Thermodynamic parameters on corresponding solid-liquid equilibrium of hydroxyapatite in pure and mixture organic solvents

The thermodynamic parameters on corresponding solid-liquid equilibrium of hydroxyapatite in different solvents are essential for a preliminary study of pharmaceutical engineering and industrial applications. In this paper, a gravimetric method was used to correct the solid-liquid equilibrium of hydroxyapatite in water, methanol, ethanol, 1-butanol, acetone, acetonitrile, ethyl acetate, dimethyl formamide and tetrahydrofuran pure solvents as well as in the (1-butanol + acetonitrile) mixture solvents in the temperatures (from 278.15 K to 328.15 K) under 0.1 MPa. For the temperature range investigation, the solubility of hydroxyapatite in the solvents increased with increasing temperature. The solubility of hydroxyapatite in 1-butanol is superior to other selected pure solvents. The modified Apelblat model, the Buchowski-Ksiazaczak λh model, and the ideal model were adopted to describe and predict the change tendency of solubility. Computational results showed that the modified Apelblat model stood out to be more suitable with the higher accuracy. The solubility data were fitted using a modified Apelblat model, a variant of the combined nearly ideal binary solvent/Redich-Kister (CNIBS/R-K) model, Jouyban-Acree model and Ma model in (1-butanol + acetonitrile) binary solvent mixture. Computational results showed that the CNIBS/R-K model had more advantages than other models. In addition, the calculated thermodynamic parameters indicated that in each studied solvents the dissolution of hydroxyapatite is endothermic, non-spontaneous and entropy-drive process.