[en] A micro-fluidic device has been specially developed to enable the study of fast nucleation kinetics involved in precipitation processes. This setup allows drops of two different reagents to be generated synchronously and to coalesce, and ensure the mixing of their reactants within few milliseconds. The results presented in this paper show that droplet based micro-fluidic devices are promising tools for studying high nucleation rates involved in precipitation processes. By using the stochastic nature of the nucleation process and the effect of the confinement on the induction time, a tailored micro-fluidic device has been used to measure nucleation rates as high as J=7.68*10¹³ m^-3 s^-1. Moreover, kinetic data deriving from nucleation experiments were found in good agreement with data deriving from 'conventional' techniques. (authors)

[en] Rare earth oxalates precipitation is extendedly used in hydrometallurgical processes related to rare earth recycling methods and treatment of radioactive liquid wastes, where rare earth elements are separated from other fission products. For a deeper comprehension of this reactive precipitation process, the thermodynamic modeling of the oxalate-rare earth systems in nitric acid aqueous media is presented for neodymium and cerium systems, due to their distinctive relevance among the rare earth elements. A Pitzer model was selected for the modeling, which was developed using the implementation present within PHREEQC software. Calculations were launched through a COM interface with Matlab (R) and PHREEQC database was complemented by adjustment of the individual Pitzer coefficients for each species interaction to experimental data reported in literature and own experimental water activity measurements required to complete the study. The implemented model is able to accurately predict oxalate-rare earth solubility in a wide range of rare earth and nitric acid concentrations up to > 10 m. (authors)