The solid-liquid equilibrium (SLE) in the ternary system 2-keto-L-gulonic acid (HKGA) + sodium-2-keto-L-gulonate (NaKGA) + water was studied experimentally at temperatures between 275 and 313 K and ambient pressure. At these conditions, HKGA and NaKGA precipitate as monohydrates: HKGA center dot H2O and NaKGA center dot H2O, respectively. Phase diagrams with one eutonic point are found for all temperatures. A thermodynamic model of the SLE that is based on an extended version of the Debye-Hiickel theory was developed and the dissociation constant of HKGA as well as the solubility products of HKGA center dot H2O and NaKGA center dot H2O were determined. The agreement between the experimental data and the results from the model is excellent. (C) 2018 Elsevier B.V. All rights reserved.