Effect of Fe(III) Impurity on the Antisolvent Crystallization of Aqueous Ammonium Dihydrogen Phosphate Solutions.

Experimental results of a study of the effect of FeCl3 impurity on the antisolvent crystallization of ammonium dihydrogen phosphate, involving processes of formation of 3D nuclei and growth of these nuclei, from its aqueous solutions saturated at 30 °C and containing different impurity concentrations ci from in situ measurements of temperatures of saturated solutions and pure water as functions of feeding time t of antisolvent ethanol at predefined rates RA are described and discussed. The processes of formation of 3D nuclei and growth of these nuclei are studied in terms of the maximum antisolvent content ΔxmaxN and ΔxmaxG, determined from intervals of temperature difference (Ts−Tw) = ΔT < 0 and ΔT > 0, respectively, obtained from measurements of temperature Ts and Tw of saturated solution, without and with impurity, and pure water. It is found that: 1) the processes of 3D nucleation in antisolvent crystallization from solutions containing impurities can be explained in the framework of theoretical expressions such as a Nývlt‐like relation and an approach based on 3D‐nucleation theory, and 2) adsorption of impurity particles accounts for the increase in the values of antisolvent contents ΔxmaxN and ΔxmaxG of solutions during 3D nucleation and growth of crystallites. [ABSTRACT FROM AUTHOR]