Calcium carbonates

Schematic representation of the formation of calcite from amorphous calcium carbonate via vaterite.

Schematic representation of the formation of calcite from amorphous calcium carbonate via vaterite.

The crystallisation of CaCO3 polymorphs is key in biomineralisation processes, which in turn control a large part of the global carbon cycle. Many of these processes involve the formation poorly-ordered (i.e., amorphous) precursor phases prior to crystallisation. However, the mechanisms of formation of these carbonates are not well known because their crystallisation rates are extremely fast (<1 – 10s of seconds).

I have quantified the kinetics and derived the mechanisms of calcium carbonate formation. In particular, I have followed the crystallisation of different CaCO3-bearing biominerals (e.g., calcite, vaterite, Mg-calcite, monohydrocalcite, dolomite) by carrying out in situ and real-time experiments at synchrotron facilities (e.g., Diamond Light Source, Advanced Photon Source). For most of this research I have used small and wide angle X-ray scattering (SAXS/WAXS), combined with high resolution microscopy, solid-state, wet-chemical and spectroscopic techniques.

By combining these techniques I have been able to elucidate the full transformation pathway from amorphous calcium carbonate (ACC) to vaterite and calcite. I have shown also that initial pH and Mg have a significant effect on the pathways and mechanisms of the transformation of ACC into crystalline CaCO3. These results have shed light on the effects of seawater ions during biomineral formation and also the structural characterisation or poorly-ordered precursor phases. My studies further provided information of the effect of simple organics and the importance of the alcohol (–OH) group in biomineral formation, where polymorph stabilisation and engineered morphology are required.

KEY PAPERS:

Rodriguez-Blanco, J.D., Shaw, S. and Benning, L.G. (2011) The kinetics and mechanisms of Amorphous Calcium Carbonate (ACC) crystallization to calcite, via vaterite. Nanoscale, 3, 265-271. doi: 10.1039/c0nr00589d   [PDF]

Sand, K.K., Rodriguez-Blanco, J.D., Makovicky, E., Benning, L.G. and Stipp, S. (2012) Crystallization of CaCO3 in water-ethanol mixtures: spherulitic growth, polymorph stabilization and morphology change. Crystal Growth and Design, 12, 842-853. doi: 10.1021/cg2012342.   [PDF] [Supl. Info]

Bots, P., Rodriguez-Blanco, J.D., Benning, L.G. and Shaw, S. (2012) Mechanistic insights into the crystallization of amorphous calcium carbonate to vaterite. Crystal Growth and Design,12,3806-3814.doi: 10.1021/cg300676b.   [PDF] [Supl. Info]

Rodriguez-Blanco, J.D., Shaw, S. and Benning, L.G. (2012) The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate. Journal of Alloys and Compounds, 536, Suppl1, S477-S479. doi: 10.1016/j.jallcom.2011.11.057.   [PDF] [Supl. Info]

Rodriguez-Blanco, J.D., Shaw, S., Bots, P., Roncal-Herrero, T., and Benning, L.G. (2014) The role of Mg in the crystallisation of monohydrocalcite. Geochimica et Cosmochimica Acta, 127, 204-220. doi: 10.1016/j.gca.2013.11.034   [PDF] [Supl. Info]

Rodriguez-Blanco, J.D., Shaw, S. and Benning, L.G. (2015) A route for the direct crystallization of dolomite. American Mineralogist, 100, 1172-1181. doi: 10.2138/am-2015-4963   [PDF] [Supl. Info]

Tobler, D.J., Rodriguez-Blanco, J.D., Dideriksen, K., Bovet, N., Sand, K.K., Stipp. S.L.S. (2015) Citrate Effects on Amorphous Calcium Carbonate (ACC) Structure, Stability, and Crystallization. Advanced Functional Materials, 25, 3081-3090. DOI: 10.1002/adfm.201500400   [PDF]