(571n) CaCO3 Crystallization in the Presence of Polycarboxylated CMC: Insights into Kinetics, Mechanisms, and Crystal Morphology

Calcium carbonate crystallization is of interest due to its relevance in different applications such as pharmaceutical, biomineralization processes, catalysis and environmental systems. It is also used as an experimental system model to study the phenomena of crystallization and nucleation in general. Compared to additive-free systems, additive-controlled crystallization of calcium carbonate is still insufficiently explained due to the complexity and varieties of the possible interactions between the different species in the system involving crystals and additives. One of the interesting phenomena of additive-controlled systems is the threshold inhibition of nucleation and crystallization of calcium carbonate by polycarboxylates at very low concentrations (i.e. 1-20 ppm) in aqueous solutions. Additionally, a spontaneous and naturally occurring phenomena is observed through the biological organism’s use of modified polysaccharides in stabilizing calcium carbonate. Understanding the influence of polycarboxylates on the calcium carbonate crystallization process is not only important in mineral scale inhibition but also crucial in elucidating biomineralization mechanisms where biomineral formation associated proteins are loaded with carboxylates (i.e. Aspartate residues).

This study explored, the impact of polycarboxylated carboxymethylcellulose (CMC) on the crystallization process of calcium carbonate. CMC was modified in a free radical polymerization reaction by grafting polyacrylic acid into the polysaccharide backbone, resulting in CMC-g-PAA. Different reaction conditions were explored to optimize a grafting copolymer with desired physicochemical properties. The crystallization process was investigated in a CSTR setup equipped with a laser system that is able to correlate crystal formation induction time with voltage difference. The real-time crystallization process done at different dosages of CMC-g-PAA is used to provide an information on the rate of the crystallization using the empirical Avrami equation. Results showed that CMC-g-PAA significantly affected the crystallization process even at low concentrations of 20 ppm. The impact of CMC-g-PAA on the crystallization was also analyzed by SEM and XRD. SEM images showed a big difference in the shape of the CMC-g-PAA treated crystals to the untreated crystals; long cylindrical crystals formed in the neat, additive-free, system compared to flowery shapes in the treated additive-controlled system. The exact phases and morphologies formed at different additive concentration levels are to be ascertained by analyzing XRD results. This study may result in better understanding of biomineralization processes and help combat undesirable calcium carbonate crystallization in different water-based environments.