therein).…”

“…Several authors have discussed the structural aspects of sulfate incorporation in oxide glasses [6,[16][17][18][19][20][21][55][56][57][58], and the consensus is that the relationship between glass composition, glass structure and sulfate incorporation is controlled by the polymerisation of the network, and hence they are all related to the relative contents of BO, NBO and free oxygen. This topic was reviewed in depth to 2011 by Backnaes and…”

Sulfur, chlorine, and fluorine in glass inclusions in olivine and clinopyroxene from basaltic hyaloclastites representing the Gran Canaria shield stage at Sites 953 and 956

“…However, the dissolved S content in a basic magma does not change significantly as a function of pressure at lithospheric depths (Wallace and Carmichael, 1992). It has also been shown that at magmatic temperatures, S is present predominantly as sulfide at fo 2 more reduced than the fayalite-magnetite-quartz (FMQ) buffer (e.g., Nagashima and Katsura, 1973;Carrol and Rutherford, 1985). The S 6+ /S tot ratio further correlates positively with fo 2 for sulfur-undersaturated melts.…”