Reactive Crystallization of Lithium Carbonate from LiCl and Na2CO3: Effect of Polyacrylic Acid Monitored by Focused Reflectance Measurement

The reactive crystallization of lithium carbonate (Li2CO3) from LiCl and Na2CO3 solutions was studied by Focused Beam Reflectance Measurement (FBRM) to evaluate the effect of polyacrylic acid (PAA) of different molecular weights (1800, 230,000, and 450,000 g/mol). In situ monitoring determined nucleation and growth rates, as well as the evolution of fine (<10 µm) and coarse (50–150 µm) particles. It was observed that maximum velocities occur in the first few seconds after mixing, decreasing subsequently due to the consumption of supersaturation. Increasing the initial LiCl concentration intensified nucleation and growth; however, at 4 M, massive nucleation and attrition predominated, resulting in an abundance of fines. Li2CO3 spherulites formed under all conditions, becoming more compact at higher LiCl concentrations. The addition of PAA significantly altered their size and morphology: the low-molecular-weight polymer inhibited spherulite formation, while the high-molecular-weight polymers reduced growth and promoted denser and more compact spherulites. SEM micrographs confirmed these trends, highlighting the role of PAA molecular weight as a key parameter modulating the kinetics and morphology of Li2CO3 in reactive crystallization processes.