Experimental determination of solubilities of tri-calcium di-citrate tetrahydrate [Ca3[C3H5O(COO)3]24H2O], earlandite, in NaCl and MgCl2 solutions to high ionic strengths. (February 2021)

• Record Type: Journal Article
• Authors: Xiong, Yongliang
• Is Part Of: Applied geochemistry. Volume 125(2021)
• Publication Date: 2021-02
• Subjects: Pitzer model -- Nuclear waste management -- Agro-food industrial waste-waters -- Organic ligands -- Waste Isolation Pilot Plant (WIPP) -- Solubility of calcium citrate tetrahydrate in food and pharmaceutical sciences; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2020.104856
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: In this study, solubility measurements on tri-calcium di-citrate tetrahydrate [Ca3 [C3 H5 O(COO)3 ]2 4H2 O, abbreviated as Ca3 [Citrate]2 4H2 O, earlandite] as a function of ionic strength are conducted in NaCl solutions up to I = 5.0 mol kg −1 and in MgCl2 solutions up to I = 7.5 mol kg −1, at room temperature (22.5 ± 0.5 °C). The solubility constant ( log K s p 0 ) for Ca3 [Citrate]2 4H2 O and formation constant ( log β 1 0 ) for Ca[C3 H5 O(COO)3 ] –, (1) Ca3 [C3 H5 O(COO)3 ]2 4H2 O (earlandite) = 3Ca 2+ + 2[C3 H5 O(COO)3 ] 3– + 4H2 O (2) Ca 2+ + [C3 H5 O(COO)3 ] 3– = Ca[C3 H5 O(COO)3 ] – are determined as −18.11 ± 0.15 and 4.97 ± 0.15, respectively, with a set of Pitzer parameters describing the specific interactions in NaCl-bearing and MgCl2 -bearing media. The solubility measurements and thermodynamic modeling indicate that earlandite could become a solubility-controlling phase for citrate in the near field of geological repositories for nuclear waste when the inventories of citrate reach the saturation concentrations for Ca3 [Citrate]2 4H2 O, and it is a solubility-limiting phase for calcium/citrate in other low temperature environments such as agro-food industrial waste-waters. The Pitzer model presented in this work will enable researchers to assess the role of citrate in low temperature environments over a wide range of ionic strengths, and is expected to find applications in many fields such as food and pharmaceutical sciences, cement and concrete industries as well as nuclear waste management. Highlights: Solubility measurements for earlandite are performed in NaCl and MgCl2 solutions to high ionic strengths up 7.5 molkg −1 . A Pitzer model is established for the interactions of citrate in various environments over a wide range of ionic strengths. The model is expected to find applications in many fields.