The Multiple Roles of Additives in CaCO₃Crystallization: A Quantitative Case Study

Abstract

To date, the knowledge of the multiple roles of additives in calcium carbonate crystallization results from empirical control of crystal growth. We present a crystallization assay generating controlled supersaturation, which allows the categorization of different modes of additive action. This facilitates a novel understanding of the action of crystallization additives.

The multiple effects of amino acids on the early stages of calcium carbonate crystallization

“…The slope of the increase of free calcium prior to nucleation bears important information as it directly reflects interactions between additives and prenucleation species [45,46]. Generally, a steeper slope implies that less calcium is bound in prenucleation clusters, indicating that they are destabilized by the particular additive, whereas flattening of the prenucleation regime in turn suggests cluster stabilization, as reported e.g.…”

“…For this purpose, a titration assay was employed that had previously been used to investigate the nucleation process [44] as well as the effect of distinct additives on precipitation scenarios [45][46][47]. As in earlier work, experiments were carried out by continually dosing 10 mM CaCl 2 solution into an excess of 10 mM sodium (bi)carbonate buffer, where the pH was kept constant at 9.75 by counter-titration of 10 mM NaOH.…”

“…In the end, this issue may relate to the question why some polymers, held together by covalent bonds, do exhibit differing modes of influence even though they carry the same chemical functions (e.g. poly(acrylic acid) vs. poly(aspartic acid) [45,46]), while other related polymers may not exhibit any influence at all. It appears that geometrical and conformational aspects could be important also in supramolecular polymers (prenucleation clusters) of amino acids [49].…”

Mineralization and non-ideality: on nature’s foundry

“…As suggested for liquid-like mineral precursors formed in the presence of ovalbumin, the dynamics of interfacial protein layers as well as charge neutralization and depletion stabilization may also be critical factors (Wolf et al 2011). As shown by previous studies, the modulation of the nucleation regime by charged additives including the inhibition of nucleation and transient stabilization of highly soluble mineral intermediates cannot be explained solely by ioncomplexation (Gebauer et al 2009;Rao et al 2014). This is validated by the experimentally determined effective valence being only one-third of that estimated from the structure of charged polysaccharides such as dextran sulfate and heparin .…”

“…Proteinaceous and saccharide additives can also tune the stability of early precursors and favor the formation of a particular phase, i.e. mediate poly(a)morph selection (Cartwright et al 2012;Chang et al 2016a;Gebauer et al 2009;Rao et al 2013Rao et al , 2014. Fig.…”