Effects of chemical inhibitors on the scaling behaviors of calcite and the associated surface interaction mechanisms

Abstract

Hypothesis: It is hypothesized that the performance of a chemical inhibitor to interfere with the precipitation and scaling of calcite (calcium carbonate, CaCO₃) is achieved through its chelating interaction with calcium ions. The effectiveness of a chemical inhibitor in removing existing scales from the mineral surfaces is proposed to rely on its ability to modify the calcite crystal structures.

Experiments: Bulk scaling tests and dynamic adsorption experiments using a quartz crystal microbalance with dissipation monitoring were conducted to systematically investigate the scaling behaviours (i.e., buildup and breakup processes) of calcite crystals, in the absence and presence of chemical inhibitors, that include polyacrylic acid, sodium hexametaphosphate, 2-phosphonobutane-1,2,4-tricarboxylic acid, and diethylenetriamine penta(methylene phosphonic acid). Scanning electron microscope imaging and thermodynamic characterization using isothermal titration calorimetry were further applied to reveal the surface interactions that contributed to the differences among the effects of the four additives.

Findings: The results indicate that sodium hexametaphosphate is most efficient in alleviating the amount of CaCO₃ deposited by reducing the concentration of free Ca²⁺, and diethylenetriamine penta(methylene phosphonic acid) shows an outstanding ability to clean the mineral surface by destroying the ordered crystal layers of the scales so that they can be washed away with water. This work provides useful insights into the fundamental interactions of chemical inhibitors and calcite, with implications for the development of effective chemical solutions for anti-scaling and descaling applications.

Keywords: Adsorption; Antiscalant; Calcium carbonate; Scale inhibition; Scaling; Surface interactions.