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Environmental fate & pathways

Hydrolysis

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Description of key information

BaS dissolves upon contact with water, releasing barium and sulfide ions. An equilibrium establishes between S2-, HS-, and H2S as a function of pH, and the  Hägg graph (see IUCLID 5.1.2 "Hägg, 1969 - sulfides") provides key information. For barium, hydrolysis is not a relevant endpoint.

Key value for chemical safety assessment

Additional information

Abiotic degradation is an irrelevant process for inorganic substances that are assessed on an elemental basis, including barium sulfide. In the aqueous environment, barium sulfide dissolves in water releasing barium cations and sulfide anions (see physical and chemical properties).

Sulfide anions react with water in a pH-dependant reverse dissociation to form bisulfide (HS-) or hydrogen sulfide (H2S), respectively (i.e., increasing H2S formation with decreasing pH). Thus, sulfide (S2-), bisulfide (HS-) and hydrogen sulfide (H2S) coexist in aqueous solution in a dynamic pH-dependant equilibrium. In oxic systems, oxidation to - eventually - sulfate occurs.

Barium in water occurs as the divalent cation in combination with other elements. Barium does not hydrolyze appreciably except in highly alkaline environments (i.e., at pH levels ≥10). Speciation is typically controlled by barium sulfate, BaSO4(barite), and to a lesser extent by barium carbonate, BaCO3(witherite).In solutions, undersatured in barite and wiltherite, barium occurs largely as free Ba2+. The Ba2+ion is stable under the pH-Eh range of natural systems.

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