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

Experimental results of a study of the effect of FeCl 3 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 c i from in situ measurements of temperatures of saturated solutions and pure water as functions of feeding time t of antisolvent ethanol at predefined rates R A 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 Δ x maxN and Δ x maxG , determined from intervals of temperature difference ( T s − T w ) = Δ T  < 0 and Δ T  > 0, respectively, obtained from measurements of temperature T s and T w 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 Δ x maxN and Δ x maxG of solutions during 3D nucleation and growth of crystallites.