{"title":"The SIT model parameters for interactions of phosphate ions with Na+ and K+ ions accounting for dimerization of the H2PO4‐ anion","authors":"Andrey V. Plyasunov, Elena V. Cherkasova","doi":"10.1016/j.apgeochem.2025.106477","DOIUrl":null,"url":null,"abstract":"<div><div>The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, which has only one binary interaction parameter for each pair of cations and anions. It has long been known that the SIT model performs poorly for the thermodynamic activity data for aqueous solutions of <span><math><mrow><mi>N</mi><msub><mtext>aH</mtext><mn>2</mn></msub><mi>P</mi><msub><mi>O</mi><mn>4</mn></msub></mrow></math></span> and <span><math><mrow><mi>K</mi><msub><mi>H</mi><mn>2</mn></msub><mi>P</mi><msub><mi>O</mi><mn>4</mn></msub></mrow></math></span>. However, the previous treatment ignored the dimerization of the <span><math><mrow><msub><mi>H</mi><mn>2</mn></msub><mi>P</mi><msubsup><mi>O</mi><mn>4</mn><mo>‐</mo></msubsup></mrow></math></span> anion with the formation of <span><math><mrow><msub><mi>H</mi><mn>4</mn></msub><msub><mi>P</mi><mn>2</mn></msub><msubsup><mi>O</mi><mn>8</mn><mrow><mn>2</mn><mo>‐</mo></mrow></msubsup></mrow></math></span>, which has been convincingly demonstrated, mainly in Raman experiments. Here we show that explicitly taking into account the dimerization of the <span><math><mrow><msub><mi>H</mi><mn>2</mn></msub><mi>P</mi><msubsup><mi>O</mi><mn>4</mn><mo>‐</mo></msubsup></mrow></math></span> anion allows to reproduce accurately the experimental data on the stoichiometric mean ionic activity coefficients for aqueous <span><math><mrow><mi>N</mi><msub><mtext>aH</mtext><mn>2</mn></msub><mi>P</mi><msub><mi>O</mi><mn>4</mn></msub></mrow></math></span> and <span><math><mrow><mi>K</mi><msub><mi>H</mi><mn>2</mn></msub><mi>P</mi><msub><mi>O</mi><mn>4</mn></msub></mrow></math></span>. The data were processed using relations from the thermodynamics of partially associated electrolytes. An additional source of information were the values of the dissociation constants of phosphoric acid in <span><math><mrow><mtext>NaCl</mtext></mrow></math></span> and <span><math><mrow><mtext>KCl</mtext></mrow></math></span> solutions. In total, we determined 8 SIT parameters for the interactions of <span><math><mrow><msup><mtext>Na</mtext><mo>+</mo></msup></mrow></math></span> and <span><math><mrow><msup><mi>K</mi><mo>+</mo></msup></mrow></math></span> with different phosphate ions at 298.15 K and 0.1 MPa.</div></div>","PeriodicalId":8064,"journal":{"name":"Applied Geochemistry","volume":"190 ","pages":"Article 106477"},"PeriodicalIF":3.1000,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Applied Geochemistry","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0883292725002008","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, which has only one binary interaction parameter for each pair of cations and anions. It has long been known that the SIT model performs poorly for the thermodynamic activity data for aqueous solutions of and . However, the previous treatment ignored the dimerization of the anion with the formation of , which has been convincingly demonstrated, mainly in Raman experiments. Here we show that explicitly taking into account the dimerization of the anion allows to reproduce accurately the experimental data on the stoichiometric mean ionic activity coefficients for aqueous and . The data were processed using relations from the thermodynamics of partially associated electrolytes. An additional source of information were the values of the dissociation constants of phosphoric acid in and solutions. In total, we determined 8 SIT parameters for the interactions of and with different phosphate ions at 298.15 K and 0.1 MPa.
期刊介绍:
Applied Geochemistry is an international journal devoted to publication of original research papers, rapid research communications and selected review papers in geochemistry and urban geochemistry which have some practical application to an aspect of human endeavour, such as the preservation of the environment, health, waste disposal and the search for resources. Papers on applications of inorganic, organic and isotope geochemistry and geochemical processes are therefore welcome provided they meet the main criterion. Spatial and temporal monitoring case studies are only of interest to our international readership if they present new ideas of broad application.
Topics covered include: (1) Environmental geochemistry (including natural and anthropogenic aspects, and protection and remediation strategies); (2) Hydrogeochemistry (surface and groundwater); (3) Medical (urban) geochemistry; (4) The search for energy resources (in particular unconventional oil and gas or emerging metal resources); (5) Energy exploitation (in particular geothermal energy and CCS); (6) Upgrading of energy and mineral resources where there is a direct geochemical application; and (7) Waste disposal, including nuclear waste disposal.