Abstract
During oxalic precipitation, three major mechanisms take place: nucleation, crystal growth and agglomeration. After the acquisition of the kinetic laws of nucleation and growth of neodymium oxalate and uranium oxalate by Andrieu (1999), the objective of this study is to determine the respective agglomeration kinetic laws. Determining the agglomeration kinetic law consists more specifically in determining a quantity called agglomeration kernel. This kernel is a measure of the frequency and efficiency of the collisions which occur between particles in the reactor. The agglomeration mechanism is complex as it is sensible to many parameters. The objective is to determine a kinetic law showing explicitly the parameters influencing the mechanism of agglomeration. Mathematical and experimental methods are firstly developed on an inactive compound (neodymium III) and then applied on uranium IV, a simulant of plutonium IV. Experiments are conducted in a perfectly mixed reactor, under operating conditions similar to the industrial ones. An original mathematical method is also developed to solve the population balance. To obtain a predictive kinetic model, it is essential to consider deviation from ideality for the calculation of supersaturation, through activity coefficients. After a thermodynamic study, the Bromley model (1973) is finally chosen to evaluate activity coefficients. The overall processing of our experimental data leads to the agglomeration kinetic laws of neodymium oxalate crystals and oxalate uranium IV over a wide range of operating conditions.