Influence of foreign salts on the CaCO3 pre-nucleation stage: application of the conductometric method

The calcium carbonate crystallization process has been studied for more than a century. Nevertheless, little is known about the early stages of nucleation since in situ observations are difficult at the nanometer scale. In this paper, an original method based on electrical conductivity modeling applied to the fast controlled precipitation (FCP) method data is used to underline the existence of different ion pairs during the prenucleation stage as a function of the foreign salts (NaCl, MgCl2, Na2SO4 and MgSO4) added to the calco-carbonic pure water (CCPW). It is shown that after the addition of each foreign salt a resistivity variation is detected during the aggregation time due to formation of several ion pairs (CaCO0(3), CaHCO3+, NaHCO0(3), NaCO3- NaCO3-, NaSO4-, CaSO0(4), MgSO0(4), MgHCO3+ and MgCO0(3)). The foreign salt, without completely inhibiting the formation of ion pairs, acts on their formation rate and subsequently influences the nucleation kinetics and thermodynamics. A meaningful comparison is obtained between the resistivity-pH curves obtained experimentally in a FCP test and modeled using the McCleskey equation in the prenucleation stage after the addition of NaCl, MgCl2, Na2SO4 and MgSO4 to CCPW. According to the modeling software, the ion pairs that have a significant effect on the change in Delta(Resistivity) are CaCO0(3) in the presence of NaCl and Na2SO4 and MgCO0(3) in the presence of MgCl2 and MgSO4.

Automated summary

This study introduces a novel method to investigate the early stages of nucleation in calcium carbonate crystallization. The research demonstrates the existence of different ion pairs during the prenucleation stage and the influence of foreign salts on their formation rate and nucleation kinetics.