2013 AIChE Annual Meeting

(439h) Kinetic Model for Stable Amorphous Calcium Carbonate

Authors

David Lignell, Brigham Young University



Amorphous calcium carbonate (ACC) is important to many industrial processes as well as biological environments. Calcium carbonate has recently attracted a lot of attention due to its potential as a carbon sink for sequestering carbon dioxide. ACC has been found to play a role in the formation of biominerals in aquatic organisms due to their ability to manipulate ACC. ACC is also a common precursor to anhydrous crystalline calcium carbonates in highly supersaturated solutions. The precipitation kinetics of calcium carbonate and consequent transformation mechanism into solid phases is not fully understood. 

Intermolecular interactions and steric effects exhibited by aqueous systems make the application of nucleation theory challenging. In this work, classical and novel nucleation mechanisms are applied to an experiment conducted by Gebauer et al. (D. Gebauer, A. Volkel and H. Colfen. Stable prenucleation calcium carbonate clusters. Science, 322:1819-1822, 2008)  for comparison. Four solid-phase kinetic models are coupled to the equilibrium chemistry model to simulate results which are compared with data from Gebauer et al.  Each of the models have a tuning parameter, optimized at a pH of 10.0. The solid-phases kinetic models consist of two classical models and two meso-crystallization models which operate within the framework of direct quadrature method of moments (DQMOM). The four models each capture various aspects of the data, and operate on the assumption that the calcium carbonate complex from legacy equilibrium expressions,  CaCO3 , is representative of stable prenucleation clusters.