LAUSR

Abstract In this study, solubility measurements on tri-calcium di-citrate tetrahydrate [Ca3[C3H5O(COO)3]2•4H2O, abbreviated as Ca3[Citrate]2•4H2O, 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 ± 0.5oC). The solubility constant ( log K s p 0 ) for Ca3[Citrate]2•4H2O and formation constant ( log β 1 0 ) for Ca[C3H5O(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 and MgCl2 media. The solubility measurements and thermodynamic modeling indicate that earlandite could become a solubility-controlling phase for citrate in geological repositories for nuclear waste when the inventories of citrate reach the saturation concentrations for Ca3[Citrate]2•4H2O, 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 as well as nuclear waste management.