A novel proton transfer model of the closed equilibrium system [H.sub.2]O--C[O.sub.2]--CaC[O.sub.3]--[NH.sub.X]

• Published in: Proceedings of the Estonian Academy of Sciences Vol. 67; no. 3; p. 260
• Main Authors: Tenno, Toomas, Rikmann, Ergo, Uiga, Kalev, Zekker, Ivar, Mashirin, Alexey, Tenno, Taavo
• Format: Journal Article
• Language: English
• Published: Estonian Academy Publishers 01.09.2018
• Subjects: Ammonia; Calcium carbonate; Carbon dioxide; Chemical properties; Chemical reactions; Mathematical models; Protons
• ISSN: 1736-6046
• DOI: 10.3176/proc.2018.3.04

Variation in the concentration of dissolved carbon dioxide [[C[O.sub.2]].sub.W] causes changes in the solubility of limestone and in the pH of an equilibrium system. An elevation of the pH will shift the equilibrium of the reversible reaction [mathematical expression not reproducible] towards the formation of free ammonia (N[H.sub.3]). This results in the inhibition of the activity of microorganisms that perform the biological waste- and reject-water treatment. The model of the system [H.sub.2]O--[(C[O.sub.2]).sub.W]-CaC[O.sub.3] was upgraded on the basis of proton transfer principles and taken as the basis for modelling the closed system [H.sub.2]O--[(C[O.sub.2]).sub.W]--CaC[O.sub.3]-[NH.sub.4]Cl. The distribution of ions and molecules in the closed system [H.sub.2]O--[(C[O.sub.2]).sub.W]--CaC[O.sub.3]-[NH.sub.X] is described in terms of a structural scheme. A novel proton transfer model was developed to calculate the pH, concentrations of the formed ions and molecules, and proton transfer parameters of the closed equilibrium system using an iteration method. In the formation of the equilibrium system [H.sub.2]O--[(C[O.sub.2]).sub.W]-CaC[O.sub.3], as a result of the dissolution of CaC[O.sub.3], the [mathematical expression not reproducible] ions are released and these will accept a certain quantity of protons [mathematical expression not reproducible], which originate from two sources: the reversible dissociation of water [mathematical expression not reproducible] or [H.sub.2]C[O.sub.3] ([mathematical expression not reproducible]), which CO is the product of the reaction between [H.sub.2]O and [(C[O.sub.2]).sub.W0]. In case the final closed system [H.sub.2]O--[(C[O.sub.2]).sub.W]--CaC[O.sub.3]-[NH.sub.4]Cl includes small initial concentrations of [[C[O.sub.2]].sub.W0], the main amount of protons ([mathematical expression not reproducible]) comes from the dissociation of [mathematical expression not reproducible], or if there are higher concentrations of [[C[O.sub.2]].sub.W0], the source of protons is [mathematical expression not reproducible] ([mathematical expression not reproducible]). The developed models were experimentally validated. Key words: proton transfer model, equilibrium system [H.sub.2]O--C[O.sub.2]-CaC[O.sub.3]-[NH.sub.X], bicarbonate, free ammonia.