Density Functional Theory-Based Thermodynamic Model for Stable Scale Formation in Lead-Water Systems

Abstract

Current safety standards for water treatment to reduce indigestible lead in drinking water utilize decades-old data and models to define risk mitigation. Limitation is achieved in part by utilizing additives to control particulate and soluble Pb(II) release through scale formation in lead pipes that rely on thermodynamic and kinetic factors. Advances in state-of-the-art computational materials science techniques allow fresh comparisons to older thermochemical data and thereby enable the formulation of new ab initio-based thermodynamic models. Here, we perform first-principles calculations to simulate electrochemical Pb Pourbaix and stability diagrams that include a limited number of non-ideal solution effects and account for variable concentration, additives, and temperature. Our data show that lead carbonates are thermodynamically driven to form a cerussite scale across a large range of conditions. Orthophosphate is a known lead corrosion inhibitor; however, the formation of lead phosphate scales, such as Pb (PO ) (OH) 5 4 3 2(s) , may rely on transient high Pb(II) concentrations with trace alkaline-earth elements. Moreover, their previously reported stability may be due to overestimated free energies of formation. Acceptable thermodynamically stabilized soluble lead levels in water can only be maintained under specific thermal and aqueous boundary conditions. Our work defines critical environmental limits on lead scale formation and provides a renewed look of E-pH lead stability and solid stabilities of lead (II) carbonate and phosphate species as a function of Pb(II) and pH using here-to-fore unavailable computational approaches for comparison to other data.

Environmental Stability of Actinide Oxides Mapped by Integrated and Accurate First-Principles Calculations

“…The above-mentioned unavoidable technical and physical issues encountered by experiments can be circumvented by the first-principles calculations based on density functional theory (DFT), which can yield the accurate Δ f G values for various transition-metal oxides and hydroxides if a precise enough electronic interaction potential (called as electronic density functional in DFT) is applied. ,,− The recently simulated transition-metal Poubaix diagrams not only can comprehensively explain a lot of electrochemical observations reported in previous decades but also have been widely used by many recent electrochemical experiments in the fields of, e.g., corrosion, catalysis, and clean energy to guide the design, synthesis, and characterization analysis of various transition-metal compounds. − Those new first-principles diagrams even have been used in the geological field to understand the rock weathering mechanisms in acid rains on both the ancient Earth and Mars, e.g., the dissolution of Ni oxides and the formation of magnetite (a Fe 3 O 4 -based mineral). ,, The first-principles electrochemical phase diagrams can be further used to study more complex transition-metal systems, e.g., conventional Ni–Cr alloys, multiprincipal element alloys, , complex compounds, and nanoscale passivating films, and have successfully helped precisely understand many passivation, corrosion, and precipitation behaviors, as well as their dependence on both material state and environmental condition. Such success in the thermodynamic and electrochemical calculations of transition-metal systems encourages the use of DFT to obtain reliable Δ f G data for all possible actinide oxides, which can bring the fundamental and historical contribution to the related nuclear fields.…”