Real-time monitoring of electrochemically induced calcium carbonate depositions: Kinetics and mechanisms

Calcium carbonate (CaCO₃) deposition plays a significant role in processes such as scale formation in power plants and in oil or gas production wells. The development of appropriate methods based on well suitable in situ sensors is important to evaluate and predict the deposition process. In this study, a combination of electrochemical techniques and quartz crystal microbalance with dissipation monitoring (QCM-D) in one analysis setup (EQCM-D) was used for the first time to monitor the CaCO₃ deposition in real time and provide kinetic details of the CaCO₃ deposition process. Through recording the frequency change of quartz crystal sensors, it allows us to perform a quantitative analysis of the morphology, coverage, deposition rate, and mass changes with nanogram sensitivity. By varying the applied voltage, it was found that a lower applied voltage resulted in more deposition of CaCO₃ mass and increase of the thickness of the deposited layer. Under the absence of flow, the CaCO₃ growth rate switched from accelerating to decelerating and this point is characterized by an inflection point (IP). A lower applied voltage resulted in a lower IP. Increasing Ca²⁺ and HCO₃⁻ concentrations, both the deposited amount of CaCO₃ mass and coating thickness increased correspondingly. With the addition of 50 mM Mg²⁺, a reduction in the deposition rate of CaCO₃ as high as 73% was achieved. The higher the Mg²⁺ concentration, the larger the deposition rate reduction, which was attributed to the incorporation of Mg²⁺ into the growing CaCO₃ mineral, resulting in the reduction of growth sites (inhibiting effect). The obtained results contribute to a better understanding of electrochemically induced CaCO₃ deposition and provide valuable insights into the determination of optimal precipitation parameters, with the aim to optimize industry scaling and anti-scaling processes.