A novel proton transfer model of the closed equilibrium system H2O–CO2–CaCO3–NHX; pp. 260–270

• Published in: Proceedings of the Estonian Academy of Sciences
• Main Authors: Toomas Tenno, Ergo Rikmann, Kalev Uiga, Ivar Zekker, Alexey Mashirin, Taavo Tenno
• Format: Article
• Language: English
• Published: Estonian Academy Publishers 2018-06-01
• Subjects: proton transfer model; equilibrium system h2o–co2–caco3–nhx; bicarbonate; free ammonia.
• Online Access: https://kirj.ee/public/proceedings_pdf/2018/issue_3/proc-2018-3-260-270.pdf

Variation in the concentration of dissolved carbon dioxide [CO2]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 NH+4â NH3 + H+ towards the formation of free ammonia (NH3). This results in the inhibition of the activity of microorganisms that perform the biological waste- and reject-water treatment. The model of the system H2Oâ(CO2)WâCaCO3 was upgraded on the basis of proton transfer principles and taken as the basis for modelling the closed system H2Oâ(CO2)WâCaCO3âNH4Cl. The distribution of ions and molecules in the closed system H2Oâ(CO2)WâCaCO3âNHX 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 H2Oâ(CO2)WâCaCO3, as a result of the dissolution of CaCO3, the CO2-3 ions are released and these will accept a certain quantity of protons (Î[H+]CO2-3), which originate from two sources: the reversible dissociation of water (Î[H+]H2O) or H2CO3 (Î[H+]H2O3), which is the product of the reaction between H2O and (CO2)W0. In case the final closed system H2Oâ(CO2)WâCaCO3âNH4Cl includes small initial concentrations of [CO2]W0, the main amount of protons (Î[H+]NH+4) comes from the dissociation of NH+4, or if there are higher concentrations of [CO2]W0, the source of protons is H2CO3 (Î[H+]H2CO3). The developed models were experimentally validated.