Modelling of the closed equilibrium system H2O–(CO2)W–CaCO3–NaH2PO4 for wastewater treatment applications

Abstract

Water pollution caused by nitrogen and phosphorus compounds triggers algal blooms and poses challenges to aquatic organisms. Wastewater treatment ap plications represent critical areas where fundamental models of phosphorus equilibria, prevalent in municipal and reject water streams, are essential. This paper focuses on studying the closed equilibrium system H2O–(CO2)W–CaCO3–NaH2PO4, elucidating the structural distribution of ions and mol ecules within this system. Utilizing the iteration method, we calculate pH, concentrations of formed ions and molecules, and proton transfer parameters based on a developed proton transfer model. Upon the initial formation of the equilibrium system H2O–(CO2)W−CaCO3, CO32– ions released from the dis solution of CaCO3 bind protons (Δ[H+]CO32–) originating from the reversible dissociation of water (Δ[H+]H2O) and H2CO3 (Δ[H+]H2CO3). In the equilibrium system H2O–(CO2)W−CaCO3–NaH2PO4, at low initial CO2 concentrations (< 3.39 × 10–5 mmol·L–1), the majority of protons (Δ[H+]H2PO4–) originate from the H2PO4− dissociation. Conversely, with increased initial CO2 con centrations, the dissociation of H2CO3 (Δ[H+]H2CO3) becomes the primary proton source. Experimental validation confirms the developed model’s accuracy.

Keywords

• proton transfer model
• equilibrium system of h2o–co2–caco3–nah2po4
• carbonate equilibrium
• phosphate equilibrium