# In Situ FBRM Analysis of Additive-Controlled Reactive Crystallization of Lithium Carbonate

## TL;DR

This study uses in situ monitoring to explore how additives affect the crystallization of lithium carbonate, showing how different additives control crystal formation and properties.

## Contribution

The study provides mechanistic insights into how specific additives control nucleation and growth dynamics in reactive crystallization of lithium carbonate.

## Key findings

- Additives like PAA, SHMP, and STPP significantly influence nucleation and growth of lithium carbonate crystals.
- PAA suppresses fine particles and promotes coarse crystal formation under high supersaturation.
- SHMP strongly inhibits nucleation and growth, while STPP shows a dose-dependent effect on crystal properties.

## Abstract

This work investigates the reactive crystallization of lithium carbonate (Li2CO3) by rapidly mixing concentrated aqueous solutions of LiCl (3.0–4.0 M) and Na2CO3 (1.5–2.0 M) at 65 °C, using focused beam reflectance measurement (FBRM) for online, in situ monitoring. The effect of low concentrations of poly(acrylic acid) (PAA), sodium hexametaphosphate (SHMP), and sodium tripolyphosphate (STPP) on nucleation and growth dynamics was systematically analyzed. The results show that the process is dominated by an intense initial supersaturation pulse, which governs early nucleation and subsequent population restructuring through growth and aggregation. Additives significantly modify the nucleation-growth coupling: PAA exhibits concentration- and time-dependent behavior, suppressing the detectable fines population and promoting consolidation into coarse fractions under high supersaturation; SHMP acts as a strong kinetic inhibitor, markedly reducing nucleation and, to a greater extent, growth; while STPP exhibits an intermediate, dose-dependent response, maintaining nucleation but limiting effective growth at high concentrations. Scanning electron microscopy observations confirm the formation of spherulitic Li2CO3 aggregates in all cases, with compactness and radial organization dependent on the additive. These results demonstrate that targeted additive selection allows for precise control of population dynamics and solid properties in reactive crystallization systems, within the investigated high-supersaturation concentration window, with useful mechanistic guidance for the design and control of Li2CO3 precipitation processes.