TY - BOOK
T1 - Functionalised inhibitors on calcium carbonates
T2 - New insights into the role of organic molecules on CaCO3 crystallisation
AU - Montanari, Giulia
PY - 2018
Y1 - 2018
N2 - Organic molecules are widely used in industry as additives to prevent calcium carbonate scaling
inside pipelines. Some of them have the same functional groups as those contained in the organic
matrices isolated from biogenic calcium carbonate, such as shells and the coccoliths of
microscopic algae. Although we know that such organic molecules interact with the calcium
carbonate surface sites and ions in solution, the exact mechanism of nucleation and the controls
on the rate of growth are still not clear.
My research focused on the effect that small organic molecules, such as amino acids and
carboxylic acids, have on calcium carbonate crystallisation. These molecules, in some cases,
linked together one by one in polymers, served as models for the long polysaccharide and
polypeptide chains that have prevented biogenic calcium carbonate dissolution and
recrystallisation through millennia. I combined wet chemistry experiments with analysis by
surface sensitive techniques and theoretical models of mineral nucleation and growth. I found that
aspartic acid (in solution, aspartate) and its polymer can inhibit calcite growth by more than 50%
and 90%, with growth inhibition clearly increasing as the molecule chain length of the polymers
increases. They do this by strongly adsorbing on calcite growth steps, thereby blocking further
growth. The fit of adsorption isotherms to the kinetic data permitted to calculate free adsorption
energies of -39 and -50 kJ/mol for the two polymers of aspartic acid and of -21 for aspartic acid,
corroborating that the polymers adsorb more strongly on calcite surface than the monomers. In
contrast, glycine and its polymer had little if any effect on calcite growth.
Another molecule I studied was citric acid (in solution citrate). Citrate interacts with calcium ions
both in solution and on the mineral surface, resulting in nucleation and growth inhibition, in
systems with and without constant saturation index. Specifically, I revealed that citrate had a more
profound effect on CaCO3 growth rates than on nucleation when CIT/Ca ≤50% ([Ca2+]=[CO3
2-]=4
mM), whereas at CIT/Ca > 50% nucleation was more inhibited than growth. I also showed that
vaterite formation was completely inhibited at citrate at CIT/Ca ≥75%. Citrate not only adsorbs on
the crystal surface but is also incorporated into the internal structure. All of these molecules change
the surface morphology by roughening specific faces, elongating the crystals and favouring
vaterite or calcite polymorphs.
The new knowledge I gained on the kinetics and mechanisms of calcium carbonate crystallisation
in the presence of these organic molecules can be applied for designing improved antiscalants and
to enhance understanding of the controls in mineral growth by organic molecules, which is also
relevant for the understanding of biomineralisation processes and the design of biocomposite
materials for industry.
AB - Organic molecules are widely used in industry as additives to prevent calcium carbonate scaling
inside pipelines. Some of them have the same functional groups as those contained in the organic
matrices isolated from biogenic calcium carbonate, such as shells and the coccoliths of
microscopic algae. Although we know that such organic molecules interact with the calcium
carbonate surface sites and ions in solution, the exact mechanism of nucleation and the controls
on the rate of growth are still not clear.
My research focused on the effect that small organic molecules, such as amino acids and
carboxylic acids, have on calcium carbonate crystallisation. These molecules, in some cases,
linked together one by one in polymers, served as models for the long polysaccharide and
polypeptide chains that have prevented biogenic calcium carbonate dissolution and
recrystallisation through millennia. I combined wet chemistry experiments with analysis by
surface sensitive techniques and theoretical models of mineral nucleation and growth. I found that
aspartic acid (in solution, aspartate) and its polymer can inhibit calcite growth by more than 50%
and 90%, with growth inhibition clearly increasing as the molecule chain length of the polymers
increases. They do this by strongly adsorbing on calcite growth steps, thereby blocking further
growth. The fit of adsorption isotherms to the kinetic data permitted to calculate free adsorption
energies of -39 and -50 kJ/mol for the two polymers of aspartic acid and of -21 for aspartic acid,
corroborating that the polymers adsorb more strongly on calcite surface than the monomers. In
contrast, glycine and its polymer had little if any effect on calcite growth.
Another molecule I studied was citric acid (in solution citrate). Citrate interacts with calcium ions
both in solution and on the mineral surface, resulting in nucleation and growth inhibition, in
systems with and without constant saturation index. Specifically, I revealed that citrate had a more
profound effect on CaCO3 growth rates than on nucleation when CIT/Ca ≤50% ([Ca2+]=[CO3
2-]=4
mM), whereas at CIT/Ca > 50% nucleation was more inhibited than growth. I also showed that
vaterite formation was completely inhibited at citrate at CIT/Ca ≥75%. Citrate not only adsorbs on
the crystal surface but is also incorporated into the internal structure. All of these molecules change
the surface morphology by roughening specific faces, elongating the crystals and favouring
vaterite or calcite polymorphs.
The new knowledge I gained on the kinetics and mechanisms of calcium carbonate crystallisation
in the presence of these organic molecules can be applied for designing improved antiscalants and
to enhance understanding of the controls in mineral growth by organic molecules, which is also
relevant for the understanding of biomineralisation processes and the design of biocomposite
materials for industry.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011892324&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Functionalised inhibitors on calcium carbonates
PB - Department of Chemistry, Faculty of Science, University of Copenhagen
ER -